The Fate, Metabolism and Toxicity of Select Contaminants of Emerging Concern in Terrestrial Environments
Increasing populations and shifting precipitation patterns put pressure on freshwater and food systems and incentivize governments and industries to exploit historically underutilized resources, such as recycled water and biosolids. Use of recycled water and biosolids in agricultural systems, however, comes with the potential risks of environmental and food contamination by trace organic contaminants including, contaminants of emerging concern (CECs). These compounds pose potential threats to humans and environmental health because they are designed to be biologically active at low concentrations and are considered “pseudo-persistent” due to their continuous release into the environment.
Using 14C tracing, mass spectrometry, stable-isotope labeling, and enzyme extractions to assess the fate, metabolism, and biological effects of four environmentally prevalent CECs (i.e. sulfamethoxazole, diazepam, naproxen and methyl paraben) in terrestrial organisms in hydroponic and artificial soil cultivations. These organisms included an agricultural bioengineer (Eisiena fetida), a model plant (Arabidopsis thaliana) and two crop plants (Cucumis sativus, Raphanus sativus,). Compounds were selected based on environmental prevalence and test organisms were selected due to their use in the literature, commercial availability, and global range.
Sulfamethoxazole was metabolized in A. thaliana cell cultures, and E. Fetida forming phase I and II metabolites. Diazepam was also metabolized in A. thaliana cell cultures and radish and cucumber seedlings, forming the phase I metabolites nordiazepam, temazepam and oxazepam, with the longevity corresponding to that of human metabolism. The major metabolites of naproxen and methyl paraben, O-desmethylnaproxen and p-hydroxybenzoic acid, respectively, were detected in treatment soils containing E. fetida and N4-acetylsulfamethoxazole was detected in E. fetida tissues, indicating CEC metabolism and excretion. Exposure to CECs resulted in changes to enzymes associated with detoxification and oxidative stress (i.e. glutathione-S-transerfase, glucuronosyl transferase, superoxide dismutase, and catalase) in crop plants and E. fetida. Our research indicates that terrestrial organisms can take and transform CECs and that CECs can change biochemistry of the exposed organisms. Accordingly, it is crucial to consider CEC fate, transformation and effects on non-target organisms of CECs when assessing risk in the agro-environment.