Pollution risks to people slip through net in tests on fish

A new class of organic pollutants in the environment which could pose risks to people's health has been identified by scientists. The chemicals, used in a wide range of pesticides and cosmetics, have been unwittingly ignored by regulators, who have assumed them to be safe. Organic chemicals such as dioxins, PCBs and the pesticide DDT are dangerous because once they get into the environment they stay there. Even small amounts in food can build up over time and contribute to health problems in later life such as cancer. As a result, more than 140 countries have endorsed a treaty to try to remove a dozen of the most dangerous chemicals from the environment. But Canadian scientists have found that there is a flaw in the models used to predict which substances are dangerous. Regulators normally do this by watching the chemicals that accumulate in fish. But Frank Gobas, at the Simon Fraser University in British Columbia, said fish flushed out chemical pollutants from their bodies in a different way from air-breathing animals and birds. Professor Gobas has identified a new class of chemicals which fish seem to be able to get rid of but which could accumulate and cause problems in people. "These ... chemicals, representing a third of organic chemicals in commercial use, constitute an unidentified class of potentially bioaccumulative substances that require regulatory assessment to prevent possible ecosystem and human-health consequences," he wrote on July 13 in Science. Organic pollutants are made up of complex molecules which do not break down easily, building up in the food chain through bioaccumulation. This means that the level of the chemicals in an animal's tissues rises the higher up the food chain it is - larvae might eat some contaminated algae, a fish eats the larvae, and bigger fish eat smaller fish. Those at the top of the food chain, such as swordfish and polar bears, have been found to contain the highest doses of pollutants. Regulators studying fish measure how readily a chemical dissolves in water. The more water-soluble a chemical is, the safer it is to the fish, because it can be easily passed out of its body. But many chemicals which are soluble in water and which do not persist in fish could remain trapped in the tissues of air-breathing land animals. Gobas identified a new class of pollutants which had slipped through the regulators' net: highly water-soluble chemicals which are not volatile enough for animals to breathe out. He confirmed that these were present in samples from a wide range of organisms in the Arctic, including beluga whales. David Santillo, a toxicologist at the Greenpeace research laboratory at Exeter University, said that the results were not surprising. "It reveals something which we've always suspected."