**2.6. Causes of soil pollution**

Soil pollution is caused by the presence of man-made chemicals or other alteration in the natural soil environment. This type of contamination typically arises from the rupture of underground storage links, application of pesticides, and percolation of contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. This occurrence of this phenomenon is correlated with the degree of industrialization and intensities of chemical usage. A soil pollutant is any factor which deteriorates the quality, texture and mineral content of the soil or which disturbs the biological balance of the organisms in the soil. Pollution in soil has adverse effect on plant growth.

Pollution in soil is associated with

Oxygen from air and water but other necessary nutrients like nitrogen, phosphorus, potassi‐ um, calcium, magnesium, sulfur and more must be obtained from the soil. Farmers generally use fertilizers to correct soil deficiencies. Fertilizers contaminate the soil with impurities, which come from the raw materials used for their manufacture. Mixed fertilizers often contain ammonium nitrate (NH4NO3), phosphorus as P2O5, and potassium as K2O. For instance, As, Pb and Cd present in traces in rock phosphate mineral get transferred to super phosphate fertilizer. Since the metals are not degradable, their accumulation in the soil above their toxic levels due to excessive use of phosphate fertilizers becomes an indestructible poison for crops. The over use of NPK fertilizers reduce quantity of vegetables and crops grown on soil over the years. It also reduces the protein content of wheat, maize, grams, etc., grown on that soil. The carbohydrate quality of such crops also gets degraded [15]. Excess potassium content in soil decreases Vitamin C and carotene content in vegetables and fruits. The vegetables and fruits grown on over fertilized soil are more prone to attacks by insects and disease.

**b.** Indiscriminate use of pesticides, insecticides and herbicides

Plants on which we depend for food are under attack from insects, fungi, bacteria, viruses, rodents and other animals, and must compete with weeds for nutrients. To kill unwanted populations living in or on their crops, farmers use pesticides. The first widespread insecticide use began at the end of World War II and included DDT (dichlorodiphenyltrichloroethane) and gammaxene. Insects soon became resistant to DDT and as the chemical did not decompose readily, it persisted in the environment. Since it was soluble in fat rather than water, it biomagnified up the food chain and disrupted calcium metabolism in birds, causing eggshells to be thin and fragile. As a result, large birds of prey such as the brown pelican, ospreys, falcons and eagles became endangered. DDT has been now been banned in most western countries. Ironically many of them including USA, still produce DDT for export to other developing nations whose needs outweigh the problems caused by it [16].

**c.** Dumping of solid wastes

**2.6. Causes of soil pollution**

10 Environmental Risk Assessment of Soil Contamination

soil has adverse effect on plant growth.

**•** Dumping of large quantities of solid waste

**•** Indiscriminate use of pesticides, insecticides and herbicides

Pollution in soil is associated with **•** Indiscriminate use of fertilizers

**•** Deforestation and soil erosion

**a.** Indiscriminate use of fertilizers

Soil pollution is caused by the presence of man-made chemicals or other alteration in the natural soil environment. This type of contamination typically arises from the rupture of underground storage links, application of pesticides, and percolation of contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. This occurrence of this phenomenon is correlated with the degree of industrialization and intensities of chemical usage. A soil pollutant is any factor which deteriorates the quality, texture and mineral content of the soil or which disturbs the biological balance of the organisms in the soil. Pollution in

Oxygen from air and water but other necessary nutrients like nitrogen, phosphorus, potassi‐ um, calcium, magnesium, sulfur and more must be obtained from the soil. Farmers generally use fertilizers to correct soil deficiencies. Fertilizers contaminate the soil with impurities, which come from the raw materials used for their manufacture. Mixed fertilizers often contain ammonium nitrate (NH4NO3), phosphorus as P2O5, and potassium as K2O. For instance, As, Pb and Cd present in traces in rock phosphate mineral get transferred to super phosphate fertilizer. Since the metals are not degradable, their accumulation in the soil above their toxic levels due to excessive use of phosphate fertilizers becomes an indestructible poison for crops. The over use of NPK fertilizers reduce quantity of vegetables and crops grown on soil over the years. It also reduces the protein content of wheat, maize, grams, etc., grown on that soil. The carbohydrate quality of such crops also gets degraded [15]. Excess potassium content in soil decreases Vitamin C and carotene content in vegetables and fruits. The vegetables and fruits

Plants on which we depend for food are under attack from insects, fungi, bacteria, viruses, rodents and other animals, and must compete with weeds for nutrients. To kill unwanted populations living in or on their crops, farmers use pesticides. The first widespread insecticide use began at the end of World War II and included DDT (dichlorodiphenyltrichloroethane) and gammaxene. Insects soon became resistant to DDT and as the chemical did not decompose readily, it persisted in the environment. Since it was soluble in fat rather than water, it biomagnified up the food chain and disrupted calcium metabolism in birds, causing eggshells to be thin and fragile. As a result, large birds of prey such as the brown pelican, ospreys, falcons

grown on over fertilized soil are more prone to attacks by insects and disease.

**b.** Indiscriminate use of pesticides, insecticides and herbicides

In general, solid waste includes garbage, domestic refuse and discarded solid materials such as those from commercial, industrial and agricultural operations. They contain increasing amounts of paper, cardboards, plastics, glass, old construction material, packaging material and toxic or otherwise hazardous substances. Since a significant amount of urban solid waste tends to be paper and food waste, the majority is recyclable or biodegradable in landfills. Similarly, most agricultural waste is recycled and mining waste is left on site. The portion of solid waste that is hazardous such as oils, battery metals, heavy metals from smelting indus‐ tries and organic solvents are the ones we have to pay particular attention to. These can in the long run, get deposited to the soils of the surrounding area and pollute them by altering their chemical and biological properties [17].

## **d.** Deforestation

Soil Erosion occurs when the weathered soil particles are dislodged and carried away by wind or water. Deforestation, agricultural development, temperature extremes, precipitation including acid rain, and human activities contribute to this erosion. Humans speed up this process by construction, mining, cutting of timber, over cropping and overgrazing. It results in floods and cause soil erosion. Forests and grasslands are an excellent binding material that keeps the soil intact and healthy. They support many habitats and ecosystems, which provide innumerable feeding pathways or food chains to all species. Their loss would threaten food chains and the survival of many species. During the past few years quite a lot of vast green land has been converted into deserts. The precious rain forest habitats of South America, tropical Asia and Africa are coming under pressure of population growth and development (especially timber, construction and agriculture). Many scientists believe that a wealth of medicinal substances including a cure for cancer and aids, lie in these forests. Deforestation is slowly destroying the most productive flora and fauna areas in the world, which also form vast tracts of a very valuable sink for CO2 [18].

**e.** Pollution due to urbanization

Pollution of surface soils materials (like vegetables, animal wastes, papers, wooden pieces, carcasses, plant twigs, leaves, cloth wastes as well as sweepings) and many non-biodegradable materials (such as plastic bags, plastic bottles, plastic wastes, glass bottles, glass pieces, stone / cement pieces) [19-20]. On a rough estimate Indian cities are producing solid city wastes to the tune of 50,000 - 80,000 metric tons every day. If left uncollected and decomposed, they are a cause of several problems such as;

**•** Clogging of drains: Causing serious drainage problems including the burst / leakage of drainage lines leading to health problems.

