Chlorinated pesticides birds

Because oceans serve as a sink for chlorinated pesticides and CACs, marine mammals and piscivorous birds are consuming relatively high amounts of these compounds, whereas they have a relatively low capacity for metabolism. As a result, they may constitute the most vulnerable organisms with regard to longterm toxicity.14 Over 90% of the whole body burden of marine mammals may be present in their blubber.14... 

Researchers were also able to establish the link between declines of other predatory species such as the European sparrowhawk and the use of organo-chlorine pesticides other than DDT. For instance, the cyclodiene insecticides aldrin, dieldrin, and he-ptachlor used as seed treatments caused massive mortality of both seed-eating species and their predators. All of the insecticides had the following points in common they were highly soluble in fats and refractory to metabolism. The impacts on the predatory species typically take place in periods of food stress when fat soluble residues are released from fat stores and returned into general circulation. In a food-stressed individual, the brain remains as the most lipid rich tissue and this is where contaminants move to. Toxicity results when threshold values in brain tissue are exceeded. At sublethal levels, documented effects of cyclodiene insecticides in birds have included changes in their reproductive, social, and avoidance behaviors. 

Hexachlorobenzene is frequently reported in analyses of samples for chlorinated pesticides, and occasionally determined in its own right. The data summarised in Tables 8 and 9 [25, 26, 38, 61, 76, 78, 86, 109, 134, 138] indicate widespread distribution in biological tissue, but at very much lower levels than PCB most of the organisms examined are either fish or birds feeding on aquatic organisms, but HCB has been reported from a range of terrestrial animals at levels up to 10 mg/kg or greater [25]. Occurrence in water, either fresh or marine, is very sporadic and at low concentrations it is not normally detected in the atmosphere. 

Biological Impact of Pesticides in the Environment. Proc. Symp. Aug 18-20, 1969 Oregon State Univ., Corvallis, OR. James W. Gillett (Ed.), Environmental Health Sciences Series No. 1. Oregon State U. Press, Corvallis (1970) 6 parts I. Transport and Accumulation, 26p. II. Impact of Chlorinated Hydrocarbons on Birds, 38p. III. Banquet Session 1 D.G. Crosby, "Chemical Ecology and Man" pp.75 ... 

Pesticide residues in fish, birds, and humans in isolated areas of the world can, in some cases, be attributed to distribution through the food chain however, it is apparent from recent evidence that dispersion by air transport must also be considered. Paul (8) reported that 71% of all specimens of waterfowl and their eggs collected from selected areas of the United States and Canada during 1961, 1962, and 1963 contained chlorinated hydrocarbon residues. Significantly, chlorinated hydrocarbons were found also in samples of aquatic vegetation and snails obtained from the Far North waterfowl nesting areas of Canada, 500 miles or more from any known pesticide-treated area. 

Dietary lipids play a unique role in the toxicity of chlorinated hydrocarbon pesticides. Dietary lipids may favor more absorption of these pesticides, but once these chemicals are absorbed into the body, they may be stored in the adipose tissue without manifestation of toxicity. For this reason, obesity in humans is considered protective against chronic toxicity of these chemicals. Similarly, the body fat in a well-fed animal is known to store organochlorine pesticides. Fat mammals, fish, and birds are thus more resistant to DDT poisoning than their thinner counterparts. In times of food deprivation, however, organic materials such as DDT and PCB can be mobilized from mammalian fat deposits and can reach concentrations potentially toxic to the animal. 

Chlorinated Aromatic Hydrocarbon Environmental Toxins. As a result of human endeavor, toxic compounds containing chlorinated benzene rings have been widely distributed in the environment. The pesticide DDT and the class of chemicals called dioxins provide examples of chlorinated aromatic hydrocarbons and structurally related compounds that are very hydrophobic and poorly biodegraded (Fig. 5.28). As a consequence of their persistence and lipophilicity, these chemicals are concentrated in the adipose tissue of fish, fish-eating birds, and carnivorous mammals, including humans. 

In recent years pesticides have received considerable unfavorable pubhcity and efforts have been made to curtail their use because of their supposedly harmful effects. This development is in most respects unfortunate, for aside from the long-lasting chlorinated hydrocarbons, such as DDT, they are rarely hazardous. DDT is harmful to birds and may upset the food chains and ecosystems, but pesticides other than chlorinated hydrocarbons are decomposed so comparatively rapidly that such effects are not encountered. This presents a challenge to the chemist to produce suitable substitutes for any pesticides that may be questioned. 

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