Pesticides present at trace concentrations are a common cause of poor water quality. Their concentrations can change dynamically, due to the stochastic nature of pesticide pollution. Consequently, characterisation of pesticide residues that are intermittently present, poses significant monitoring and analytical challenges. Traditional approaches rely on quantitation of a limited number of pesticides present in a discrete water sample. Expanding the analytical suite and/or the frequency of sampling to meet these challenges is often impractical. Comprehensive methods are needed, with selectivity and sensitivity for the hundreds of pesticides potentially present, and temporal representativeness to ensure changing conditions are understood, in order to identify and prioritise risk. Recent analytical advances have enabled the targeted screening of hundreds of compounds in the same run, and automated work-flows can now reliably identify compounds through the comparison of retention time and accurate mass with spectral libraries. Screening generates large qualitative data sets, therefore, there is a need for improved monitoring methods and data interpretation strategies to reduce the need for repetition, and increase the quality of information for end-users. Passive sampling is an in-situ time integrative technique, increasingly used for monitoring pesticides in water. Here, we describe a method using the Chemcatcher® passive sampler, coupled to targeted screening using liquid chromatography-quadrupole-time-of-flight mass spectrometry, and a commercially available library. Statistical analysis was performed using Agilent Mass Profiler Professional software. Water sampling took place over one year, at three riverine sites in the south of England, UK. Statistical interpretation of time integrative data from passive sampling could distinguish regular and episodic pesticide inputs, and detected compounds neglected by routine monitoring methods. One hundred and eleven pesticides were identified including legacy and current use compounds with diverse origins and uses. Spatial and temporal trends were identified enabling prioritisation of seasonal monitoring at each site. This approach maximises the utility of qualitative assessment and may help water quality managers to rationalise pesticide fate in future, providing significant additional insight without the need to increase the scope and cost of monitoring.
- Passive sampling