Persistently high pesticide levels found in small streams.
A study commissioned by the Federal Office for the Environment and published today shows that the legal requirements specified for water quality are not met in any of the five Swiss streams investigated.
Wide variety of agents and high concentrations It had been suspected that small watercourses are heavily contaminated with plant protection products (PPPs), and this has now been confirmed.
In 80% of samples, the limit (0.1 µg/L) specified in the Waters Protection Ordinance was exceeded by at least one substance – for over 60 days in all five streams investigated, and for almost the entire six-month study period in the Weierbach (Basel-Landschaft) and Eschelisbach (Thurgau).
Concentrations as high as 40 µg/L were detected for individual substances.
Chronic and acute toxicity of mixtures Because the limit of 0.1 µg/L per individual substance specified in the Waters Protection Ordinance does not adequately reflect the actual risks for organisms – and 20 to 40 substances, on average, were detected in each sample – the analytical data were also compared with ecotoxicological water quality criteria.
The results leave little room for interpretation: in all cases, chronic water quality criteria were exceeded (sometimes many times over) for a period ranging from two weeks (Ticino) to as much as five-and-a-half months (Basel-Landschaft, Thurgau).
In four of the watercourses, concentrations exceeded the thresholds for acute toxicity to sensitive organisms, for periods of up to two months (Valais).
The lowest level of contamination was found at the monitoring site in the canton of Ticino, where the catchment area shows a lower intensity of agricultural use.
Action Plan under development to reduce risks of pesticides For Stephan Müller, Head of the Water Division at the FOEN, these findings confirm that agricultural PPPs – alongside micropollutants released from wastewater treatment plants – are currently the most important source of contaminants in Swiss surface waters.