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One hundred specimens of human body fat, 50 necropsy and 50 biopsy, were collected in 1964 from a semi-rural area in south-eastern England. The specimens were analysed by two methods and the concentrations of seven organo-chlorine insecticides were determined. The results of the two analytical methods were in good agreement. Endrin and heptachlor epoxide were not detected in any of the specimens analysed for these compounds. The average concentrations of lindane, op'-DDT, and op'-DDE were very small: 0-015 p.p.m., 0 03 p.p.m., and 0-02 p.p.m. respectively. The average concentration of HEOD in the 100 specimens of fat (no significant difference in the means of the necropsy and biopsy fats was detected) was 0-21 p.p.m., as in the 1961 survey. The average concentration of total equivalent-DDT (DDT + DDE) in the 50 necropsy fats was 3-9 p.p.m., as compared with 2-2 p.p.m. in 1961. In the biopsy fats the average concentration for males was 4 9 p.p.m., and for females 3-4 p.p.m. One method was suitable for the separate determination of pp'-DDT and pp'-DDE. The average concentration of pp'-DDT was 1-0 p.p.m. in the 100 necropsy and biopsy fats. The average concentration ofpp'-DDE was 2-2 p.p.m. in the 50 necropsy fats, and 3 1 p.p.m. and 2-0 p.p.m. in male and female biopsy fats respectively. The variability ofthe concentrations of these compounds in the necropsy specimens was generally greater than in the biopsy specimens. No significant differences were found which were attributable to age or to the cause of death. It is considered that the amounts found of these compounds do not constitute a hazard to the population sampled in this survey. The design of surveys to determine the concentrations of organo-chlorine insecticides in man is discussed.

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Dispersal affects the distribution, dynamics and genetic structure of natural populations, and can be significantly different between sexes. However, literature records dealing with the dispersal of migratory birds are scarce, as migratory behaviour can notably complicate the study of dispersal. We used the barn swallow Hirundo rustica as model taxon to investigate patterns of genetic variability in males and in females of a migratory species showing sex-biased dispersal. We collected blood samples (n = 186) over the period 2006 to 2011 from adults (H. r. rustica subspecies) nesting in the same breeding site at either high (Ireland, Germany and Russia) or low (Spain, Italy and Cyprus) latitude across Europe. We amplified the Chromo Helicase DNA gene in all birds in order to warrant a sex-balanced sample size (92 males, 94 females). We investigated both uniparental (mitochondrial ND2 gene) and biparental (microsatellite DNA: 10 loci) genetic systems. The mtDNA provided evidence for demographic expansion yet no significant partition of the genetic variability was disclosed. Nevertheless, a comparatively distant Russian population investigated in another study, whose sequences were included in the present dataset, significantly diverged from all other ones. Different to previous studies, microsatellites highlighted remarkable genetic structure among the studied populations, and pointed to the occurrence of differences between male and female barn swallows. We produced evidence for non-random patterns of gene flow among barn swallow populations probably mediated by female natal dispersal, and we found significant variability in the philopatry of males of different populations. Our data emphasize the importance of taking into account the sex of sampled individuals in order to obtain reliable inferences on species characterized by different patterns of dispersal between males and females.

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