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Methodology uncertainty

For surface waters, effects thresholds could be identified for only 48% of the pesticides reported; 52% of all pesticides reported could not be considered in the assessment.

The calculation method used to determine exceedance rates with country weightings reduces any imbalance in the data reported with respect to the numbers of monitoring sites and pesticides reported. This reduces the impact of high levels of reporting by a few countries on the overall percentage of monitoring sites with exceedances.

This country weighting means that unusually high or low exceedance rates within a country may affect the overall indicator. This can also occur if data for only a few monitoring sites are reported but a relatively high or low proportion of these are exceedances. A minimum number of monitoring sites reported per country and year would be needed to reduce this imbalance.

There is a lack of a consistent time series of comparable data. Instead, the data for many monitoring sites were not reported for more than a few years, which disperses the spatial and temporal coverage of the data set.