Status of lakes and streams

Through the national environmental monitoring program in Sweden, pesticide status in the environment has been continuously monitored since 2002. Pesticides are analysed in streams in four small catchments and in two slightly larger rivers. The results of these analyses show that small amounts of pesticides are present in all streams and rivers, and that in approximately one in three samples, there is some compound that exceeds the guideline value, which indicates that some organism that live in water can be harmed. Between 5 and 20 compounds are found at some point per year in concentrations that may pose risks to plants or animals in the watercourses.

With the help of a calculated toxicity index, it is possible to compare water quality between different sampling areas and within the same area at different times. A higher index value means a greater risk of effects on aquatic organisms.

The combined index values for each year vary quite a bit, but overall a weak, generally downward trend is seen over the period 2009–2023. Viewed per catchment, however, only Halland has a significant downward trend, mainly due to the unusually high index of the first two years. These index peaks also affect the statistics of the average index, so the trend should be interpreted with some caution.

Västra Götaland's catchment generally has a lower toxicity index over the years than the other catchments, followed by Östergötland, while Skåne's and Halland's catchments have relatively similar levels. The background to this is the complex relationship between soil type, climate and the use of plant protection products. The use is at least partly linked to the choice of crops, where, for example, cereals, which are the main crop in Västra Götaland's catchment area, require comparatively fewer plant protection treatments than, for example, potatoes and sugar beets, which are grown in the other catchments. The toxicity index is an indicator within one of Sweden's environmental goals, A Non-Toxic Environment.

The Vemmenhög stream in Skåne has the longest time series of measurements of pesticides in surface water in Sweden. During the 1990s, the levels fell dramatically, even though the amount of pesticides used remained at about the same level. The reduction in measured concentrations is a result of several information campaigns on the good management of plant protection products to the area's farmers that were carried out in the mid-1990s, as well as various initiatives with economic stimulus and new regulations at the national level that were introduced a few years later.

Read more about the Vemmenhög project here.

The use of persistent pesticide compounds has decreased, but the acute toxic compounds have been retained and refined. The aim is for these to have a rapid effect and then be broken down before they reach streams and aquatic organisms. This means that the compounds should not be able to have any effect over a longer period, but since they are very toxic in the initial stage, it is critical that they do not reach streams too quickly. There is evidence that heavy rain after spraying can wash out pesticides rapidly to surface waters, and that the concentrations can then become very high in the watercourse.

The efforts to decrease the risk of bioaccumulation have involved avoiding compounds that are fat-soluble and instead prioritizing compounds that are very soluble in water. A disadvantage with this is that the new pesticides do not attach as easily to soil particles and are therefore transported relatively quickly through the soil down to the groundwater and out to surface waters, bringing increased risks of acute effects on organisms living in lakes and streams. Compounds that are acutely toxic even at low concentrations are often used to control insect attacks. In environmental monitoring, concentrations of these insecticides are occasionally recorded that exceed the guideline values several hundred-fold. 

Acute effects also arise due to accidents and carelessness, e.g. due to sprayers and other spraying equipment being washed in inappropriate ways or to spraying being carried out too close to streams. It is difficult to assess the frequency of toxic effects arising as a result of inappropriate spraying or accidents. The episodes are very short but can still have tangible consequences if the compound washed out is toxic to aquatic organisms. With instantaneous sampling, which is the most common method, a water sample is taken at a specific time that gives a snapshot of the levels in the water. There is very little likelihood of successfully taking a sample precisely when the high concentration occurs. With time-integrated sampling, which is used in the national environmental monitoring programme and elsewhere, all peaks are included, but the samples are analysed as collective samples over an entire week, which makes it very difficult to say how high the peak concentrations were.

It is important to be able to determine whether lakes and watercourses are affected by pesticides in order to be able to implement the correct measures, and to ensure that the water has a good ecological status (in accordance with the EU Water Directive). The sharply varying concentrations of pesticides pose a difficulty as regards assessing the risks of damage in water on the basis of a few samples. Since the concentration peaks may be short-lasting, it is difficult to ascertain anything about the highest levels. Another difficulty is that as a rule, a number of compounds occur simultaneously in water, and this makes it difficult to assess the combined effect on aquatic flora and fauna. Analysis of pesticides is also costly. Investigating aquatic flora and fauna may therefore be a more effective approach, since the communities of species are continuously exposed and therefore reflect the combined effect. The status of aquatic organisms is also central to Swedish water management and the EU's Water Directive.

CKB conducts annual sampling of benthic fauna and diatoms in four watercourses in southern Sweden. Read more about biological effects.

Environmental monitoring of pesticides at national level started in 2002, funded by the Swedish Environmental Protection Agency. The aim of environmental monitoring is to determine the extent to which different pesticides leak into surrounding waters and to monitor any long-term changes over time.

Monitoring is being carried out in four small catchment areas (800-1700 hectares), representing the four large agricultural regions in Sweden; Skåne, Halland, Östergötland and Västra Götaland. In all of these catchments about 90 percent of the land is agricultural. Time-integrated composite samples are taken every week in the streams from May to November and the samples are analyzed for approximately 160 different substances. The farmers in these areas are interviewed about their cropping practices and pesticide use, and groundwater samples as well as sediment samples are also taken. The environmental monitoring also covers two rivers in Skåne for surface water sample-taking and two locations (one in Skåne and one in Uppland) for rainwater collection, with the one in Skåne also used for air-sampling.

• On the Department of Aquatic Sciences and Assessment's web pages, you can read more about national environmental monitoring of pesticides in the environment, see results and download data.