Application of the Chemcatcher passive sampler for monitoring acidic herbicides in two UK river catchments
Acidic herbicides are used to control broad-leaved weeds. They are stable, water soluble, and with low binding to soil are found frequently in surface waters, often at concentrations above the EU Drinking Water Directive limit of 0.10 µg L−1. This presents a problem when such waters are abstracted for potable supplies. Understanding their sources, transport and fate in river catchments is important. We developed a new Chemcatcher® passive sampler, comprising a 3M Empore™ anion-exchange disk overlaid with a polyethersulphone membrane, for monitoring acidic herbicides (2,4-D, dicamba, dichlorprop, fluroxypyr, MCPA, MCPB, mecoprop, tricolpyr). Sampler uptake rates (Rs = 0.044-0.113 L day-1) were measured in the laboratory.
Two field trials using the Chemcatcher® were undertaken in the River Exe (14 and 16 day trials) and River Dee (22 month trial with devices replaced every 14 days) catchments, UK. Time-weighted average (TWA) concentrations of the herbicides obtained using the Chemcatcher® were compared with concentrations measured in spot samples of water collected regularly (typically between 2-14 day intervals) over the same time period. Both types of sample were analysed using either GC-MS (River Exe) or LC-MS (River Dee) procedures.
The two techniques gave complimentary monitoring data, with the samplers being able to measure stochastic inputs of MCPA and mecoprop occurring in the River Exe trial. In the longer River Dee trial it was evident that inputs of the acidic herbicides were linked to seasonal application and rainfall events in the catchment. On occasions for some herbicides (e.g. MCPA, 2,4-D) the concentration in the surface water exceeded the EU Drinking Water Directive limit of 0.10 µg L−1. Devices were also able to detect other pesticides and pharmaceuticals with acidic properties.
Information obtained using the Chemcatcher® can be used to develop improved risk assessments and catchment management plans and to assess the effectiveness of any mitigation and remediation strategies.
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Prof Gary Fones (University of Portsmouth)
Gary Fones joined the University of Portsmouth in 2006 as a Senior Lecturer in Marine Biogeochemistry and was promoted in 2013 to Reader and in 2017 to Professor of Environmental Aquatic Chemistry. Previous to this he held a number of research posts at the University of Southampton, Woods Hole Oceanographic Institution (USA) and Lancaster University. He has a background in oceanography (BSc and MSc) and environmental analytical chemistry (PhD). He is a Fellow of the Royal Society of Chemistry (Water Science Forum committee member and Co-Editor of the WSF newsletter), the Editor-in-Chief of the journal 'Continental Shelf Research' and is a core member of the NERC Peer Review College. His main research interests are water and sediment quality monitoring using in-situ passive samplers for trace metals, nutrients and polar organic contaminants. Other research interests include trace metal and nutrient sediment water interactions (including sediment resuspension), benthic fluxes, transformations and benthic-pelagic coupling. He has worked on a number of NERC funded projects (Macronutrients and Shelf-Sea Biogeochemistry) and currently works closely with a number of UK water supply companies on integrating passive sampling monitoring into their catchment management strategies.
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