Executive summary:

 Polychlorinated biphenyls or PCBs are numerous biphenyl based artificial products that are extensively used as a dielectric fluid as well as lubricants in the 1960s and 1970s. Hence, the article explored distribution and effects in the environment and toxicokinetics of Polychlorinated biphenyls. Polychlorinated biphenyls frequently discharged into the natural environment from a hazardous waste site. After frequent discharge in the waste, PBCs may remain in an eco-system for a long time in soil, water, and air.  They can be accumulated in air through evaporation and move across the distance.  Considering the food chain, PBCs consumption is highest amongst animals since it can be consumed by fish and other organisms with the food.  The single-molecule is colorless and can absorb the low wavelength of UV light where the main area of the absorption is near to 200nm and slightly towards 240nm which are not present in the troposphere. The maximum wavelength is depending on the number and location of chlorine present. Reaction with hydroxyl radicals (OH) is considered as one of the crucial reactions for identifying PCBs in the atmosphere.  It is often observed that products of photo transformation PCBs in the troposphere are hydroxylated biphenyls and the upper layer of the water light participates in this reaction.  The microbial transformation of PCBs is usually observed in the soil since bacteria can decompose it by using the dioxygenase enzyme which catalyzes the reaction of inserting two oxygen atoms in the substrate.   Since various bacteria can transform it, a large quantity of it observed in the soil. The complete degradation is not possible without degrading chlorobenzoate during the decomposition.  Since higher organisms have monooxygenase enzymes, some of them are capable of involving in the biotransformation and mammals metabolize PCBs by forming sulfones. Fish are also capable of biotransformation by introducing one atom of oxygen form OH PCBs derivatives.

 In order to conduct appropriate waste management, it is crucial to gain an understanding of the toxico-kinetics of PCBs. While very limited studies could provide evidence of half-lives of PCBs, the majority of these studies suggested that the single or their mixture can be easily observed in the gastrointestinal tract (66% to 96%) where the amount of chlorine determines the absorption. The initial uptake is observed in liver and muscle due to high blood perfusion and a large volume of muscle.  The large amount can be absorbed by the skin and adipose tissue they are liposoluble. The degradation is observed in the liver and it is hepatocytes with cytochrome P-450-dependent monooxygenase system.  The elimination is biphasic and it is eliminated through bile, urine, and feces. One of the prominent instances of the toxicity is that it can cross the placental barrier and accumulate in fetal tissues.

 The acute toxicity of it for oral LD50-values in rats ranging from 0.4–11 g/kg and death occurs after 3 days after the oral exposure and after intravenous administration.  Considering the long term toxicity,   impact on human and rats include edema at various sites, cancer development, neurodevelopment, reproductive toxicity. Monkey, minks and guinea pigs are more sensitivity compared to the rats and mice.  After exposure to PCBs, severe effects are observed in humans and few incidents were well documented in Japan in 1968 (Yusho) and Taiwan in 1979 (Yu-Cheng). Around 2000 patients experienced toxicity after each accident. Symptoms and toxic effects of the PCBs include hyperpigmentation, other dermal effects, chronic bronchitis, liver effects, immunosuppression, neuropathy, enzyme induction, and hormonal effects.  The carcinogenic impact of the product was also observed such as biliary tract, skin, and intestines and it also induces brain cancer. However, the evidence of the carcinogenic impact is inconsistence and limited with a small sample size.  The extensive studies are required to conduct for gathering sufficient evidence regarding impact of the carcinogenic effect. Lastly,   PCBs are capable if inducing negative impact on neurological development of animals. Amongst children and infants, abnormal reflexes, memory dysfunction, learning, and low IQ are usually observed due to exposure to PCBs. Various epidemiological studies highlighted that PCBs play a significant role in neuro-developmental toxicity in offspring whose mothers were exposed to PCBs by eating contaminated fish. Consumption of   contaminated fish is associated with abnormally weak reflexes along with delayed newborn autonomic maturity.  Hence, in order to reduce severe toxicity, it is crucial to design an appropriate hazard management plan that can reduce PCBs leakage and exposure.