Highly variable soil dissipation of metaldehyde can explain its environmental persistence and mobility

Nathan Keighley,Carmel Ramwell,Chris Sinclair,David Werner

doi:10.1016/j.chemosphere.2021.131165

Abstract

There are increasing concerns about the hazard posed to drinking water resources by persistent, mobile, and toxic (PMT) substances in the environment. For example, the extensive use of metaldehyde-based molluscicide to control slug populations in agricultural fields has frequently led to pollution of surface waters and contamination of drinking water at levels exceeding the statutory limit. Regulatory environmental fate assessments and studies in the literature did not predict that metaldehyde would be persistent in the environment, contrary to observations from monitoring schemes. To understand the reasons for this disparity, this study conducted a suite of degradation experiments, covering different soil types and environmentally realistic conditions in Northern Europe, and generated a distribution of DT50 values for metaldehyde to examine whether degradation rates are underestimated by current risk assessments. The results were found to vary, showing DT50 values ranging from 3.0 to 4150 days, which indicated that metaldehyde had the potential to become persistent. Lack of prior metaldehyde exposure, high moisture content, low temperature, and locally high metaldehyde concentration under pellets were identified as high-risk conditions for low pesticide biodegradation in UK soils.

Highlights

In Europe there are increasing regulatory activities to address con cerns about persistent, mobile, and toxic (PMT) substances in the envi ronment (Rüdel et al, 2020; Hale et al, 2020a, b)
The measured degradation rates for metaldehyde were lower for the permanent pasture clay loam soil, while in the arable soils, metaldehyde was shown to degrade quickly, in line with findings from the literature (EFSA, 2010)
The most conspicuous result was that of the pasture clay loam under high soil moisture

Summary

Introduction

Salvestrini et al, 2017; Busquets et al, 2014) This has necessitated catchment-based interventions and modelling of metaldehyde concen trations in surface waters to predict peak concentrations and manage abstraction times (Asfaw et al, 2018; Castle et al, 2017; Kay and Grayson, 2014; Lu et al, 2017). These models rely on input parameters, such as pesticide degradation rates, derived from laboratory experi ments. This study aimed to investigate the cause of this disparity

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Conclusion