Underground soil in cities is likely to be polluted by

Many dangerous chemicals like cadmium, chromium, lead, arsenic, selenium products are likely to be deposited in underground soil. Similarly underground soils polluted by sanitary wastes generate many harmful chemicals. These can damage the normal activities and ecological balance in the underground soil

#### **2.7. Effects of soil pollution**

**•** Barrier to movement of water: Solid wastes have seriously damaged the normal movement of water thus creating problem of inundation, damage to foundation of buildings as well as

**•** Increased microbial activities: Microbial decomposition of organic wastes generate large quantities of methane besides many chemicals to pollute the soil and water flowing on its

**•** When such solid wastes are hospital wastes they create many health problems: As they may

Many dangerous chemicals like cadmium, chromium, lead, arsenic, selenium products are likely to be deposited in underground soil. Similarly underground soils polluted by sanitary wastes generate many harmful chemicals. These can damage the normal activities and

have dangerous pathogen within them besides dangerous medicines, injections.

public health hazards.

12 Environmental Risk Assessment of Soil Contamination

**f.** Pollution of underground soil

surface

**•** Foul smell: Generated by dumping the wastes at a place.

Underground soil in cities is likely to be polluted by

ecological balance in the underground soil

**2.7. Effects of soil pollution**

**•** Reduced nitrogen fixation

**•** Larger loss of soil and nutrients

**•** Imbalance in soil fauna and flora

**•** Deposition of silt in tanks and reservoirs

**•** Dangerous chemicals entering underground water

**•** Release of radioactive rays causing health problems

**a.** Agricultural

**•** Reduced soil fertility

**•** Increased erodibility

**•** Reduced crop yield

**•** Ecological imbalance

**•** Increased salinity

**•** Release of pollutant gases

**b.** Industrial

**•** Chemicals released by industrial wastes and industrial wastes

**•** Decomposed and partially decomposed materials of sanitary wastes

#### **2.8. Control of soil pollution**

The following steps have been suggested to control soil pollution. To help prevent soil erosion, we can limit construction in sensitive area. In general we would need less fertilizer and fewer pesticides if we could all adopt the three R's: Reduce, Reuse, and Recycle. This would give us less solid waste.

**a.** Extraction and separation techniques

In solvent extraction, the contaminated & oil is mixed with an extracting agent in general (an aqueous solution but preferably an organic solvent). Potential applications include the removal of metals such as cadmium, copper, zinc, nickel, chromium, arsenic, antimony and lead using a mineral solution, zinc lead, organo-metallic compounds and some cyanides using sodium hydroxide solution. Hydrocarbons and halogenated hydrocarbons can also be removed [21]. Contamination is often preferentially present in the finer or coarser fraction of the soil or the organic components (ex. humus), contamination can therefore, be removed in some cases using a process which separates the soil into fractions on the basis of specific gravity or particle size or settling velocity.

**b.** Thermal methods

In thermal methods, there are two ways of heat treatment; removal of contaminants by evaporation either by direct heat transfer from heated air or an open flame or by indirect heat transfer, and destruction of the contaminants directly or indirectly at an appropriate temper‐ ature. The gas leaving the heating appliance must be treated to destroy or remove any contaminants or unwanted products of combustion. A related process is stream stripping in which steam is injected into soil to aid evaporation of relatively volatile contaminants which may be water soluble or insoluble.

**c.** Chemical methods

Treatment of the soil in suspension in a suitable liquid and without sludging is the two possible methods. In these, intimate, contact between soil and chemical is essential and should be frequently done so that the process of detoxification is complete.

**d.** Microbial treatment methods

The microbial treatment methods appear to be more promising which can deal with whole range of organic contaminants including phenol, polychlorinated hydrocarbons, oil and oil products, dioxins, etc. There are two different ways of approaching the problems.

Excavation of the soil prior to treatment offers the greatest scope for creating optimum conditions. The excavated soil can be placed on thin layers to various depth using standard earth moving techniques and microbes and nutrients applied using standard agricultural techniques such as fertilizing, ploughing, harrowing, etc.

**e.** Reducing chemical fertilizer and pesticide use

Applying bio-fertilizers and manures can reduce chemical fertilizer and pesticide use. Biological methods of pest control can also reduce the use of pesticides and thereby minimize soil pollution.

**f.** Reusing of materials

Materials such as glass containers, plastic bags, paper, cloth etc. can be reused at domestic levels rather than being disposed, reducing solid waste pollution.

**g.** Recycling and recovery of materials

This is a reasonable solution for reducing soil pollution. Materials such as paper, some kinds of plastics and glass can and are being recycled. This decreases the volume of refuse and helps in the conservation of natural resources. For example, recovery of one tonne of paper can save 17 trees.

**h.** Reforesting

Control of land loss and soil erosion can be attempted through restoring forest and grass cover to check wastelands, soil erosion and floods. Crop rotation or mixed cropping can improve the fertility of the land.

### **i.** Solid waste treatment

ature. The gas leaving the heating appliance must be treated to destroy or remove any contaminants or unwanted products of combustion. A related process is stream stripping in which steam is injected into soil to aid evaporation of relatively volatile contaminants which

Treatment of the soil in suspension in a suitable liquid and without sludging is the two possible methods. In these, intimate, contact between soil and chemical is essential and should be

The microbial treatment methods appear to be more promising which can deal with whole range of organic contaminants including phenol, polychlorinated hydrocarbons, oil and oil

**1.** A community of microbes already existing on the site is collected and cultured in the

**2.** Strains of microbes are developed in the laboratory that is capable of metabolizing

Excavation of the soil prior to treatment offers the greatest scope for creating optimum conditions. The excavated soil can be placed on thin layers to various depth using standard earth moving techniques and microbes and nutrients applied using standard agricultural

Applying bio-fertilizers and manures can reduce chemical fertilizer and pesticide use. Biological methods of pest control can also reduce the use of pesticides and thereby minimize

Materials such as glass containers, plastic bags, paper, cloth etc. can be reused at domestic

This is a reasonable solution for reducing soil pollution. Materials such as paper, some kinds of plastics and glass can and are being recycled. This decreases the volume of refuse and helps in the conservation of natural resources. For example, recovery of one tonne of paper can save

Control of land loss and soil erosion can be attempted through restoring forest and grass cover to check wastelands, soil erosion and floods. Crop rotation or mixed cropping can improve

products, dioxins, etc. There are two different ways of approaching the problems.

frequently done so that the process of detoxification is complete.

techniques such as fertilizing, ploughing, harrowing, etc.

levels rather than being disposed, reducing solid waste pollution.

**e.** Reducing chemical fertilizer and pesticide use

may be water soluble or insoluble.

14 Environmental Risk Assessment of Soil Contamination

**d.** Microbial treatment methods

**c.** Chemical methods

laboratory.

soil pollution.

17 trees.

**h.** Reforesting

the fertility of the land.

**f.** Reusing of materials

**g.** Recycling and recovery of materials

particular chemicals.

Proper methods should be adopted for management of solid waste disposal. Industrial wastes can be treated physically, chemically and biologically until they are less hazardous. Acidic and alkaline wastes should be first neutralized; the insoluble material if biodegradable should be allowed to degrade under controlled conditions before being disposed. As a last resort, new areas for storage of hazardous waste should be investigated such as deep well injection and more secure landfills. Burying the waste in locations situated away from residential areas is the simplest and most widely used technique of solid waste management.


*3.3. Mechanical Tests*

The results obtained in the mechanical tests display differences for the different mixes, in terms of both compressive and flexural strength, during the test period (120 days). The results obtained from the mechanical tests are set out in Table 6 (samples without added pigments) and Table 7 and Figure 5 (binders and samples after 120 days).

