Calibration and application of the Chemcatcher\xae passive sampler for monitoring acidic herbicides in the River Exe, UK catchment

Ian Townsend,Martin Broom,Anthony Gravell,Richard Greenwood,Gary R Fones,Melanie Schumacher,Lewis Jones,Graham A Mills

doi:10.1007/s11356-018-2556-3

Abstract

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 catchment, UK. Time-weighted average (TWA) concentrations of the herbicides 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 MCPA and mecoprop occurring in field trial 1. Chemcatcher® detected a large input of MCPA not found by spot sampling during field trial 2. Devices also detected 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.

Highlights

Auxin mimicking acidic herbicides, including phenoxy- and pyridyloxy-acids, are applied widely to control broad-leaved weeds in grassland and some cereal crops and to combat unwanted woody plants in forests and railways (HSE 2018)
The company uses an extensive water quality monitoring programme that targets a wide range of pesticides (60 compounds, including 16 acidic herbicides)
The first field trial was conducted to assess the performance of the Chemcatcher® alongside repeated high-frequency spot water sampling; the second to investigate if the passive sampler could provide information on which specific tributaries were primarily responsible for pollution by acidic herbicides in the lower Exe catchment

Summary

Introduction

Auxin mimicking acidic herbicides, including phenoxy- and pyridyloxy-acids, are applied widely to control broad-leaved weeds in grassland and some cereal crops and to combat unwanted woody plants in forests and railways (HSE 2018). Measurement of Chemcatcher® uptake rates for acidic herbicides In order to simulate monitoring conditions in the field, untreated River Exe water, sampled at the inlet to Pynes Water Treatment Works (national grid reference coordinates SX93009710, Fig. 1), was used as the matrix for the laboratory calibration tests.

Results

Conclusion