Insecticide contamination of global surface waters substantially higher than expected
April 17, 2015
Pesticide application on arable land in Northwest Germany, Photograph: Renja Bereswill (University of Koblenz-Landau)
The results are alarming
A study performed at the Institute for Environmental Science of the University of Koblenz-Landau evaluated for the first time comprehensive global insecticide contamination data for agricultural surface waters using the legally-accepted regulatory threshold levels (RTLs) as defined during the official pesticide authorisation procedures. The results are alarming: more than 40% of the water-phase samples with a detection of an insecticide concentration, exceeded respective RTLs. Concerning the exposure of sediments (i.e., deposits at the bottom of the surface water bodies), more than 80% of the insecticide concentrations exceeded RTLs, which, however, often are less binding from a regulatory perspective. Overall, the results of this study indicate that insecticides pose substantial threats to the biodiversity of global agricultural surface waters and that the current regulatory risk assessment schemes and pesticide authorisation procedures fail to protect the aquatic environment.
The results of this study fundamentally challenge the current regulatory risk assessment procedures for pesticides and indicate threats to the freshwater biodiversity at the global scale. “Potential reasons for these findings are failures of current risk assessment procedures or farmers` non-adherence to pesticide application prescriptions“ says Ralf Schulz, one of the authors of this study. Fundamentally reforming global conventional agricultural systems and the adoption of promising approaches from organic farming are possible ways to meet the twin challenges of providing sufficient food for a growing human population and reversing the adverse impacts of agricultural pesticides on global ecosystems such as surface waters.
The environmental risk assessment for pesticides, which is mandatorily conducted by regulatory agencies prior to their authorisation, is generally perceived as highly elaborated. These risk assessment procedures should ensure that the agricultural pesticide applications do not lead to unacceptable adverse effects on aquatic and terrestrial ecosystems or on the human health. During the authorisation procedure of a given pesticide, a specific concentration level (i.e., the RTL) is defined at which the ecological effects are considered to be acceptable, e.g., at which no unacceptable effects on the ecological integrity of surface waters and aquatic organisms are expected to occur. After a pesticide is authorised and in use, farmers must adhere to specific application prescriptions, e.g. a 20 m no-spray buffer zone next to a surface water body. These prescriptions should ensure that the RTL is not exceeded in the field. In essence, pesticide registration in the US or the EU is granted only if all risk assessment requirements are met and assuming that farmers adhere to the respective application prescriptions. However, it is important to note that the RTLs defined during the prospective pesticide authorisation procedures do not denote official water quality criteria as the regulatory risk assessment is based on the assumption that these RTL are never exceeded in the field due to the comprehensive risk assessment schemes and farmers application prescriptions.
The meta-analysis performed by the researchers from the University Koblenz-Landau considered 28 insecticide compounds, of which the majority is currently authorised in the EU or the US, respectively, and it comprised in total 11,300 insecticide concentrations detected in more than 2,500 surface water sites located in 73 countries and that were reported between 1962 and 2012 in 838 peer-reviewed, scientific studies. Overall, 8,166 insecticide concentrations were detected in the water-phase and 3,134 in sediments of global water bodies. However, out of all 11,300 insecticide concentrations, more than 52% (5,915 cases, more than 68.5% of the surface water sites analysed) exceeded the RTL, in parts up to a factor of 10,000 and beyond. According to the authors, these findings indicate substantial threats to global surface waters as insecticide concentrations equalling the RTL (i.e., those considered still acceptable from a regulatory perspective) already led to a 30% reduction of freshwater biodiversity.
The researchers from the University Koblenz-Landau list in their study several reasons why the actual situation in the field potentially is even worse:
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