Accumulation of Micropollutants, Byproducts, and Metabolites in Vegetables Cultivated with Treated Water

Abstract

Due to a lack of water resources, people are starting to use treated wastewater to irrigate crops and vegetables. However, the risk of micropollutant exposure from vegetables cultivated with treated wastewater has been largely underestimated. To elucidate this underestimation, a hydroponic system for lettuce cultivation using a nutrient solution spiked with three pharmaceuticals with different log K_OW values (acetaminophen (0.46), ketamine (2.18) and methadone (3.93)) was examined, and the total bioconcentration factors (BCFs) (including the transformation of metabolites) of the pharmaceuticals were found to be 0, 120±7.76 and 176±16.0 L/kg, respectively. To simulate treated wastewater, these nutrient solutions were first treated by sunlight photolysis, chlorination, and sunlight/chlorine before use in lettuce cultivation. During the treatment, ketamine and methadone were transformed into norketamine (up to 6.0%) and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) (up to 16%), respectively; the BCF of norketamine (162±22.6 L/kg) was found to be even greater than ketamine. In addition, other degradation byproducts (including 3 trace and 13 undetected byproducts in the nutrient solutions) were taken up by the lettuce. In parallel, ketamine and methadone can also undergo metabolism in lettuce; the conversion rate to norketamine increased from 22±7.0% to 45±0.062 when the ketamine concentration decreased from 1000 to 50 μg/L.