The impact of time-integrated active or passive sampling methods on bioanalytical water quality risk assessment

Since traditional chemical analytical methods only consider a minor fraction of substances present in the water cycle, biological effect monitoring (BEM) is required for a more reliable assessment of the chemical status. BEM integrates the effects of all micropollutants activating molecular events that may trigger adverse outcome pathways. For reliable risk assessment it is important that substances are efficiently recovered from the water matrix by the environmental sampling and extraction methods. The present study compared the performance of five time-integrated sampling and extraction methods for large effluent volumes at three wastewater treatment plants (WWTPs). Both chemical and bioassay data were evaluated to select the most suited method for bioanalytical monitoring. Large volumes of WWTP effluents, collected for three weeks by flow-proportional active sampling, were extracted with XAD resins and large-volume solid-phase extraction (SPE). Simultaneously, three types of passive samplers (silicone rubber, POCIS and Speedisk) were deployed in the effluent channels. Clear differences were observed between both chemical and bioanalytical profiles for the five time-integrated sampling/extraction methods. Higher levels of extracted chemicals did not necessarily lead to higher responses in the bioassays. This may be because both agonistic and antagonistic compounds are extracted, and therefore the total observed bioactivity may not always reflect higher levels of extracted chemicals. The SPE active sampling method was more effective than XAD, concentrating more compounds and at higher concentrations. The results obtained with passive samplers were highly dependent on estimations of average extracted water volumes, which are difficult to predict for complex environmental mixtures. POCIS appeared to be the most efficient passive sampler for concentration of polar organic micropollutants. The preference between active SPE and passive POCIS depends on the desired application. Since differences in sampling and extraction methods significantly affect the assessments of environmental risks, effect-based trigger values (EBT) need to be specifically evaluated for each method.