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It is not yet possible to determine a trend in Figure 1. Losses from the application of pesticides may vary considerably between years depending upon e.g. crop type and the weather (EC, 2008), and the frequency of monitoring of pesticides in surface waters can be limited to one year out of three. For these reasons, changes between years may not be significant. It is anticipated that a trend will become apparent in the next few years.
Fig. 1 shows the percentage of monitoring sites with threshold exceedances in surface waters and groundwater. In surface waters, the peak in 2017 is driven by an exceedance rate in Spain ten times more than compared to other years. In groundwater, the peak in 2014 is driven by an exceedance rate in Italy ten times more than other years, and in Slovakia three times more.
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The appearance of a meaningful trend will very much depend the stability of the monitoring programme. In the period considered in this study, there is a rather clear temporal trend (increase) in the number of monitored substances, monitoring sites, and overall records. While this trend is welcome to get a better picture of the overall situation, it hampers a meaningful year-by-year comparison, especially when using the one-out-all-out principle.
Further explaination needed, as this will raise questions - text needs to explain in simple English how the exceedance rate in Spain jumped 10 times in 2017. in the absence of a clear explaination, this will reduce confidence in the indicator.
In case of insecure data (e.g., due to analytical or sampling method issues) or suspected reporting issues (i.e., no reasonable explanation could be given for the excessive exceedance rates in these years), we suggest to exclude these anormal years as outliers from the exceedance rate calculations.
Additional information regarding the exceedance rate in Italy reported in the years excluding 2014 is needed to explain the stated highest percentage of pesticide exceeding the common threshold value of 0.1 ug/l. Furthermore, it is significant to specify if the numbers and/or locations of groundwater monitoring sites with exceedance of the quality standard or the types of pesticides analyzed in 2014 were considerably different than the rest of monitoring period.
We suspect wrong Spanish data are being used to calculate the indicator. The right file was uploaded from Spain (and apparently accepted) in the web WISE SoE Data Deliveries (WISE-SoE_WaterQuality_2017_SW_v4.xls) in July, 2019. There was a Final Feedback which informed us that the delivery had been accepted. This is the source we analysed last July when we answered the mail about the high values reported from Spain in relation to the headline indicator. Our data are not consistent with the information contained in the file “PiRLG_4_Reported data and exceedance rates by country and year”, for the years 2016 and 2017. According to the information of this file, nº of reported monitoring sites for Spain is 2 for 2016 and 3 for 2017, which is clearly a mistake, especially if you compare the data with the whole historic series.