The usefulness of total concentrations and pore water concentrations of pesticides in soil as metrics for the assessment of ecotoxicological effects ‐ Scientific Opinion of the Panel on Plant Protection Products and their Residues (PPR)

Abstract

SUMMARYThe European Food Safety Authority (EFSA) asked its Panel on Plant Protection Products and their Residues (PPR Panel) for an opinion regarding the relative utility of total concentration and pore water concentration as exposure metrics in the assessment of ecotoxicological risks from pesticides and their metabolites in soil.The PPR Panel has reviewed the relevant available scientific literature on effect assessment and bioaccumulation for plants and soil invertebrates. The literature search resulted in 137 hits which needed further consideration and which were supplemented by relevant literature published before 2000 already known by the working group experts.Based on this literature review on effect assessment, the PPR Panel concludes that for softbodied soil organisms (earthworms, enchytraeids, nematodes) and plants in close contact with the soil solution, pore water mediated uptake of pesticides seems mainly responsible for the effects caused, and would therefore be the relevant metric for effects assessment, and consequently also for exposure assessment. For hard-bodied soil organisms in close contact with the soil solution, less scientific evidence is available, but the evidence found for Collembola generally supports the conclusion arrived at for soft-bodied soil organisms. However, for a number of relevant soil taxa with different life and feeding strategies (e.g. mites and isopods), no information is available. For these organisms, additional routes of uptake (e.g. The usefulness of total concentrations and pore water concentrations of pesticides in soil as metrics for the assessment of ecotoxicological effectsThe EFSA Journal (2009) 922, 2-90 feed, contact with substrates in soil and litter) may need to be considered for terrestrial risk assessment.The PPR Panel is of the opinion that pore water is the driving factor for uptake and toxicity of pesticides for the particular species used in the current test guidelines (i.e. earthworms, Collembola, plants, microorganisms). In these tests, the actual measurement of concentrations is recommended regardless of the metric.The PPR Panel recognises that exposure assessments based on pore water could be more complicated than the current approach. It is therefore pertinent to consider whether it would materially alter the outcome of the risk assessment. The Panel examined the only three available examples and concluded that these were insufficient to reach a general conclusion on whether using pore water concentrations would make a difference. However, independent of the pesticide concentration metric used in exposure assessments, the PPR Panel has identified more important issues regarding terrestrial risk assessment that need to be resolved.-The desired level of protection goals, serving as the basis of the whole risk assessment process, needs to be defined by risk managers.-All exposure routes (pore water, food, contact), considering the habitat structure (soil depth, litter layer), as well as the organisms' vertical, horizontal, and temporal distributi...

Scientific Opinion on the effect assessment for pesticides on sediment organisms in edge‐of‐field surface water

“…Within this context, EFSA is also in the process of updating guidance on risk assessment for pesticides and soil organisms. The usefulness of total concentrations and pore water concentrations of pesticides in soil as metrics for the assessment of ecotoxicological effects on soil organisms was already the subject of an EFSA opinion (EFSA PPR Panel, 2009). Currently, the linking of exposure to effects and possible effect assessment procedures for soil organisms are discussed in an EFSA PPR Panel working group.…”

“…aqueous exposure (microbes, plants and animals) and food or ingestion exposure (particularly animals). According to EFSA PPR Panel (2009) and ECHA (2014) for non-ionic organic chemicals (the majority of pesticides) the most appropriate metric for bioavailability in soils and sediments appears to be the 'freely dissolved pore water concentration' rather than the total sediment concentration, particularly for compounds with a log K ow < 5. Two pragmatic approaches have regularly been used to support that the concentration in pore water is usually a more precise exposure metric: changes in effect over time (ageing; see Figure 1) and the usual normalisation of effects on basis of OC content observed in various sediment types.…”