Determination of Watch List chemicals in Irish surface waters: Chemical occurrence and analytical method challenges.

Contaminants of emerging concern (CECs) which do not have adequate data on occurrence in the environment are being added to the Watch List under the Water Framework Directive. The WL contains multiple CECs or groups of CECs with differing chemistries which can make analysis of surface water samples increasingly complicated due to the multiple extraction and analysis methods needed 1,2. Because of the low levels (ng.L -1 range) at which WL chemicals may occur in surface waters, reaching the detection and quantification limits needed to monitor these micropollutants presents a challenge. In this work, an analytical approach involving solid phase extraction (SPE) and liquid chromatography tandem mass spectrometry (LC-MS) was developed for monitoring 2nd Watch List substances in Irish surface waters. This is the first time data for the full expanse of the Watch List has been generated in Ireland. Conditions from extraction to analysis were optimized for recovery of this broad range of compounds at the ng.L-1 concentration level. It was found that the pesticide metaflumizone was not compatible with the evaporation and solvent exchange step of SPE, and therefore analysis of the direct eluent was performed for this compound prior to blow down. Two LC-MS methods were used for detection of the full suite of 15 analytes, in which estrogens were determined separately to the other analytes due to inefficient ionization of these analytes when used in the main method. Matrix-matched calibrations were used resulting in good linearities (R2<0.99) for the majority of compounds excluding the estrogens. Detection limits were in the low ng.L-1 range. All studied analytes aside from estrogens are below the EU stated target LODs. The methods were applied to 21 field samples taken from surface waters across Ireland over a three-year period from 2018-2020. Frequently detected analytes from the second Watch List, occurring in approximately 50% or more Irish samples, were the three estrogens, three macrolide antibiotics and four out of five studied neonicotinoid pesticides. The majority of these detections were below quantifiable levels. This work represents the first data on monitoring of all Watch List chemicals in Ireland. 1. R. N. Carvalho, L. Ceriani, A. Ippolito, T. Lettieri, European Commission, Joint Research Centre and Institute for the Protection and the Security of the Citizen, Development of the first watch list under the environmental quality standards directive., Publications Office, Luxembourg, 2015. 2. J. C. G. Sousa, A. R. Ribeiro, M. O. Barbosa, C. Ribeiro, M. E. Tiritan, M. F. R. Pereira and A. M. T. Silva, Monitoring of the 17 EU Watch List contaminants of emerging concern in the Ave and the Sousa Rivers, Science of The Total Environment, 2019, 649, 1083–1095.