Environmental partitioning of monophthalate esters

Di-phthalate esters are widespread chemicals in the environment. Monophthalate esters are the primary metabolites of di-phthalate esters. The sorption coefficients of nine monophthalate esters in marine and fresh water sediments were determined in laboratory and field studies. Sorption of various monophthalate esters onto sediment reached equilibrium within 24 h. Organic carbon-normalized sorption coefficients for 9 monophthalate esters in laboratory experiments ranged between 38 and 603 L/kg for marine sediment and between 21 and 380 L/kg for fresh water sediment. Sorption coefficients measured in the field sediments were greater, and ranged between 200 and 46,000 L/kg. Sorption coefficient of MEHP increased with decreasing pH. Sorption coefficients of MPEs from laboratory studies were substantially lower than predicted based on octanol-water partition coefficient of the undissociated form. These results demonstrate that the dissociation of MPEs at environmental pH levels needs to be considered when assessing the fate of these substances in aquatic environments.