Correspondence/Rebuttal
Response to Comment on “Regulatory FOCUS Surface Water Models Fail to Predict Insecticide Concentrations in the Field”
W
Furthermore, Reichenberger claims that the MFCs included in our analysis are not independent and should therefore not be plotted against a single estimated point. In fact, the insecticide concentrations were measured either during different seasons or originated from clearly distinguishable entry events and are therefore independent. However, even when adopting the method suggested by Reichenberger there is also no statistically significant relationship (p = 0.16 for null hypothesis of slope ≠0) between step 3 PECsw and the MFCsw based on the maximum measured concentration for a substance in each study (Figure 1). In addition, the amount of underprediction increased from 23 to 29% when only the maximum measured concentrations per substance and study were used. Concerning the second part of the hypothesis questioned by Reichenberger, FOCUS2 correctly claims that the realism of PECs increases when proceeding from FOCUS step 1 to step 4. Consequently, the relationship between MFCs and PECs should definitely improve.
e appreciate the comment by Reichenberger on our study evaluating FOCUS predictions for insecticides in surface water.1 Overall, we do not think that the arguments given by Reichenberger question the suitability of the first two hypotheses for evaluating the protectiveness of the FOCUS surface water modeling approach1 for the EU. In the following, we respond to the criticism. Hypothesis 1 was based on the claim made by the FOCUS surface water working group that the highest predicted environmental concentration (PEC) in surface water estimated from the 10 scenarios would represent at least the 90th percentile (worst-case) for surface water exposure in Europe2 and not just in the 10 scenarios. The overall aim of the EU risk assessment is to prevent unacceptable effects on the aquatic environment. Therefore, real measured field concentrations in the EU should never or only very rarely (i.e., at most 10%) exceed modeled PECs. Thus, the explanation of Reichenberger that the 90% would only apply if all agro-environmental scenarios would be represented by the studies is not plausible. Beyond that, we performed step 3 realistic calculations, which are not part of the regulatory risk assessment. As claimed by the FOCUS surface water group and cited in our study, the FOCUS scenarios “do not mimic specific fields [...] crops or situations have been adjusted with the intention of making the scenario more appropriate to represent a realistic worst-case for a wider area.”2 To overcome this generalizing nature and particularly to make the modeling conditions as similar as possible to the field conditions, we used all information available for (1) the application scenario, (2) agro-environmental conditions, and (3) water body and landscape factors in the step 3 realistic calculations. The amount of measured field concentration (MFC) underpredicition was higher for step 3 realistic as for the standard calculations (43 instead of 31% of step 4 surface water calculations), which indicates that a higher degree of realism and representativeness for single agroenvironmental FOCUS scenarios even reduces the protectiveness of model results. The claim that the field studies performed outside Europe are not suitable is also unsubstantiated as already outlined in the response to another comment.3 Hypothesis 2: In our study we aimed at an absolute rather than a relative assessment of exceedances. We therefore only used peak concentrations and compared them to maximum predicted concentrations (cf. EU pesticide risk assessment procedure) instead of exposure frequencies to test whether the model outcomes are protective or not. Even if the correlation between predicted and measured data exhibits noise due to different study boundaries and claimed worst-case conditions, there should be at least a positive trend. Moreover, when correlating data from individual studies to reduce the noise, still for only 1 of 10 suitable monitoring data sets a statistically significant positive relationship between measured and predicted concentrations was found (Anderson et al 2006,4 chlorpyrifos, R = 0.43, p = 0.025, n = 10). © 2013 American Chemical Society
■
