Agricultural insecticides threaten surface waters at the global scale

Abstract

Compared with nutrient levels and habitat degradation, the importance of agricultural pesticides in surface water may have been underestimated due to a lack of comprehensive quantitative analysis. Increasing pesticide contamination results in decreasing regional aquatic biodiversity, i.e., macroinvertebrate family richness is reduced by ∼30% at pesticide concentrations equaling the legally accepted regulatory threshold levels (RTLs). This study provides a comprehensive metaanalysis of 838 peer-reviewed studies (>2,500 sites in 73 countries) that evaluates, for the first time to our knowledge on a global scale, the exposure of surface waters to particularly toxic agricultural insecticides. We tested whether measured insecticide concentrations (MICs; i.e., quantified insecticide concentrations) exceed their RTLs and how risks depend on insecticide development over time and stringency of environmental regulation. Our analysis reveals that MICs occur rarely (i.e., an estimated 97.4% of analyses conducted found no MICs) and there is a complete lack of scientific monitoring data for ∼90% of global cropland. Most importantly, of the 11,300 MICs, 52.4% (5,915 cases; 68.5% of the sites) exceeded the RTL for either surface water (RTLSW) or sediments. Thus, the biological integrity of global water resources is at a substantial risk. RTLSW exceedances depend on the catchment size, sampling regime, and sampling date; are significantly higher for newer-generation insecticides (i.e., pyrethroids); and are high even in countries with stringent environmental regulations. These results suggest the need for worldwide improvements to current pesticide regulations and agricultural pesticide application practices and for intensified research efforts on the presence and effects of pesticides under real-world conditions.

Keywords: agriculture; biodiversity; global surface waters; insecticide contamination; regulatory risk assessment.

Fig. 1.

Global crop area and the distribution of regulatory threshold level (RTL) exceedance rates for reported measured insecticide concentrations (MICs, n = 10,659) aggregated in 1° grid cells. Information on insecticide surface water exposure was available for only 1.62 million km² (10.6%) of the 15.3 million km² of global croplands (1). Rectangles (n = 307) represent subclassified cropped areas with five or more MICs, and triangles (n = 290) display grid cells with fewer than 5 MICs. Please note that 641 MICs could not be allocated to a specific grid cell due to the provision of imprecise location information in the studies. The horizontal bars in the legend illustrate the relative distributions of the respective insecticide RTL exceedance classes among the global cropped area with information on insecticide exposure.

Fig. 2.

Observed ecological effects of pesticide exposure on regional surface water biodiversity and distribution curves for global reported measured insecticide concentrations (MICs) in water and sediment relative to regulatory threshold levels (RTLs). (A) Dependency of mean macroinvertebrate family richness at 60 agricultural stream sites on mean aqueous pesticide concentration to RTL_SW ratios. Data on family richness, pesticide exposure levels, and categories were taken from ref. . The vertical dashed line indicates the RTL_SW, and the error bars denote 95% confidence intervals. (B) Blue represents the concentrations in water relative to the substance-specific RTL_SW (n = 8,166), and brown represents the concentrations in sediment relative to the substance-specific RTL_SED (n = 3,131). The vertical dashed line indicates the RTL.

Fig. 3.

Effect of insecticide class and country environmental regulations on the distribution curves for reported measured insecticide concentrations in the water phase (MIC_SW) relative to substance-specific regulatory threshold levels (RTL_SW). (A) Black represents data obtained for organochlorine insecticides (n = 2,021), blue represents data obtained for organophosphate insecticides (n = 5,095), and red represents data obtained for pyrethroid insecticides (n = 919); 6.1% of the MIC_SW of neonicotinoids (n = 131) exceeded the RTL_SW (not displayed). (B) Distribution curves for MIC_SW relative to substance-specific RTL_SW. Blue represents concentrations measured in countries with low environmental regulatory quality (LERQ; n = 3,177), and red represents data measured in countries with high environmental regulatory quality (HERQ; n = 4,989). The vertical dashed lines indicate the RTL_SW.