AS166: On-line Monitor for Metaldehyde in Surface and Ground Water

Martin Perkins

15th February 2017

AS166: On-line Monitor for Metaldehyde in Surface and Ground Water

Metaldehyde is primarily used as a contact molluscicide in the control of slugs and snails in the UK and its use in the agricultural industry is common. However, its impact on karstic groundwater abstractions due to its persistence in the environment, its moderate solubility in water and the difficulty in treating it with conventional pesticide processes (granular activated carbon and ozone) has led to the outdoor UK ban of its use effective from Spring 2020. For this reason, its needs to be rigorously tested for. The UK regulatory limit for Metaldehyde in drinking water is set at 0.1 µg/L.

Prior to this work taking place, it could take up to 10 working days to get results back for Metaldehyde due to the sheer volume of required analysed samples. Despite meeting industry norms, Affinity Water had ambitions to drastically reduce their sample turnaround times. This coupled with the design of a new Metaldehyde treatment process were the key drivers for the Affinity Water Pesticide Programme team to explore a new approach to detecting Metaldehyde in waters. In 2015, Affinity Water and Element Ltd started discussions about the application of this instrument to take quasi real-time samples of the raw and partially treated water on a Water Treatment Works (WTW).

The aim of the trial for Affinity Water was to determine whether this type of automated system could provide robust and reliable metaldehyde results in real time under the varying water quality conditions in an operational environment. Faster reaction to changes in metaldehyde levels would facilitate a better management of abstraction and reduce the risk of exceedances.

In September 2016, an ‘online Metaldehyde monitor’ trial commenced at a 36 ML/d Affinity Water karstic groundwater treatment works with four sources in Hertfordshire analysing Metaldehyde concentrations from three inlets at different stages of treatment. Evaluation of linearity obtained using the GERSTEL MPS system, had an r² of 0.999 and precise and accurate results and a LOD of 0.003 µg/L. Based on the success of this trial, Affinity Water have an On-line Monitor for Metaldehyde in Surface and Ground Water working at their WTW.