Chemicals in Commercial Use Need to be Re-assessed

Approximatley 10,000 chemicals require new testing procedures as conventional tests underestimate how some substances accumulate along the food chain.These include some pesticides, and possibly some pharmaceuticals.

A recent study published in the journal Science states that the conventional tests that are used to show how certain substance accumulate along the food chain are not adequate to the task. According to the study’s authors, the conventional tests underestimate this accumulation. The substances of concern include some pesticides and possibly some pharmaceuticals. The reports authors say that approximately one-third of the organic substances in commercial use will need to be re-tested. The researchers say that ,out of the approximately 10, 000 substances, that will need retesting, they anticipate that most will turn out to be benign.In June, European Union legislation on the Registration, Evaluation, Authorisation and Restriction of Chemicals (Reach) became reality. The result of this legislation is that about 30,000 chemicals in industrial use will be tested for health and safety impacts. The cost of this re-testing is nearly 10bn euros ($13bn). If a substance is bio-accumulative it will remain in the body after it has been consumed. Bio-accumulative or persistent substances rise in concentration as they move up for the food chain. For example, a substance that is found at a certain concentration in plankton will be at a higher concentration in the small fish that feed on the plankton, the concentration will increase in the bigger fish that consumes the small fish and even higher in the bears that eat the fish. Over the years there have been twelve (12) types of toxic persistent organic pollutants (pops) that have been banned under the Stockholm Convention (Pops Treaty). The twelve include DDT, dioxins and polychlorinated biphenyls (PCBs). The bio-accumulative potential of a chemical is assessed using a ratio that is called the octanol-water partition co-efficient (Kow). Kow is a measure of how effectively the substance dissolves in fat versus water. If the substance shows a partiality for water this means that the substance is likely to be transported out of a fish's body as it respires, while a fondness for fat means it is likely to remain. According to the researchers, this works fine when used to measure the accumulative potential in food chains involving fish, shellfish and plankton. However, when assessing the effect on air-breathing animals a different measure is needed, according to the report. The researchers refer to this new measure as Koa and Koa looks at whether the substance being examined can be lost across the lung membrane during respiration. The researchers compared the accumulation of two chemicals: PCB-153 and beta-hexachlorocyclohexane (beta-HCH), a close relative of the well-known insecticide lindane, in three different food chains. One food chain goes from plankton to fish, the second from lichen to caribou to wolves, and the third from plankton through fish to walruses, seals and polar bears. PCB-153 has a high Kow and accumulated across all three food chains. However, beta-HCH, which has a low Kow but high Koa, only showed accumulation along the lichen/caribou/wolf and marine mammal food chains. In the case of beta-HCH the conventional tests would have missed this potential to accumulate. Low Kow and high Koa compounds include endosulfans and HCHs, which are used as insecticides, musk xylene, an ingredient of perfumes and soaps, and the tetrachlorobenzenes.

"About one-third of these organic chemicals are not on the radar screen.”They won't all be bio-accumulative, but they all have the potential to be bio-accumulative." Frank Gobas from Simon Fraser University in Burnaby, British Columbia.

The body will metabolize many of these chemical and thus dispose of them in that way. Gobas and his team want to use this new measure of bio-accumulation to see if there is a hitherto unexpected threat to health and environmental well-being.