You can't see, taste or smell them, but the pesticide residues found in almost all meat, fruit, veg, milk and poultry are consistently one of the public's greatest environmental and health concerns. Now the Ministry of Agriculture has come up with an alternately reassuring and worrying report.
The good news is that Professor Ian Shaw, outgoing chair of the pesticides residues committee, believes that the short-term effects of the minute doses of poisons we consume with many foods are so low as to be of "no concern". His team took 2,300 random samples from shops and suppliers and analysed them for more than 85,000 pesticide/commodity combinations.
Less than 1.6% had residues above the minimum recommended levels, and less than 1% had residues of pesticides banned from the UK. The sampling was deliberately biased towards common foods and fruits that were most likely to be contaminated.
And the worrying news? There's plenty. A few thousand samples from the many hundreds of thousands of tons of food sold every year in Britain may be statistically slight, but 1% of samples translates into a great number of potential poisoning incidents.
To give an indication, official figures from the US - where sensitivity to pesticide residues is far higher and regulatory standards generally tighter - suggest that 74,000 children were involved in pesticide-related poisonings in 1994. Adjusting populations, this could mean that something like 20,000 children in Britain are being poisoned to some degree each year.
Secondly, testing pesticides for their impact on health is inexact and, critics say, flawed. Many of the thousands of pesticides routinely applied to food cannot be easily detected by government laboratories. Few have been tested on humans, and almost nothing is known about potential effects on the immune system. The US National Academy of Sciences has estimated that the data needed to conduct a thorough assessment of the health effects of pesticides is available for only 10% of the ingredients used.
The third and most worrying point is that toxicologists such as Shaw admit they haven't much of a clue about the long-term effects of residues. Many foods are laced with not just one pesticide, but many. How they interact and perhaps accumulate, and the effects they may have on humans, remains a mystery. The Food Standards Agency is setting up a working group to investigate the impact of cumulative exposure.
A further cause for concern is that children are most at risk. They have unique vulnerabilities because their excretory systems are not fully developed and they are not always able to fully remove pesticides from their bodies.
Another area for concern is the globalisation of the food industry. Britain is importing more and more food, often from countries without strictly monitored pesticide regulations and grown by farmers who may be untrained in agri-chemical use. Furthermore, pesticides banned from use in this country may still be legally used overseas.
It is not easy for the consumer. Cooking, washing and peeling food normally minimises the level of pesticide residues on foods, but not all, especially those grown with "systemic" pesticides - those that are absorbed into the plant. Some residues have been shown to concentrate, not diminish, through cooking and processing. Labelling is nonexistent.
Governments, and the increasingly allied chemical and food industries, are reassuring. The risks, they say repeatedly, are minimal, and standards are improving as farmers steadily decrease pesticide use with updated farming systems. Nevertheless, they advise people to wash all food thoroughly and to eat a wide variety of foods to reduce exposure.
Much baby food is now organic, using ingredients grown virtually without pesticides, and millions of adults who can afford it are following the same route with their own diets. Organically grown food can, of course, be contaminated with micro-organisms, and all foods may contain natural carcinogens, but in all cases washing food is considered the best short- and long-term precaution.