Benzotriazoles (BTs) are xenobiotic contaminants of emerging concern (CECs) due to their mobility, pervasive use, microbial recalcitrance, and low removal during wastewater treatment. Indeed, BT has been measured in recycled water sources following reverse osmosis. Because recycled water is used for irrigation purposes in arid regions, we investigated the uptake and fate of BT in plants. Uptake was rapid (t1/2&lt;3h), repeatable (multiple spikes), and extensive (&lt;1% of the parent compound mass remained) in a hydroponic system with the model plant Arabidopsis. Using LC-QTOF-MS untargeted metabolomics, we discovered two main types of novel transformation products: glycosylated BT conjugates and conjugation with amino acids via incorporation into the tryptophan biosynthesis pathway. The latter structurally resemble tryptophan and important plant growth hormones. We observed via proteomics that BT was not significantly incorporated into plant proteins; however, bioassays reveal BT acts as a weak phytohormone. Through synthesis of four major metabolites we were able to close &gt;60% of the mass balance on a BT model system. Glycosylated BT formed in planta was subsequently excreted, a phenomenon not previously observed. To examine if the same processes occurred in the field, we extracted plant tissues from crops grown in greenhouses and irrigated with BT-spiked water as well as crops from agricultural fields. Crops were separated into roots, shoots, and fruits. BT and BT plant metabolites were present in trace quantities in all samples (including controls) and most plant compartments with varying distributions depending on crop type and metabolites. Despite rigorous quality assurance measures, the presence of trace BT and BT plant metabolites in the greenhouse control plant samples irrigated with tap water was curious. Subsequently, we discovered BT at trace levels in tap water in California and Colorado; to our knowledge this is the first report of BT in US tapwater. Trace exposure to BT may cause accumulation in the plant tissues. Overall, this research suggests that plant processes rapidly change the form of some CECs in the environment to novel metabolites, the toxicity of which is unknown. Furthermore, we observe that BT is conjugated but that the core structure remains unaltered, thus plant processes may act to mask CEC presence in the environment by evading detection and thereby underestimate true CEC loads.

Discovery of benzotriazole and novel plant metabolites in Arabidopsis and food crops

251st National Meeting (2016)

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