**Table 6.** Results of the mechanical tests (120 days) and standard deviation for the different pastes tested.

**Table 7.** Results for mechanical tests and standard deviation for the different pastes containing added pigments tested after 120 days.

**Table 7.** *Cont.*

**Figure 5.** Mechanical strength values (MPa) of binders at 120 days and their corresponding pigmentcolored pastes (PPS, PALS, PHLS and PWGS). Blue bar plot corresponds to compressive strength. Line plot with red circles corresponds to flexural strength.

#### 3.3.1. Compressive Strength

#### PPS + Pigment Samples

In the plaster paste samples containing added pigment (PPS + PIGMENT), the maximum compressive strength after 120 days was 5.52 MPa ± 0.02 for the PPS + PGE (Green Earth pigment) sample. The minimum value was 5.3 MPa ± 0.05 for the PPS + PZY (Zinc yellow pigment) pigment sample.

In percentage terms, the variation among the pastes containing added pigment was 3.98%, and the difference among the pastes without added pigment was 2.17%. This shows full compatibility between the pastes and the pigments used.

### PALS + Pigment Samples

The compressive strength of the plaster + lime pastes exhibits a slight increase in the results, compared to the previous group. In this case, the values range between 5.74 MPa ± 0.05 for the PALS + PGE (Green Earth pigment) samples and 5.56 MPa ± 0.03 for the PALS + PCG (chromium green pigment) samples. This represents an average increase of 3.74% compared to the pure plaster samples.

#### PWGS + Pigment Samples

The compressive strength levels of the plaster + sodium silicate pastes were higher compared to the previous groups. In this case, the values range between 8.72 MPa ± 0.01 for the PWGS + PGE (Green Earth pigment) samples and 8.62 MPa ± 0.01 for the PWGS + PUB (Ultramarine Blue pigment) samples. This represents average increases of 37.6% compared to the pure plaster samples and 35.2% compared to the plaster and air lime samples.


*Article* **Radionuclides Transfer from Soil to Tea Leaves and Estimation of Committed Effective Dose to the Bangladesh Populace**

**Nurul Absar 1, Jainal Abedin 1, Md. Mashiur Rahman 2, Moazzem Hossain Miah 3, Naziba Siddique 3, Masud Kamal 4, Mantazul Islam Chowdhury 4, Abdelmoneim Adam Mohamed Sulieman 5, Mohammad Rashed Iqbal Faruque 6, Mayeen Uddin Khandaker 7,\*, David Andrew Bradley 7,8 and Abdullah Alsubaie 9**

**Abstract:** Considering the probable health risks due to radioactivity input via drinking tea, the concentrations of 226Ra, 232Th,40K and 137Cs radionuclides in the soil and the corresponding tea leaves of a large tea plantation were measured using high purity germanium (HPGe) γ-ray spectrometry. Different layers of soil and fresh tea leaf samples were collected from the Udalia Tea Estate (UTE) in the Fatickchari area of Chittagong, Bangladesh. The mean concentrations (in Bq/kg) of radionuclides in the studied soil samples were found to be 34 ± 9 to 45 ± 3 for 226Ra, 50 ± 13 to 63 ± 5 for 232Th, 245 ± 30 to 635 ± 35 for 40K and 3 ± 1 to 10 ± 1 for 137Cs, while the respective values in the corresponding tea leaf samples were 3.6 ± 0.7 to 5.7 ± 1.0, 2.4 ± 0.5 to 5.8 ± 0.9, 132 ± 25 to 258 ± 29 and <0.4. The mean transfer factors for 226Ra, 232Th and 40K from soil to tea leaves were calculated to be 0.12, 0.08 and 0.46, respectively, the complete range being 1.1 × 10−2 to 1.0, in accordance with IAEA values. Additionally, the most popularly consumed tea brands available in the Bangladeshi market were also analyzed and, with the exception of 40K, were found to have similar concentrations to the fresh tea leaves collected from the UTE. The committed effective dose via the consumption of tea was estimated to be low in comparison with the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reference ingestion dose limit of 290 μSv/y. Current indicative tea consumption of 4 g/day/person shows an insignificant radiological risk to public health, while cumulative dietary exposures may not be entirely negligible, because the UNSCEAR reference dose limit is derived from total dietary exposures. This study suggests a periodic monitoring of radiation levels in tea leaves in seeking to ensure the safety of human health.

**Keywords:** soil; tea leaves; HPGe γ-ray spectrometry; terrestrial and anthropogenic radionuclides; threshold consumption rate; committed effective dose

**Citation:** Absar, N.; Abedin, J.; Rahman, MM.; Miah, M.M.H.; Siddique, N.; Kamal, M.; Chowdhury, M.I.; Sulieman, A.A.M.; Faruque, M.R.I.; Khandaker, M.U.; et al. Radionuclides Transfer from Soil to Tea Leaves and Estimation of Committed Effective Dose to the Bangladesh Populace. *Life* **2021**, *11*, 282. https://doi.org/10.3390/ life11040282

Academic Editors: Fabrizio Ambrosino and Supitcha Chanyotha

Received: 2 March 2021 Accepted: 24 March 2021 Published: 27 March 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### **1. Introduction**

The most common forms of ionizing radiation on earth, resulting from terrestrial, extraterrestrial and anthropogenic sources, are α- and β-particles and γ-rays [1,2]. According to the National Council on Radiation Protection and Measurements (NCRP), environmental radiation is the most significant source of radiation exposure to humans [3]. Interestingly, although the International Atomic Energy Agency (IAEA) reported that the public exposure from natural radiation is of little health concern [4], the World Nuclear Association (WNA) states that any dose of radiation involves a possible risk to human health [5]. Since 238U and 232Th decay series and singly occurring 40K are the most abundant radionuclides found naturally in soil, air, water, rocks, plants and foodstuffs [5], to protect the public against unwanted exposures to natural radiation, the radioactivity in environmental samples, including foodstuffs, needs to be monitored periodically [4].

The surface soil, especially the top layer in the earth, is a mixture of various components in the natural environment [6,7]. Although the main source of U, Th and K is the earth crust, their contents appear at varying levels in the soils of different regions in the world following the variation of the local geology [8]. In addition to the prevailing concentration of terrestrial radionuclides in acidic soils, at high altitudes the contribution from extraterrestrial radioactivity may be enhanced, moreover with fallout of artificial radionuclides that may be subject to greater deposition. The latter concerns atmospheric nuclear device testing or unplanned phenomena such as the Three Mile Island power plant accident, the Chernobyl accident and the Fukushima Dai-ichi nuclear power plant accident [9–12]. Regardless of origin (i.e., natural or artificial), the radionuclides may appear in plants along with the uptake of minerals and nutrients required for their vitality, majorly by the root system [13]. Their availability in plant life enables them to be transported to humans via the daily intake of foodstuffs [14–16]. Thus, it is necessary to know the natural radioactivity in a particular area to obtain their distribution, modelling and transport processes leading to the estimation of radiation dose and hazards to the general population [6].

