Because so much of our food contains small amounts of pesticides, the Government has adopted something called Maximum Residue Level (MRL). These are the officially acceptable limits for chemicals in our food. An MRL is expressed in milligrams of chemical per kilogram of produce.
For example, the MRL for Cypermethrin is 1.0 mg/kg. If 1.0 kg of morning glory contains 0.5 mg of Cypermethrin (i.e. half the MRL), this is considered to be acceptable by the Government. But a sample containing 2.0 mg of Cypermethrin (i.e. twice the MRL) is considered unsuitable for consumption because of the danger to human health.
The MRLs used in Thailand are based on the recommendations of a United Nations organisation called the Codex Alimentarius Commission (usually know as ‘Codex’). A recommendation is made by Codex after reviewing all the available scientific information about the short-term and long-term affects a particular chemical might have on human health. Since 1962, Codex has recommended 2,500 MRLs. Thai scientists are conducting their own studies to establish MRLs for local crops that are not included in the Codex recommendations.
The European Union and the USA have their own system of MRLs, but the details are similar to Codex. The MRLs adopted in these countries – like those adopted in Thailand – are the maximum residues that are legally permitted. Food producers and importers can be prosecuted if the residues are higher than the MRL.