Streams are too heavily polluted with pesticides

45,000 kilometers, three quarters of the Swiss water network, are considered small streams and brooks. So far, however, there are no measuring stations that monitor water quality there over longer periods of time. The informative value of random samples is limited. On behalf of the Federal Office for the Environment (FOEN), Eawag and the Ecotox Centre Eawag-EPFL, together with five cantons (TG, BL, BE, VS, TI) and the Swiss Water Pollution Control Association (VSA), have therefore taken a closer look at five watercourses. Their catchment areas are typical of heavy agricultural use. Between March and August 2015, around 1800 water samples were collected. Today, the participants have now published the evaluations in two technical articles in the journal Aqua&Gas. (Here and here)

A smorgasbord of active ingredients and high concentrations

The suspicion that the small water bodies are heavily polluted with plant protection products (PPPs) has been substantiated. The number of substances is very high: 128 different active substances from arable, vegetable, fruit and vine cultivation were detected by the researchers in the samples, 61 herbicides, 45 fungicides and 22 insecticides. In 80% of the samples, the requirement of the Water Protection Ordinance (≤0.1 µg/L) was not met by at least one substance - in all five streams studied for more than 60 days, in the Weierbach (BL) and in the Eschelisbach (TG) practically during the entire six-month study period. Concentrations of up to 40 µg/L were detected for individual substances. Short-term peaks are likely to be even higher, because all samples were averaged over at least half a day.

Chronic and acute toxic mixtures

Because the maximum value of 0.1 µg/L per individual substance in the Water Protection Ordinance says too little about the true risk to organisms, the researchers also compared the analytical data with ecotoxicological quality criteria. In addition, bioassays were conducted with algae and stream fleas, and the diversity of invertebrates was examined. On average, not one, but 20 to 40 substances were found in each sample. The results leave little room for interpretation: in all water bodies, quality criteria for chronic ecotoxicity were exceeded, in some cases many times over, for a minimum of two weeks (TI) and a maximum of up to five and a half months (BL, TG). In four water bodies, even concentrations above which the pesticide mix is an acute toxic risk to sensitive organisms were exceeded, for a maximum of two months (VS). Stream fleas exposed in one of the streams showed increased mortality rates and lethargic behavior, concomitant with high pesticide concentrations. Scores at all sites were unsatisfactory and poor. The lowest load was found at the Ticino monitoring site, as the catchment area in question has a comparatively lower intensity of agricultural use. Marion Junghans of the Ecotox Center summarizes: "The constantly changing mix of many substances in problematic concentrations and the long-lasting high risks leave organisms no recovery time in many cases."

Action plan for risk reduction of plant protection products under development

For Stephan Müller, head of the FOEN's Water Division, the results confirm that PPPs from agriculture - along with micropollutants that enter waterbodies via wastewater treatment plants - are currently the most significant material pollutants in Swiss surface waters. This is especially true in small streams; they are of special interest because they are refuges and "nurseries" for aquatic life, especially for fish.

The technical measures recently adopted by Parliament will halve the amount of micropollutants produced by wastewater treatment plants. Now, according to Müller, the contamination with PPPs must also be significantly reduced. An important step in this direction is the PPP action plan, which is being developed under the leadership of the Federal Office for Agriculture and in which water protection is a priority topic. Furthermore, users are required to handle these environmental toxins carefully and to use them as little as possible.

Text: FOEN