An initial evaluation of data collected in Switzerland on pesticide load revealed that only 20% of the data came from small watercourses, even though these make up 75% of the total distance covered by Switzerland’s network of watercourses (Munz et al. 2012). Moreover, the monitoring programmes were often temporally limited, or restricted to random sampling. The aim of the second NAWA SPEZ study was therefore to close these gaps.
Five small watercourses in areas with heavy agricultural use were screened for 213 active PPP substances. The work was carried out with a variable temporal resolution, whereby half-day mixed samples were taken during rainfall events, and longer mixed samples (from 24 hours to a maximum of 24 days) were taken during dry periods. The analytics employed enabled 70% of the PPPs permitted in 2015 to be measured. Also measured were numerous PPPs which were no longer permitted, but which were still found to be present in the environment because of their slow degradation times.
Altogether 128 PPPs were found to be present. Chronic quality criteria were exceeded in all of the catchment areas, and in four of the catchment areas acute quality criteria were also exceeded. The comparison with NAWA SPEZ 2012 showed that the peaks in contaminants in small watercourses are short-lived, but concentrations are, on the other hand, higher. A significant proportion of the instances of acute quality criteria being exceeded are attributable to this effect.
The catchment areas surveyed were all subject to a comparable level of agricultural use. Estimates indicated that although pollution levels may be lower in areas that are less heavily used for agricultural purposes, effects on sensitive aquatic organisms could not be ruled out in these areas. In terms of recommendations for routine monitoring going forward, it was shown that it is also possible to gather a substantial amount of pollution data with a reduced amount of effort: so, for the 41 PPP substances that were proposed in the Assessment Strategy for diffuse inputs, 72% of the chronic quality criteria, and 87% of the acute quality criteria were found to have been exceeded as a result of PPP inputs. It is important that measurements are taken over a sufficiently long period, as in some of the catchment areas the concentration levels were found to be increasing even at the end of the monitoring period.