July 11, 2012

expert reaction to study of bisphenol A (BPA) and cross-species breeding in fish

The chemical BPA was found to impact the mating choices of fish when released into rivers, a study in Evolutionary Applications found. By altering an individual’s appearance and behavior, BPA exposure led to inter-species breeding.

Professor Richard Sharpe, Principal Investigator at the MRC Human Reproductive Sciences Unit, said:

“The best way to describe the level of exposure to bisphenol A in this experiment would be ‘heroic’ or even ‘astronomical’.

“The researchers added 1280 g/L (~5 molar) which bears no relationship to exposures that occur in the real world.

“Although the authors did not claim any relevance to humans, others may extrapolate from this study to humans. Therefore, it is appropriate to give this a human perspective: average intake of bisphenol A per day (main route of exposure is oral, via food/drink) is 0.02-0.3ug/kg/day, resulting in blood/urine levels in the pM (picomolar = 10−9 mol/m3) range. It’s not easy to compare with the exposure of the fish in this experiment as they were literally bathed in it, but simple maths says human exposure is at least 10 orders of magnitude lower. In other words, this study has no human health relevance.

“These sorts of doses may be useful for teasing out mechanisms/pathways in fish mating behaviour but in the wild such levels of bisphenol A would never occur unless there was a spillage!”

Professor Ieuan Hughes, Foundation Professor of Paediatrics at the University of Cambridge and Society for Endocrinology spokesperson, said:

“The experiments appear well organised and the results quite clear in terms of changes observed. I note exposure was only to one concentration of BPA so wonder why it was not possible to conduct dose response studies. This is not a study that has relevance to human exposure and therefore human health. What is important to highlight are the potential effects of man-made chemical waste on the biodiversity of wildlife through the hybridisation mechanism the authors talk about. That has to be of concern to environmentalists.”

Professor Charles Tyler, Director of Research for Biosciences, University of Exeter, said:

“The comments made relating to potential effects on fish populations are very ‘ambitious’ given the depth of the data. The exposure regime is not environmentally realistic, so extrapolating the findings to populations in the wild is not really appropriate. One can argue for such high exposure regimes to investigate for effect mechanisms, but I would argue not for population-level relevant outcomes.

“The authors (in fact) have no idea what the exposure regime was as there are no measured exposures, only nominal.”

‘Exposure to an environmental estrogen breaks down sexual isolation between native and invasive species’ by Ward, J. et al., published in Evolutionary Applications on Wednesday 11th July.