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Research Suggests That Risk Assessments for POPs Need Revision

(Beyond Pesticides, July 17, 2007) A study conducted by Canadian researchers show that high concentrations of POPs, or Persistent Organic Pollutants, can be observed in humans and other air-breathing animals even though they may not accumulate in fish. This suggests that current risk assessment methodologies need to be changed for identifying potential POPs in birds and mammals.

POPs are synthetic, toxic chemicals that persist in the environment, bioaccumulate in food chains and are common contaminants in fish, dairy products and other foods. These compounds are generally accepted to be hydrophobic and fat-soluble. Screening for these bioaccumulative compounds is normally conducted with laboratory tests using fish. However researchers Barry C. Kelly, and Frank Gobas, Ph.D., at Simon Fraser University in Burnaby, British Columbia report that this methodology may overlook a significant number of pollutants that pose health risks to air-breathing animals.

The study entitled “Food Web–Specific Biomagnification of Persistent Organic Pollutants” (Science 2007, v317, p236) examines the biomagnification of moderately hydrophobic compounds with octanol-water partition coefficients (Kow) between 100 and 100,000 (currently, compounds with Kow greater than 100,000 are generally categorized as bioaccumulative compounds and tend to be hydrophobic and fat-soluble) and compounds with high octanol-air partition coefficients (Koa). The compounds have been tested within a variety of food webs including one with only water-respiring organisms, one with only air-breathing organisms, and one with both (including humans). Compounds with a high Koa and Kow, such as PCB 153, biomagnify in all food webs. However, compounds such as lindane, which has a high Koa and low Kow do not biomagnify in food webs including only water-respiring organisms, but do accumulate in food webs with air-breathing animals.

According to Lynn Goldman, M.D., of the John Hopkins University Bloomberg School of Public Health, the study suggests, “a broader range of chemicals, with high Koa but lower Kow, should perhaps be considered to be persistent organic pollutants.” Dr. Gobas points out that even though the degree to which chemicals are transformed in organisms is difficult to predict, he hopes that environmental regulations will change in light of this new work. EPA research chemist, Lawrence Burkhard says, “[C]urrent risk assessments that classify a chemical as a persistent organic pollutant have based their conclusions primarily on science drawn from aquatic toxicology. This paper strongly suggests risk assessment methodologies need to be changed to include data on bioaccumulation in birds and mammals. If this is done, more chemicals may be classified as POPs than have been in the past.”

The finding is important since many Americans may carry enough POPs in their bodies to cause subtle but serious health effects, including reproductive and developmental problems, cancer, and disruption of the immune system. According to the World Wildlife Fund (WWF), POPs pose a particular hazard because of four characteristics: they are toxic; they are persistent, resisting normal processes that break down contaminants; they accumulate in the body fat of people, marine mammals, and other animals and are passed from mother to fetus; and they can travel great distances on wind and water currents. Even minute quantities can cause nervous system damage, diseases of the immune system, reproductive and developmental disorders, cancers and other diseases like diabetes. Most vulnerable are those in the womb or egg, and in infancy, as vital organ systems are being developed.

The Stockholm Convention on Persistent Organic Pollutants (see Daily News) represents one of the most important efforts by the global community to rein in and ultimately halt the proliferation of toxic chemicals. This treaty, ratified on May 17, 2004 is an attempt to reduce the impact of these persistent chemicals throughout the world. The U.S. has yet to be among 150 ratifying countries. In 2001, President Bush promised to support the treaty, but his administration has sought to undermine it with legislation that would make it harder, rather than easier, for EPA to comply.

Source: Chemical and Engineering News


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