A tiered procedure for assessing the formation of biotransformation products of pharmaceuticals and biocides during activated sludge treatment

Abstract

Upon partial degradation of polar organic micropollutants during activated sludge treatment, transformation products (TPs) may be formed that enter the aquatic environment in the treated effluent. However, TPs are rarely considered in prospective environmental risk assessments of wastewater-relevant compound classes such as pharmaceuticals and biocides. Here, we suggest and evaluate a tiered procedure, which includes a fast initial screening step based on high resolution tandem mass spectrometry (HR-MS/MS) and a subsequent confirmatory quantitative analysis, that should facilitate consideration of TPs formed during activated sludge treatment in the exposure assessment of micropollutants. At the first tier, potential biotransformation product structures of seven pharmaceuticals (atenolol, bezafibrate, ketoprofen, metoprolol, ranitidine, valsartan, and venlafaxine) and one biocide (carbendazim) were assembled using computer-based biotransformation pathway prediction and known human metabolites. These target structures were screened for in sludge-seeded batch reactors using HR-MS/MS. The 12 TPs found to form in the batch experiments were then searched for in the effluents of two full-scale, municipal wastewater treatment plants (WWTPs) to confirm the environmental representativeness of this first tier. At the second tier, experiments with the same sludge-seeded batch reactors were carried out to acquire kinetic data for major TPs that were then used as input parameters into a cascaded steady-state completely-stirred tank reactor (CSTR) model for predicting TP effluent concentrations. Predicted effluent concentrations of four parent compounds and their three major TPs were corroborated by comparison to 3-day average influent and secondary effluent mass flows from one municipal WWTP. CSTR model-predicted secondary effluent mass flows agreed within a factor of two with measured mass flows and confidence intervals of predicted and measured mass flows overlapped in all cases. The observed agreement suggests that the combination of batch-determined transformation kinetics with a simple WWTP model may be suitable for estimating aquatic exposure to TPs formed during activated sludge treatment. Overall, we recommend the tiered procedure as a realistic and cost-effective approach to include consideration of TPs of wastewater-relevant compounds into exposure assessment in the context of prospective chemical risk assessment.

Elucidating the impact of microbial community biodiversity on pharmaceutical biotransformation during wastewater treatment

“…The ability of the microbes in WWTPs to biotransform these chemicals is an area of great interest (Carballa et al ., 2004; Castiglioni et al ., 2005; Nakada et al ., 2006; Kasprzyk‐Hordern et al ., 2009). Substantial research has advanced our knowledge of pharmaceutical biotransformation pathways (Ellis et al ., 2006) and the transformation products formed during treatment (Kern et al ., 2010). However, only one study to our knowledge has linked chemical transformation data with wastewater microbial community composition and activity (Helbling et al ., 2015), and no studies to date have identified specific functions associated with biotransformation to develop predictive relationships between functional characteristics of the microbial community and pharmaceutical biotransformation pathways and extents.…”

Biodegradation of atenolol by an enriched nitrifying sludge: Products and pathways

“…Product ion spectra of atenolol and atenolol acid have been described in previous studies as well as the structural identification process of the transformation products [22,43]. However, to date only one biodegradation product, i.e., atenolol acid (P267), has been identified in the biodegradation of atenolol by conventional activated sludge, membrane bioreactor sludge or activated sludge from a full-scale aerobic nitrification reactor [22,44].…”

Targeted and non-targeted liquid chromatography-mass spectrometric workflows for identification of transformation products of emerging pollutants in the aquatic environment

“…In the tiered approach proposed by Kern et al, batch experiments with activated sludge can be used to verify the findings and to quantify transformation rates [52].…”

“…As UM-PPS is freely accessible and all rules applied are clearly assigned, it is the most common prediction tool in suspect screening, and many researchers have tried to evaluate and to improve its prediction power [34,[50][51][52]. The prediction rules behind UM-PPS come from the University of Minnesota Biocatalysis/ Biodegradation Database (UM-BBD) and literature [85].…”