Further review of certain persistent organochlorine pesticides used in Great Britain.

  • Great Britain. Advisory Committee on Pesticides and Other Toxic Chemicals
Date:
1969
Catalogue details

Licence: Public Domain Mark

Credit: Further review of certain persistent organochlorine pesticides used in Great Britain. Source: Wellcome Collection.

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    (b) EVIDENCE ON INDIVIDUAL PESTICIDES Aldrin and Dieldrin 19. Following applications of aldrin and dieldrin to the soil there is initially a rapid decrease in residues of each chemical followed by a period of slower decline. Dieldrin appears to affect some soil micro-arthropod populations very — markedly and for considerable periods of time. Different groups of animals vary in their susceptibility to the chemical and a few species appear to be particularly resistant. The change of population produced is dependent on the rate and frequency of application, actual species present, and soil type [Appendix V (i)]. 20. In Great Britain some cases have come to light where mortality among fish populations due to dieldrin was attributable to industrial effluents. However, the main evidence of the adverse effects of organochlorine insecticides on fish in nature has been gathered in North America. Normally, direct uptake from water is likely to be the most important source for fish but some aquatic organisms, such as caddis larvae, have been found to accumulate dieldrin and predators feeding on them would also acquire the chemical from this source. The level of residues of dieldrin found in samples of marine and freshwater fish is shown in Appendix V (ii). Such residues may be transferred to fish-eating birds and must largely account for the residues of dieldrin found in their eggs [Appendix V (iii)]. 21. Since the introduction of voluntary restrictions on certain uses of these chemicals, incidents involving the acute poisoning of seed-eating birds have greatly decreased in number, although some casualties still occur, particularly from spring-sown seed which has been prepared for autumn sowing. Much larger residues are found in predatory land birds than in other species and the periods during which the marked population declines in the peregrine falcon and sparrowhawk occurred (paragraph 17) roughly correspond with known periods of usage of these pesticides. Detailed studies since 1964 suggest that the declines were not due to factors such as decreases in food supply or in breeding sites, weather changes, intentional and unintentional human disturbance, or to the cyclical fluctuations recorded in the kestrel and barn owl. The additional data support our previous hypothesis that aldrin and dieldrin cereal seed dressings reached the predators through their prey and were an important contributory cause of the population declines. Following the withdrawal of use of these chemicals on spring-sown cereals in 1962 and the restrictions following our 1964 Review, some population increases have been observed in the peregrine falcon, sparrowhawk, and kestrel. It also seems likely that the golden eagle benefited from the ban on the use of dieldrin in sheep dips, since the reported recovery in its breeding success commenced at about that time (paragraph 18). 22. Mammals too may acquire dieldrin residues directly by eating dressed seed or treated plants. They may also acquire such residues indirectly by eating other animals containing residues of the chemical. Thus cases have been reported in which foxes and badgers may have been poisoned by eating pigeons which had consumed cereals dressed with aldrin and dieldrin. No evidence has, however, come to light to suggest that this has substantially affected the total population of these mammals. 23. There is some experimental evidence that non-fatal doses can produce effects the ecological significance of which has not yet been established (see also
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