methanol. unlike the c-alkylation, the o-alkylation replaces the hydrogen atom on the -oh group with the methyl group (from the methanol). the product of the o-alkylation is methoxybenzene, better-known as anisole, and water, which is not shown in the diagram. anisole is listed as an acute hazard to aquatic life with long-term effects. bioaccumulation bioaccumulation is the process by which an organism takes in chemicals through ingestion, exposure, and inhalation. bioaccumulation is broken down into bioconcentration (uptake of chemicals from the environment) and biomagnification (increasing concentration of chemicals as they move up the food chain). certain species of aquatic organisms are affected differently from the chemicals released from creosote preservatives. one of the more studied organisms is a mollusk. mollusks attach to the wooden, marine pilings and are in direct contact with the creosote preservatives. many studies have been conducted using polycyclic aromatic hydrocarbons (pah), which are low molecular hydrocarbons found in some creosote-based preservatives. in a study conducted from pensacola, florida, a group of native mollusks were kept in a controlled environment, and a different group of native mollusks were kept in an environment contaminated with creosote preservatives. the mollusks in the contaminated environment were shown to have a bioaccumulation of up to ten times the concentration of pah than the control species. the intake of organisms is dependent on whether the compound is in an ionized or an un-ionized form. to determine whether the compound is ionized or un-ionized, the ph of the surrounding environment must be compared to the pka or acidity constant of the compound. if the ph of the environment is lower than the pka, then the compound is un-ionized which means that the compound will behave as if it is non-polar. bioaccumulation for un-ionized compounds comes from partitioning equilibrium between the aqueous phase and the lipids in the organism. if the ph is higher than the pka, then the compound is considered to be in the ionized form. the un-ionized form is favored because the bioaccumulation is easier for the organism to intake through partitioning equilibrium. the table below shows a list of pkas from compounds found in creosote preservatives and compares them to the average ph of seawater (reported to be 8.1). compound pka ph of seawater form (ionized or un-ionized) m-cresol 10.09 8.1 un-ionized o-cresol 10.29 un-ionized p-cresol 10.30 un-ionized 2-ethylphenol 10.20 un-ionized guaiacol 9.98 un-ionized phenol 9.99 un-ionized each of the compounds in the table above is found in creosote preservatives; all are in the favored un-ionized form. in another study, various species of small fish were tested to see how the exposure time to pah chemicals affected the fish. this study showed that an exposure time of 24–96 hours on various shrimp and fish species affected the growth, reproduction, and survival functions of the organisms for most of the compounds tested. biodegradation biodegradation can be seen in some studies that biodegradation accounts for the absence of creosote preservatives on the initial surface of the sediment. in a study from pensacola, florida, pahs were not detected on the surface on the aquatic sediment, but the highest concentrations were detected at a depth of 8-13 centimeters. a form an anaerobic biodegradation of m-cresol was seen in a study using sulfate-reducing and nitrate-reducing enriched environments. the reduction of m-cresol in this study was seen in under 144 hours, while additional chemical intermediates were being formed. the chemical intermediates were formed in the presence of bicarbonate. the products included 4-hydroxy-2-methylbenzoic acid and acetate compounds. although the conditions were enriched with the reducing anaerobic compounds, sulfate and nitrate reducing bacteria are commonly found in the environment. for further information, see sulfate-reducing bacteria. the type of anaerobic bacteria ultimately determines the reduction of the creosote preservative compounds, while each individual compound may only go through reduction under certain conditions. btex is a mixture of benzene, toluene, ethylbenzene, and xylene, that was studied in the presence of four different anaerobic-enriched sediments. though the compound, btex, is not found in creosote preservatives, the products of creosote preservatives' oxidation-reduction reactions include some of these compounds. for oxidation-reduction reactions, see the following section. in this study, it was seen that certain compounds such as benzene were only reduced under sulfate-enriched environments, while toluene was reduced under a variety of bacteria-enriched environments, not just sulfate. the biodegradation of a creosote preservative in an anaerobic enrichment depends not only on the type of bacteria enriching the environment, but also the compound that has been released from the preservative. in aerobic environments, preservative compounds are limited in the biodegradation process by the presence of free oxygen. in an aerobic environment, free oxygen comes from oxygen saturated