Due to its pleasant taste, aroma and positive physiological functions, tea is one of the most popular stimulating drinks in the world after water [17–19]. It is generally obtained by processing the leaves and leaf buds of the Camellia sinensis plant. Primarily there are four types of processed teas: green, black, oolong and brick tea [20]. Green tea is obtained by drying and roasting the tea leaves without any fermentation, whereas an additional fermentation produces black tea leaves. A partial fermentation of tea leaves results in oolong tea. Brick tea is made from the blocks of whole or finely ground black tea, compressed in a form under extremely high pressure. Asian populations generally drink the semi-fermented green tea and fermented black teas [21] as a hot drink. While, at present, tea is cultivated in more than 40 countries in the world, the major portion (90%) is produced by Asian countries [22]. Due to the presence of biologically active compounds (antitoxin, antioxidant, anti-inflammatory, antibacterial, antiviral, anti-carcinogenic, etc.) like polyphenols, amino acids and vitamins in tea [23,24], tea drinking has been promoted for centuries [25–27]. Controversies about the benefits and risks due to the consumption of tea are not completely absent, but the few reported toxic effects are outclassed by its countless health-promoting benefits [28]. Harmful effects like stomach ache, intestinal gas, heartburn and abdominal pain from over consumption of tea are identified due to the presence of caffeine, aluminum and the influence of tea polyphenols on iron bioavailability [29].

Following the suitable geographical location and weather conditions for tea plantation, tea plantations were established in the hilly areas of Sylhet, Moulavibazar, Comilla and Chittagong regions in Bangladesh, centuries ago [30]. Moreover, due to recent developments in socio-economic conditions, tea consumption is increasing at a significant level among Bangladeshi population [31]. In producing more than 95 million kg of tea in 2019, harvested from about 115,757 hectares of land, Bangladesh has become the world's tenth largest tea producer and the world's ninth tea exporting country [32]. As a member of Bangladesh Tea Board and Bangladesh Tea Association, the Udalia Tea Estate (UTE), since 1962, has played a very important role in quality tea production. In recent times, the UTE

has come to be ranked highly among the existing tea estates in Bangladesh. In meeting the growing domestic demand for premium black and green tea as well as that of international markets, UTE has secured a position not only as a tea producer but also as a multi-product estate. In particular, it enjoys abundant rainfall, is in an area of elevated altitude above sea level and has acidic and well-draining soils, all combining to make favorable conditions for tea production.

Since plants produce their necessary energy via the use of leaves together with the photosynthesis process, the leaves may have more activity than the other parts of plants, therefore they may contain relatively more radionuclides which are normally taken up by the root system along with other minerals. Moreover, leaves are more exposed to aerial deposition, e.g., radionuclides in dust or radionuclide particles themselves, if there are any artificial phenomena in the surrounding environment or nearby countries. Therefore, tea plants may be subjected to direct and indirect contamination of various radionuclides, and these radionuclides can be distributed in different parts of the plants according to the chemical characteristics and parameters of the plants and soil [33]. Since tea forms the second most popular drink (after water) in all populations in Bangladesh, the presence of a low level of radioactive material in tea leaves may produce a non-negligible health hazard via cumulative exposures. By acknowledging that ingestion doses above permissible levels are harmful for human beings [34], assessment of radionuclides due to the consumption of foodstuffs is important for public health. Furthermore, assessment of any release of radioactivity to the environment is important for the protection of public health, especially if the released radioactivity can enter into the food chain [35].

While studies of natural radioactivity in various foodstuffs are available in the literature, information on the distribution and enrichment of radionuclides in tea leaves is sparse, especially in tea leaves collected from the major tea gardens including the UTE in Bangladesh. The main objectives of the present study are to determine the transfer of radionuclides from soil to tea leaves harvested from the Udalia Tea Estate, further calculating the associated health hazards following the consumption of tea by the populace in Bangladesh. The activity concentrations of marketed tea leaves were also analyzed to observe the effect of manufacturing processes. This study may also help to enrich the radioactivity database on tea, i.e., the most popular stimulating drink.

#### **2. Experimental**

#### *2.1. Local Geology of the Udalia Tea Estate*

The Udalia Tea Estate (UTE) is located in the hilly region of Fatickchari Upazilla in the Chittagong district of Bangladesh (see in Figure 1). The UTE can be addressed as latitude 22◦36 39–22◦39 41 N and longitude 91◦45 6–91◦51 15 E. The estate is covered by low hill ranges and terraces having an altitude of 30–46 m above sea level and contains an area of 3096 acres (3.9 km × 3.2 km = 12.5 square kilometer) [36]. The climate of this area is tropical monsoon. An average annual rainfall of about 2794 mm is recorded in this area, while July is the wettest month. The soils in this area are mainly yellowish to reddish brown, the texture is mostly clay loam on flat land while the hilly soil is mostly sandy loam to coarse sand, which is characterized by broken shale or sandstone and mottled sand at different depths [37]. The soils are strongly acidic and poor in organic matter and nutrients.

#### *2.2. Sample Collection and Preparation*

The samples (soil and tea leaves) were collected from different places in the Udalia Tea Estate (UTE). The sampling location was chosen on a random basis, but the distance between each sampling location was almost 700–800 m. Since the estate consists of ranges of low lying hills, separate hills were chosen as different sampling locations. A total of 5 locations were chosen for collecting the tea leaves and the surrounding soil samples throughout the garden. While an approximate amount of 2.5 kg of fresh tea leaf samples were collected from each selected location around the UTE, a total of 4 (×3) soil samples were also collected from three different depths, 0 to 5 cm, 6 to 12 cm and 13 to 20 cm, of the corresponding locations to the tea leaves samples. More specifically, the soil samples were collected from four different points within an area of 1 m2 around the tea tree. The 25-year-old tea trees were selected for collection of the tea leaf samples. Usually, the branches of the tea plant are cut and are fertilized twice per year, and in some cases fertilizers are used more than twice for influencing the growth of the tea plant in the garden. At present, the UTE produces approximately 0.7 million tons of tea per year with six separate grades of tea including the export quality one. In the local market and throughout the country, this estate supplies one of the popular tea brands "Mostafa tea". Five marketed tea leaf samples were also collected from the local market, allowing comparison of the measured radioactivity from these with that from the fresh tea leaves collected from the UTE.

**Figure 1.** Location of the Udalia Tea Estate at the Fatikchari Upazila of the Chittagong district in Bangladesh.

The procedure for sample collection followed that recommended by the IAEA [4]. The collected samples were stored separately in sealed plastic bags and tagged with an identification number, and with the date and location of sampling. The samples were dried under direct sunlight for several days to allow evaporation of moisture content, subsequently being further dried for a period of 24 h in an oven maintained at 85 ◦C to remove any remaining moisture. The dried samples were then mechanically crushed into a fine powder, homogenized with a mortar and pestle and filtered through a sieve of 0.395 mm mesh size to obtain similarly sized particles. A constant dry weight was measured out for each sample evaluation. For the determination of activity concentration, the dried sample was transferred to an individual cylindrical container having dimension of 3.5 cm height and 8.5 cm diameter. To settle and obtain a homogeneous mixture of the samples, the containers were simply shaken by hand. The containers were then sealed

tightly by using an insulating tape to reduce the possibility of moisture contamination. The samples were then kept undisturbed for 5–7 weeks at room temperature to attain secular equilibrium between short-lived progeny with the respective long-lived parents, 226Ra (from 238U) and 228Ra (from 232Th) [38,39]. It was assumed that 222Rn and 220Rn could not escape from the sealed containers during the period of storage. The samples were then ready for subsequent measurement and analysis by γ-ray spectrometry.