RESPONSE TO THE OTHER COMMENTS - The aim of our study was to test whether the FOCUS model is protective in predicting insecticide concentrations and we stated that a detailed sensitivity analysis is needed to clarify the general influence of physicochemical substance properties on model outcomes. The study of Luo and Zhang5 was cited by us as one possible explanation for the significantly lower ratios between PECs and MFCs for hydrophobic pyrethroids. Even if the USEPA statement is incorrect, this does not affect our conclusion of FOCUS predictions being less protective for pyrethroids. - For FOCUS step 4 calculations we used mitigation options given in the EU or US registration documents or from the producers’ product labeling. When step 4 was used as basis for registration of a specific insecticide compound, mitigation measures must de jure be in place. Even if this assumption was not true, our results for step 3 realistic calculations that ignore mitigation measures exhibited a higher amount of MFC underprediction than step 4 calculations. - We only simulated granular application in the step 3 realistic calculations, if runoff was reported to be the only input pathway. Although additional pathways can not be completely excluded, 60% of all studies used an eventrelated sampling that would only capture runoff-related pesticide input. - The minimum “no spray buffer zone” mandated in practice is 5 m and is often more than 10 m for insecticides.6 Reichenberger suggests that FOCUS step 3 may underestimate field conditions because it assumes 1−3 m buffer strip. However, buffer strips are often
Published: February 22, 2013 3017
dx.doi.org/10.1021/es4007965 | Environ. Sci. Technol. 2013, 47, 3017−3018
Environmental Science & Technology
Correspondence/Rebuttal
Figure 1. Relationship between FOCUS step 3 simulated and maximum measured insecticide surface water concentrations (only highest concentration per substance and study used). The simulated concentrations are displayed on the y-axis so that the MFC underestimations are plotted below the 45° line.
considerably larger in the field than the FOCUS assumptions,7,8 so that this can not explain the failure of the FOCUS predictions observed in our paper.1 - The amount of underprediction in FOCUS step 3 is exactly the same when considering the total (dissolved + suspended) predicted concentrations instead of the dissolved pyrethroid concentrations only. Hence, although we appreciate the overall conclusion of this comment, the lower PECsw to MFCsw ratios for pyrethroids can not be explained by chemical analysis of pyrethroid field samples as suggested by Reichenberger.
surface water scenarios, EC Document Reference SANCO/4802/ 2001-rev.2, 2001. (3) Knäbel, A.; Stehle, S.; Schäfer, R. B.; Schulz, R. Response to comment on “Regulatory FOCUS surface water models fail to predict insecticide concentrations in the field. Environ. Sci. Technol. 2013, 47, 1179−1180. (4) Anderson, B. S.; Phillips, B. M.; Hunt, J. W.; Worcester, K.; Adams, M.; Kapellas, N.; Tjeerdema, R. S. Evidence of pesticide impacts in the Santa Maria River watershed, California, USA. Environ. Toxicol. Chem. 2006, 2, 1160−1170. (5) Luo, Y. Z.; Zhang, M. H. Environmental modeling and exposure assessment of sediment-associated pyrethroids in an agricultural watershed. Plos ONE 2011, 6, No. e15794. (6) DG SANCO. E.U. Pesticide Database, 2008; http://ec.europa. eu/sanco_pesticides/public/index.cfm. (7) Ohliger, R.; Schulz, R. Water body and riparian buffer strip characteristics in a vineyard area to support aquatic pesticide exposure assessment. Sci. Total Environ. 2010, 408, 5405−5413. (8) Bereswill, R.; Streloke, M.; Schulz, R. Current-use pesticides in stream water and suspended particles following runoff: Exposure, effects, and mitigation requirements. Environ. Toxicol. Chem. 2013, DOI: 10.1002/etc.2170.
Anja Knab̈ el* Sebastian Stehle Ralf B. Schaf̈ er Ralf Schulz
■
Institute for Environmental Sciences, University Koblenz-Landau, Landau, Germany
AUTHOR INFORMATION
Corresponding Author
*Phone: +49-6341-28031313; e-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
REFERENCES
(1) Knäbel, A.; Stehle, S.; Schäfer, R. B.; Schulz, R. Regulatory FOCUS surface water models fail to predict insecticide concentrations in the field. Environ. Sci. Technol. 2012, 46, 8397−8404. (2) FOCUS. FOCUS Surface Water Scenarios in the EU Evaluation Process Under 91/414/EEC; Report of the FOCUS working group on 3018
dx.doi.org/10.1021/es4007965 | Environ. Sci. Technol. 2013, 47, 3017−3018
