Evaluation of models to estimate the bioaccumulation of organic chemicals in earthworms.

Modelling approaches to estimate the bioaccumulation of organic chemicals by earthworms are important for improving the realism in risk assessment of chemicals. However, the applicability of existing models is uncertain, partly due to the lack of independent datasets to test them. This study therefore conducted a comprehensive literature review on existing empirical and kinetic models that estimate the bioaccumulation of organic chemicals in earthworms and gathered two independent datasets from published literature to evaluate the predictive performance of these models. The Belfroid et al. (1995a) model is the best-performing empirical model, with 91.2% of earthworm body residue simulations within an order of magnitude of observation. However, this model is limited to the more hydrophobic pesticides and to the earthworm species Eisenia fetida or Eisenia andrei. The kinetic model proposed by Jager et al. (2003b) which out-performs that of Armitage and Gobas (2007), predicted uptake of PCB 153 in the earthworm E. andrei to within a factor of 10. However, the applicability of Jager et al.'s model to other organic compounds and other earthworm species is unknown due to the limited evaluation dataset. The model needs to be parameterised for different chemical, soil, and species types prior to use, which restricts its applicability to risk assessment on a broad scale. Both the empirical and kinetic models leave room for improvement in their ability to reliably predict bioaccumulation in earthworms. Whether they are fit for purpose in environmental risk assessment needs careful consideration on a case by case basis.

Ecotoxicological soil risk assessment under the new soil exposure framework - an impact assessment.

For the European risk assessment (RA) for soil organisms exposed to plant protection products (PPPs) endpoints from ecotoxicological laboratory studies are compared with predicted environmental concentrations in soil (PECSOIL) at first tier. A safety margin must be met; otherwise, a higher tier RA is triggered (usually soil organism field studies). A new tiered exposure modeling guidance was published by EFSA to determine PECSOIL. This work investigates its potential impact on future soil RA. PECSOIL values for >50 active substances and metabolites were calculated and compared with the respective endpoints for soil organisms to calculate the RA failure rate. Compared to the current (FOCUS) exposure modeling, PECSOIL values for all EU regulatory zones considerably increased, e.g., resulting in active substance RA failure rates of 67%, 58% and 36% for modeling Tier-1, Tier-2 and Tier-3A, respectively. The main driving factors for elevated PECSOIL were soil bulk density, crop interception and wash-off, next to obligatory modeling and scenario adjustment factors. Spatial PECSOIL scenario selection procedures result in agronomically atypical soil characteristics (e.g., soil bulk density values in Tier-3A scenarios far below typical European agricultural areas). Consequently, exposure modeling and ecotoxicological study characteristics are inconsistent, which hinders scientifically reasonable comparison of both in the RA.

Soil-specific outcomes in the OECD 216 Nitrogen Transformation Test.

The Organisation for Economic Co-operation and Development (OECD) 216 test guideline investigates the impact of agrochemicals on soil nitrogen transformation. After an evaluation of 465 OECD 216 studies, we describe two distinct yet contrasting outcomes in control nontreated samples that are possible in this testing framework, which we term the "rise" (consistent increases in nitrate concentrations throughout the test period) and "dip" (initial decline in nitrate concentration between Days 0-7, followed by a net-generation of nitrate across Days 7-28) responses. We raise significant concerns that control data from standardized, internationally recognized test guidelines can demonstrate such dissimilar patterns. We propose that, when present, the dip response undermines the intended functioning of the test system and removes the ability to draw appropriate ecotoxicological inferences from the data. In this work, we hypothesize the dip response is a product of conducting the study in low nitrogen content soils. Our results indicate that the dip response can be alleviated by using ammonium sulfate as an immediately available inorganic nitrogen source in place of the guideline-mandated complex, organic lucerne meal, demonstrating the influence of nitrogen availability and accessibility. However, not all low nitrogen soils exhibited the dip response, indicating the involvement of additional unidentified factors. Using our data and real-world regulatory examples, we advocate that datasets displaying the dip response should not be considered valid OECD 216 studies due to the influence of soil properties precluding an assessment of whether any impacts observed are driven solely by the test compound in question or are instead a product of the soil used. We propose methods to account for these soil-specific responses that could be integrated into the conduct and interpretation of OECD 216 studies. Such amendments will improve the reliability and robustness of the study system and enhance confidence in ecotoxicological conclusions derived from OECD 216 datasets. Integr Environ Assess Manag 2024;00:1-14. © 2024 SETAC.