#### *2.3. Measurement of Radionuclides*

This study used a co-axial high-purity germanium (HPGe) γ-ray detector (GC2018, CANBERRA, USA), having a relative efficiency of 20%, resolution of 1.8 keV at 1332 keV of peak of 60Co source, to measure the samples and standards obtained from the IAEA. The detector was coupled with a digital spectrum analyzer and GENIE 2000 to acquire the γ-ray spectra emitted from the samples. To ensure a low background environment, a cylindrical lead shielded arrangement (5.08 cm thick) with fixed bottom and movable cover was installed. The efficiency of the detector was measured using the reference samples RGU-1, RGTh-1 and RGK-1 provided by the IAEA [40], with results as presented in Figure 2. The standard sources containing known concentrations of 226Ra, 232Th and 40K were supplied by the Canada Center for Mineral and Energy Technology (CAMET) under a contract with the IAEA. Considering the leaves' texture and density, a radioactive standard with leafy vegetables was prepared by mixing/spiking 226Ra standard source of solid matrices in identical containers to the samples, and using them accordingly. Necessary information on the calibration of the efficiency of the detector is available elsewhere [41]. In this study, each sample was measured for 10,000 seconds to achieve reasonable statistics. The net count rate from the primordial radionuclides originating from the samples was obtained by subtracting the background count from the gross count, both acquired for the same counting time. The activity concentrations of 226Ra and 232Th radionuclides were assessed using the characteristic gamma lines of their short-lived progeny [42,43]. The concentrations of 40K and 137Cs were determined by the gamma ray lines of 1460.77 keV and 661 keV, respectively. For evaluation of 226Ra and 232Th, a weighted mean approach was applied following reference [14].

**Figure 2.** Counting efficiency curve of the HPGe (high-purity germanium) detector.

#### *2.4. Calculation of Activity Concentration*

Activity concentrations of radionuclides (Bq kg−1) in surface soil, sub-surface soils and plant samples were calculated using Equation (1) [41]:

$$\text{Activity concentration} = \frac{\text{CPS} \times 100 \times 1000}{\varepsilon\_f (\%). \times I\_\gamma \times w\_\text{s} (\text{kg})} \tag{1}$$

where CPS represents the net counts per second, *εf* the efficiency of the detector, *Iγ* the branching ratio and *Ws* the weight of the sample in kg. The statistical uncertainties were expressed in terms of standard deviation (±σ), where σ is expressed in Equation (2) [41]:

$$
\sigma = \sqrt{\left[\frac{N\_s}{T\_s^2} + \frac{N\_b}{T\_b^2}\right]}\tag{2}
$$

where *Ns* and *Nb* represent the sample and background counts in time *Ts* and *Tb*, respectively. The total uncertainty for each measured sample was calculated taking into account the statistical and other components of uncertainty. The combined uncertainty of the activity was estimated by using the quadratic sum of relevant quantities, which can be defined by Equation (3) [44]:

$$
\Delta A = A \times \sqrt{\left(\frac{\Delta N}{N}\right)^2 + \left(\frac{\Delta \varepsilon\_\gamma}{\varepsilon\_\gamma}\right)^2 + \left(\frac{\Delta \rho\_\gamma}{\rho\_\gamma}\right)^2 + \left(\frac{\Delta m\_s}{M\_s}\right)^2} \tag{3}
$$

where Δ*A* is the combined uncertainty of each measured value. The symbols Δ*N*, Δ*εγ*, Δ*ργ* and Δ*ms* represent the uncertainties due to the counting statistics, *N* (<7%), detection efficiency, *ε*γ (4%), gamma ray emission probability, *ργ*(<1%), and sample weight, *MS* (<2%), respectively. The determined radioactivity levels, together with the uncertainties, are presented in Table 1.

**Table 1.** Concentrations of 226Ra, 232Th, 40K and 137Cs in the analyzed soil and tea leaf samples (both fresh and marketed tea leaves) and calculated transfer factors from soil-to-tea leaf (fresh tea leaves from UTE (Udalia Tea Estate)).

The lower limit of detection or the minimum detectable activity concentration (MDA) of the measurement system was calculated using Equation (4) [45,46]:

$$\text{MDA} = \frac{k\_a \times \sqrt{\beta}}{\varepsilon\_\gamma \times \rho\_\gamma \times T\_s \times M\_s} \tag{4}$$

where *Kα* represents the statistical coverage factor which is equal to 1.64 (at the 95% confidence level), *β* is the background count in the energy of interest and the other symbols *ε*γ, *ργ*, *TS* and *MS* represent detection efficiency, gamma-ray emission probability, counting time, and sample weight, respectively. The MDAs for the studied radionuclides 226Ra, 232Th, 40K and 137Cs were calculated to be 0.32 Bq kg−1, 0.60 Bq kg−1, 2.5 Bq kg−1 and 0.4 Bq kg−1, respectively.

#### *2.5. Soil to Tea Leaves Transfer Factor (TF)*

Within the food we eat, plants are the principal recipients of radioactive contamination, a result of atmospheric or other releases of radionuclides and from naturally occurring radioactivity within the soil [40]. Basically, the transfer factor defines the uptake of radionuclides from soil to plants, which can be calculated by the ratio of the radioactivity per unit dry weight of plant (*CP*) to the radioactivity per unit dry weight of soil (*CS*) in the rooting zone, using the Equation (5) [47,48]:

$$\text{TF} = \frac{\text{C}\_P}{\text{C}\_S} \tag{5}$$

Dry weight analysis is preferred, the amount of radioactivity per kilogram dry weight being subject to much less variability than the amount per unit fresh weight, thereby reducing uncertainties in the measured TF (transfer factor) [49]. The calculated TFs for the studied tea leaf samples are shown in Table 1.

#### *2.6. Annual Committed Effective Dose (ACED)*

Following the consumption characteristics of foodstuffs, the committed effective dose due to the ingestion of radionuclides can be calculated using Equation (6), as below [50]:

$$\text{AECD} \left(\upmu \text{Sv/y}\right) = \mathcal{C}\_r \times \sum\_{i=1}^{3} D\_{cfi} \; \times \; A\_i \tag{6}$$

where *Cr* is the intake of radionuclides through use of the tea leaves, *DCF,i* are the ingestion dose conversion coefficients of 2.8 × 10−7 Sv Bq−1, 2.2 × 10−7 Sv Bq−1 and 6.2 × 10−9 Sv Bq−1 for 226Ra, 232Th and 40K, respectively, for an adult [51] and Ai is the measured activity concentration (Bq.kg−1) of each radionuclide. According to the typical statistics, an average of 2 g of tea leaves is needed to prepare a cup of tea and if one person drinks two cups of tea per day, then an amount of some 1.5 kg/year is consumed by an individual. The two cups of tea is a typical tea consumption characteristic for the Bangladeshi population. The *Cr* is also defined as the consumption rate.

#### *2.7. Threshold Consumption Rate of Tea (kg/y)*

The threshold consumption rate (*DIthresh*) represents a reference dietary level to avoid deleterious health hazards due to the intake of radionuclides via foodstuffs [52]. The particular threshold data due to the drinking of tea can be estimated by using the following Equation (7) [53]:

$$DI\_{\text{threshold}} \left(\text{kg/y}\right) = \frac{E\_{\text{ave}}}{\sum\_{i=1}^{3} D\_{cfi} \times A\_i} \tag{7}$$

were *Eave* (290 μSv/y) is the threshold committed effective dose due to the ingestion of radionuclides of interest via the consumption of foodstuffs [54,55], A1, A2 and A3 are the activity concentrations of 226Ra, 232Th and 40K, respectively, in the tea leaf samples and *Dcfi* is the activity to dose conversion coefficient for the radionuclides of interest, as before.

