Oestrogenic hormone mimics

In the case of some oestrogenic chemicals (that mimic the effects of the female hormone oestrogen) it has been shown that what should be added to predict the combined effect of a mixture is not the effects of the individual chemicals but their concentrations (Silva et al, 2002). This means that a substance present at a concentration at which on its own it has no oestrogenic effect will contribute to the total oestrogenic effect of a mixture containing other oestrogenic chemicals. For such substances there is in practice no real threshold concentration below which they do not have an effect. Such no-effect levels are a crucial part of chemicals risk assessment, as I will explain in Chapter 7. 

Endosulfan, a chemical cousin of DDT that mimics the female hormone oestrogen in the human body was found illegally on 10 crops. 

PVC plasticisers have recently come under suspicion as a possible reason for the observed reduction in human sperm count. The causal link between plasticisers and reduced human fertility has not been established to the satisfaction of most epidemiologists and it is essentially based on the theory that the similar shape of plasticiser molecules to the oestrogens allow them to mimic the sex hormones in vivo. 

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