Authors:
Karmaus, W., Huang, S., Cameron, L.

Title:
Parental Concentration of Dichlorodiphenyl Dichloroethane and Polychlorinated Biphenyls in Michigan Fish Eaters and Sex Ratio.

Journal:
Journal of Occupational and Environmental Medicine: 44; 8-13. 2002.

Summary:
Demonstration of a change in the birth sex ratio in North America and Europe has prompted several studies designed to explore the association between this outcome and exposure to environmental contaminants. The objective of this study was to determine the association between exposure to DDT and PCBs and birth sex ratio. DDT had widespread use as an insecticide between 1940 and 1960 in North America while PCBs were made useful in electrical, heat transfer and hydraulic equipment due to their inflammability and insulating properties. Animal studies have demonstrated that DDE, a metabolite of DDT, and some PCBs can induce changes in endocrine physiology. Both PCBs and DDT were banned over 2 decades ago in North America due to their health effects but they remain ubiquitous in the environment owing to their persistence and ability to bioaccumulate in the fatty tissues of animals. High levels of these contaminants have been found in fish of the Great Lakes raising concerns about potential health effects associated with consuming contaminated fish. Thus, 3 surveys were conducted between 1973 and 1991 on Michigan fisherman and anglers, whom it was assumed consume large amounts of fish in their diet and that recall of consumption patterns would provide an accurate estimate of exposure. Subjects were recruited by field visits to fishing sites in 11 Lake Michigan shoreline counties. Direct contacts and referrals were used to recruit a total of 1177 subjects for the study. At the time of each survey, a non-fasting blood sample was given and analyzed for PCBs and other contaminants. Blood samples were collected and analyzed 3 times for PCBs (1973-1974, 1979 to 1982, and 1989 to 1991) and twice for DDE (1979 to 1982, and 1989 to 1991).

In 2000, the authors approached the cohort again with the objective of determining if the sex ratio in their offspring was associated with maternal or paternal DDE or PCB levels. The sex ratio is the number of boys to girls ascertained at birth. Excluding deceased individuals, a total of 361 subjects participated in the current study (64.1% participation rate). An interview was conducted regarding the birth date, sex, birth weight, gestational age, and breastfeeding or bottle-feeding history for each subject's offspring. The total number of children was 1050. Only children born after 1963 for whom the authors had both biological parents' serum measurements were analyzed. For quality control, 30 parents were randomly chosen to be re-interviewed. The agreement between each response was found to be very high (kappa statistic =0.91 for number of children, total agreement on the children's sex).

In the analysis, the sex ratio was expressed as a sex odds ratio (SOR). Maternal and paternal PCB and DDE exposures were significantly correlated (spearman's rank correlation coefficient 0.59, p<0.0001 and 0.56, p<0.0001 respectively). Maternal PCB and DDE values were correlated and the same held true for paternal values. Fathers with PCB concentrations exceeding 8.1ug/L were more likely to have boys than those with PCB concentrations less than this level (SOR=2.29, 95% CI=1.11-4.74). Adjustment was made for the calendar period, age of mother at birth, and whether there were older brothers in the family. Having a previous brother in the family reduced the chance of having more boys (SOR=0.56, CI=0.32-0.96).

It is interesting to note that the authors adjusted for the sex of older siblings which has not been included in other studies of sex ratio. However, the implication of this outcome to the sex of subsequent children is unclear. Studies of sex ratio have had inconsistent findings and it is not apparent whether exposures to the mother, father, or both parents are important. This study included serum measurements on both parents and the findings of this study seem to suggest that fathers with high PCB levels are more likely to have sons. However, the biological mechanisms are not understood. A major difficulty facing all investigators working in this area is the paucity of evidence in the literature concerning the factors that can alter sex ratio in the human population. Some postulate that the endocrine disrupting effects of organochlorines may contribute to altered sex ratio in offspring but others have suggested that the altered sex ratio is mainly due to a decrease in family size, biological heterogeneity, and child sex preference. An additional limitation to this study is that the authors assume that the study subjects consumed the same species of fish throughout the study periods and that the contamination of the fish has been consistent.