Earthworm lipid content and size help account for differences in pesticide bioconcentration between species.

The uptake and elimination kinetics of pesticides from soil to earthworms are important in characterising the risk of pesticides to soil organisms and the risk from secondary poisoning. However, the understanding of the relative importance of chemical, soil, and species differences in determining pesticide bioconcentration into earthworms is limited. Furthermore, there is insufficient independent data in the literature to fully evaluate existing predictive bioconcentration models. We conducted kinetic uptake and elimination experiments for three contrasting earthworm species (Lumbricus terrestris, Aporrectodea caliginosa, Eisenia fetida) in five soils using a mixture of five pesticides (log Kow 1.69 - 6.63). Bioconcentration increased with pesticide hydrophobicity and decreased with soil organic matter. Bioconcentration factors were comparable between earthworm species for hydrophilic pesticides due to the similar water content of earthworm species. Inter-species variations in bioconcentration of hydrophobic pesticides were primarily accounted for by earthworm lipid content and specific surface area (SSA). Existing bioconcentration models either failed to perform well across earthworm species and for more hydrophilic compounds (log Kow < 2) or were not parameterised for a wide range of compounds and earthworm species. Refined models should incorporate earthworm properties (lipid content and SSA) to account for inter-species differences in pesticide uptake from soil.

The influence of soil organic matter content and substance lipophilicity on the toxicity of pesticides to the earthworm Eisenia andrei.

To account for potential differences in bioavailability (and toxicity) due to different soil organic matter (OM) contents in natural and artificial soil (AS), in the current European environmental risk assessment (ERA) a correction factor (CF) of 2 is applied to toxicity endpoints for so called lipophilic pesticides (i.e. log Kow > 2) generated from laboratory tests with soil invertebrates. However, the appropriateness of a single CF is questioned. To improve the accuracy of ERA, this study investigated the influence of soil OM content on the toxicity to the earthworm Eisenia andrei of five active substances used in pesticides covering a wide range of lipophilicity. Laboratory toxicity tests were performed in AS containing 10 %, 5 % and 2.5 % peat, and a natural LUFA 2.2 soil (4.5 % OM), assessing effects on survival, biomass change and reproduction. Pesticide toxicity differed significantly between soils. For all pesticides, toxicity values (LC50, EC50) strongly correlated with soil OM content in AS (r2 > 0.82), with toxicity decreasing with increasing OM content. Obtained regression equations were used to calculate the toxicity at OM contents of 10.0 % and 5.0 %. Model-estimated toxicity between these soils differed by factors of 1.9-3.6, and 2.1-3.2 for LC50 and EC50 values, respectively. No clear relationships between pesticide lipophilicity and toxicity-OM relationships were observed: the toxicity of non-lipophilic and lipophilic pesticides was influenced by OM content in a similar manner. The results suggest that the CF of 2 may not be appropriate as it is based on incorrect assumptions regarding the relationships between lipophilicity, OM content and toxicity. Further research should be conducted to understand the mechanistic link between toxicity and soil OM content to better define more chemically and ecologically appropriate CFs for ERA.

Considerations for the inclusion of metabarcoding data in the plant protection product risk assessment of the soil microbiome.

