Analyzing (Initial) Biotransformation Reactions as an Organizing Principle for Unraveling the Extent of Trace Organic Chemical Biotransformation in Biofiltration Systems

Abstract

Due to the low environmental concentrations and substance-specific behavior of trace organic chemicals (TOrCs), general mechanistic insights can hardly be gained from biotransformation studies with individual substances. In this study, we aimed to identify prevalent enzymatic reactions under different redox and substrate conditions in a well-defined laboratory-scale column system. Biotransformation of chemicals in the first column, which was characterized by a relatively high biomass and rapid depletion of dissolved oxygen, was initiated by frequent and fast reactions such as the oxidation of alcohols or amide hydrolysis. Slower reactions, e.g., the initial dealkylation of primary and secondary amines, were inefficient in the first column and benefited from oxic and carbon-limited conditions prevalent in the second column system after reaeration. Moreover, several compound-specific reactions such as the cleavage of C–Cl and C–O bonds through substitution with glutathione occurred only under carbon-limited conditions. The link between system-specific TOrC removal and suggested initial reactions from the literature can serve as a starting point for a suspect screening of relevant enzymes for the biotransformation of TOrCs based on metagenomic or metatranscriptomic data. Complementary batch experiments with media from the columns confirmed the observed removal under carbon-rich conditions but revealed a limited reproducibility of microbial degradation under oligotrophic conditions.

Persistent Trace Organic Contaminants Are Transformed Rapidly under Sulfate- and Fe(III)-Reducing Conditions in a Nature-Based Subsurface Water Treatment System

“…We suspected that transformation of carbamazepine was sensitive to modifications at the 10−11 olefinic bond because it is the electron-rich site involved in abiotic and biotic reactions of carbamazepine, such as oxidation by ozone 37 and enzymatic metabolism in humans. 38 However, these results and those from other studies 8,36 suggested that predictions of metabolite fate based on parent compound behavior may be inaccurate and should be interpreted with caution. Analysis of porewater data collected after the treatment plant that supplied water to the wetland was upgraded suggested that nitrate-reducing conditions were not essential for trace organic contaminant removal in the horizontal levee.…”

“…We suspected that transformation of carbamazepine was sensitive to modifications at the 10–11 olefinic bond because it is the electron-rich site involved in abiotic and biotic reactions of carbamazepine, such as oxidation by ozone and enzymatic metabolism in humans . However, these results and those from other studies , suggested that predictions of metabolite fate based on parent compound behavior may be inaccurate and should be interpreted with caution.…”

“…10−15 Anaerobic microorganisms employ different enzymes and metabolic strategies than the aerobes that dominate carbon processing during wastewater treatment (e.g., activated sludge) and may promote biotransformation of trace organic contaminants that are more slowly biotransformed under aerobic or nitrate-reducing conditions. 8,16 This article is licensed under CC-BY 4 Despite the potential for better performance with respect to trace organic contaminant removal, subsurface flow treatment systems have not typically been designed to reach anaerobic conditions due to a lack of labile organic carbon in the water. The addition of labile organic carbon to drive conditions to a lower redox potential is also usually avoided due to concerns about clogging and the formation of undesirable byproducts [e.g., sulfide, Fe(II)].…”

Identifying Functional Groups that Determine Rates of Micropollutant Biotransformations Performed by Wastewater Microbial Communities

“…Based on data from previous studies, we hypothesized that amide- and ester-containing MPs would be biotransformed rapidly and that amine- and ether-containing MPs would be biotransformed slowly. ,− To test this hypothesis, we selected a biotransformation rate constant of 0.5 d –1 as a threshold to define relatively fast and slow biotransformations. We found that, in aggregate and in agreement with our expectation, ester-containing MPs were biotransformed relatively fast and that ether-containing MPs were biotransformed relatively slowly.…”

Using Physical Organic Chemistry Knowledge to Predict Unusual Metabolites of Synthetic Phenolic Antioxidants by Cytochrome P450

“…Cytochrome CYP450 enzymes (CYP450) are a superfamily of monooxygenases responsible for most phase-I biotransformation reactions, which may produce even more toxic metabolites than parent compounds in living organisms; although in most cases, the metabolic system can transform the hazardous environmental chemicals into readily extractable metabolites . In order to provide full support for scientific assessment of environmental health risk of pollutants during the whole life cycle, the development of methods for analyzing and predicting pollutant biotransformation, especially by human CYP450, has become a thriving field in environmental science. − Emerging pollutants are synthetic or naturally occurring chemicals that are not commonly monitored or regulated in the environment with potentially known or suspected adverse ecological and human health effects . The continuing onslaught of emerging pollutants has provided a tremendous source of new projects and also yielded needs for new mechanistic explanations of their biotransformation .…”