September 19, 2019

expert reaction to study looking at contaminants in US tap water and cancer risk

Research, published in Heliyon, reports that more than 100,000 cancer cases in the US could stem from contaminants in tap water.

Prof John Fawell, Visiting Professor at the Cranfield University Water Institute, said:

“This is an interesting approach but the figures should not be taken too seriously because there are many assumptions in the study, not least in the risk values, and piling worst case assumptions on worst case assumptions can be very misleading.  The risk models used to calculate possible risks from animal studies make worst-case-scenario assumptions that do not take account of mitigating factors, and the figure used is the upper 95% confidence interval.  The lower 95% confidence interval is much lower and is often close to or below zero – meaning it’s possible there’s no effect at all.  This is data from the US.

“In addition it’s been previously shown in other research that the way a number of the substances mentioned can cause cancer is through mechanisms for which there is a threshold, e.g. chloroform (so below that threshold there is no problem), and others have been shown to have a non-linear dose response so that at low doses the risk is negligible or non-existent, e.g. chromium and bromate.  The values also relate to lifetime exposure at these concentrations and not all supplies will contain all, or even most of these substances mentioned.  Overall I would not be too worried.”

Prof Jim Smith, Professor of Environmental Science, University of Portsmouth, said:

“This paper attempts to model cancer risks from drinking water.  But it fails both to put the results of the study into their proper context of other environmental risk factors, and to fully explain the many uncertainties in the analysis.  It therefore risks arousing an exaggerated public concern over this issue.  The uncertainties in such analyses are huge – at the very low levels found in drinking water, none of the chemical or radiological contaminants have been shown experimentally or epidemiologically to be harmful, so the assessment is necessarily based on uncertain model extrapolations.

“The study fails to give proper context to the results found.  The comparison of carcinogenic risk from drinking water and those from air pollution fails to mention that carcinogenic risk from organic contaminants is only a very small factor in total air pollution risk.  So the lay reader is led to believe, wrongly, that drinking water risk is similar to that from air pollution.  Similarly, the reader is led to believe that risk from natural radioactive contaminants in drinking water is significant, when actually it is a tiny fraction of the (very low) radiation risk we all have from natural terrestrial radiation, cosmic rays and medical diagnostic procedures.

“Scientists should always be careful to put their findings in a proper context, otherwise their work may result in an understandable public overreaction to risks and to wrong policy decisions, both of which can harm public health.”

Prof Sir Colin Berry, Emeritus Professor of Pathology, Queen Mary University of London, said:

“This is data from the US, not the UK, where the provision of water supplies is differently managed.  The main problem with this study is the assumption of cumulative activity.  There are many studies on both radiation (of varying types) and arsenic and both are true carcinogens but there is no evidence here, or in other studies, of the activity of these and other compounds acting together as a carcinogenic collective.  For arsenic, there are data that suggest a clearly dose related effect with small quantities being of little significance, and radiation effects are clearly dose dependent (some would say low doses are protective; the phenomenon of hormesis).

“This is documentation of exposure but not of hazard – let alone risk.”

‘Cumulative risk analysis of carcinogenic contaminants in United States drinking water’ by Sydney Evans et al. was published in Heliyon at 05:01 UK time on Thursday 19 September 2019. 

DOI: 10.1016/j.heliyon.2019.e02314

Declared interests

Prof John Fawell: “Independent advisor to organisations like the WHO and the European Commission.”

Prof Jim Smith: “I have recently had a Natural Environment Research Council (NERC) grant (ca. £450k) studying the effects of radiation on fish at Chernobyl.  This was part of a programme jointly funded by NERC, the Environment Agency and Radioactive Waste Management Ltd.  I have done a small (about £10k, paid to the university) consultancy job for Horizon Nuclear Power (completed 2012) and other small contracts to customers including the Japan Atomic Energy Agency and Radioactive Waste Management Ltd.  I have also in the past carried out a variety of consultancy to independent regulatory bodies (including Environment Agency; Food Standards Agency, International Atomic Energy Agency) worth about £100k to my institution.  I don’t do consultancy in a personal capacity.  I currently lead a small (£100k) research project funded by NERC on re-use of radioactively contaminated lands in Ukraine.”

Prof Sir Colin Berry: “I have consulted for BASF, Monsanto, I Chair the Ethics Committee of Syngenta and have consulted for agencies of the Portuguese government and a number of pharmaceutical companies and the  DHS.  All these since retirement – prior to that I was usually engaged with some Government body or the other.”