Bio-Accumulation: Effects of spraying

Roy C Dudgeon

Bio-Accumulation (also referred to as biological amplification and biological magnification) refers to the process by which persistent organic pollutants (POPs) accumulate in higher levels as they are passed from one trophic level to another through food chains.

POPs are a class of artificial chemicals with the following five characteristics. 1. they are persistent (do not break down quickly through natural or biological processes). 2. they are organic compounds (or have a carbon based molecular structure). 3. they are polluting (toxic, or poisonous, many are known carcinogens or mutagens). 4. they are fat-soluble (absorbable by fatty tissues, and therefore subject to accumulation in living tissues). 5. they occur in forms which allow them to travel great distances throughout the biosphere.

Not all pesticides used in the agricultural sector are POPs, and pesticides are not the only chemicals to be concerned about. Some of the most notorious POPs include, but are not limited to, the organochlorine insectides (DDT, aldrine, chlordane), PCBs, and Dioxins. Many such chemicals last for decades or, like DDT can break down into even more toxic compounds.

Understanding how the process works:

An field has been sprayed with DDT, which accumulates on the grain, each contaminated with 1ppm (part per million) of the chemical. An insect eats many plants and the chemical accumulates in their bodily tissues, leading to a concentration of 10 ppm. A frog eats many such insects, leading to a concentration of 100 ppm. A fish eats many such frogs, leading to a concentration of 1000ppm. A human eats many such fish and the concentration increases further.

This implies that species higher up the food chain, such as humans, are at greater risk from the effects of biomagnification of POPs, or food pollution. Carnivores (meat eaters) generally are also at greater risk. This is because, as a general rule, the levels of such toxins are higher in meat than in fruits, grains and vegetables. This provides a good ecological argument for limiting the amount of meat in your diet, and particularly your animal fat intake.

For example, orcas or killer whales are carnivores who eat literally tons of meat on an annual basis and are also quite long lived. A dead orca was found not too many years ago washed up on the California coast. An autopsy revealed that the cause of death was toxic contamination of its bodily tissues with PCBs. Ironically, the rates

were so high that its carcass was classified as toxic waste, which it was illegal to dispose of at sea under American law.

The fact that the sale and use of many of the worst POPs (such as the organochlorine insecticides) have been banned by environmental regulations in the industrial countries does not mean the problem has gone away. Many such chemicals, even while being banned domestically, continued to be sold internationally to countries where environmental regulations were more lax. Countries from which we import food.

Conclusion:

The solution to food pollution is simple, and requires the following:

1. enforceable international bans concerning the manufacture and sale of the worst offenders at the global level.

2. required testing of artificial chemicals to determine whether they are POPs prior to their being allowed into the marketplace, also regulated at the global level.

By weeding out POPs from our chemical repertoire we can minimize the risk to both ecosystems and to human health. Because many POPs are incredibly persistent,however, it may be decades before our food supply is safe, even if we eliminate them all immediately.

References, further reading:

Anne Platt McGinn (2000) “POPs Culture,” World Watch March-April.

Anne Platt McGinn (2000) “Oceans Are on the Critical List,” USA Today Magazine.

Ted Williams, (1999) “:Lessons from Lake Apopka,” Audubon, July-August.