The organic industry has responded to research suggesting organic food offered no significant health benefits by pointing to the dangers of pesticide residues. However, Ben Cooper writes, the evidence supporting those contentions also appears far from conclusive suggesting the industry may face more challenges about how it promotes organic food.

In their stout defence in recent weeks, organic advocates have stressed that research by the UK's Food Standards Agency (FSA) suggesting organic food has no health benefits over non-organic is flawed because it ignores the issue of pesticide residues.

What is desperately needed, they protest, is more research into the levels of chemical residues in food.

And only a few weeks later, the New Zealand Food Safety Authority (NZFSA) published its five-yearly Total Diet Study (TDS), measuring exposure to chemical residues and contaminants in 120 commonly consumed foods, which concluded there were "no chemical residue food safety concerns" in the average diet.

While it only covers one country, the study and its timing appear to deflate the organic sector's arguments further.

Pesticides were specifically excluded from the FSA review because, according to FSA CEO Tim Smith, "pesticides are rigorously assessed and their residues are closely monitored". The use of pesticides in both organic and conventional food production "does not pose an unacceptable risk to human health and helps to ensure a plentiful supply of food", Smith said.

The New Zealand study supports the view expressed by many that the organic movement over-eggs the issue of pesticide residues.

Professor Anthony Trewavas of the Institute of Plant Molecular Biology at University of Edinburgh believes there is an exaggerated and irrational fear of synthetic pesticides, and questions the validity of the distinction the organic movement makes between synthetic pesticides and the some 100,000 pesticides which occur naturally in plant life.

"Unfortunately those that believe in organic think anything natural is benign. It is not," he tells just-food. "All fruit and vegetables contain many thousands of pesticides, all natural. There has been an arms race between plants and insects over hundreds of millions of years and plants have become past masters of chemistry producing chemicals to kill insect herbivores."

Among the toxic compounds found naturally in plant life are carcinogens, oestrogen mimics, nerve toxins, goitrogens, Trewavas points out, while others inhibit respiration or cell division or damage chromosomes.

He also points out that we eat around a quarter of a teaspoon of natural pesticides every day, but the traces of synthetic pesticides we consume are less than a tenth of a grain of salt. "The problem is all the concern is directed to things that the chemical industry creates and the much bigger risk (but still tiny) from natural pesticides is ignored," he says.

Trewavas adds: "Are synthetic pesticides poisonous? Of course they are otherwise they would not be used but in the dilution applied by farmers much less so, and after several days most of them have disappeared having done their job."

But campaigners, such as agricultural pressure group Sustain, Greenpeace and the Soil & Health Association of New Zealand, believe the levels prescribed as safe by regulators do not take sufficient account of multiple residues, or the so-called 'cocktail effect'.

The problem, says Sustain's Jeanette Longfield, is that researching the effects of "unknowable combinations" of pesticide residues is very difficult to do. "It's an undoable research question. How many different combinations of the many hundreds of pesticides that are available would you have to test, what would be your control population, and how long would you have to follow people?"

Longfield questions the limits set by organisations like the FSA. "One of the things that regulators are supposed to take into account is the precautionary principle," she says. "If there's a doubt, let's give people the benefit of the doubt. It's a risk. It's a risk that you don't really want to take."

Dr David Santillo, senior scientist at the Greenpeace Research Laboratories, says that the levels set by regulators are based on "what is achievable rather than what is desirable". He adds: "Low risk does not mean zero risk. There are people who understandably want to minimise further their exposure or limit it as much as they can."

A further problem, says Santillo, is that risk assessment is based on typical consumption patterns, which can vary, and also points out that individuals have differing sensitivities to the chemicals in question. "While there are pesticide residues that can be detected in food that is something the consumer needs to know about. So it's down to an individual judgment."

So the pesticides issue appears complex and nuanced, with strident views on both sides of the argument. This alone suggests it is not a strong premise on which the organic sector can build or re-build its image.

True, Sustain says that taking a holistic view of the benefits of organic, including pesticide residues along with environmental and animal welfare, anti-biotic residues and any small micro-nutrient variations that might exist, is the best way forward. But it remains the case that pesticides featured prominently in much of what was said in the organic sector's defence in the weeks after the FSA review was published.

Jules Pretty, Professor of Environment & Society at the University of Essex, believes generalisations about levels of harmful contaminants in non-organic or in organic food are unhelpful.

"Some organics are good, some not; some conventional systems good, some not," Pretty tells just-food. "Organics use some unpleasant products; some plants contain them anyway. Some conventional systems use dangerous pesticides, some don't. It all depends on what you are comparing. Generalisations are unhelpful or indeed wrong."

Pretty says that finding some pesticide residues in a food does not necessarily mean there is a hazard. He also says that pesticide residues in the UK food supply "are very much lower and safer" nowadays. "We have a very good system of controls. So, I am not worried about foods here. But in some other countries, I would have altogether different concerns."

But in general, Pretty believes the black and white distinction made between organic and conventional agriculture represents a "false dichotomy". He adds: "We should be seeking to make all foods and agricultural systems more sustainable and healthy. And this, to my mind, means being objective about the evidence."

And that brings us back to the question of how the organic industry presents the benefits of organic food. Last month, organic advocates had to concede that the case for organic food having nutritional benefits was not strong. They argued this was not a particularly decisive element in consumer motivation anyway, and a much more compelling reason for buying organic was the lack of pesticide residues, among other factors.

But the evidence on pesticides also appears sketchy at best and, if the considerable attention given to the FSA report is anything to go by, the organic industry can expect increased scrutiny of its claims over pesticides going forward.