The physicochemical basis of QSARs for baseline toxicity.

The physico-chemical properties relevant to the equilibrium partitioning (bioconcentration) of chemicals between organisms and their respired media of water and air are reviewed and illustrated for chemicals that range in hydrophobicity. Relationships are then explored between freely dissolved external concentrations such as LC50s and chemical properties for one important toxicity mechanism, namely baseline toxicity or narcosis. The 'activity hypothesis' proposed by Ferguson in 1939 provides a coherent and compelling explanation for baseline toxicity of chemicals in both water- and air-respiring organisms, as well as a reference point for identifying more specific toxicity pathways. From inhalation studies with fish and rodents, narcosis is shown to occur at a chemical activity exceeding approximately 0.01 and there is no evidence of narcosis at activities less than 0.001. The activity hypothesis provides a framework for directly comparing the toxic potency of chemicals in both air- and water-breathing animals. The activity hypothesis is shown to be consistent with the critical body residue concept, but it has the advantage of avoiding the confounding effect of lipid content of the test organism. It also provides a theoretically sound basis for assessing the baseline toxicity of mixtures. It is suggested that since activity is readily calculated from fugacity, observed or predicted environmental abiotic and biotic fugacities can be used to evaluate the potential for baseline toxicity. Further, models employing fugacity or activity can be used to improve the experimental design of bioassays, thus possibly reducing unnecessary animal testing.

An assessment of the toxicity of phthalate esters to freshwater benthos. 1. Aqueous exposures.

Tests were performed with the freshwater invertebrates Hyalella azteca, Chironomus tentans, and Lumbriculus variegatus to determine the acute toxicity of six phthalate esters, including dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), butylbenzyl phthalate (BBP), di-n-hexyl phthalate (DHP), and di-2-ethylhexyl phthalate (DEHP). It was possible to derive 10-d LC50 (lethal concentration for 50% of the population) values only for the four lower molecular weight esters (DMP, DEP, DBP, and BBP), for which toxicity increased with increasing octanol-water partition coefficient (Kow) and decreasing water solubility. The LC50 values for DMP, DEP, DBP, and BBP were 28.1, 4.21, 0.63, and 0.46 mg/L for H. azteca; 68.2, 31.0, 2.64, and > 1.76 mg/L for C. tentans; and 246, 102, 2.48, and 1.23 mg/L for L. variegatus, respectively. No significant survival reductions were observed when the three species were exposed to either DHP or DEHP at concentrations approximating their water solubilities.

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 freshwater 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 C7, C9, and C11 isophthalate esters (711P). All seven esters were tested in a sediment 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 concentrations 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 higher molecular weight phthalate esters (DHP, DEHP, DINP, DIDP, 711P), two of 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 phthalate 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 tests and EqP theory. The 10-d LC50 values for DBP and H. azteca were >17,400, >29,500, and >71,900 mg/kg dry weight for the low, medium, and high TOC sediments, respectively. These values are more than 30x greater than predicted by EqP theory and may reflect the fact that H. azteca is an epibenthic 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 with EqP theory predictions to within a factor of 1.5. The LC50 value for DEP and C. tentans was >3,100 mg/kg dry weight, which is approximately 10x that predicted by EqP theory. It is postulated that test chemical loss and reduced organism exposure to pore water may have accounted for the observed discrepancies with EqP calculations for DEP

Comparative toxicity of fluoranthene to freshwater and saltwater species under fluorescent and ultraviolet light.

The acute and chronic toxicity of fluoranthene was determined for a diverse group of freshwater and saltwater species under both standard laboratory fluorescent light and ultraviolet (UV) light test conditions. Acute tests with 21 species demonstrated that fluoranthene was not lethal within its water solubility limit to most species tested under fluorescent light, but was lethal well below this limit to nearly all of the species tested under UV light. In general, the acute sensitivity of freshwater and saltwater species from the same class was similar, although UV light exposure changed the relative sensitivity of some species. Crustaceans were the most sensitive to fluoranthene, but in the presence of UV light, an oligochaete and a fish were the most sensitive. Overall, UV light increased acute fluoranthene toxicity approximately one to three orders of magnitude. In chronic tests, sublethal concentrations of fluoranthene were toxic under both fluorescent and UV light, but as in most acute tests, UV light increased chronic toxicity approximately an order of magnitude. Comparison of data from tests conducted in the laboratory and outdoors demonstrated that acute toxicity increased with increased UV light intensity.http://link. springer-ny.com/link/service/journals/00244/bibs/37n4p496.++ +html

Integrated assessment of contaminated sediments in the lower Fox River and Green Bay, Wisconsin.

Samples of sediment and biota were collected from sites in the lower Fox River and southern Green Bay to determine existing or potential impacts of sediment-associated contaminants on different ecosystem components of this Great Lakes area of concern. Evaluation of benthos revealed a relatively depauperate community, particularly at the lower Fox River sites. Sediment pore water and bulk sediments from several lower Fox River sites were toxic to a number of test species including Pimephales promelas, Ceriodaphnia dubia, Hexagenia limbata, Selenastrum capricornutum, and Photobacterium phosphorum. An important component of the observed toxicity appeared to be due to ammonia. Evaluation of three bullhead (Ictalurus) species from the lower Fox River revealed an absence of preneoplastic or neoplastic liver lesions, and the Salmonella typhimurium bioassay indicated relatively little mutagenicity in sediment extracts. Apparent adverse reproductive effects were noted in two species of birds nesting along the lower Fox River and on a confined disposal facility for sediments near the mouth of the river, and there were measurable concentrations of potentially toxic 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), and planar polychlorinated biphenyls (PCBs) both in the birds and in sediments from several of the study sites. Based on toxic equivalency factors and the results of an in vitro bioassay with H4IIE rat hepatoma cells, it appeared that the majority of potential toxicity of the PCB/PCDF/PCDD mixture in biota from the lower Fox River/Green Bay system was due to the planar PCBs. The results of these studies are discussed in terms of an integrated assessment focused on providing data for remedial action planning.

Uptake, elimination, and metabolism of three phenols by fathead minnows.

Uptake rates of total 14C in fathead minnows (Pimephales promelas) exposed to sublethal concentrations of radiolabeled test compounds followed the order: phenol > 2,4,5-trichlorophenol > p-nitrophenol. Mean whole body 14C concentration factors were 15,800, 1,850, and 180 for phenol, 2,4,5-trichlorophenol, and p-nitrophenol exposures, respectively. Only minor amounts of tissue 14C was parent compound after 28 days of exposure in fish exposed to phenol and p-nitrophenol, while 78.6% of the 14C was parent compound in 2,4,5-trichlorophenol exposed fish. Tissue 14C in fish exposed to 2,4,5-trichlorophenol was eliminated at a faster rate than in fish exposed to phenol or p-nitrophenol. Observed mean 14C depuration half-lives for lower and higher exposures combined were 387, 150, and 12 hours for phenol, p-nitrophenol, and 2,4,5-trichlorophenol, respectively. Parent compound comprised 1.5, 2.7, and 0.7% of total 14C for phenol, 2,4,5-trichlorophenol, and p-nitrophenol, respectively, after 28 days of depuration. The percentage of acetone-unextractable 14C increased from the end of uptake to the end of depuration for phenol and 2,4,5-trichlorophenol, and decreased slightly for p-nitrophenol. 14C contribution from polar metabolites increased relative to total 14C during the depuration phase for 2,4,5-trichlorophenol and p-nitrophenol.