An assessment of the toxicity of phthalate esters to freshwater benthos. 2. Sediment exposures

Seven phthalate esters were evaluated for their 10-d toxicity to the freshw ater invertebrates Hyalella azteca and Chironomus tentans in sediment. The esters were diethyl phthalate (DEP), di-n-butyl phthalate (DBP), di-n-hexyl phthalate (DHP), di-(2-ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), and a commercial mixture of C-7, C-9, and C-11 isophthalate esters (711P). All seven eaters were tested in a sedi ment containing 4.80% total organic carbon (TOC), and DBP alone was tested in two additional sediments with 2.45 and 14.1% TOC. Sediment spiking conce ntrations for DEP and DBP were based on LC50 (lethal concentration for 50% of the population) values from water-only toxicity tests, sediment organic carbon concentration, and equilibrium partitioning (EqP) theory. The five h igher molecular weight phthalate esters (DHP DEHP, DINP, DIDP, 711P), two o f which were tested and found to be nontoxic in water-only tests (i.e., DHP and DEHP), were tested at single concentrations between 2,100 and 3,200 mg /kg dry weight. Preliminary spiking studies were performed to assess phthal ate ester stability under test conditions. The five higher molecular weight phthalate esters in sediment had no effect on survival or growth of either C. tentans or H, azteca, consistent with predictions based on water-only t ests and EqP theory. The 10-d LC50 values for DBP and H. azteca were > 17,4 00, > 29,500, and > 71,900 mg/kg dry weight for the low, medium, and high T OC sediments, respectively. These values are more than 30x greater than pre dicted by EqP theory and may reflect the fact that H. azteca is an epibenth ic species and not an obligative burrower The 10-d LC50 values for DBP and C. tentans were 826, 1,664, and 4,730 mg/kg dry weight for the low, medium, and high TOC sediments, respectively. These values are within a factor of two of the values predicted by EqP theory. Pore-water 10-d LC50 values for DBP (dissolved fraction) and C. tentans in the three sediments were 0.65, 0 .89, and 0.66 of the water-only LC50 value of 2.64 mg/L, thereby agreeing w ith EqP theory predictions to within a factor of 1.5. The LC50 value for DE P and C. tentans was >3,100 mg/kg dry weight, which is approximately 10x th at predicted by EqP theory. It is postulated that test chemical loss and re duced organism exposure to pore water may have accounted for the observed d iscrepancies with EqP calculations for DEP.