Influence of Different Sewer Biofilms on Transformation Rates of Drugs

Abstract

To estimate drug consumption more reliably, wastewater-based epidemiology would benefit from a better understanding of drug residue stability during in-sewer transport. We conducted batch experiments with real, fresh wastewater and sewer biofilms. Experimental conditions mimic small to medium-sized gravity sewers with a relevant ratio of biofilm surface area to wastewater volume (33 m m). The influences of biological, chemical, and physical processes on the transformation of 30 illicit drug and pharmaceutical residues were quantified. Rates varied among locations and over time. Three substances were not stable-that is, >20% transformation, mainly due to biological processes-at least for one type of tested biofilm for a residence time ≤2 h: amphetamine, 6-acetylcodeine, and 6-monoacetylmorphine. Cocaine, ecgonine methyl ester, norcocaine, cocaethylene, and mephedrone were mainly transformed by chemical hydrolysis and, hence, also unstable in sewers. In contrast, ketamine, norketamine, O-desmethyltramadol, diclofenac, carbamazepine, and methoxetamine were not substantially affected by in-sewer processes under all tested conditions and residence times up to 12 h. Our transformation rates include careful quantification of uncertainty and can be used to identify situations in which specific compounds are not stable. This will improve accuracy and uncertainty estimates of drug consumption when applied to the back-calculation.

Potential impact of the sewer system on the applicability of alcohol and tobacco biomarkers in wastewater‐based epidemiology

“…The faster degradation is probably due to the presence of biofilms on the walls of RM and GS. These results are in agreement with previous studies where selected chemicals degraded faster in the presence of sewer biofilms or suspended than in wastewater …”

“…We hypothesise that a higher A/V ratio would provide more bacteria and more surface for contact between chemicals and biofilms that lead to more degradation of chemicals in the sewer system. However, McCall et al did not observe any significant difference in the level of chemical degradation among increasing values of A/V ratios. Additionally, the reaction processes in the sewer is likely to be the result of the combined effects of the A/V ratio and the hydraulic retention time of wastewater in the sewer .…”

“…These results are in agreement with previous studies where selected chemicals degraded faster in the presence of sewer biofilms or suspended than in wastewater. 13,14,18,30…”

“…Biofilms are capable of transforming/degrading various chemical compounds more strongly than the suspended microbes in wastewater alone . The capacity of sewer biofilms to enhance degradation of certain chemicals including cocaine, 6‐acetylmorphine (heroin metabolite), creatinine, and paracetamol has been reported …”

“…13,14 The capacity of sewer biofilms to enhance degradation of certain chemicals including cocaine, 6-acetylmorphine (heroin metabolite), creatinine, and paracetamol has been reported. 13,14,17,18 Therefore, in this study, we aimed to investigate the stability of EtG, EtS, Cot, and HCot under different sewer conditions using laboratory-scale sewer reactors and to assess the impact of in-sewer degradation of these biomarkers to their applicability in WBE studies including for consumption estimation and population estimation purposes.…”