The first large-scale risk assessment of organic chemicals in European rivers and lakes has revealed an extensive problem with pesticides. Nearly half of these water bodies had levels that could harm fish, invertebrates, and algae. "We were surprised that it was so widespread," says environmental engineer Egina Malaj of the Helmholtz Centre for Environmental Research in Leipzig, Germany. The concern is greatest for insects and algae, but the researchers say that in areas where the levels are highest, people should not drink untreated river water.
"It’s really an impressive assessment," says Deborah Swackhamer, an environmental chemist at the University of Minnesota, Twin Cities, who was not involved in the work. Many studies have looked at single watersheds, but the new research is by far the most comprehensive. "Whole river basins are potentially at risk," she says.
Malaj is a Ph.D. student in a research group that focuses on the environmental effects of organic chemicals. These molecules contain carbon atoms, and they include pollutants such as pesticides, herbicides, and other synthesized compounds. Curious about the risk posed to aquatic life, the researchers turned to a database on water quality run by the European Environment Agency.
After downloading monitoring data for 223 chemicals at 4001 testing sites across the continent, Malaj and colleagues at several other institutions evaluated the likelihood that the concentrations would be toxic. The thresholds for death and chronic illness are well known for three kinds of laboratory organisms that are commonly used in ecotoxicology: the fathead minnow; a water flea; and a solitary, microscopic alga that is part of the base of the aquatic food web.
Levels of organic chemicals were high enough to likely cause chronic problems, such as fewer offspring, at 42% of the sites. And at 14% of sites, the levels were high enough to kill a significant number of individuals of one or more of the three test species, the team reports online today in the Proceedings of the National Academy of Sciences. Pesticides were by far the most common culprit. That’s what the team expected, Malaj says, because environmental monitoring tends to test for these chemicals.
Although many people assume that pesticides tend to be local to agricultural areas, they turn up much more widely, Malaj says. Pesticides and herbicides are sprayed onto fields, and they can waft or wash into adjacent streams, where they persist and float downstream. "It’s surprising that despite extensive regulations, we still find the pesticides," she says. Rules specify how close to a stream farmers can spray pesticides and what the concentrations should be. "Our study shows that pesticides are a key pollutant," Malaj says. Also common were brominated flame retardants, which are used in many consumer products. Often, these are spread by dust into waterways. Another ubiquitous pollutant is polycyclic aromatic hydrocarbons, which typically come from vehicle exhaust or petroleum spills from boats.
The risk from organic chemicals appears to be higher in streams and lakes in northern Europe than in southern Europe. Malaj doesn't think this difference is necessarily because of varying amounts of chemical use. Rather, countries in northern Europe tend to test their streams and lakes for more kinds of chemicals, and their measurements are more sensitive and accurate. That means the chemical risk in southern Europe could be underestimated.
"The real situation of European waters is probably even worse," said the study’s senior author, ecotoxicologist Ralf Schäfer of the University of Koblenz-Landau, in a statement.
The best approach for reducing the risk to aquatic life would be to design pesticides and other products that are safer, the authors say. In the meantime, farmers could help by spraying fewer pesticides and herbicides, or by planting more vegetation around streams to reduce the polluted runoff from fields. And, Malaj adds, regulators should assess the cumulative risk of the many chemicals in the environment. Not only would this better protect fish, insects, and algae, Schäfer says, but it would also likely help safeguard water quality. Because the health risk of many chemicals has not been studied, a more protective approach could help prevent people from getting sick.