ecotox consult - Dr. Michael Meller - ecotoxicological consulting service

Abstract

The mesocosm/microcosm risk assessment process for deriving a regulatory acceptable concentration (RAC) via ecological threshold option (ETO) and/or ecological recovery option (ERO) involves extensive data processing and the assessment of complex relationships found in higher tier studies. The present work gives a comprehensive insight on how the requirements of the new EFSA aquatic guidance document (AGD) [1] can be applied in the practical risk assessment of higher tier studies.

For deriving an ETO-RAC, the number of scenarios to be assessed can exceed the number of 50 – as Beta-Cypermethrin in the present work with 51 scenarios – depending on the intended use patterns of a substance. As one scenario can contain several exposure peaks with a predicted dissipation to be assessed, this implies a massive workload. In this work, automated data processing and use of parameters was evaluated to minimize the workload without reducing the accuracy of the data comparison. Further possible approaches could include the use of generalized exposure profiles as outlined by Brock et al. (2010) [2] instead of assessing every single exposure profile.

When looking at the input for the dissipation comparison, the available mesocosm/microcosm data base has direct influence on the reliability of the dissipation rate since more data points require less interpolation and thus represent the mesocosm exposure more accurately.

Various parameters exist to characterize a decline in a time dependent curve. This work evaluated three approaches to meet the requirements for characterizing the dissipation rates. Visual comparison and comparison of the area under the curve (AUC) produced similar results on the present dataset, whereas the comparison based on the vertical differences of data points rated twice as much scenarios to be unrealistic and not worst case when compared to visual comparison and AUC. This implies that the AUC calculation could be used for the assessment of the mesocosm dissipation when compared to that predicted for the field. If the mesocosm dissipation for a scenario is falsely rated unrealistic and not worst case, the effect estimate will be based on time weight average mesocosm concentrations according to the AGD [1]. From a regulatory point of view this would be acceptable since it comprises a higher margin of safety when compared to the use of nominal or initially measured concentrations. This shows that the use of automated calculations can reduce the extensive workload with an appropriate result. Further research is needed to evaluate more data and more parameters and possible combinations of these for an appropriate and efficient assessment of every scenario.

The ERO-RAC upgrading process represents a verification of the ERO-RAC concerning the predicted exposure exceeding the threshold level. This verification is highly based on the definition of the specific protection goal and effect class 3A which provides the effect characterization the ERO-RAC is based on and takes the recovery potential into account.

When extrapolating from a higher tier study to the field by comparing mesocosm/microcosm results to predicted exposure (exceeding the threshold level), the effect results have to be assessed in context of the new spatial and temporal conditions. Thus the ecological and toxicological (in)dependence of exposure pulses is relevant for upgrading the ERO-RAC. The mesocosm/microcosm recovery time responsible for the effect class 3A assignment was used in the present work to assess the ecological independence. The ERO-RAC curve was compared to the total period of possible effects exceeding the threshold level to show that their exposure is considered in the mesocosm/microcosm exposure regime. This approach does not consider toxicological (in)dependence and only requires mesocosm/microcosm study results. This makes it a convenient process. As this issue is not sufficiently discussed in the present work, this approach is presented as conception to encourage discussion in context of the new AGD risk assessment requirements [1].

The idea of taking into account the time course of exposure for risk assesment seems scientifically sound. When applying this in practice, the risk assessment relies (partly) on the exact time course of the predicted exposure profiles. It might be questionable if this is regulatory reasonable and adequate for the environment. The exposure profiles are predictions with many assumptions like an ideal water body, and rely on weather data from 1986. The different scenarios were idealized to cover most of the European agricultural area, and thus are less realistic. Does an artificial mesocosm study get more relevant for the natural environment when comparing the dissipation with a predicted exposure profile? The selection of appropriate assessment factors might have a similar effect of the risk assessment with much less work load. The massive amount of data to be processed for the AGD [1] requirements seems not practical in the regulatory process for pesticides. There are many open questions concerning the application of the AGD [1] requirements addressed in this work, which should be answered by the regulatory authority to maintain a uniform approach on this issue.

For deriving more relevance for the environment in pesticide regulation, the analysis of monitoring data from the field would be much more adequate.

References:

[1] EFSA (2013) EFSA Journal, 2013;11(7):3290, 268 pp. doi: 10.2903/j.efsa.2013. 3290.

[2] Brock, T.C.M., Alix, A., Brown, C.D., Capri, E., Gottesbüren, B.F.F., Heimbach, F., Lythgo, C.M., Schulz, R., Streloke, M. (2010) Linking Aquatic Exposure and Effects, Risk Assessment of Pesticides. SETAC Press, ISBN: 978-1-4398-1347-8