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Pesticides and health

Readers of the Guardian last Saturday would have opened their paper to find the headline Roundup weedkiller ‘probably’ causes cancer, says WHO study. Roundup is the trade name used by Monsanto for glyphosate, a very widely used, broad action herbicide. It is now no longer covered by patent, so is also supplied by a range of different manufacturers, but the direct association with Monsanto is too good to miss for anti-pesticide campaigners.

If such a commonly-used chemical as glyphosate, found in many a garden shed across Europe, really was a significant cancer risk, this would be a very serious health concern and mean that the whole risk-based safety assessment system for pesticides would have been demonstrated to be fatally flawed. The fact that this story only makes it into the inside pages and no longer appears on the Guardian’s environment web page, nor among the ten most popular environmental stories, is probably a better indication of its importance.

The WHO agency responsible for this work – the International Agency for Research on Cancer (IARC) – says that glyphosate is now “classified as probably carcinogenic to humans”. This is the finding published in the Lancet of a study of five pesticides (Carcinogenicity of tetrachlorvinphos, parathion, malathion, diazinon and glyphosate), based on a review of the literature rather than new research.

The reclassification is based on occupational exposure which reported increased risks of a specific cancer, non-Hogdkin lymphoma, together with some evidence of very specific carcinogenesis in mice (almost certainly at very high dose rates, but not reported). This was sufficient for the pesticide to be put into classification 2A (probably carcinogenic to humans).

That a study like this has not caused any particular public alarm probably means that it has simply confirmed people’s preconceptions of pesticides as intrinsically dangerous, which is a pity considering the care with which they are used and the great contribution they have made towards guaranteeing food security.

Monsanto themselves are, not surprisingly, demanding an explanation of the IARC decision, but there are some more objective views on the Science Media Centre website: Expert reaction to carcinogenicity classification of five pesticides by the IARC. For example, Emeritus Professor of toxicology Tony Dayan (a member of the Scientific Alliance Advisory Forum) is quoted as saying “In the present report the classification of glyphosate and malathion as carrying a Class IIA risk of causing cancer in humans reflects a variety of laboratory results with a small number of studies in man of varied quality and mixed conclusions. Detailed analysis of the nature and quality of the evidence overall does not support such a high level classification, which at the most should be Class IIB.”

Professor Alan Boobis of Imperial College said in part “The IARC process is not a risk assessment. It determines the potential for a compound to cause cancer, but not the likelihood….The UK Committee on Carcinogenicity has evaluated possible links between pesticide exposure and cancer on several occasions. It has found little evidence for such a link.”

And Dr Oliver Jones of RMIT University, Melbourne, raises some other interesting points: People might be interested to know that there are over 70 other things IARC also classifies as ‘probably carcinogenic’, including night shifts. In the highest category of known carcinogens are ‘alcoholic beverages’ and ‘solar radiation’ (sunlight) – along with plutonium. So yes, pesticides can be dangerous, but are many other common things which are also dangerous in sufficient amounts or over long periods of time – the dose makes the poison.”

None of this will carry any weight with members of the Pesticides Action Network, the Asia and Pacific chapter of which has released an alarming glyphosate fact sheet. If only a small proportion of the apparent harmful effects of glyphosate were true, it seems extremely unlikely that regulatory authorities would still allow its use.

A similarly scary picture is painted on the Sustainable Pulse website: Children suffer genetic damage from pesticides in Argentina GM soy region. This suggests that genetic damage was 44% higher in children exposed to pesticides than those not exposed, but rather curiously says that “the level of genetic damage detected in this experiment is reversible”, which is not a normal characteristic of such damage.

The IARC classification will have to be taken seriously by regulatory authorities, even though it appears at most to indicate a particular hazard rather than any real risk. The IARC panel is probably simply doing its job, although it does seem to be taking a highly precautionary view of a pesticide which has been widely and safely used for many years. But PAN and others are ideologically opposed to synthetic pesticides and operate on the basis of policy-driven evidence.

Pesticide campaigners won a significant victory when they managed to get a two year ban on the use of neonicotinoids in the EU because of a supposed link to loss of bees. Having got to that stage, of course, campaigners will be lobbying hard to make the ban permanent, despite any lack on hard evidence.

In the USA, an EPA task force is about to look at the threat to honey bees, particularly in respect of the impact of pesticides. This is despite a reported 14% rise in honey production last year (USDA figures). Scientists from the University of Maryland have also published a study done in cooperation with the USDA bee laboratory (Assessment of chronic sub-lethal effects of imidacloprid on honey been colony health).

Essentially, this reports no ill-effects when bees were exposed to levels of this particular neonic expected in the field, and no major impact at significantly higher levels. Their measured conclusion was “Given the weight of evidence, chronic exposure to imidacloprid at the higher range of field doses (20 to 100 μg/kg) in pollen of certain treated crops could cause negative impacts on honey bee colony health and reduced overwintering success, but the most likely encountered high range of field doses relevant for seed-treated crops (5 μg/kg) had negligible effects on colony health and are unlikely a sole cause of colony declines.”

Pesticides, like so many things, can be misused and need to be properly handled. But the benefits of well-regulated use far outweigh the risks and it is important that policymakers don’t allow over-zealous environmental activists to set the agenda.