Sex ratios

There have been suggestions of alterations in sex ratios following accidental environmental exposure to dioxin in Seveso, Italy, in 1976. Between 1977 and 1984, 74 births occurred in the most heavily contaminated zone which showed an excess of females (26 males and 48 females born). Preliminary evidence suggests that the excess was associated with high dioxin exposure in both parents. Over a later period, between 1985 and 1994, the ratio declined (60 males and 64 females) and was no longer statistically significant. 

Another possible example of endocrine disruption in situ relates to the hndings of Moore and Stevenson" of altered sex ratios and intersex harpacticoid copepods in the vicinity of Edinburgh s long sea sewage outfall. Intersexiiality is common in some crustaceans but is extremely rare in harpacticoid copepods. There was no relationship between the frequency of intersex and distance from the most contaminated sites and nor was there evidence that other benthic species had been adversely affected. Additional work is required to prove conclusively that endocrine disruption is involved in this case. 

Culture a range of invertebrate species from the major phyla, preferably species with short life cycles. The effects of potential endocrine disrupting chemicals on growth rate, reproductive output, viability of offspring and sex ratio, and the vulnerability of different stages of the life cycle, can then be determined. 

There is some evidence for chemically mediated endocrine disruption in amphibians. The egg yolk protein, vitellogenin, is inducible in amphibians by exposure to DDT. " Males of the short clawed toad Xenopus laevis given 250 fig/g or 1 fig/g o,p -DDT for seven days have been shown to produce vitellogenin, although the induction was less than that achieved by treatment with 1 fig/g of either 17/1-oestradiol or diethylstilboestrol. Research has also shown that endocrine disrupting chemicals can alter sex ratios in wild populations of certain species PCB congeners and organochlorine compounds have been linked with male domination of sex ratios in polluted compared to unpolluted sites. ... 

Hill, R.L. and Janz, D.M. (2003). Developmental estrogenic exposure in zebrafish (Danio rerio) I. Effects on sex ratio and breeding success. Aquatic Toxicology 63, 417 29. 

Perret M. (1996). Manipulation of sex ratio at birth by urinary cues in a prosimian primate. Behav Ecol Sociobiol 38, 259-266. 

McGraw, K. J., Adkins-Regan, E., and Parker, R. S. 2005. Maternally derived carotenoid pigments affect offspring survival, sex ratio, and sexual attractiveness in a colourful songbird. Naturwissenschaften 92 375-380. 

In a study by Haun et al. (1970), male and female rhesus monkeys (three to five per group, sex ratio per exposure varied) and male squirrel monkeys (two to four per exposure group) were exposed to monomethylhydrazine for 60 min (rhesus monkeys) and 15, 30, or 60 min (squirrel monkeys) (Table 3-3). For the rhesus monkeys (three males and two females), there were no deaths following a 60-min exposure to a mean concentration of 160 ppm (range, 145-170 ppm),... 

Aroclor 1260/kg BW after 3 h. Survival normal for all groups. Altered sex ratios and gonadal abnormalities in juvenile females reduction in number of females produced in groups that accumulated 2.5 mg/kg BW about 18% of females that initially contained 2.1 mg/kg BW had abnormal gonads vs. 2.7% in controls 50% increase in liver EROD activity 12... 

Studies of non-cancer effects in children have indicated neurodevelopmental delays and neurobehavioural effects, including neonatal hypotonia. In children in Seveso who were highly exposed to TCDD, small, transient increases in hepatic enzymes, total lymphocyte counts and subsets, complement activity, and non-permanent chlo-racne were observed. Also, an alteration of the sex ratio (excess female to male) was observed in children born to parents highly exposed to TCDD. 

Exposure of pregnant Alderley-Park rats to 1,4-dichlorobenzene via inhalation at levels up to 508 ppm for 6 hours per day on Gd 6-15 did not result in developmental effects in the offspring (Hodge et al. 1977). End points examined included the number of viable fetuses, fetal weight, litter weight, sex ratio, external abnormalities, and skeletal and visceral abnormalities. 

Berger, P. J., Negus, N. C., and Rowsemitt, C. N. (1987). Effect of 6-methoxybenzoazolin-one on sex ratio and breeding performance inMicrotus montanus. Biology of Reproduction 36,255-260. 

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