sediments, sources of precipitation, and plume edges. the free oxygen allows for the compounds to be oxidized and decomposed into new intermediate compounds. studies have shown that when btex and pah compounds were placed in aerobic environments, the oxidation of the ring structures caused cleavage in the aromatic ring and allowed for other functional groups to attach. when an aromatic hydrocarbon was introduced to the molecular oxygen in experimental conditions, a dihydrodiol intermediate was formed, and then oxidation occurred transforming the aromatic into a catechol compound. catechol allows for cleavage of the aromatic ring to occur, where functional groups can then add in an ortho- or meta- position. oxidation-reduction even though many studies conduct testing under experimental or enriched conditions, oxidation-reduction reactions occur naturally and allow for chemicals to go through processes such as biodegradation, outlined above. oxidation is defined as the loss of an electron to another species, while reduction is the gaining of an electron from another species. as compounds go through oxidation and reduction in sediments, the preservative compounds are altered to form new chemicals, leading to decomposition. an example of the oxidation of p-cresol and phenol can be seen in the figures below: p-cresol this reaction shows the oxidation of p-cresol in a sulfate-enriched environment. p-cresol was seen to be the easiest to degrade through the sulfate-enriched environment, while m-cresol and o-cresol where inhibited. in the chart above, p-cresol was oxidized under an anaerobic sulfate reducing condition and formed four different intermediates. after the formation of the intermediates, the study reported further degradation of the intermediates leading to the production of carbon dioxide and methane. the p-hydroxylbenzyl alcohol, p-hydroxylbenzaldehye, p-hyrdoxylbenzoate, and benzoate intermediates all are produced from this oxidation and released into the sediments. similar results were also produced by different studies using other forms of oxidation such as: iron-reducing organisms, copper/manganese oxide catalyst, and nitrate- reducing conditions. phenol this reaction shows the oxidation of phenol by iron and peroxide. this combination of iron, which comes from iron oxide in the sediment, and the peroxide, commonly released by animals and plants into the environment, is known as the fenton reagent. this reagent is used to oxidize phenol groups by the use of a radical hydroxide group produced from the peroxide in the p-benzoquinone. this product of phenol's oxidation is now leached into the environment while other products include iron(ii) and water. p-benzoquinone is listed as being a very toxic, acute environmental hazard. environmental hazards sediment in aquatic sediments, several reactions can transform the chemicals released by the creosote preservatives into more dangerous chemicals. most creosote preservative compounds have hazards associated with them before they are transformed. cresol (m-, p-, and o-), phenol, guaiacol, and xylenol (1,3,4- and 1,3,5-) all are acute aquatic hazards prior to going through chemical reactions with the sediments. alkylation reactions allows for the compounds to transition into more toxic compounds with the addition of r-groups to the major compounds found in creosote preservatives. compounds formed through alkylation include: 3,4-dimethylphenol, 2,3-dimethylphenol, and 2,5-dimethylphenol, which are all listed as acute environmental hazards. biodegradation controls the rate at which the sediment holds the chemicals, and the number of reactions that are able to take place. the biodegradation process can take place under many different conditions, and vary depending on the compounds that are released. oxidation-reduction reactions allow for the compounds to be broken down into new forms of more toxic molecules. studies have shown oxidation-reduction reactions of creosote preservative compounds included compounds that are listed as environmental hazards, such as p-benzoquinone in the oxidation of phenol. not only are the initial compounds in creosote hazardous to the environment, but the byproducts of the chemical reactions are environmental hazardous as well. other from the contamination of the sediment, more of the ecosystem is affected. organisms in the sediment are now exposed to the new chemicals. organisms are then ingested by fish and other aquatic animals. these animals now contain concentrations of hazardous chemicals which were secreted from the creosote. other issues with ecosystems include bioaccumulation. bioaccumulation occurs when high levels of chemicals are passed to aquatic life near the creosote pilings. mollusks and other smaller crustaceans are at higher risk because they are directly attached to the surface of wood pilings that are filled with creosote preservative. studies show that mollusks in these environments take on high concentrations of chemical compounds which will then be transferred through the ecosystem's food chain. bioaccumulation contributes to the higher concentrations of chemicals within the organisms in the aquatic ecosystems.