Extrapolation of imidacloprid toxicity between soils by exposing Folsomia candida in soil pore water

Afolarin O Ogungbemi,Cornelis A M Van Gestel

doi:10.1007/s10646-018-1965-x

Abstract

Soil properties like organic matter (OM) content show great variation, making it hard to predict the fate and effects of a chemical in different soils. We therefore addressed the question: can we remove the complexity of the soil matrix and yet accurately predict soil toxicity from porewater exposures? Folsomia candida was exposed to imidacloprid in natural (LUFA 2.2 [4.02% OM], Grassland [12.6% OM]) and artificial soils (OECD 5 [6.61% OM], OECD 10 [10.8% OM]), in pore water extracted from spiked LUFA 2.2 soil and in water. Toxicity decreased with increasing OM content except for Grassland soil, which had the highest OM content but the lowest clay content, suggesting a role of clay minerals in the binding of imidacloprid. Distribution coefficients for imidacloprid based on toxicity (Toxicity-Kd) were derived by comparing effect concentrations in LUFA 2.2 soil and in water. Using these Toxicity-Kds to recalculate soil LC50s/EC50s to porewater concentrations, the differences in LC50/EC50s almost disappeared. The recalculated porewater LC50s did not differ by more than a factor of 0.55–1.43 from the LC50 obtained upon water exposure. This similarity suggests that the toxicity in the soil is dependent on porewater concentrations and can be obtained from water exposure. The porewater test and the corresponding “pore-water extrapolation concept” developed in this study may be used to predict the toxicity of chemicals in the soil and extrapolate among different soils.

Highlights

In soil ecotoxicology, it is standard practice to expose soil organisms to chemicals in soil media, and the effect endpoint is usually estimated based on the concentration of the chemical in the soil
Van Gestel and Ma (1988) exposed earthworms to chlorophenols in four soils and recalculated the soil LC50 to porewater concentrations. They found a factor of 4.4–12.8 difference for soil LC50s, which significantly reduced to a factor of 1.2–2.4 when LC50s were based on porewater concentrations
Several studies have shown that pore water is the most important route of chemical exposure for in-soil dwelling organisms by correlating toxicity to porewater concentrations (Martikainen and Krogh 1999; Styrishave et al 2010)

Summary

Introduction

It is standard practice to expose soil organisms to chemicals in soil media, and the effect endpoint is usually estimated based on the concentration of the chemical in the soil. A. M. van Gestel chemicals via the soil pore water (Belfroid et al 1996; Fountain and Hopkin 2005). Van Gestel and Ma (1988) exposed earthworms to chlorophenols in four soils and recalculated the soil LC50 to porewater concentrations. They found a factor of 4.4–12.8 difference for soil LC50s, which significantly reduced to a factor of 1.2–2.4 when LC50s were based on porewater concentrations. They postulated the porewater hypothesis which states that the concentration of a chemical in an organism is considered to be related to the porewater concentration which in turn depends on the sorption behavior of the chemical in the soil

Methods

Results

Conclusion