Isothiazolinone biocides are used extensively as preservatives in paints and building products. During rain events, these biocides wash off of the sides of buildings and interact with plants. Nevertheless, there are no published data on terrestrial plant uptake / processing of isothiazolinones to inform environmental risk assessment or phytoremediation potential. With this field context, we determined the uptake kinetics of four isothiazolinone biocides [benzisothiazolinone (BIT), methylisothiazolinone (MIT), methylchloroisothiazolinone (CMI), and octylisothiazolinone] by aseptic hydroponic Arabidopsis thaliana plants. All four tested isothiazolinone compounds were rapidly and actively taken up from the hydroponic medium by the plants, with second-order removal of ≥98% after 24 h at all tested concentrations, far exceeding transpiration rates. Differences in chemical structure (i.e., benzene ring, methylation, chlorination, or addition of a carbon chain), did not impact plant uptake. OIT and BIT did not exhibit competitive inhibition, indicating either a robust shared plant uptake pathway or different pathways. BIT uptake rate varied at four different initial concentrations (8–2,100 μg/L), appearing to follow substrate inhibition Michaelis-Menten kinetics, indicating that an active uptake pathway with a transporter protein is likely. Repeated BIT spiking only led to a slight increase in plant uptake, thus the uptake pathway is likely constituently active. There was no change in BIT plant uptake rate when mixed with chemically-similar compounds, suggesting either a robust and shared plant uptake pathway or different pathways. We also screened six inhibitors to probe potential isothiazolinone plant uptake pathway(s); inhibition was not evident. Finally, we conducted a semi-untargeted metabolomics study to elucidate novel in planta transformation products of BIT. We discovered at least one abundant and novel amino acid conjugate of BIT. Future field validation is needed, but these results indicate the potential for plant uptake and transformation / phytoremediation of isothiazolinone biocides from stormwater.

Rapid active plant uptake and metabolism of isothiazolinone biocides by hydroponic Arabidopsis

ACS Spring Meeting 2021

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