SETAC Spotlight: Integrating Terrestrial Model Ecosystems into Soil Risk Assessment – A Tier 3 Refinement Option

CEA presented 1 platform and 9 posters at SETAC Seville in May 2024. We will be showcasing each of these presentations in a series of ‘SETAC Spotlight’ articles. This week it is:

SETAC Spotlight: Integrating Terrestrial Model Ecosystems into Soil Risk Assessment – A Tier 3 Refinement Option

Authors: : Hanna Schuster¹, Johanna Oellers², Abdul Abu¹, Zoe Parker-Crosse¹, Nadine Taylor¹, Ellie Welch¹, Monika Hammers-Wirtz²

¹Cambridge Environmental Assessments, RSK ADAS, Boxworth, UK

²gaiac Research Institute for Ecosystem Analysis and Assessment, Aachen, Germany

Soil dwellers are an essential part of healthy soils that support ecosystem functions and services, such as nutrient cycling essential for ensuring crop growth (EFSA 2017).
In the European Union (EU), there is the requirement to assess and understand the risk of plant protection products (PPPs) to soil dwelling organisms. The current risk assessment for soil organisms compares the NOEC (No Observed Effect Concentration) and/or EC10/20 (Effect Concentration with a 10 %/20 % effect) to the maximum Predicted Environmental Concentration in the soil (PECsoil) calculated according to FOCUS (FOCUS 1997). The proposed introduction of a new exposure assessment procedure for in-field soil organisms is expected to impact the current risk acceptability of many PPPs. Specifically, Tier 1 and 2 of the EFSA (2017) exposure assessment procedure uses the Persistence in Soil Analytical Model (PERSAM), which integrates European scale environmental and agronomic data for calculation of PECsoil values for the three EU Regulatory Zones and Individual Member States. Therefore, existing PECsoil values (FOCUS) are subject to change, and it is also likely that the new PECsoil values (PERSAM) will be higher than current ecotoxicological endpoints, causing many existing PPP risk assessments to fail.
Where a compound fails the risk assessment at Tier 1 of the ecotoxicological risk assessment, field studies are often the only option for endpoint refinement. Intermediate tiers such as extended laboratory studies (Tier 2: non-standard species, exposure refinement, modelling) and soil mesocosm studies (Tier 3) to address issues in the risk assessment are rarely conducted.
This lack of regulatory accepted interim tiers necessitates an increased need for the development of robust intermediate tier options to close this growing gap in soil risk assessment. Terrestrial Model Ecosystems (TMEs), where soil cores are taken from a pasture or meadow to ensure sufficient abundance and biodiversity for reliable outcomes, have been shown to be a robust testing system, however, they have yet to be incorporated into soil risk assessments. As soil risk assessments aim to protect in-field soil dwellers, TMEs represent a worst-case scenario and results can be regarded as protective of in-field organisms, in a similar concept to aquatic mesocosms representing edge-of-field systems. Here we present ideas and concepts on how to use TMEs, as a Tier 3 refinement option, for the effects on soil dwelling organisms. At CEA we are working to implement TMEs as a Tier 3 refinement option in the near future.