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Development of a passive sampler for monitoring sources and fluxes of metaldehyde in natural waters

Student thesis: Doctoral Thesis

  • Glenn David Castle
Metaldehyde is the active ingredient in most forms of slug pellets used globally in the aid of pest prevention. High usage, physio chemical properties and removal difficulties all lead to metaldehyde presence in the aquatic environment, often above the EU Drinking Water Directive limit of 100 ng L-1 for a single pesticide in drinking water. This presents a problem when such waters are abstracted for potable supplies. Understanding metaldehyde sources, transport and fate in river catchments is important in order to minimise its presence within drinking water supplies. This thesis documents the successful development and calibration of a new variant of the Chemcatcher® passive sampler for the monitoring of metaldehyde in surface waters. Sampler uptake rates were measured in a laboratory as well as In situ (15.7, 17.8 mL day-1) and both revealed a linear uptake with limited offloading and no lag phase.
Two field trials using the Chemcatcher® were undertaken in the Greater Thames catchment, UK. Time-weighted average (TWA) concentrations of metaldehyde obtained using the Chemcatcher® were compared with concentrations measured in spot samples of water. The two techniques gave complimentary monitoring data, with the samplers being able to measure stochastic inputs of metaldehyde in surface waters. Chemcatcher® was able to detect large inputs of metaldehyde missed using infrequent spot sampling procedures due to constant sampling. A final field trial was undertaken in the Mimmshall Brook catchment (Hertfordshire, UK). TWA concentrations obtained were compared to concentrations measured at varying frequencies. The data collected by all techniques provided a concurring picture with low variability in terms of metaldehyde concentrations present in surface waters. The three targeted field trials highlight the potential value of using the Chemcatcher® passive sampler alongside spot water sampling to improve monitoring of metaldehyde and hence facilitate a better understanding of this sporadic pollutant in river systems.
Original languageEnglish
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Award dateSep 2018

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