Time-Dependent Toxicity of Fluoranthene to Freshwater Invertebrates and the Role of Biotransformation on Lethal Body Residues

摘要

The time-dependent toxicity of fluoranthene was examined for Hyalella azteca, Chironomus tentans, and Diporeia spp. C. tentans appeared to be the most sensitive species, and Diporeia was the least sensitive. Incipient LC{sub}50 values, the concentration at which the LC{sub}50 reaches an asymptote and does not change with increasing duration of exposure, for H. azteca and C. tentans were approximately 60 and 40μg·L{sup}(-1), respectively. Incipient levels were not reached for Diporeia; however, the 28-d LC{sub}50 concentration was 95.5 μg·L{sup}(-1). There was a temporal relationship with respect to lethal body residues for each of the test species. For H. azteca, the LR{sub}50, the median lethal residue at an identified exposure time required to cause 50% mortality, based on total fluoranthene equivalents (parent + metabolite compounds) decreased from 3.19μ mol·g{sup}(-1) at 5 d to 0.80 μmol·g{sup}(-1) at 28 d. For C. tentans, the LR{sub}50 decreased from 0.43 to 0.17 μmol-g{sup}(-1) from 2 to 10 d. The 10-d LR{sub}50 for Diporeia was 9.97 μmol·g{sup}(-1), and the 28-d value was 3.67 μmol·g{sup}(-1). The toxicokinetics are not sufficient to address the temporal changes in LR{sub}50 values. Thus, the data were fit to a Damage Assessment Model that also accounts for toxicodynamic processes. This analysis provides estimates of the incipient lethal residues for H. azteca, C. tentans, and Diporeia: 0.84, 0.21, and 3.00μmol·g{sup}(-1), respectively. When comparing the relative sensitivity among species using lethal body residues, special attention should be given to ensure that comparisons are made at a common point in relation to exposure duration (i.e., time to steady state, T{sub}(ss)). When the LR{sub}50(lipid)) values among the three species were compared at steady state, C. tentans is more sensitive than H. azteca and Diporeia spp.; however, there are no significant differences between the amphipod species. The greater sensitivity of C. tentans to fluoranthene as compared to the amphipods may be due, in part, to a potential toxic metabolite.