There is increasing interest in further developing the plant protection product (PPP) environmental risk assessment, particularly within the European Union, to include the assessment of soil microbial community composition, as measured by metabarcoding approaches. However, to date, there has been little discussion as to how this could be implemented in a standardized, reliable, and robust manner suitable for regulatory decision-making. Introduction of metabarcoding-based assessments of the soil microbiome into the PPP risk assessment would represent a significant increase in the degree of complexity of the data that needs to be processed and analyzed in comparison to the existing risk assessment on in-soil organisms. The bioinformatics procedures to process DNA sequences into community compositional data sets currently lack standardization, while little information exists on how these data should be used to generate regulatory endpoints and the ways in which these endpoints should be interpreted. Through a thorough and critical review, we explore these challenges. We conclude that currently, we do not have a sufficient degree of standardization or understanding of the required bioinformatics and data analysis procedures to consider their use in an environmental risk assessment context. However, we highlight critical knowledge gaps and the further research required to understand whether metabarcoding-based assessments of the soil microbiome can be utilized in a statistically and ecologically relevant manner within a PPP risk assessment. Only once these challenges are addressed can we consider if and how we should use metabarcoding as a tool for regulatory decision-making to assess and monitor ecotoxicological effects on soil microorganisms within an environmental risk assessment of PPPs. Integr Environ Assess Manag 2024;20:337-358. © 2023 SETAC.

Intermediate-tier options in the environmental risk assessment of plant protection products for soil invertebrates-Synthesis of a workshop.

The European environmental risk assessment (ERA) of plant protection products follows a tiered approach. The approach for soil invertebrates currently consists of two steps, starting with a Tier 1 assessment based on reproduction toxicity tests with earthworms, springtails, and predatory mites. In case an unacceptable risk is identified at Tier 1, field studies can be conducted as a higher-tier option. For soil invertebrates, intermediate tiers are not implemented. Hence, there is limited possibility to include additional information for the ERA to address specific concerns when the Tier 1 fails, as an alternative to, for example, a field study. Calibrated intermediate-tier approaches could help to address risks for soil invertebrates with less time and resources but also with sufficient certainty. A multistakeholder workshop was held on 2-4 March 2022 to discuss potential intermediate-tier options, focusing on four possible areas: (1) natural soil testing, (2) single-species tests (other than standard species), (3) assessing recovery in laboratory tests, and (4) the use of assembled soil multispecies test systems. The participants acknowledged a large potential in the intermediate-tier options but concluded that some issues need to be clarified before routine application of these approaches in the ERA is possible, that is, sensitivity, reproducibility, reliability, and standardization of potential new test systems. The definition of suitable assessment factors needed to calibrate the approaches to the protection goals was acknowledged. The aims of the workshop were to foster scientific exchange and a data-driven dialog, to discuss how the different approaches could be used in the risk assessment, and to identify research priorities for future work to address uncertainties and strengthen the tiered approach in the ERA for soil invertebrates. This article outlines the background, proposed methods, technical challenges, difficulties and opportunities in the ERA, and conclusions of the workshop. Integr Environ Assess Manag 2023;00:1-14. © 2023 SETAC.

Influence of soil organic matter content on the toxicity of pesticides to soil invertebrates: A review.

A better understanding of how soil organic matter (OM) content influences pesticide toxicity to soil invertebrates is needed to improve the ecological relevance of risk assessment approaches. In the current study, soil invertebrate toxicity data (LC50 and EC50 values) were collected from studies determining the toxicity of organic chemicals in soils with varying OM content. Relevant studies were identified by performing a literature search and through the use of toxicity databases. The data were used to address the following questions: (1) Can the relationship between toxicity and soil OM content be quantified? (2) Does soil OM content influence different toxicity endpoints in a similar way? (3) Is the influence of soil OM content on sensitivity to pesticides different between species? The results indicate that toxicity-OM relationships are chemical dependent, differ between endpoints, and are species-specific. Hence, the grouping of chemicals based solely on their lipophilicity, as well as having only one correction factor for multiple species, may not be an appropriate approach to risk assessment. Integr Environ Assess Manag 2023;19:1457-1472. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Applying a tiered environmental risk assessment framework to estimate the risk of pesticides to soil organisms in Latin America.

