plastic is exported into the ocean by just 10 major rivers. an organism can accumulate pcbs by consuming other organisms that have previously ingested pcbs from terrestrial, freshwater, or marine environments. the concentration of pcbs within an organism will increase over their lifetime; this process is called bioaccumulation. pcb concentrations within an organism also change depending upon which trophic level they occupy. when an organism occupies a high trophic level, like orcas or humans, they will accumulate more pcbs than an organism that occupies a low trophic level, like phytoplankton. if enough organisms with a trophic level are killed due to the accumulation of toxins, like pcb, a trophic cascade can occur. pcbs can cause harm to human health or even death when eaten. pcbs can be transported by birds from aquatic sources onto land via feces and carcasses. biochemical metabolism overview pcbs undergo xenobiotic biotransformation, a mechanism used to make lipophilic toxins more polar and more easily excreted from the body. the biotransformation is dependent on the number of chlorine atoms present, along with their position on the rings. phase i reactions occur by adding an oxygen to either of the benzene rings by cytochrome p450. the type of p450 present also determines where the oxygen will be added; phenobarbital (pb)-induced p450s catalyze oxygenation to the meta-para positions of pcbs while 3-methylcholanthrene (3mc)-induced p450s add oxygens to the ortho–meta positions. pcbs containing ortho–meta and meta–para protons can be metabolized by either enzyme, making them the most likely to leave the organism. however, some metabolites of pcbs containing ortho–meta protons have increased steric hindrance from the oxygen, causing increased stability and an increased chance of accumulation. species dependent metabolism is also dependent on the species of organism; different organisms have slightly different p450 enzymes that metabolize certain pcbs better than others. looking at the pcb metabolism in the liver of four sea turtle species (green, olive ridley, loggerhead and hawksbill), green and hawksbill sea turtles have noticeably higher hydroxylation rates of pcb 52 than olive ridley or loggerhead sea turtles. this is because the green and hawksbill sea turtles have higher p450 2-like protein expression. this protein adds three hydroxyl groups to pcb 52, making it more polar and water-soluble. p450 3-like protein expression that is thought to be linked to pcb 77 metabolism, something that was not measured in this study. temperature dependent temperature plays a key role in the ecology, physiology and metabolism of aquatic species. the rate of pcb metabolism was temperature dependent in yellow perch (perca flavescens). in fall and winter, only 11 out of 72 introduced pcb congeners were excreted and had halflives of more than 1,000 days. during spring and summer when the average daily water temperature was above 20 °c, persistent pcbs had halflives of 67 days. the main excretion processes were fecal egestion, growth dilution and loss across respiratory surfaces. the excretion rate of pcbs matched with the perch's natural bioenergetics, where most of their consumption, respiration and growth rates occur during the late spring and summer. since the perch is performing more functions in the warmer months, it naturally has a faster metabolism and has less pcb accumulation. however, multiple cold-water periods mixed with toxic pcbs with coplanar chlorine molecules can be detrimental to perch health. sex dependent enantiomers of chiral compounds have similar chemical and physical properties, but can be metabolized by the body differently. this was looked at in bowhead whales (balaena mysticetus) for two main reasons: they are large animals with slow metabolisms (meaning pcbs will accumulate in fatty tissue) and few studies have measured chiral pcbs in cetaceans. they found that the average pcb concentrations in the blubber were approximately four times higher than the liver; however, this result is most likely age- and sex-dependent. as reproductively active females transferred pcbs and other poisonous substances to the fetus, the pcb concentrations in the blubber were significantly lower than males of the same body length (less than 13 meters). health effects labelling transformers containing pcbs the toxicity of pcbs varies considerably among congeners. the coplanar pcbs, known as nonortho pcbs because they are not substituted at the ring positions ortho to (next to) the other ring, (such as pcbs 77, 126 and 169), tend to have dioxin-like properties, and generally are among the most toxic congeners. because pcbs are almost invariably found in complex mixtures, the concept of toxic equivalency factors (tefs) has been developed to facilitate risk assessment and regulation, where more toxic pcb congeners are assigned higher tef values on a scale from 0 to 1. one of the most toxic compounds known, 2,3,7,8-tetrachlorodibenzodioxin, a pcdd, is assigned a tef of 1. in june 2020, state impact of pennsylvania stated that "in 1979, the epa banned the use of pcbs, but they still exist in some products produced before 1979. they persist in the environment because they bind to sediments and soils. high exposure to pcbs can cause birth defects, developmental delays, and liver changes." exposure and excretion in general, people are exposed to pcbs overwhelmingly through food, much less so by breathing contaminated air, and least by skin contact. once exposed, some pcbs may change to other chemicals inside the body. these chemicals or unchanged pcbs can be excreted in feces or may remain in a person's body for years, with half lives estimated at 10–15 years. pcbs collect in body fat and milk fat. pcbs biomagnify up the food web and are present in fish and overflow of contaminated aquifers. human infants are exposed to pcbs through breast milk or by intrauterine exposure through transplacental transfer of pcbs and are at the top of the food chain.: 249ff workers recycling old equipment in the electronics recycling industry can also be exposed to pcbs. humans the most commonly observed health effects in people exposed to extremely high levels of pcbs are skin conditions, such as chloracne and rashes, but these were known to be symptoms of acute systemic poisoning dating back to 1922. studies in workers exposed to pcbs have shown changes in blood and urine that may indicate liver damage. in japan in 1968, 