#### *2.8. Carcinogenic Risk*

The carcinogenic risk for a population is estimated by assuming a linear no threshold, dose–effect relationship as per ICRP practice. For low doses, the ICRP suggest a fatal cancer

risk factor of 0.05 Sv−1 [56], which indicates that the probability of a person dying of cancer is increased by 5% for a total dose of 1 Sv received during a lifetime. The estimated average annual committed effective dose for tea leaves is used herein to calculate the carcinogenic risk for an adult, made of the following relationship Equation (8):

$$ElCR = \text{AECD}(\mu Sv/y) \times R\_f \left(Sv^{-1}\right) \times A\_{ls}(y) \tag{8}$$

where *Rf* is the risk factor per sievert of annual effective dose received by the consumption of tea and *Als* is the cumulated time of tea consumption by Bangladeshi populace. Considering the local typical tea consumption characteristics, a duration of 50 years was used for both sexes.

#### **3. Results and Discussion**

#### *3.1. Activity Concentration in the Tea Garden Doil Samples*

The mean activity concentrations of 226Ra, 232Th, 40K and 137Cs in the soil samples collected from five locations of UTE are given in Table 1. The measured values in the investigated soil samples are found in the order 40K > 232Th > 226Ra > 137Cs. 40K dominates over the other nuclides, which is not unexpected. This is because potassium is the seventh most abundant element in the Earth's crust, making up 2.6% of the weight of the earth's crust [57]. The greater activity concentration of 232Th over that of 226Ra may be attributed to the differences in the physical and chemical characteristics in a natural environment. In the earth's crust, both uranium and thorium tend to occur together due to the some inherent characteristics. However, throughout the various superficial processes like weathering and transportation, and the soil characteristics (pH and redox), they become fractionated. In general, thorium possesses low solubility and accumulates on particular phases whereas uranium is chemically more soluble and mobile. Consequently, uranium can easily be redistributed and transported in various environmental matrices compared to thorium [48].

Table 1 shows the mean activity concentrations of 226Ra in soil samples for all locations other than that at location 2 to be greater than the UNSCEAR reported worldwide mean value of 35 Bq.kg−1 [49]. Among the three studied layers/depths of soil, the greatest concentration of 226Ra (53 ± 8 Bq.kg−1) was at location 5, at a depth of 13- to 20 cm, whereas, the minimum concentration of 226Ra (27 ± 7 Bq.kg−1) was at location 2, at a depth of 6 to 12 cm. This may be correlated to the ambient environment, i.e., the presence of high moisture content in the clay silty sand soil of this location which allows better solubility of 226Ra [58].

For all locations the mean activity concentrations of 232Th are greater than the worldwide mean value of 30 Bq.kg−1 [49], while the 40K data for all locations other than location 2 are less than the UNSCEAR [49] reported mean concentration of 400 Bq.kg−1. In respect to the vertical distribution, the greatest concentration of 232Th (82 ± 11 Bq.kg−1) was in soil from location 4, at a depth of 6 to 12 cm, whereas the minimum 232Th concentration (29 ± 7 Bq.kg−1) was from soil at location 5, at a depth of 0 to 5 cm. Soil samples from location 5 are clay silty sand and have large carbonate content, a matter correlating with the low 232Th concentration. The data show the level of natural radioactivity forming a similar distribution in the surface and deep layered soils.

The greatest concentration of 40K (672 ± 81 Bq.kg−1) was shown to be at location 2, at a depth of 6 to 12 cm, whereas the minimum 40K concentration (201 ± 78 Bq.kg−1) was at location 1, at a depth of 6 to 12 cm. The majority of 40K is a part of a clay mineral component rather than organic matter and its mobility depends on its solubility in the soil [59]. The low concentration of 40K may be correlated to the soil texture, i.e., the presence of more sandy soil. Moreover, use of NPK fertilizer at least two times per year for better yield of leaves may contribute to the higher values of 40K activity [60,61].

137Cs, an anthropomorphic nuclide, as detected in trace amounts in the UTE soil, predominantly in the topsoil layers and less so or otherwise not detectable in sub-surface layers. The greatest 137Cs mean activity concentration, at 10 ± 1 Bq.kg−1, was found

in surface soil at location 1, at a depth of 0 to 5 cm, while the lowest concentration of 3 ± 1 Bq.kg−1 was found at location 5, at the same depth. 137Cs in other locations was not detected, the one exception being at location 1, at a depth of 6 to 12 cm. The mean 137Cs concentrations at the different locations were found to be less than the world average value 51 Bqkg−1 as reported by UNSCEAR [49]. The 137Cs is a quasi-permanent source of external gamma ray exposure, the activity slowly decaying in accordance with a half-life of some 30 years. The small likelihood that this nuclide will form a significant soil to plant pathway is generally acknowledged, the contaminant for the most part being linked to widely publicized nuclear establishment accidents. When detected, most typically at very low levels, the variation in the activity concentrations of the radionuclides are due to meteorological factors, the difference in sampling depth, physiochemical soil characteristics and the time of deposition.

#### *3.2. Activity Concentration in Tea Leaf Samples*

The measured activity concentrations of 226Ra, 232Th, 40K and 137Cs radionuclides in tea leaf samples collected from the Udalia Tea Estate as well as from the local market are summarized in Table 1. The concentrations of radionuclides in tea leaf samples are reported in Bq.kg−1 dry weight. The activity concentrations of studied radionuclides in the investigated tea leaf samples were in the order 40K > 226Ra > 232Th > 137Cs. The activity concentrations of 226Ra were found to be greater than that of 232Th in most of the tea leaf samples collected from UTE. One probable reason is that the 238U (226Ra) tends to move towards the outer extremities of the tree and accumulates more greatly in new leaves and sprouts [62].

The greater concentration of 40K in tea leaf samples can be attributed for the most part to the specific metabolic processes of potassium involved in plant growth. Furthermore, for faster plant growth, the extra use of muriate (potassium chloride) of potassium fertilizer may be another factor causing the increase of 40K concentration in the tea leaf samples [60]. It has been reported that about 88–96% of K is taken up by the plant from the soil through the root system [61]. Since plants take up a high amount of potassium and natural potassium contains 0.0117% of 40K, the detection of high level of 40K in plants is not unexpected.

#### *3.3. Transfer Factors (TF) of Radionuclides from Soil-to-Tea Leaf*

Soil to tea leaf transfer factor (TF) values from the five different locations are also presented in Table 1, the values depending on soil properties such as nutrient and moisture contents and pH [51]. It can be observed from the results that the TF values for 226Ra, 232Th and 40K lie within the range 1.1 × 10−2 to 1.0, in accordance with values reported by the IAEA [63]. 137Cs in all of the tea leaf samples was found to be below the detection limit, therefore the transfer factors could not be calculated. Note that the IAEA report a TF range of 0.02–3.2 for 137Cs [63]. This indicates that, compared to 226Ra, 232Th and 40K, 137Cs is less efficiently transported from soil to the tea bush, as well as to the leaves

The transfer factors in the studied tea leaves are in the order 40K > 226Ra > 232Th > 137Cs, that for 40K being significantly greater than those of other radionuclides in all samples. It is well known that K is a very essential nutrient for plants metabolism and depending upon the particular metabolism a variable amount of K is taken up by plants from soil. Since elemental potassium is homeostatically controlled by the body (intake and excretion maintaining balance), such amounts of 40K in tea leaves are not to be considered to be of any particular concern as a potential radiation hazard. The actual concentration of radium in plant species clearly depends on the radium content of soil, its uptake by the plants species and also the metabolic characteristics of the plants [14]. Moreover, the chemical factors such as the presence of exchangeable amount of calcium in the soil may influence the absorption rate of radium by the plants [64]. The calculated TF show mean values of less than 1 for all radionuclides. It is worth mentioning that a value of TF >1 is indicative of radiation hazards to human health via the soil–plant–human body pathway. On the other hand, a TF = 1 would be indicative of a particular species or plant forming a useful natural process for decontamination of soil affected by a nuclear accident or deliberate nuclear device testing.

