Allocating biocide sources and flow paths to surface waters using passive samplers and flood wave chemographs

Biocide emissions have been shown to pose a comparable risk to aquatic life as pesticides in urbanized catchments. Sources of biocides have been reported to be steady flows from wastewater treatment plants as well as direct building wash off during rain events. A simple methodology to separate wastewater from surface runoff contribution during flood waves had been missing until now. This study introduces an elegant passive sampler method used to derive source allocation during flood waves based on the recalcitrant wastewater tracer carbamazepine. Field calibration of sampling rates during low- and high-flow with continuous autosampler monitoring indicated that uptake rates of polar compounds in caged POCIS are very close in both hydrological situations, allowing for a direct comparison. The passive sampler regressions showed that on a regional level carbendazim originated essentially from wastewater flows, while surface runoff contributed 31% and 74% respectively to terbutryn and diuron mass flows during flood-waves. A local autosampler campaign on a 38 km² catchment using the same wastewater marker approach found increasing surface runoff allocations with event flow in the order terbutryn < carbendazim < diuron in accordance with results from a nearby combined sewer overflow. Both source allocation methods can be used to establish pertinent regional and local biocide mitigation plans. The passive sampler approach is by far the more cost efficient method.