Abstract
Metaldehyde is recognised as an emerging contaminant. It is a powerful molluscicide and is the active compound in many types of slug pellets used for the protection of crops. The application of pellets to land generally takes place between August and December when slugs thrive. Due to its high use and physico-chemical properties, metaldehyde can be present in the aquatic environment at concentrations above the EU Drinking Water Directive limit of 100 ng L−1 for a single pesticide. Such high concentrations are problematic when these waters are used in the production of drinking water. Being able to effectively monitor this pollutant of concern is important. We compared four different monitoring techniques (spot and automated bottle sampling, on-line gas chromatography/mass spectrometry (GC/MS) and passive sampling) to estimate the concentration of metaldehyde. Trials were undertaken in the Mimmshall Brook catchment (Hertfordshire, UK) and in a feed in a drinking water treatment plant for differing periods between 17th October and 31st December 2017. This period coincided with the agricultural application of metaldehyde. Overall, there was a good agreement between the concentrations measured by the four techniques, each providing complementary information. The highest resolution data was obtained using the on-line GC/MS. During the study, there was a large exceedance (500 ng L−1) of metaldehyde that entered the treatment plant; but this was not related to rainfall in the area. Each monitoring method had its own advantages and disadvantages for monitoring investigations, particularly in terms of cost and turn-a-round time of data.
Highlights
Metaldehyde (C8H16O4) is considered an emerging pollutant of concern
This study aimed to investigate a number of different monitoring approaches for the measurement of metaldehyde in surface water and in an influent stream entering a drinking water treatment plant
Metaldehyde was quantifiable in all samples collected, and there were frequent marginal exceedances of the European Union’s Drinking Water Directive limit of 100 ng L−1 for a single pesticide (European Commission 1998)
Summary
Metaldehyde (C8H16O4) is considered an emerging pollutant of concern. It is a cyclic tetramer of acetaldehyde and is used as potent molluscicide. It is used agriculturally to protect a wide range of crops, including oil seed rape, wheat and winter barley from unwanted pests (Simms et al 2006). It is most frequently used in the autumn and winter when slugs and snails tend to thrive in the wetter environment (Green 1996). Metaldehyde is polar (log Kow = 0.12 at 20 °C), soluble in water (0.188 g L−1 at 20 °C) and mobile in soil (PPDB 2018). Issues relating to metaldehyde in the environment have been reviewed (Castle et al 2017)
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