Table 2 shows a comparison of results from the present study with reported data for tea leaves from the Chittagong region of Bangladesh. Considering the similar geographical conditions, humidity and quality of soil, comparability of data might thus be expected. Within the Chittagong region, there are 17 tea growing estates in Fatickchari, 3 in Rangunia and 1 in Banskhali. In this respect, Table 2 shows the measured radioactivity of 226Ra to be similar to the available literature data, while UTE values for 232Th and 40K show much lower values compared to the reported data in the literature. Moreover, radioactivity in the estate tea leaves from Rize in Turkey also show higher values than the present results from UTE. The activity concentration of the artificial 137Cs radionuclide for the UTE sample is shown to be below the detection limit (<0.4), while a substantial amount of 137Cs was reported in estate tea leaf samples from Turkey. Such a result indicates the contamination of sampling area via some known/unknown nuclear activities. There are no available studies on the radioactivity of marketed tea samples in Bangladesh, therefore studies on marketed tea leaf samples imported from abroad have been chosen for comparison. The average activity concentration of 226Ra and 232Th and 40K in tea leaf samples collected from the local market show greater values than the reported data from Turkey (except 40K) and Serbia. The fact that the concentrations of 226Ra, 232Th and 40K vary substantially across the various regions depends mainly on their concentrations in the bedrock from which the soil originates [65].

**Table 2.** Average activity concentrations of 226Ra, 232Th, 40K and 137Cs in tea leaf samples from various countries compared with that from present work.

#### *3.4. Committed Effective Dose, Threshold Consumption Rate and Carcinogenic Risk*

The calculated values of committed effective dose, threshold consumption rate and carcinogenic risk are shown in Table 3. The committed effective dose due to the intake of the studied radionuclides via tea consumption was found to be in the range of 4.7–5.6 μSv y−1 with a mean of 5.0 μSv y−1. This compares with an average worldwide ingestion dose of 226Ra and 232Th of 120 μSv y−1 and 170 μSv y−1 for 40K, making a total annual dose estimate of 290 μSv y−1 from the total diet [49]. The annual effective doses from the ingestion of tea leaves were found much lower than the limiting value recommended by UNSCEAR [49]. Note that the estimated 5.0 μSv y−1 is contributed to by only a single dietary element (here tea leaf), thus such a low value is not unexpected. However, the radiation risk via the cumulative consumption of tea leaf may not be totally negligible, because tea forms only a minor part of the total dietary habits [70,71]. Figure 3 shows the dose contribution due to the individual radionuclides. Among the studied radionuclides, 226Ra incurred the maximum dose (38%) followed by 40K (33%) and 232Th (29%). Exposure to radioactive materials, especially radium, over a prolonged time may result in an increased carcinogenic risk. In addition, higher doses of radium are found to have links with anemia, cataracts, reduction of bone growth, etc. [72].

**Table 3.** Calculated hazard parameters due to the consumption of studied tea leaves collected from the UTE, Chittagong, Bangladesh.

**Figure 3.** Dose contribution by individual radionuclides due to the consumption of tea leaves.

The estimated mean threshold consumption rate for the studied tea leaf samples was found to be 88 kg/y (equivalent to 241g/d), an untenable value. This parameter indicates that the consumption of tea below the estimated value poses only a negligible radiological health hazard, while a greater rate than the calculated ones indicates enhanced radiological health risk.

Accordingly, the mean cumulative carcinogenic risk via tea leaf consumption (for a period of 50 years) was estimated at 1.3 × 10−5, significantly lower than the ICRP given cancer risk of 2.5 × 10−3, based on an annual effective dose limit of 1 mSv for the general population [52].

#### **4. Conclusions**

Activity concentrations of 226Ra, 232Th, 40K and 137Cs in soil and tea leaf samples collected from a large tea estate in the Chittagong region of Bangladesh were measured by HPGe γ-ray spectrometry. In addition, the most popular tea brands available in the local market were also measured to observe the effect of production processes. The transfer factor of radionuclides from soil to tea leaves was found to be less than 1, indicating the corresponding uptake by the tea plant to be insignificant. The estimated committed effective dose and the carcinogenic risk all show values far below the limiting ranges as suggested by various international bodies. Thus, the consumption of tea (at 4 g/day/person or two cups/day/person) produced from the Udalia Tea Estate provides an insignificant radiation risk to the health of the local populace. Considering a number of facts such as the non-availability of the literature data on TFs of the UTE tea leaves, the recommended limiting values for total dietary habits and that for the tea arising from this single entity, and that the radiation risk follows the linear no threshold model, the measured data can act as reference values for any future experimental or modelling studies for the protection of human health.

**Author Contributions:** Conceptualization, N.A., M.M.R., and N.S.; methodology, N.A. and M.M.R.; software, M.I.C. and M.U.K.; validation, M.M.H.M. and J.A.; formal analysis, N.A. and J.A.; investigation, N.A., M.M.R., and N.S.; resources, M.K. and M.I.C.; data curation, N.A. and M.M.H.M.; writing—original draft preparation, N.A. and J.A.; writing—review and editing, M.U.K. and D.A.B.; visualization, A.A.; supervision, M.M.R. and N.S.; project administration, M.R.I.F. and A.A.M.S.; funding acquisition, A.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Taif University Researchers Supporting project number (TURSP-2020/163), Taif 21944, Saudi Arabia.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All data are available in the manuscript.

**Acknowledgments:** Contributions from the staff of the gamma ray spectrometry laboratory of Atomic Energy Centre Chittagong are greatly acknowledged.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


**1.1. Social anxiety disorders**

SAD is among the most prevalent mental disorders (lifetime prevalence, 7–16%) [1]. It is characterized by fear of negative evaluation (e.g. rejection, humilation, embarrassment) or offending others lasting six or more months, accompanied by actively avoiding social situations, or staying with them with intense fear or anxiety. The fear is out of proportion to the actual threat posed by the social situation, depending on the sociocultural context. The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) updated SAD criteria with a special focus on separating social interactions (e.g., conversations), felt observation (e.g., dinner), and performance

situations (e.g., oral exams); "humiliation" and "embarrassment" are subsumed under the broader term "negative evaluation," the core fear in SAD; and including patients' sociocultural context allows for the better evaluation of the "excessive or unreasonable" fear described in the former version of the DSM [2, 3]. SAD is associated with considerable psychosocial and occupational handicaps and with an increased risk of comorbid mental impairment and suicidality [4, 5]. Remission rates are low (e.g., 20% in the first 2 years) compared with affective disorders and other anxiety disorders [6]. Thus, effective treatments are in high demand.

