Determination of pesticide residues in drinking water using LC-MS/MS method

The wording of the applicable legal regulations governing the requirements for drinking water quality does not provide detailed criteria for the control of pesticide substances. According to the Decree of the Ministry of Health of the Slovak Republic 91/2023 Coll., which establishes indicators and limit values ​​for the quality of drinking water and hot water, only pesticides whose presence can be assumed are detected. The limit value applies to each relevant pesticide and is set at 0.1 μg/l. Pesticide metabolites (pesticide residues) are divided into relevant (they pose a comparable or a higher risk than that of the parent pesticide) and irrelevant (they do not pose a significant risk), with their relevance assessed when approving the active substance. A list of pesticides and the relevance of their analysable metabolites in drinking water is published on the website of the Public Health Authority of the Slovak Republic.

Low limits of determination and detection are required. This is associated with the high demands on the sensitivity of the method used and instrumentation. High-performance liquid chromatography with tandem mass spectrometric detection (LC-MS/MS) was used to analyse the final samples.

The results of the analyses of the drinking water samples showed the presence of relevant and irrelevant pesticide metabolites. Trace amounts of pesticides (atrazine and its metabolites, metazachlor ESA, metolachlor OA, chlorpropham, prometrin, and chloridazone with its metabolites) were detected. Values ​​of atrazine and its degradation products and the irrelevant metabolite chloridazone desphenyl that exceeded the limits were also detected.

The picture of problem-free drinking water is gradually changing, and more and more pesticide substances are being found in drinking water. not only in trace amounts (below the limit of quantification) but also at concentrations that exceed the limit values. This is primarily related to the selection and monitoring of an ever-increasing number of pesticides and their metabolites.