Structure-Dependent\nDistribution, Metabolism, and\nToxicity Effects of Alkyl Organophosphate Esters in Lettuce (<i>Lactuca sativa</i> L.)

This study provides a comprehensive investigation into\nthe structure-dependent\nuptake, distribution, biotransformation, and potential toxicity effects\nof alkyl organophosphate esters (OPEs) in hydroponic lettuce (Lactuca sativa L.). Trimethyl, triethyl, and tripropyl\nphosphates were readily absorbed and acropetally translocated, while\ntributyl, tripentyl, and trihexyl phosphates accumulated mainly in\nlateral roots. The acropetal translocation potential was negatively\nassociated with log <i>K</i><sub>ow</sub> values. Trimethyl\nand triethyl phosphates are less prone to biotransformation, while\na total of 14 novel hydrolysis, hydroxylated, and conjugated metabolites\nwere identified for other OPEs using nontarget analysis. The extent\nof hydroxylation decreases from tripropyl phosphate to trihexyl phosphate,\nbut multiple hydroxylations occurred more frequently on longer chain\nOPEs. Further comparative toxicity test revealed that hydrolyzed and\nhydroxylated metabolites have stronger toxic effects on Ca<sup>2+</sup>-dependent protein kinases (CDPK) than their parent OPEs. Dibutyl\n3-hydroxybutyl phosphate particularly induces upregulation of CDPK\nin lateral roots of lettuce, probably associated with adenine reduction\nthat may play an important role in the self-defense and detoxification\nprocesses. This study contributes to understanding the uptake and\ntransformation behaviors of alkyl OPEs as well as their associations\nwith a toxic effect on lettuce. This emphasizes the necessary evaluation\nof the environmental risk of the use of OPEs, particularly focusing\non their hydroxylated metabolites.