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Monks Wood Experimental Station. Report for 1966–68.
302
REVIEWS OF RECENT PUBLICATIONS
In another part of the report, the replacement of benzene and asbestos by safe substitutes is applauded. It is noted that the use of highly toxic materials entails expensive equipment for the protection of workers, and at least one major manufacturer has found it to be economically advantageous to redesign his product and re-equip his factories for the use of safer ingredients. Monks Wood Experimental Station. Report for 1966-68. The Nature Conservancy, Natural Environment Research Council, Abbots Ripton, Huntingdon, 1969. pp. 88. 10s. Interesting details of the work of the Toxic Chemicals and Wildlife Division of the Monks Wood Experimental Station are given in the Station's report for the period 19661968. The severe and widespread decline in the population of certain predatory birds, dating from the late 1950s, was to some extent reversed by the voluntary ban on the treatment of spring-sown seed with aldrin and dieldrin in 1962. However, continuing scattered and smallscale use of these compounds in the spring, in spite of the ban, has apparently resulted occasionally in spectacular local kills of both predatory birds and mammals. The livers of six badgers found dead during the time of spring cereal-sowing contained 17--46 ppm dieldrin, and the deaths of another six were also attributed to dieldrin poisoning. Poisoned woodpigeons, which are more resistant to dieldrin than are the predators, were believed to be the direct cause of these deaths. Breeding failure in some predatory birds, first noted in the late 1940s, does not appear to have had a major effect on their populations but may now be reducing their rate of recovery. Sample populations of sparrowhawks, peregrines and golden eagles have in most areas shown a gradual increase in recent years and levels of dieldrin in eagle eggs and dead chicks have decreased. This last finding corresponds with a decrease in dieldrin residues in mutton fat following the ban on the use of dieldrin as a sheep dip. A 50 ~o decrease in dieldrin in heron eggs between 1966 and 1968 is also attributed to this move. A major factor in the breeding failure is thought to have been the interference of organochlorine pesticides with calcium metabolism, leading to a significant decrease in shell weight and a consequent increase in parental egg-breaking. Examination of seabird eggs has shown that there has been no major change in the level of pollution in coastal waters since 1963, despite voluntary bans on several substances. Residues here reflect both industrial and agricultural pollution, however, and it is significant that levels of polychlorinated biphenyls (PCB) of up to 10 ppm have been recorded in some specimens. Since 1964 the value of DDT in the control of the Small Cabbage White butterfly has been studied in detail. Although there is good initial control of the caterpillars present at the time of spraying, the accumulation of D D T in the soil with subsequent applications so greatly reduces the viability of natural predators that the survival of the pest is greatly improved. Moreover, the predators of other unwanted species, such as Cabbage Aphids and slugs, are also killed, with the result that these pests, too, increase in number. Laboratory studies on the effects of organochlorine compounds have included an investigation of the passage of dieldrin from soil to earthworms and thence to thrushes. The dynamics of dieldrin at various dose levels have also been studied in thrushes. D D T has been shown to delay ovulation and decrease egg weight in a passerine bird (the Bengalese Finch). Comparative studies in this species to determine lethal levels of PCB, D D E and DDT have suggested that D D T is the most toxic of the three compounds.
REVIEWS OF RECENT PUBLICATIONS
In another part of the report, the replacement of benzene and asbestos by safe substitutes is applauded. It is noted that the use of highly toxic materials entails expensive equipment for the protection of workers, and at least one major manufacturer has found it to be economically advantageous to redesign his product and re-equip his factories for the use of safer ingredients. Monks Wood Experimental Station. Report for 1966-68. The Nature Conservancy, Natural Environment Research Council, Abbots Ripton, Huntingdon, 1969. pp. 88. 10s. Interesting details of the work of the Toxic Chemicals and Wildlife Division of the Monks Wood Experimental Station are given in the Station's report for the period 19661968. The severe and widespread decline in the population of certain predatory birds, dating from the late 1950s, was to some extent reversed by the voluntary ban on the treatment of spring-sown seed with aldrin and dieldrin in 1962. However, continuing scattered and smallscale use of these compounds in the spring, in spite of the ban, has apparently resulted occasionally in spectacular local kills of both predatory birds and mammals. The livers of six badgers found dead during the time of spring cereal-sowing contained 17--46 ppm dieldrin, and the deaths of another six were also attributed to dieldrin poisoning. Poisoned woodpigeons, which are more resistant to dieldrin than are the predators, were believed to be the direct cause of these deaths. Breeding failure in some predatory birds, first noted in the late 1940s, does not appear to have had a major effect on their populations but may now be reducing their rate of recovery. Sample populations of sparrowhawks, peregrines and golden eagles have in most areas shown a gradual increase in recent years and levels of dieldrin in eagle eggs and dead chicks have decreased. This last finding corresponds with a decrease in dieldrin residues in mutton fat following the ban on the use of dieldrin as a sheep dip. A 50 ~o decrease in dieldrin in heron eggs between 1966 and 1968 is also attributed to this move. A major factor in the breeding failure is thought to have been the interference of organochlorine pesticides with calcium metabolism, leading to a significant decrease in shell weight and a consequent increase in parental egg-breaking. Examination of seabird eggs has shown that there has been no major change in the level of pollution in coastal waters since 1963, despite voluntary bans on several substances. Residues here reflect both industrial and agricultural pollution, however, and it is significant that levels of polychlorinated biphenyls (PCB) of up to 10 ppm have been recorded in some specimens. Since 1964 the value of DDT in the control of the Small Cabbage White butterfly has been studied in detail. Although there is good initial control of the caterpillars present at the time of spraying, the accumulation of D D T in the soil with subsequent applications so greatly reduces the viability of natural predators that the survival of the pest is greatly improved. Moreover, the predators of other unwanted species, such as Cabbage Aphids and slugs, are also killed, with the result that these pests, too, increase in number. Laboratory studies on the effects of organochlorine compounds have included an investigation of the passage of dieldrin from soil to earthworms and thence to thrushes. The dynamics of dieldrin at various dose levels have also been studied in thrushes. D D T has been shown to delay ovulation and decrease egg weight in a passerine bird (the Bengalese Finch). Comparative studies in this species to determine lethal levels of PCB, D D E and DDT have suggested that D D T is the most toxic of the three compounds.