The residues detected on a food item will depend on which pesticides have been used and how persistent they are or, put another way, how long they take to decompose. Many pesticide residues are contained within the entire piece of produce rather than just on the surface. As a result, peeling fruit and vegetables before eating is often not enough to prevent exposure to pesticides. In addition, residue safety levels are set for just one pesticide at a time but items on supermarket shelves can contain traces of as many as 14 different pesticides.
All UK supermarkets conduct their own residue testing programmes. Their tests are largely aimed at identifying produce containing residues above the standard set by government which is known as the ‘Maximum Residue Level’ (MRL). When an exceedance of an MRL is identified, a supermarket will often work with the farmer to reduce residues and ensure the problem doesn’t happen again. Sometimes supermarkets will identify a residue problem with a particular food item from a specific country – for example, grapes from South Africa – and put in place an action plan for tackling it. Many supermarkets used to publish the results of their residue testing programmes but no longer do so.
Given the huge uncertainty around how exposure to multiple pesticides through food residues impacts upon human health, we should be taking a precautionary approach and reduce pesticide use whenever possible. Residues are also highly unpopular with UK shoppers who tend not to want traces of chemicals in their food.