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Jan‐Dieter Ludwigs, Markus Ebeling, Timothy B. Fredricks, Roger C. Murfitt, Steven Kragten, Response to David R. Crocker and Steven D. Langton “When is it Legitimate to Downplay Individual Differences?”, Environmental Toxicology and Chemistry, Volume 38, Issue 8, 1 August 2019, Pages 1604–1605, https://doi.org/10.1002/etc.4455
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Authors’ Response:
In their letter, Crocker and Langton (2019) critically discuss the approach of 21‐d Monte Carlo PT (portion of diet from a pesticide‐treated area) simulations proposed in Ludwigs et al. (2017). The aim of this method is to assess realistic 21‐d PT values by including daily variability in habitat use for individual animals. Crocker and Langton (2019) believe that the method described by Ludwigs et al. (2017) is 1) unsuited to most radiotracking datasets; 2) statistically not valid; and 3) could lead to misleading and unprotective risk assessment. In our letter, we want to respond to the comments and concern raised by Crocker and Langton (2019). We still believe that use of the 90th percentile value for many PT datasets, irrespective of data quantity and quality, does not provide a good representation of exposure over the regulatory default time window of 21 d. Therefore, intra‐individual variability of daily PT values, if available, should be taken into account. Our 2017 publication used one dataset as an example of how this could potentially be achieved. Of course, some datasets might be unsuitable for such an approach, and depending on the available data and potentially new data, the statistical approach and pooling of data might need to be adapted as well. However, if these points are addressed appropriately in the future, the method would in our opinion not lead to misleading and unprotective risk assessments. A follow‐up publication using different datasets for other species is in preparation, to further demonstrate the benefits and constraints of our proposal.