*Clark and Wells* added characteristics of information processing to explain the maintenance of SAD: (1) self-focused attention, (2) safety and/or avoidance behavior, and (3) fearful anticipation before an event and negative rumination after it. *Rapee and Heimberg* [16] emphasize the anticipated while overestimated performance standards that others have stimulating fear of scrutiny and contributing to SAD. Differences between these models refer to the attentional focus that is understood as a person's shift to monitoring internal versus external cues. In the first model, treating SAD primarily means to direct the patient's attention toward inward to increase the person's sense of self so that safety behaviors are identified, understood, and finally dropped. In the second model, treatment is aimed at training socially anxious individuals to direct their attention away from the mental representation of the self toward the

Cognitive Behavioral Therapy for Social Anxiety Disorder: Intrapersonal and Interpersonal…

http://dx.doi.org/10.5772/intechopen.74302

51

The second generation of cognitive behavioral models of SAD argues that the former approaches are too unspecific considering disorder-specific characteristics and with regard to the importance of the self in understanding SAD. *Hofmann* [17] agrees with the former models in hypothesizing that people with SAD anticipate social standards too high while heavily doubting to achieve them which results in an increased apprehension when entering social situations and heightened self-focused attention. The new component in his model refers to the affected person's strategy to purposefully fail so that others' expectations of them do not increase. People with SAD are described of perceiving their inability to meet expectations in tandem with the deficiency in setting social goals as well as planning and implementing actions for goal attainment. All models so far agree in hypothesizing that socially anxious people have intact social skills, but anxiety, negative cognitions, and avoidance behaviors impede social interactions. Consequently, treating SAD primarily highlights the work with defining and achieving social goals and with improving the patients' perception of their social skills rather than training them in specific skills. *Moscovitch* [18] and Stopa [19] criticize the former models having approached the self too little in understanding SAD. According to Moscovitch [18], they imprecisely concentrated on the negative evaluation as the feared consequence rather than the feared stimulus that occurs in SAD. The feared stimulus refers to the characteristics of the self that the person with SAD perceives as being deficient. It is these selfattributes themselves rather than the social situation, which are the most direct and sensible targets to work with. Self-attributes are understood quite stable compared to the activation of self-schemata at certain times and in certain social situations as proposed by the abovedescribed models. These self-attributes can be divided into four dimensions: (1) perceived deficiency in social skills ("I will make a mistake!"), (2) perceived visibility of anxiety ("I will blush!", "I will sweat!"), (3) perceived deficiency in physical appearance ("I am ugly!"), and (4) perceived personal deficiency ("I am damn stupid!"). Treating SAD thus means the functional analysis of these self-attributes and dimension-specific exposure aiming at the discovery of the person's authentic, non-concealed selves to others in the service of correcting their maladaptive perception of themselves . According to *Stopa* [19], maladaptive self-perception grounds in limited retrieval of multiple self-representations rather than the understanding of the self as a whole and self-attributes to be feared stimuli. The complexity of the self emerges in its conceptualization unfolding three categories: (1) content refers to information about the self (e.g., many negative statements in SAD) as well as the way in which that information is represented (e.g., logical versus figural verbalization) and is addressed by the former cognitive

task at hand and to indicators of nonnegative reactions from others [16].

Cognitive behavioral therapy (CBT) for SAD appears effective in a range of formats demonstrating a general effect size of *d* = 0.70 [7]. Effect sizes however vary considerably. The following parameters have shown substantial influence on CBT's efficacy: *setting*, with larger effect sizes in individual versus group settings; *data collection*, with larger effect sizes in observer ratings (e.g., *d* = 1.93, Liebowitz Social Anxiety Scale (LSAS)) versus self-reports (e.g., *d* = 1.23, LSAS-SR); *number of measures* and *treatment duration*, with larger effect sizes on composite measures in short treatments (e.g., *d* = 2.14 on the Social Phobia Composite, in a 4-month treatment) versus single measures in long treatments (e.g., *d* = 1.23–1.32 on the LSAS-SR, in an 8-month treatment); and *calculation of outcome*, with larger effect sizes calculated by odds ratios of remission and response (e.g., 36–86 and 56–86%, respectively) versus calculation of pre-post differences [8–13].


**About the Editor**

#### **C ´eline Ternon**

Celine Ternon graduated with PhD degrees from the University of Caen in 2002. Her ´ doctoral research involved the growth, modelling and study of luminescent silica and silicon-based nanostructures. She joined the Grenoble INP Institute of Engineering, Univ. Grenoble Alpes in 2003, where she is currently associate professor, gender equality officer and head of the department Physical Engineering for Photonics and Microelectronics.

She conducts research at LMGP in France in the field of nanomaterials and nanotechnologies. Her research interest lies at the interface between material science and device application, with a particular interest for the field of biosensing. One of her main objective is to develop new processes allowing the easy manipulation and integration of the nanomaterials into devices. In 2010, she launched an original activity based on semiconducting randomly oriented nanowire networks also called nanonets. Since then, she has worked tirelessly to demonstrate the value of these extremely versatile and innovative materials. She has more than 50 peer-reviewed scientific papers and several pedagogical publications.

## *Editorial* **Silica- and Silicon-Based Nanostructures**

**Céline Ternon**

Univ. Grenoble Alpes, CNRS, Grenoble INP (Institute of Engineering Univ. Grenoble Alpes), LMGP, F-38000 Grenoble, France<EMAIL_ADDRESS>
As depicted in Figure 1, studies on silicon and silica-based nanostructures first appeared in the early 1990s, and their numbers grew until the mid-2010s. Since then, the level of scientific research has decreased for silica-based nanostructures and started to decrease for silicon-based nanostructures. An extensive literature review of silicon-based nanostructures clearly shows that the major areas affected by the decline in the number of studies are "applied physics" and "engineering electrical electronic", whereas numerous applied fields are the subject of increased interest, particularly the applications of energy.

**Citation:** Ternon, C. Silica- and Silicon-Based Nanostructures. *Nanomaterials* **2022**, *12*, 1270. https:// doi.org/10.3390/nano12081270

Received: 16 March 2022 Accepted: 25 March 2022 Published: 8 April 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

**Figure 1.** Number of articles published per year about silicon or silica nanostructures, based on a search using the keywords "Silicon AND Nano\*" or "Silica AND Nano\*" on the website Web of Science. The star \* at the end of nano means that all words beginning with "nano" are considered in the search (nanoparticles, nanowires . . . ).

For silicon nanostructures, such a decrease in research is a sign that structures and technologies have been mastered and that the most popular applications, such as electronic devices, have been explored. Research teams are now exploring new areas and applications for these nanostructures.

The purpose of this Special Issue is to bring together state-of-the-art innovations in the field and allow the emergence of novel ideas and concepts for silicon- and silica-based nanostructures. The three reviews in this Special Issue [1–3] offer an original view of the last 10 years of research on silicon nanostructures, especially for black silicon [1], bottom-up nanowires [2], and mesoporous silicon [3]. Most interestingly, these reviews outline the areas of interest for the future of these materials. In line with this, some studies [4–10] clearly illustrate the thematic shift of research into these materials, with a growing interest in ecoresponsive areas, such as biomass synthesis [4], environmental sensors [5], batteries [6,7] or depollution [3].

In conclusion, we hope that the readers will enjoy the works and articles collated in this Special Issue, inspiring ideas and providing information to inform further studies of these fascinating nanomaterials, as well as generating new projects and topics.

**Acknowledgments:** I would like to thank all the authors who contributed their most recent research to this Special Issue. We would like to thank all those who contributed to the success of this Special Issue for their patience, help and dedication.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**