Re-evaluation of groundwater monitoring data for glyphosate and bentazone by taking detection limits into account

Abstract

Current regulatory assessment of pesticide contamination of Danish groundwater is exclusively based on samples with pesticide concentrations above detection limit. Here we demonstrate that a realistic quantification of pesticide contamination requires the inclusion of “non-detect” samples i.e. samples with concentrations below the detection limit, as left-censored observations. The median calculated pesticide concentrations are shown to be reduced 104 to 105 fold for two representative herbicides (glyphosate and bentazone) relative to the median concentrations based upon observations above detection limits alone.