Further review of certain persistent organochlorine pesticides used in Great Britain.
- Great Britain. Advisory Committee on Pesticides and Other Toxic Chemicals
- Date:
- 1969
Licence: Public Domain Mark
Credit: Further review of certain persistent organochlorine pesticides used in Great Britain. Source: Wellcome Collection.
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![interpretation of the findings in the light of relevant information obtained from experimental work. This situation rarely enables a firm conclusion to be reached on incidents in the field. It is therefore very difficult to interpret the significance of the small residues of DDT frequently found in wildlife. 48. Chemical analyses of specimens collected from various places indicate that many wild birds in Great Britain contain residues of DDT or its metabolite DDE [Appendix V (iii a), (iii b), (iv)]. The amounts found and the ratios between DDE and other metabolites in different birds and in different organs of individual birds have varied widely. Residues in birds in feeding tests have mostly been much higher than in those found dead in the field. Whilst these findings suggest that very few of the wild birds examined could have died solely from DDT poisoning, it is important to appreciate that caution is necessary because other organo- chlorines were often also present and, in any event, adequate experimental data are not available for most of the wild species examined. Furthermore, wild birds often experience stresses of a kind different from those that arise under con- trolled conditions in laboratories; residue levels which do not indicate hazard in the laboratory may however be deleterious in the field. 49. Some of the highest residues have been found in carcases, particularly of blackbirds, from orchards where DDT was known to have been extensively used [Appendix V (vi)]. Although the evidence suggests that some casualties from DDT could have occurred in such sites in particular seasons, there are no indications that such occurrences are sufficient substantially to affect populations of these birds, other than in very restricted areas. 50. There is experimental evidence that DDT can delay attainment of sexual maturity in some species of birds. This could affect breeding success in the wild by disturbing the synchronisation of breeding with the availability of food suitable for the young. Experiments have also shown that DDT (and dieldrin) can influence the endocrine system by altering the balance of steroid hormones. However, egg production, fertility, and embryo viability, are not seriously affected by DDT except at levels that affect the general physiological state of the birds. DDT or its metabolites have been found in the eggs of many species of wild birds in Great Britain; with the exception of a few samples from orchards which contained over 100 p.p.m. the levels in eggs have been below 10 p.p.m. 51. Analyses of specimens from the field show that birds of prey usually contain higher residues of DDT and its metabolites than other species. Nevertheless there is no close correlation between the declines in populations in predatory birds, particularly in the peregrine falcon and the sparrowhawk, referred to in paragraph 17, and the use of DDT. Therefore DDT does not appear to have been the principal cause. 52. Reports regarding the effects of DDT on eggshell thickness, eggshell breakage, and in production of young, have been discussed in paragraph 18. Since these reports appeared in Britain, similar observations have been reported in the U.S.A., where it has also been shown experimentally that DDT can affect eggshell thickness in some species. Other causes of thinning of eggshells are known and there is no certainty that DDT was responsible for the effects reported from the field. 1]](https://iiif.wellcomecollection.org/image/b32173076_0017.jp2/full/800%2C/0/default.jpg)
