Multiple residues of plant protection products

There is a legal mandate to consider the cumulative effects of various substances when approving active substances for use in plant protection products, when determining maximum residue levels, and as part of the product authorisation procedure. BfR has therefore developed a concept to integrate cumulative risk assessment into these various procedures. The concept builds on previous work by EFSA and touches upon the assessment areas of application safety and consumer safety. The concept is currently in the internal test phase.

How do multiple residues occur?

Modern active substances in plant protection products are characterised by their targeted effect on specific harmful organisms. Substances of earlier generations often had a wider effect with more side effects. The alternating use of active substances with different mechanisms of action is necessary in order to prevent resistance in harmful organisms; otherwise it is impossible to fight the organisms on a permanent basis. The use of broadband active substances has decreased significantly in recent years with a corresponding increase in the use of plant protection products with a specific effect. The result of this trend is that, depending on the infestation situation, many different plant protection products are used, residues of which can remain in the harvested crops. Multiple residues can therefore occur as a result of proper and prudent use of plant protection products.

Multiple residues have existed for quite some time. They have come into focus in recent years because the use of various active substances is increasing and the ongoing development of residue analysis has resulted in the ability to detect higher numbers of active substances in ever lower concentrations.

BfR’s concept for the assessment of multiple residues

The BfR’s concept for cumulative risk assessment is based on the principle of dose addition and consists of multiple steps. The assessment begins with a calculation of the hazard index (HI). Here, in a first step for each individual substance under consideration the quotient of the expected exposure and the toxicological limit is calculated and in a second step these values are added together. The extent to which a substance reaches its specific limit value through its application or residue is calculated for each individual substance. For example, substance A may account for 10%, while substance B may account for 7% of the limit value. The HI is calculated by adding together these individual values of substance A and substance B, in this case 17% of the limit value. If an HI of 1 (corresponding to 100%) is exceeded, then additional assessment steps are required. Refinements can be made both on the exposure side and the toxicological evaluation side of the equation. Which refinement options are chosen depends on the availability of the required data and the complexity of the assessment. If the value of HI is still >1, even after refinements have been made, then an unacceptable risk cannot be ruled out.

This concept is suitable for the cumulative assessment of user exposure or the acute exposure of consumers, as the active substances present in a plant protection product or a proposed tank mix are considered together. However, the approach is not suitable for determining the chronic cumulative exposure of consumers to active substance residues from different plant protection products. Representative data from food monitoring should be used for this purpose. 


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