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Is there still a place for recovery endpoints from mesocosm studies?

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Is there still a place for recovery endpoints from mesocosm studies?

In an earlier article we demonstrated how mesocosm community studies with insecticides, herbicides and fungicides can provide effect endpoints which are typically at least x10 higher than Tier 1 equivalents. Mesocosm studies mimic real edge-of-field surface waters and enable the effects of plant protection products (PPPs) on aquatic organisms to be assessed at the population and community level. According to the current EU aquatic guidance, Regulatory Acceptable Concentrations (RACs) can be derived using two options: the ecological threshold option (ETO), which allows for only negligible population effects; and the ecological recovery option (ERO), where some population-level effects may occur, but recovery is demonstrated within an accepted time period.

In recent years, the acceptability of the ERO-RAC has decreased, with the more conservative ETO-RAC approach preferred by many Member States when assigning endpoints and determining RACs. This is due to concerns around multiple stressors at the wider catchment scale leading to exceedance of acceptable exposure levels – the ETO-RAC option providing more certainty of no adverse effects. The EFSA (2013) guidance states, however, that it is feasible to determine an ERO-RAC where ‘all relevant processes that determine population viability and the propagation of effects to the community, ecosystem and landscape level’ have been considered.

The application of a justifiable ERO-RAC should not, therefore, be discounted in all cases, particularly when the study has been carefully designed with the objective of assessing recovery in the system and to address the current concerns surrounding this endpoint. One concern is the effect of multiple exposures on the ability of aquatic organisms to recover, such as successive inputs from the target crop (e.g. drainflow events), or by exposure to other products used within the same catchment. Since the EFSA guidance proposes a maximum 8-week recovery period to establish the ERO-RAC, it is possible that multiple exposures may occur during this time; however, there may be scenarios where recovery is demonstrated to be rapid (e.g. within 1-2 weeks) and the potential for compounds with a similar mode of action entering the waterbody within that shorter period is reduced.

As a way to address this concern, mesocosm studies should have a well-defined pre-treatment phase to establish a system baseline and be designed with multiple and frequent sampling occasions within the first week of any test item application(s). This will enable rapid recovery to be captured and assessed. If such rapid recovery cannot be determined, but recovery according to the current guidelines can be demonstrated, then consideration should be given to landscape scale analysis of the surrounding catchment, including the proximity of other agricultural practices and the potential for recolonization of affected water bodies can also be assessed to justify the use of an ERO-RAC.

We would like to generate an active discussion around the use of recovery as an endpoint across industry, policy makers and regulators.  We are presenting a poster on this topic at SETAC Helsinki (May 2019) and would like to organise a discussion group to help move this topic forward. Please contact Nadine.Taylor@cea-res.co.uk if you would be interested in being involved in such a discussion during SETAC Helsinki.

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