Structure-Dependent Distribution, Metabolism, and Toxicity Effects of Alkyl Organophosphate Esters in Lettuce (Lactuca sativa L.)

Abstract

This study provides a comprehensive investigation into the structure-dependent uptake, distribution, biotransformation, and potential toxicity effects of alkyl organophosphate esters (OPEs) in hydroponic lettuce (Lactuca sativa L.). Trimethyl, triethyl, and tripropyl phosphates were readily absorbed and acropetally translocated, while tributyl, tripentyl, and trihexyl phosphates accumulated mainly in lateral roots. The acropetal translocation potential was negatively associated with log K_ow values. Trimethyl and triethyl phosphates are less prone to biotransformation, while a total of 14 novel hydrolysis, hydroxylated, and conjugated metabolites were identified for other OPEs using nontarget analysis. The extent of hydroxylation decreases from tripropyl phosphate to trihexyl phosphate, but multiple hydroxylations occurred more frequently on longer chain OPEs. Further comparative toxicity test revealed that hydrolyzed and hydroxylated metabolites have stronger toxic effects on Ca²⁺-dependent protein kinases (CDPK) than their parent OPEs. Dibutyl 3-hydroxybutyl phosphate particularly induces upregulation of CDPK in lateral roots of lettuce, probably associated with adenine reduction that may play an important role in the self-defense and detoxification processes. This study contributes to understanding the uptake and transformation behaviors of alkyl OPEs as well as their associations with a toxic effect on lettuce. This emphasizes the necessary evaluation of the environmental risk of the use of OPEs, particularly focusing on their hydroxylated metabolites.