Atrazine in the environment 20 years after its ban: long-term monitoring of a shallow aquifer(in western Germany) and soil residue analysis

Atrazine, one of the worldwide most widespread herbicides, was banned in Germany in 1991 and in the European Union in 2004, due to findings of atrazine concentrations in ground- and drinking waters exceeding the threshold value of 0.1 μg L-1. Nevertheless atrazine and the metabolite deethylatrazine were still detected in German aquifers more than 10 years after its prohibition, often without any considerable decreasing trend in groundwater concentration. Because atrazine was already found to be persistent in soils for more than two decades after the last application, the hypothesis was raised that a continued release of atrazine residues from the soil into groundwaters might sustain atrazine groundwater concentrations on elevated levels. The overall objective of this study was to investigate the occurrence and concentration trends of atrazine and its main metabolites in the groundwater-soil environment after the prohibition of its use. Accordingly, in this study results of i) 20 years of atrazine groundwater monitoring of a a shallow aquifer in western Germany since its ban and ii) atrazine soil residue analyses in the vadose zone of the same study area 21 years after its ban are presented. The phreatic Zwischenscholle aquifer located in the Lower Rhine Embayment is exposed to intensive agricultural land use and is highly susceptible to contaminants due to a shallowwater table. In total 60 observation wells (OWs) have been monitored since 1991, of which 11 are sampled monthly today. Descriptive statistics of monitoring data were derived usingthe “regression on order statistics” (ROS) data censoring approach, estimating values for nonquantifiable values rather than substitute them by e.g. half of the limit of quantification and taking the risk of biasing statistical parameters. The monitoring data shows that even 20 years after the ban of atrazine, the groundwater concentrations of sampled OWs remain on a level close to the threshold value of 0.1 μg L-1 without any considerable decrease ..