Statistical screening for descriptive parameters for pesticide occurrence in a shallow groundwater catchment

SummaryWe have assessed the ability of a range of pesticide, site and climate parameters to discriminate between detected and non-detected pesticides as observed by long-term monitoring data of pesticide use and groundwater occurrence in a small catchment in southern Sweden. Of seventeen investigated parameters, six demonstrated such an ability: dosage applied, the Henry’s Law Constant (HLC), the octanol–water partitioning coefficient (log Pow), the amount of precipitation the week before application, the amount of precipitation the month after application, and the substance degradation potential (DT50). The apparent influence of the investigated parameters on pesticide occurrence in groundwater, and their apparent suitability as descriptive parameters in terms of assessment of related risks, is accordingly discussed.We conclude that knowledge of actual pesticide use appear fundamental for risk assessment of groundwater contamination potential. We further suggest that chemical property-parameters of specific pesticides, although clearly valuable, should be applied in groundwater contamination risk assessments with care. If site-specific values are unattainable, tabular values of log Pow, HLC and water solubility (Ws) are demonstrated to exhibit a superior explanatory ability than those of substance adsorption potential (Koc) and DT50 which, in the latter case, is shown to be able to lead to misleading conclusions on actual risks.The demonstrated explanatory ability of precipitation both before and after application suggests that relatively greater precipitation amounts occur in relation to application of non-detected substances. Increased dilution and run-off as well as decreased soil matrix retainment and decreased top-soil cracking are potential explanations although higher-resolution monitoring records are needed in order to confirm these hypotheses.

► We seek descriptive parameters for pesticide occurrence in shallow groundwater.
► We analyse long-term monitoring data of pesticide use and groundwater occurrence.
► We find descriptive ability for dosage, chemistry and precipitation parameters.
► Descriptive ability of spatially dependent parameters is lacking.