280 kg of pcb-contaminated rice bran oil was used as chicken feed, resulting in a mass poisoning, known as yushō disease, in over 1800 people. common symptoms included dermal and ocular lesions, irregular menstrual cycles and lowered immune responses. other symptoms included fatigue, headaches, coughs, and unusual skin sores. additionally, in children, there were reports of poor cognitive development. women exposed to pcbs before or during pregnancy can give birth to children with lowered cognitive ability, immune compromise, and motor control problems. there is evidence that crash dieters that have been exposed to pcbs have an elevated risk of health complications. stored pcbs in the adipose tissue become mobilized into the blood when individuals begin to crash diet. pcbs have shown toxic and mutagenic effects by interfering with hormones in the body. pcbs, depending on the specific congener, have been shown to both inhibit and imitate estradiol, the main sex hormone in females. imitation of the estrogen compound can feed estrogen-dependent breast cancer cells, and possibly cause other cancers, such as uterine or cervical. inhibition of estradiol can lead to serious developmental problems for both males and females, including sexual, skeletal, and mental development issues. in a cross-sectional study, pcbs were found to be negatively associated with testosterone levels in adolescent boys. high pcb levels in adults have been shown to result in reduced levels of the thyroid hormone triiodothyronine, which affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate. it also resulted in reduced immunity and increased thyroid disorders. animals animals that eat pcb-contaminated food, even for short periods of time, suffer liver damage and may die. in 1968 in japan, 400,000 birds died after eating poultry feed that was contaminated with pcbs. animals that ingest smaller amounts of pcbs in food over several weeks or months develop various health effects, including anemia; acne-like skin conditions (chloracne); liver, stomach, and thyroid gland injuries (including hepatocarcinoma), and thymocyte apoptosis. other effects of pcbs in animals include changes in the immune system, behavioral alterations, and impaired reproduction. pcbs that have dioxin-like activity are known to cause a variety of teratogenic effects in animals. exposure to pcbs causes hearing loss and symptoms similar to hypothyroidism in rats. cancer in 2013, the international agency for research on cancer (iarc) classified dioxin-like pcbs as human carcinogens. according to the u.s. epa, pcbs have been shown to cause cancer in animals and evidence supports a cancer-causing effect in humans. per the epa, studies have found increases in malignant melanoma and rare liver cancers in pcb workers. in 2013, the iarc determined that the evidence for pcbs causing non-hodgkin lymphoma is "limited" and "not consistent". in contrast an association between elevated blood levels of pcbs and non-hodgkin lymphoma had been previously accepted. pcbs may play a role in the development of cancers of the immune system because some tests of laboratory animals subjected to very high doses of pcbs have shown effects on the animals' immune system, and some studies of human populations have reported an association between environmental levels of pcbs and immune response. lawsuits related to health effects in the early 1990s, monsanto faced several lawsuits over harm caused by pcbs from workers at companies such as westinghouse that bought pcbs from monsanto and used them to build electrical equipment. monsanto and its customers, such as westinghouse and ge, also faced litigation from third parties, such as workers at scrap yards that bought used electrical equipment and broke them down to reclaim valuable metals. monsanto settled some of these cases and won the others, on the grounds that it had clearly told its customers that pcbs were dangerous chemicals and that protective procedures needed to be implemented. in 2003, monsanto and solutia inc., a monsanto corporate spin-off, reached a $700 million settlement with the residents of west anniston, alabama, who had been affected by the manufacturing and dumping of pcbs. in a trial lasting six weeks, the jury found that "monsanto had engaged in outrageous behavior, and held the corporations and its corporate successors liable on all six counts it considered – including negligence, nuisance, wantonness and suppression of the truth." in 2014, the los angeles superior court found that monsanto was not liable for cancers claimed to be from pcbs permeating the food supply of three plaintiffs who had developed non-hodgkin's lymphoma. after a four-week trial, the jury found that monsanto's production and sale of pcbs between 1935 and 1977 were not substantial causes of the cancer. in 2015, the cities of spokane, san diego, and san jose initiated lawsuits against monsanto to recover cleanup costs for pcb contaminated sites, alleging that monsanto continued to sell pcbs without adequate warnings after they knew of their toxicity. monsanto issued a media statement concerning the san diego case, claiming that improper use or disposal by third-parties, of a lawfully sold product, was not the company's responsibility. in july 2015, a st louis county court in missouri found that monsanto, solutia, pharmacia and pfizer were not liable for a series of deaths and injuries caused by pcbs manufactured by monsanto chemical company until 1977. the trial took nearly a month and the jury took a day of deliberations to return a verdict against the plaintiffs from throughout the usa. similar cases are ongoing. "the evidence simply doesn't support the assertion that the historic use of pcb products was the cause of the plaintiffs' harms. we are confident that the jury will conclude, as two other juries have found in similar cases, that the former monsanto company is not responsible for the alleged injuries," a monsanto statement said. in may 2016, a missouri state jury ordered monsanto to pay $46.5 million to three plaintiffs whose exposure to pcb caused non-hodgkin lymphoma. in december 2016, the state of washington filed suit in king county. the state sought damages and clean up costs related to pcbs. in march 2018 ohio attorney general mike dewine also filed a lawsuit against monsanto over health issues posed by pcbs. on november 21, 2019, a federal judge denied a bid by monsanto to dismiss a lawsuit filed by la county calling the