Press release 31 May 2012

Study: Pesticide authorisation procedures fail to adequately protect biodiversity in rivers

Before a pesticide is allowed to go on sale, it has to pass a standard EU authorisation process. However, the current procedure does not sufficiently protect the environment, according to a joint study by the University of Koblenz-Landau, the Helmholtz Centre for Environmental Research (UFZ), the University of Aarhus (Denmark), and the University of Technology, Sydney just published in the international journal Environmental Science and Technology. To carry out this meta-analysis, a number of globally available field studies on the effect of pesticides were compared and evaluated.

Application of pesticides

Application of pesticides in agriculture. According to a joint study of researchers from Australia and Germany the standard EU authorisation process for pesiticides is not sufficient in order to protect rivers sustainable from the impact of pesticides.
Photo: Ralf Schäfer/Uni Landau

Pesticides used in agriculture can be washed into surface water during strong rain events and impair the organisms therein. The main aim of this study was hence to assess the effect thresholds of pesticides for organisms in rivers. The meta-analysis only examined field studies addressing rivers in agricultural areas and which were not subject to the discharge of sewage or industrial effluent. Eight studies from six different European countries as well as Siberia and Australia carried out between 1998 and 2010 were analysed. The studies covered periods ranging from 2½ to 36 months and considered a total of 111 different rivers.

A dose-response curve was derived from the individual studies, reflecting a correlation between the toxicity of a pesticide and the quantity of sensitive organisms in the river. This enabled comparison with the concentrations deemed harmless for the purpose of authorisation. The researchers concluded that the existing evaluation process is insufficient to sustainably protect river ecosystems from the effects of pesticides. Under concentrations which are rated as safe in standard methods, the populations of sensitive organisms were reduced by 27–61% depending on the presence of unpolluted river stretches upstream, which can partly buffer the effects. One especially serious finding is that these effects may also reduce ecosystem functions, impairing vital ecosystem services for human society such as fish stocks and water purity.

Standard authorisation procedures are too narrow

According to the researchers, the reasons for this result are obvious. “Substance authorisation procedures only consider individual pesticides,” explained Ralf B. Schäfer from the Institute of Environmental Sciences at the University of Koblenz-Landau. Yet substances never occur in isolation. Instead, organisms are subject to mixtures of pesticides, multiple stressors and repeated exposure such as flooding. “The standard pesticide authorisation tests also largely ignore the fact that in nature animals are exposed to different sorts of stress,” declared Matthias Liess from UFZ, pointing out another registration snag. After all, stress greatly increases species’ vulnerability to pesticides. The current standard procedures for pesticide authorisation should therefore be reconsidered, say the researchers.

The new study also contradicts some earlier publications in which effect thresholds were determined by means of studies in mesocosms – set-ups with controlled research conditions in the field. The effect thresholds determined in the meta-analysis were found to be a factor of between 10 and 100 lower than those assumed in the authorisation process and calculated in several mesocosm studies. The authors attribute this discrepancy to two factors: a) previous studies only addressed individual substances and stressors, and b) suitable methods of the type since developed at UFZ to gauge threshold effects were not used during risk assessment (Ecotoxicology DOI 10.1007/s10646-011-0689-y).

In the researchers’ view, one reason why the study findings are so alarming is because according to a previous study by the University of Koblenz-Landau, UFZ and Freiberg University of Mining and Technology, pesticides are by no means diluted even in large rivers and lakes, and in fact are among the main pollutants there. Moreover, the new study revealed that the good chemical and ecological status of large European rivers and lakes required under the European Water Framework Directive (WFD) is unlikely to be achieved by 2015 since the levels of pollutants such as pesticides even exceed the safety limits in the authorised procedures (Environmental Science and Technology, DOI: 10.1021/es2013006) and sensitive water organisms are often killed by insecticides (Ecological Applications doi: 10.1890/10-1993.1).

Recommendations for the improved protection of rivers and lakes

Since pesticides are not going to be abandoned in agriculture in the foreseeable future, the researchers have the following recommendations in order to protect biodiversity in rivers: a) widening banks and woodlands near rivers in agricultural areas; b) building water retention basins which can almost completely remove some pesticides from water (as demonstrated by previous studies conducted by the University Koblenz Landau); c) reducing the use of pesticides in order to com-ply with the directive on the sustainable use of pesticides adopted by the Europe-an Parliament and the European Council in 2009.


Ralf B. Schäfer, Peter Carsten von der Ohe, Jes Rasmussen, Ben J. Kefford, Mi-khail A. Beketov, Rals Schulz and Matthias Liess:
„Threshold for the Effects of Pesticides on Invertebrate Communities and Leaf Breakdown in Stream Ecosystems”., DOI: 10.1021/es2039882
Environmental Science & Technology, 46, (9) 5134–5142.

Participating institutions

  • Institut für Umweltwissenschaften der Universität Koblenz-Landau
  • Helmholtz-Zentrums für Umweltforschung
  • Faculty of Science and Technology der University of Aarhus (Dänemark)
  • Centre of Environmental Sustainability der University of Technology Sydney (Australien)

Further information

Universität Koblenz-Landau, Campus Landau
Institut für Umweltwissenschaften
Jun.-Prof. Dr. Ralf B. Schäfer
Phone +49 6341 280 31536

Helmholtz Centre for Environmental Research (UFZ)
Department System Ecotoxicology
PD Dr. Matthias Liess
phone +49 341 235 1578
PD Dr. Matthias Liess

At the Helmholtz Centre for Environmental Research (UFZ) scientists are researching the causes and consequences of far-reaching changes to the environment. They are concerned with water resources, biological diversity, the consequences of climate change and adaptability, environmental and biotechnologies, bioenergy, the behaviour of chemicals in the environment, their effect on health, modelling and social science issues. Their guiding theme: Our research contributes to the sustainable use of natural resources and helps to secure this basis for life over the long term under the effects of global change. The UFZ employs 1,000 people in Leipzig, Halle and Magdeburg. It is financed by the federal government and the federal states of Saxony and Saxony-Anhalt.

The Helmholtz Association contributes towards solving major and pressing social, scientific and economic issues with scientific excellence in six research areas: Energy, Earth and Environment, Health, Key Technologies, Structure of Matter, Aeronautics, Aerospace and Transport. The Helmholtz Association is Germany’s largest scientific organisation with over 33,000 employees in 18 research centres and an annual budget of approximately 3.4 billion euros. Its work stands in the tradition of the naturalist Hermann von Helmholtz (1821-1894).