Effects of Binary Mixtures and Transpiration on Accumulation of Pharmaceuticals by Spinach

Many pharmaceuticals are present in reclaimed wastewater and effluent-dominated water bodies used to irrigate edible crops. Previous research has shown that plants irrigated with reclaimed wastewater can accumulate pharmaceuticals. However, plant-driven processes that contribute to differences in accumulation among compounds are not well understood. Here, we tested the effects of exposure to mixtures on spinach accumulation and metabolism of four psychoactive pharmaceuticals found in reclaimed wastewater: carbamazepine, fluoxetine, amitriptyline, and lamotrigine. Coexposure of plants to carbamazepine and fluoxetine or amitriptyline decreased accumulation of the toxic carbamazepine metabolite 10,11-epoxycarbamazepine. Furthermore, we tested a simple transpiration-based accumulation model and found that transpiration is a strong predictor for accumulation of the studied compounds. Amitriptyline accumulated to a larger extent than predicted from transpiration alone, and we suggest the possibility that a transporter protein may be involved in its uptake. Our findings highlight the need to consider plant physiology and mixture effects in studying accumulation of polar and ionizable organic contaminants and their metabolites.