Simon Heap displays a naive confidence in the ability of science to reach certain conclusions (Letters, THES, February 25). He claims that direct-to-mouth PVC products containing phthalate plasticisers "have sold for over 40 years without any child coming to harm". How can he possibly know? The best that can be said is that he has taken the absence of conclusive proof of an adverse effect to be conclusive proof of the absence of any such effect.
The Environment Agency lists phthalate plasticisers among chemicals with reported endocrine-disrupting properties. Phthalates are well-known for the ease with which they migrate out of PVC. There is evidence of increasing incidence of male generative problems, for example low sperm count, from a number of industrialised countries. This may be a long way from "conclusive evidence" that sucking a plasticised PVC teether necessarily leads to low sperm counts, but surely the European Commission's emergency product ban on phthalates in toys children might put in their mouths is a prudent precaution?
David Packham Department of materials science and engineering, University of Bath