This work investigates the application of a tiered risk assessment scheme for soil organisms based on the risk quotient (RQ) and the toxicity exposure ratio (TER). Forty-five pesticides registered in Latin America were chosen and the ecotoxicological endpoints for earthworms, Collembola, and microorganisms were collated. Tier I assessment was made on conservative assumptions in which no refinements were applied. There, 14 pesticides (31%) exceed the RQ regulatory trigger indicating unacceptable risk, whereas 27 (60%) indicate unacceptable risk on the TER approach. In a Tier II evaluation when refinement options such as foliar interception, field half-life, and the dissipation following the peak estimated environmental concentration are considered, eight (18%) pesticides indicate unacceptable risk based on the RQ, and 15 (33%) indicate unacceptable risk based on the TER. A nonmetric multidimensional scaling evaluation was performed to understand the relevant characteristics involved in how each pesticide poses a risk to soil organisms. Based on the outcome of this analysis, we observed that, for a given pesticide, the combination of high persistence, low or no crop interception, and high toxicity are likely to require higher tier risk assessment. Refinement options can consider either or both the exposure and/or the effect side of the framework. Exposure refinements are potentially simpler and can be conducted with data already available to risk assessors, whereas effect refinements involving further testing with the organisms potentially at risk are still under discussion for intermediate and higher tiers. A sensitive, simple, and logical environmental risk assessment framework can be used to adequately identify risks based on the relevant protection goals that, in turn, will help to protect the desired soil multifunctionality of the ecosystem. We encourage academia and industry to further investigate these topics to provide the most scientifically robust and evidence-based information to decision makers. Integr Environ Assess Manag 2023;19:446-460. © 2022 SETAC.

Arbuscular Mycorrhizal Fungi and the Need for a Meaningful Regulatory Plant Protection Product Testing Strategy.

Arbuscular mycorrhizal fungi (AMF) perform key soil ecosystem services and, because of their symbiotic relationship with plant roots, may be exposed to the plant protection products (PPPs) applied to soils and crops. In 2017, the European Food Safety Authority (EFSA) released a scientific opinion addressing the state of the science on risk assessment of PPPs for in-soil organisms, recommending the inclusion of AMF ecotoxicological testing in the PPP regulatory process. However, it is not clear how this can be implemented in a tiered, robust, and ecologically relevant manner. Through a critical review of current literature, we examine the recommendations made within the EFSA report and the methodologies available to integrate AMF into the PPP risk assessment and provide perspective and commentary on their agronomic and ecological relevance. We conclude that considerable research questions remain to be addressed prior to the inclusion of AMF into the in-soil organism risk assessment, many of which stem from the unique challenges associated with including an obligate symbiont within the PPP risk assessment. Finally, we highlight critical knowledge gaps and the further research required to enable development of relevant, reliable, and robust scientific tests alongside pragmatic and scientifically sound guidance to ensure that any future risk-assessment paradigm is adequately protective of the ecosystem services it aims to preserve. Environ Toxicol Chem 2022;41:1808-1823. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Investigating the role of soil mesofauna abundance and biodiversity for organic matter breakdown in arable fields.

Intact soil food webs are pivotal to maintaining essential soil functions, such as carbon recycling, sequestering, and biomass production. Although the functional role of micro- (e.g., bacteria and fungi) and macrofauna (e.g., earthworms) is comparatively well established, the importance of the mesofauna community (e.g., abundance and diversity of Acari and Collembola) in maintaining soil functionality is less clear. We investigated this question in a six-month field experiment in arable soil by actively manipulating mesofauna abundance and biodiversity through the application of two legacy insecticides (lindane and methamidophos) at sufficiently high doses to reduce mesofauna abundance (well above previously registered application rates; 2.5 and 7.5 kg a.s./ha for lindane, and 0.6 and 3 kg a.s./ha for methamidophos) and measure the impact on organic matter degradation. Our results demonstrate that both insecticides had reduced Collembola and Acari abundances by up to 80% over the study's six-month duration. In addition, we observed less pronounced and more complex changes in mesofauna biodiversity over time. These included insecticide-dependent temporal fluctuations (both reduction and increase) for different estimates (indices) of local (alpha)-diversity over time and no lasting impact for most estimates after six months. Even at these exceptionally high field rates, Collembola and Acari diversity was observed to generally recover by six months. In contrast, considering organic matter breakdown, we found no evidence of a treatment-related effect. These results suggest that organic matter breakdown in arable soils is likely driven by other trophic levels (e.g., microorganisms or earthworms) with only a limited influence of the mesofauna community. We discuss these findings with regard to their implications for our current understanding of soil food web function and future European soil risk assessments. Integr Environ Assess Manag 2022;18:1423-1433. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).