Questions when interpreting the results of analysis of pesticide residues in food
Sometimes in the agri-food companies there are doubts when interpreting the analytical data on the pesticide residues reports, such as doubts related to the real value of a result, the meaning of a positive result, the uncertainty or whether the active matter detected exceeds the maximum residue limit allowed (MRL) by legislation. A good interpretation of results can be key when making decisions both in the export and import of food.
What is a positive MRL?
A positive is any result of the analyzed parameter that equals or exceeds the limit of quantification (LOQ). In other words, the LOQ is the minimum concentration of analyte that can be quantified with an analytical method. In general, it is usually 0.01 mg/kg and depends on the validation of the laboratory’s analytical method. A positive can exceed an MRL which are legislated (in South Africa, the Foodstuffs, Cosmetics and Disinfectants Act (54/1972) and in Europe the Regulation (EC) 396/2005 on maximum pesticide residue limits in food and feed of plant and animal origin).
Definition of uncertainty
When detecting and quantifying a positive in our result reports, that value is not an exact mathematical number, but a value within a range called uncertainty.
The measurement uncertainty is the interval of the experimental result in which the true value can be expected to lie, within a defined probability. The uncertainty must incorporate all possible sources of error in the method: pattern, material used, labor, instrumentation, etc.
Should we apply uncertainty to a result that may exceed the MRL?
When detecting a positive that is in the allowed limit, it is important to know the uncertainty data and to know the interpretation of results. To do this, we detail the possible cases that can occur when we detect a positive in an analyzed sample close to the MRL.
The diagram shows how measurement uncertainty can be considered in relation to the assessment of the conformity of an individual item against a specification (MRL). For each scenario, the red dot represents a single test result, and the vertical bar represents the range of expanded measurement uncertainty.
- Scenario 1: The analytical result bounded by the extreme points of measurement uncertainty is greater than the MRL. The result indicates that the residue found in the sample lot exceeds the MRL.
- Scenario 2: The analysis result is greater than the MRL and the lower end of the measurement uncertainty is less than the MRL.
- Scenario 3: The analysis result is less than the MRL and the upper end of the measurement uncertainty is greater than the MRL.
- Scenario 4: The analytical result bounded by the expanded endpoints of measurement uncertainty is less than the MRL.
The decision making in Scenario 1 is clear with an evident exceedance of the MRL established by legislation. In Scenario 4, the sample is clearly in compliance with the MRL.
In scenarios 2 and 3, the analytical result differs from the maximum level by less than the expanded measurement uncertainty. The interpretation of results in this case is that the result is not conclusive, since the result can be interpreted as exceeding the MRL and in the same way, as a compliant and defensible result by the client. Action on this outcome depends on existing agreements between trading partners.
This issue is addressed in Section 4 of CXG 83-2013 (Principles for the use of sampling and analysis in international trade in food). Principle 5 states that “the exporting country and the importing country should agree on how the uncertainty of the analytical measurement is taken into account when assessing the conformity of a measurement with respect to a limit legal”.
According to document CXG 59-2006, The distribution of products in domestic markets or in international trade when the results of the analyzes correspond to scenarios 2 and 3 should be carried out with caution. For example, when certifying products for export, it may be inadvisable to export consignments whose residue results correspond to scenarios 2 and 3. For countries importing products with residue levels corresponding to scenario 2, it may be difficult to verify compliance with the MRL with an acceptable level of confidence. Generally, scenario 3 cannot lead to the adoption of measures by the importing party.
Pesticide residues normative
The official standard “Analytical Quality Control and Method Validation Procedures For Pesticide Residues Analysis In Food And Feed SANTE 11312/2021” aims to provide guidance to all official laboratories that participate in the official control of pesticide residues in food throughout the European Union.
This standard indicates a default measurement uncertainty of 50%, which corresponds to a confidence level of 95%, and has been calculated from EU proficiency tests. In general, this 50% value covers the interlaboratory variability between European laboratories and is recommended to be used by regulatory authorities in cases of enforcement decisions (MRL exceedances).
A prerequisite for using the default expanded measurement uncertainty of 50% is that the laboratory must demonstrate that its own expanded uncertainty is less than 50%.
AGQ Labs and measurement uncertainty
AGQ Labs has validated and accredited the method under two different accreditation entities, IAS and ENAC. This validation yields a specific uncertainty for each analyte in the scan, both gas and liquid chromatography, and an uncertainty of 50% is stated.
Contact us if you have any questions regarding the interpretation of the results of your analysis of pesticide and phytosanitary residues in food.
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