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.

Large-scale determination of micropollutant elimination from municipal wastewater by passive sampling gives new insights in governing parameters and degradation patterns.

A simple balancing method using passive samplers over a week's period has been developed and tested successfully to determine elimination rates of 22 common micropollutants of household and industrial sources in 18 full-scale wastewater treatment plants of different design and performance. Independent reactor tests to delineate elimination rates with native sludge of the treatment plants correlated very well with the full-scale elimination rate determinations. As opposed to common assumptions, this large dataset indicated that shorter sludge retention times - read: higher active biomass - showed higher micropollutant elimination rates in many cases. Multivariate statistical analysis of the elimination rates over the 18 treatment plants was able to group compounds according to common degradation pathways and showed that sensitivity to SRT drove the grouping. The dataset also allowed to determine population equivalent normalized loads of the investigated micropollutants. The application of WWTP balancing with passive sampling makes it relatively easy to gather elimination rates and inlet loads on a much broader basis than before and gives orientation for more in-depth analysis of degradation pathways.

Predicting pesticide attenuation in a fractured aquifer using lumped-parameter models.

Neighboring springs draining fractured-rock aquifers can display large differences in water quality and flow regime, depending on local variations of the connectivity and the aperture size distribution of the fracture network. Consequently, because homogeneous equivalent parameters cannot be assumed a priori for the entire regional aquifer, the vulnerability to pollution of such springs has to be studied on a case by case basis. In this paper, a simple lumped-parameter model usually applied to estimate the mean transit time of water (or tracer) is presented. The original exponential piston-flow model was modified to take land-use distribution into account and applied to predict the evolution of atrazine concentration in a series of springs draining a fractured sandstone aquifer in Luxembourg, where despite a nationwide ban in 2005, atrazine concentrations still had not begun to decrease in 2009. This persistence could be explained by exponentially distributed residence times in the aquifer, demonstrating that in some real world cases, models based on the groundwater residence time distribution can be a powerful tool for trend reversal assessments as recommended for instance by current European Union guidelines.