Uptake Efficiency of the Gills of English Sole (Parophrys vetulus) for Four Phthalate Esters

Abstract

Uptake efficiencies of the gills of English sole (Parophrys vetulus) for four homologous phthalic acid esters were directly measured and compared with octanol–water partition coefficients (Kow). Test compounds were diethyl phthalate (DEP), butyl benzyl phthalate (BBP), bis(2-ethylhexyl) phthalate (DEHP), and di-n-octyl phthalate (DOC). Mean uptake efficiencies in a single pass through the gills were 11% for DEP (log Kow = 3.2), 42% for BBP (log Kow = 5.8), 3% for DEHP (log Kow = 8.7), and 12% for DOC (log Kow = 9.2). Uptake efficiencies for DEP and BBP were inversely correlated with weight-specific ventilation volume and did not correlate with aqueous concentration. Uptake efficiencies for DOC and DEHP were uncorrelated with any measured parameter. Solubilities of phthalic acid esters were measured by generator column. DEP and BBP had aqueous solubilities similar to published values, but DEHP was 1/700 and DOC was 1/3000 below published solubility values. DOC and DEHP used to determine uptake efficiencies were most likely in colloidal or micellar form, which may be less bioavailable than soluble forms of the compound; this would reduce the apparent uptake efficiency, regardless of Kow value.