In addition to the aforementioned compounds, animals are also known to concentrate environmental pollutants such as heavy metals, pesticides, herbicides and industrial toxins. These toxins become concentrated in the tissues of organisms as they pass through the food chain. The concentrating process is called biological magnification and is responsible for widespread decimation of animal life on earth. Moreover, if species are harvested for human consumption from the top of the food chain (largely marine species), then these concentrated toxins are transferred to the human consumer. The extent of biological magnification of toxins such as DDT is well documented, and it has been shown that the concentrating potential can induce several million fold increases in the concentration of these substances in the tissues of animals. Concentrations of DDT in the water as low as 0.000005 parts per million can be concentrated to over 26 parts per million in top carnivores.
Animals accumulate toxins particularly in their fatty tissues, and when called upon to utilize their fat reserves, the release of these toxins into the bloodstream can lead to various diseases and death. In this regard, it has been established that the deaths of hundreds of thousands of marine mammals can largely be attributed to lowered immune capacity owing to the immune system being compromised by the presence of accumulated toxins. It has been found that even the paint used on the hulls of ships can add sufficient toxins to the oceans to cause widespread death of marine life. The paint contains tributyl tin (TBT) which prevents barnacles from sticking to the hull of vessels. The substance has been banned for use on small vessels but is still widely used on larger vessels. TBT is probably the most potent toxin deliberately introduced into the sea, as even a few nanograms in water can cause abnormal development such as female dog whelks developing male organs. However, the immunosuppression capabilities of the toxin could be one of the factors contributing to the widespread death of dolphins and other marine life. It was found, that marine mammals concentrate TBT in their tissues in concentrations of up to 10 parts per million.18
Marine pollution is a worldwide problem, particularly in industrialized or highly populated areas. In the Mediterranean, more than 500 million tonnes of sewage alone pours into the water every year. Sewage is not the only pollutant flowing into this sea, it is estimated that annually 120 000 tonnes of marine oils, 60 000 tonnes of detergents, 100 tonnes of mercury, 3 800 tonnes of lead, 1 million tonnes of crude oil and 3600 tonnes of phosphates enter this sea. In 1985 the Mediterranean nations set themselves cleanup goals which were to be achieved by 1995, but none of these goals have been achieved.19 If the wealthier nations of the world are struggling with clean up goals, one wonders how the less fortunate are faring.
It is known that fish and shell-fish in particular, concentrate heavy metals such as mercury in their tissues, and these compounds can also be carcinogens. Already in 1953, cats and birds on the island of Minamata in Japan got the ‘staggers’ and died. Then the humans developed headaches, ataxia, fatigue, foetal deformities and mental abnormalities. Some 15 000 people were affected and at least 3500 died. A government investigation showed that the culprit was mercury salts that had been dumped in the river and had accumulated in the sediment of Minimata Bay. There the salts had become methylated and converted to methyl mercury, a highly toxic organic compound. Once this compound had found its way into the food chain, it was accumulated in the tissues of marine organisms, and biological accumulation led to high concentrations in tuna which in turn was consumed by the human population. A more recent episode involving mercury pollution can be found in the pollution of the river Rhine in Germany in November 1986, when a blaze in the giant chemical company Sandoz caused some 30 tonnes of mercury and pesticides to be washed into the Rhine. Only direct and targeted intervention by the industrialized European nations prevented this disaster from permanently destroying the delicate ecosystem of this river.
The TBT example illustrates the fact, that very minor concentrations of toxins can attain catastrophic proportions due to biological accumulation, not to mention the very high levels of pollutants in some areas. Humans that rely largely on animal products for their sustenance, will experience similar accumulations of toxic compounds as do the top carnivores in nature, and a reduction, or even avoid