Do initial concentration and activated sludge seasonality affect pharmaceutical biotransformation rate constants?

Abstract

Pharmaceuticals find their way to the aquatic environment via wastewater treatment plants (WWTPs). Biotransformation plays an important role in mitigating environmental risks; however, a mechanistic understanding of involved processes is limited. The aim of this study was to evaluate potential relationships between first-order biotransformation rate constants (kb) of nine pharmaceuticals and initial concentration of the selected compounds, and sampling season of the used activated sludge inocula. Four-day bottle experiments were performed with activated sludge from WWTP Groesbeek (The Netherlands) of two different seasons, summer and winter, spiked with two environmentally relevant concentrations (3 and 30 nM) of pharmaceuticals. Concentrations of the compounds were measured by LC–MS/MS, microbial community composition was assessed by 16S rRNA gene amplicon sequencing, and kb values were calculated. The biodegradable pharmaceuticals were acetaminophen, metformin, metoprolol, terbutaline, and phenazone (ranked from high to low biotransformation rates). Carbamazepine, diatrizoic acid, diclofenac, and fluoxetine were not converted. Summer and winter inocula did not show significant differences in microbial community composition, but resulted in a slightly different kb for some pharmaceuticals. Likely microbial activity was responsible instead of community composition. In the same inoculum, different kb values were measured, depending on initial concentration. In general, biodegradable compounds had a higher kb when the initial concentration was higher. This demonstrates that Michealis-Menten kinetic theory has shortcomings for some pharmaceuticals at low, environmentally relevant concentrations and that the pharmaceutical concentration should be taken into account when measuring the kb in order to reliably predict the fate of pharmaceuticals in the WWTP. Key points • Biotransformation and sorption of pharmaceuticals were assessed in activated sludge. • Higher initial concentrations resulted in higher biotransformation rate constants for biodegradable pharmaceuticals. • Summer and winter inocula produced slightly different biotransformation rate constants although microbial community composition did not significantly change. Graphical abstract

Determination of cytotoxicity following oxidative treatment of pharmaceutical residues in wastewater

“…This leads to incomplete WWTP removal or enzymatic conversion of metabolites into the original bioactive structure. Emissions of insufficiently treated WWTP may have adverse effects in the aquatic environment (Ajo et al, 2018;Abbas et al, 2019;Moermond et al, 2020;van Bergen et al, 2021). The occurrence of pharmaceutical residues in the environment is a known risk for aquatic ecosystems, antimicrobial resistance and drinking water quality (Isidori et al, 2016;Peake et al, 2016;Vasiliadou et al, 2018).…”

Daily Monitoring at a Full-Scale Wastewater Treatment Plant Reveals Temporally Variable Micropollutant Biotransformations

“…In Figure 1C, we observe a weak yet significant positive relationship between average % R and average logtransformed INF concentration indicating that, in aggregate, average % R increases with increasing INF concentration (r = 0.4, p < 0.05), a phenomenon that has been observed for MPs at other WWTPs. 34 Most MPs exhibiting either very high (>85) or very low (<15) average %R were consistently measured as such (i.e., low SD). MPs in this category are likely biotransformed via microbial community functions with stable activity levels.…”

“…Most previous studies investigating the variable biotransformation of MPs have utilized batch reactors seeded with wastewater microbial communities to measure the rate and extent of MP biotransformation − and to identify biotransformation products (TPs). , Data from these types of experiments have been useful for delineating biotransformation pathways and for linking biotransformation rates to experimental variables such as dissolved oxygen levels or the taxonomic composition of the microbial community . However, there are a variety of limitations that have prevented the extrapolation of results from these types of studies to performance in full-scale systems.…”

Biodegradation Kinetics of Fragrances, Plasticizers, UV Filters, and PAHs in a Mixture─Changing Test Concentrations over 5 Orders of Magnitude

“…19,20,31 These descriptions predict the proportionality between the chemical concentration and degradation rate found at low concentration to remain intact when decreasing concentrations even further. However, van Bergen et al 21 found higher degradation rate constants in activated sludge at 30 nM compared to 3 nM for a number of pharmaceuticals.…”

“…At higher concentrations, a stagnation of the increase in the biodegradation rate is expected because of limitations on the growth of degraders or due to enzyme saturation. , This pattern is complicated by the possibility for substrate inhibition (toxicity) that can lower the rate of biodegradation at high substrate concentrations. ,, These descriptions predict the proportionality between the chemical concentration and degradation rate found at low concentration to remain intact when decreasing concentrations even further. However, van Bergen et al found higher degradation rate constants in activated sludge at 30 nM compared to 3 nM for a number of pharmaceuticals. Boethling and Alexander also observed that for two of four test chemicals (2,4-D and carbaryl) degradation rates in stream water decreased more than expected at the lowest concentrations used (low μg/L) .…”