Do the statistics used in your ecotoxicology studies meet current EU requirements?

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Do the statistics used in your ecotoxicology studies meet current EU requirements?

Updated EU data requirements for plant protection products (PPPs) mean that older ecotoxicology studies may not be in line with current statistical approaches. Valuable data already obtained from these studies can, however, be re-analysed using recommended statistical techniques to make them acceptable for current regulatory submissions.

Although existing studies may not have been designed with the updated statistical techniques in mind, re-analysis may still result in robust and useable endpoints to fulfil the EU data requirements. Re-analysis of existing data helps to minimise or prevent re-testing and thereby reduces costs. At CEA, we have the expertise to conduct the most appropriate statistical tests for re-analysing data and to re-interpret endpoints in consideration of the latest EU opinions and guidance.  

Effective Concentration (ECx) values for chronic studies

The No Observed Effect Concentration (NOEC) and/or the lowest observed effect concentration (LOEC) have long been the main endpoints for certain ecotoxicology study designs. Recently, however, scientific opinion has favoured additional statistical techniques to be used for chronic laboratory studies, including regression analysis to derive Effective Concentration (ECx) values. Regression analysis fits a concentration response curve to the data and the ECx values are estimated using interpolation methods. This means that, unlike the NOEC value, the ECx values are not as constrained to the number and spacing of test concentrations. The Panel on Plant Protection Products and their Residues (PPR) recommended the use of the ECx approach for all chronic studies, provided that the reliability and usability of the data is taken into account (EFSA 2009; EFSA 2015).  In particular, the EC10 and EC20 values along with corresponding 95% confidence intervals should be reported, together with the NOEC from chronic studies  (Commission Regulation (EU) No. 283/2013 in accordance with Regulation (EC) No. 1107/2009). At CEA, we use the existing data from these studies to calculate the additional ECx values and assess the reliability of all values based on their associated 95% confidence intervals.

Minimum Detectable Difference (MDD) values for historical mesocosm studies

Aquatic mesocosms aim to mimic edge-of-field waterbodies and are used to assess realistic risk of PPPs to aquatic communities as part of the PPP authorisation process. The increased realism of these studies reduces uncertainty when extrapolating effects to the natural environment; however, the statistical power, and thus the reliability of an observed effect, can be impaired by high intrinsic variability in these dynamic and complex systems. To address this issue (in the EU), the latest EFSA aquatic guidance (2013) has introduced the requirement to report minimal detectable differences (MDDs) alongside the NOEC and No Observed Ecologically Adverse Effect Concentration (NOEAEC) as a reverse power analysis to aid interpretation of these studies.

As with laboratory studies, the data from existing mesocosm studies can be re-analysed to generate MDDs to obtain a reliability measure for each endpoint. Furthermore, at CEA, we use these newly generated MDDs to assign the corresponding Effect Classes according to the EFSA guidance and recommendations by Brock et al (2015). Applying our in-depth knowledge and experience of successfully conducting mesocosm studies, we can then assess the applicability and reliability of the original overall NOEC and NOEAEC endpoints to meet the updated regulatory requirements.

If you think that some of your studies may require statistical re-analysis and you’d like to know more, please contact


Commission Regulation (EU) No 283/2013 of 1 March 2013 setting out the data requirements for active substances, in accordance with Regulation (EC) No 1107/2009 of the European Parliament and of the Council concerning the placing of plant protection products on the market:

Brock, T. C. M., Hammers-Wirtz, M., Hommen, U., Preuss, T. G., Ratte, H-T., Roessink, I., Strauss, T. and Van den Brink, P. J., (2015). The minimum detectable difference (MDD) and the interpretation of treatment-related effects in experimental ecosystems. Environ Sci Pollut Res. (22), 1160.

EFSA (European Food Safety Authority), 2009. Scientific Opinion of the Panel on Plant Protection Products and their Residues on a request from EFSA updating the opinion related to Annex II and III: Ecotoxicological studies. The EFSA Journal 2009, 1165, 25 pp. doi:10.2903/j.efsa.2009.1165.

EFSA  PPR  Panel  (EFSA  Panel  on  Plant  Protection  Products  and  their  Residues),  2013.  Guidance  on tiered  risk  assessment  for  plant  protection  products  for  aquatic  organisms  in  edge-of -field  surface  waters.  EFSA Journal 2013;11(7):3290, 268 pp. doi:10.2903/j.efsa.2013.3290. 

EFSA (European Food Safety Authority), 2015. Technical report on the outcome of the pesticides peer review meeting on general recurring issues in ecotoxicology. EFSA Supporting Publication 2015; 12(12):EN‐924. 62 pp. doi:10.2903/sp.efsa.2015.EN‐924.

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