Persistent organic pollutants (POPs) are organic compounds, which resist photolytic, biological and chemical degradation to varying degrees. POPs are often halogenated and very dispersable. They are characterized by low water solubility and high lipid solubility, leading to their bioaccumulation in fatty tissues. They are also semi-volatile, enabling them to move long distances in the atmosphere before deposition occurs. There are 12 commonly found chemicals causing biomagnification, which can be called as “Dirty Dozen”!
1.Aldrin
2.Chlordane
3.DDT
4.Dieldrin
5.Endrin
6.Heptachlor
7.Hexa chloro benzene
8.Mirex
9.Toxaphene
10.PCB’s (poly chlorinated biphenyls)
11.Furans
12.Dioxins
Many of these compounds have been or continue to be used in large quantities. These compounds have the ability to bioaccumulate and biomagnify due to their environmental persistence. Compounds such as polychlorinated biphenyls PCBs may persist in the environment for periods of years and may bioconcentrate by factors of up to 70,000 fold. The semi-volatile property of POPs permit them to occur either in vapor phase or adsorbed on atmospheric particles, thereby facilitating their long range transport through the atmosphere.
POPs are ubiquitous. They have been measured on every continent, at sites representing every major climatic zone and geographic sector throughtout the world. These include remote regions such as the open oceans, the deserts, the Arctic and the Antarctic, where no significant local sources exist and the only reasojnable explanation for their presence is long-range transport from other parts of the globe. PCBs have been reports in air, in all areas of the world, at concentrations up to 1ng/m3; in industrialized areas, concentrations may be several orders of magnitude greater. PCBs have also been reported in rain and snow.
POPs are represented by two important sub groups including both the polycyclic aromatic hydrocarbons and some halogenated hydrocarbons. This latter group includes several organochlorines which, historically, have proven to be most resistant to degradation and which have had wide production, use and release characteristics. These chlorinated derivatives are generally the most persistent of all the halogenated hydrocarbons. In general, it is known that the more highly chlorinated biphenyls tend to accumulate to a greater extent than the less chlorinated PCBs. Also, metabolism and excretion is also more rapid for the less chlorinated PCBs than for the highly chlorinated biphenyls.
We can be exposed to POPs through diet, occupational accidents and the environment (including indoor). Exposure to POPs, either acute or chronic, can be associated with a wide range of adverse health effects, including illness and death. Laboratory investigations and environmental impact studies in the wild have implicated POPs in endocrine disruption, reproductive and immune dysfunction, neurobehavioral disorders and cancer. Recently, some POPs have been implicated in reduced immunity in infants and children, and the concomitant increase in infection, also with developmental abnormalities, neurobehavioral impairment and cancer and tumor induction or promotion. Some POPs are also being considered as a potentially important risk factor in the etiology of human breast cancer by some authors.
Immunotoxicity in association with exposure to different POPs has been reported by several authors. Investiagtors have demonstrated immune dysfunction as a plausible cause for an increased mortality among marine mammals and have also demonstrated that consumption of POP contaminated diets in seals may lead to vitamin and thyrois deficiencies and concomitant susceptibility to microbial infections and reproductive disorders.
The risk is greatest in developing countries where the use of POPs in tropical agriculture has resulted in a large number of deaths and injuries. In addition to other exposure rioutes, worker exposure to POPs during waste management is a significant source of occupational risk in many countries.
By Shilpa C
