18 million measurements analyzed: Pollutants threaten rivers and streams even in protected areas

Organic pollutants such as pesticides and industrial chemicals commonly pose risks to aquatic ecosystems, even in protected rivers and streams. This is the conclusion of a new study by RPTU University Kaiserslautern-Landau, based on the analysis of more than 180 million water measurements from the French long-term monitoring program “Naïades” The study shows that pollutants are detectable in nearly all of the water bodies examined and that groups of substances often overlooked in earlier studies contribute significantly to environmental risks.

The study, published in the journal Water Research, thus provides one of the most comprehensive pictures to date of chemical pollution in flowing waters. While earlier studies were often limited to individual groups of substances such as pesticides, the current analysis considers a total of 1,731 chemicals, thereby enabling a significantly more comprehensive assessment of ecological risks.

Unique Data Set Enables Comprehensive Risk Analysis

Hundreds of thousands of chemicals are in use worldwide and can enter water bodies. However, detecting them is often time-consuming and costly, which is why the actual extent of contamination has been only partially understood until now. Led by environmental scientists Danisa Lione and Jakob Wolfram from Landau, the research team analyzed more than two decades of French monitoring data. The researchers compared the measured concentrations of organic pollutants with their known toxicity to aquatic organisms and examined the resulting risks in protected and unprotected water bodies.

“The scope of the French data provides us with unprecedented insight into the complexity of chemical pollution and its potential impacts on these ecologically important habitats,” says Jakob Wolfram.

Pollutants Detected Almost Everywhere

The analysis shows that organic pollutants are present in nearly all of the water bodies studied. In protected areas, an average of nine different chemicals were detected per water sample; outside these areas, the average was 13. Although pollutants occurred less frequently overall in protected areas, concentrations capable of causing ecological risks were still regularly measured there as well.

“Protected areas do significantly reduce the number and frequency of pollutants. Nevertheless, adverse effects continue to occur frequently. Rivers and streams are open systems, so chemicals can also be carried by the current into ecologically valuable refuges,” explains Danisa Lione.

PFAS Are Gaining Significance

Particularly striking is the increasing occurrence of per- and polyfluoroalkyl substances (PFAS), the so-called “forever chemicals”. In recent years, they have risen to become the second most frequently detected group of pollutants. PFAS were found at around 60 percent of the sites studied. In urban areas, an average of six to eleven different PFAS compounds were detected annually.

“We still know relatively little about the effects of PFAS on aquatic ecosystems, even though more than 10,000 different PFAS molecules are in use. Their long-term and widespread presence, even in protected areas, is therefore particularly concerning,” emphasizes Danisa Lione.

Aquatic Plants Particularly Affected

Aquatic plants, which form the basis of aquatic food webs, were the most severely affected, followed by aquatic invertebrates and fish. The study also shows that agricultural use has a significant impact on environmental risks. While regulatory restrictions on particularly problematic pesticides led to improvements for aquatic plants, no comparable positive effects were observed for aquatic animals.

“Our findings from this large-scale study highlight the far-reaching impacts of organic pollutants, especially pesticides, on aquatic ecosystems. At the same time, they show that risks can be reduced if particularly problematic substances are consistently replaced or phased out,” said Jakob Wolfram.

Comprehensive monitoring programs reveal previously overlooked risks

A key finding of the study is that the extent of exposure changes significantly when other organic pollutants are taken into account in addition to pesticides. By including these substances, the estimated environmental risk increased by 26 percent for fish and by 48 percent for aquatic invertebrates compared to an analysis that considered only pesticides. “Many earlier studies were likely unable to fully capture the actual environmental risks because chemical analysis covered only a limited subset of the substances present. To reveal previously unrecognized ecological pressures, environmental monitoring programs must be significantly expanded in the future, as the French program exemplifies” Danisa Lione emphasizes.

The results show that protected areas remain important refuges for biodiversity but do not offer complete protection against chemical contamination. At the same time, the data make it clear that comprehensive environmental monitoring and the regulation of problematic substances are crucial prerequisites for the long-term protection of aquatic ecosystems.