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Common Terms Used in Pesticide Science

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Pesticide residues: the acronyms

Pesticide residues are a matter of great and increasing public pressure since the public perceives a risk (in practice, the product of hazard and exposure) but feel they have little control. In response, authorities attempt to regulate by setting standards and monitoring exposure. This results (necessarily) in an arcane set of procedures and terminologies. Two acronyms- Maximum Residue Levels (MRLs: specifications for food safety) and Acceptable Daily Intake (ADI: a function of pesticide approval) - are especially prominent in public debate, but it is often not appreciated how tenuously the two are linked. Renwick (2002) gives a useful general overview of residues and the deficit in transparency in risk assessment; Matthews (2006) describes the issues in greater depth.

A pesticide can only be approved for use if the risk to consumers, based on potential exposure, is acceptable. The limit set for a pesticidal active ingredient (a.i.), the ADI, is based on estimates of hazard and dietary intake.

Dietary intake may be based on the National Estimated Dietary Intake (NEDI) of a given foodstuff using surveys by national food standards agencies. Ideally, judgements would be carried out on Theoretical Maximum Daily Intake (TDMI), but there may be substantial variations between infants, children and adults even after adjusting for body weight.

Operator risk (via the inhalation, dermal, oral routes): pesticides are also approved (or otherwise) on Acceptable Operator Exposure Levels (AOEL).

Once it has passed these hurdles, a pesticide in use is monitored with reference to a MRL, based on analysis of quantity of a.i. remaining on a food product. For many pesticides, however, this is set at the Limit of Determination (LOD) - since understanding of ADI is incomplete (i.e. producers or public bodies have not submitted MRL data - often because these were not required in the past). Adoption of GAP at the farm level would eliminate use of the more toxic pesticides, but with increasingly sensitive detection equipment, a certain amount of pesticide residue will often be measured following field use of new generation, low toxicity pesticides.

Residues in commodity crops
The EU agricultural pesticides directive (91/414/EEC), where many of the older compounds that are still used in developing countries are being withdrawn from permitted use, and good agricultural practice (GAP) will only include the use of permitted products, correctly applied. For any compound not on lists of permitted substances the MRL is set at the level of detection, so producers take a risk of consignments being refused they continue to use products containing these active substances. More here.

Renwick, A.G. (2002) Pesticide residue analysis and its relationship to hazard characterisation (ADI/ARfD) and intake estimations (NEDI/NESTI). Pest Management Science, 58: 1073-1082