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Predictive models for relative toxicity of divalent metal ions using ion characteristics have been produced with both Microtox®, a 15 min microbial bioassay, and the 24 h Caenorhabditis elegans bioassay. Relative toxicity of mono-, di- and trivalent metal ions has also been successfully modeled using ion characteristics with the Microtox® bioassay. This study extends this approach to include longer exposure durations (24 h) and a more complex organism (metazoan). Twenty-four-hour LC50s (expressed as total and free ion concentrations) for the free-living soil nematode, C. elegans , were determined for Li, Na, Mg, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Cd, Cs, Ba, La, and Pb in an aqueous medium. Relative metal toxicity was predicted with least squares linear regression and several ion characteristics. Toxicity was most effectively predicted ( r 2 =0.85) with a two-variable model containing |log K OH | (where K OH is the first hydrolysis constant) and χ 2 m r (the covalent index). The first hydrolysis constant reflects a metal ion's tendency to bind to intermediate ligands such as biochemical groups with O donor atoms, while χ 2 m r reflects binding to soft ligands such as those with S donor atoms. The use of LC50s based on free ion concentrations did not significantly improve model fit. The results of this study are consistent with earlier models generated with Microtox® data, with the exception of barium, which was much more toxic to C. elegans than would be predicted from the model. We conclude that, with thoughtful application, ion characteristics can be used to predict the relative toxicity of metal ions that vary widely in both valence and binding tendency.

Quantitative Structure Activity Relationships (QSAR) predict relative toxicity of a family of chemicals from fundamental and surrogate molecular qualities. Most QSARs are developed for organic toxicants, with inorganic toxicants (metals) being under-represented. Successful predictive models for relative toxicity of divalent metal ions using ion characteristics have been produced using Microtox®, a 15 min microbial bioassay. The present study extends this approach to longer exposure durations (24 h), and a more complex organism (metazoan). Twenty-four hour LC50s (expressed as total metal concentration) for the free-living soil nematode, C. elegans were determined for Ca, Cd, Cu, Hg, Mg, Mn, Ni, Pb, and Zn in an aqueous medium. Relative metal toxicity was predicted with least squares linear regression and several ion characteristics. Toxicity was most effectively predicted (r2 = 0.89) with ¦ log K OH ∣ (where KOH is the first hydrolysis constant), which reflects a metal ion's tendency to bind to intermediate ligands such as biochemical functional groups with O donor atoms. The best fitting model was obtained using LC50 metameters based on total metal concentration, indicating that the identification of the bioactive species of metals can be ambiguous, and does not necessarily aid in the prediction of relative metal toxicity with ion characteristics. The modelling of relative metal toxicity using ion characteristics was successful for 24 h exposure durations using this more complex organism.

Anthracene, a polycyclic aromatic hydrocarbon, is acutely toxic to fish when they are exposed simultaneously to solar ultraviolet radiation (SUVR). However, the physiological mechanism of acute anthracene photo-induced toxicity is not known. The purpose of this study was to investigate possible modes of action associated with simultaneous anthracene and SUVR exposure using blood and gill biochemistry in bluegill sunfish (Lepomis macrochirus). Fish were exposed to anthracene (< 0.01 and 7.04 μg/l) and SUVR in a flow-through system. Following 96 h of anthracene and SUVR exposure, fish exhibited significant increases in hematocrit and significant decreases in whole blood hemoglobin content when compared to no-anthracene controls. Evidence of hemolysis was also observed in anthracene and SUVR exposed fish. Using in vitro enzyme analysis, both Na,K-ATPase and Mg-ATPase were signficantly inhibited in gill tissue homogenates exposed to anthracene and SUVR when compared to homogenates exposed to SUVR alone. These blood and gill measurements provide evidence of osmotic stress in exposed fish. Given the results presented in this and in previous studies, we conclude that there are numerous sites of acute toxic action with anthracene and SUVR exposure in fish and that this toxicity appears to be associated with a general disruption of cell membrane function.

Polycyclic aromatic hydrocarbons (PAHs) are widespread pollutants in the aquatic environment and demonstrate a wide variety of toxic effects in freshwater and marine organisms. We have previously documented photo-induced toxic effects of a model PAH (i.e. anthracene) in fish. The goal of our ongoing studies is to examine environmental factors which may enhance or mitigate this toxicity in order to better estimate the risks of phototoxic PAHs to aquatic organisms. The purpose of the present study was to determine the effect of water temperature and oxygen concentration on the photo-induced toxicity of anthracene to juvenile bluegill sunfish (Lepomis macrochirus). Bluegill sunfish were exposed to anthracene ( μg l ) and solar ultraviolet radiation (SUVR) at different water temperatures (20 and 30°C) and oxygen concentrations (5.0, 6.9 and 8.1 mg O2/1 for 120 h in a laboratory flow-through system. A trend toward an inverse relationship was found between water temperature and LC50 values, although no significant temperature effect was observed. A nonlinear relationship was found between oxygen concentration and LC50 values, with significantly increased toxicity at the middle oxygen concentration. Opercular ventilation rates were inversely related to oxygen concentration and directly related to anthracene concentration. A statistical relationship was developed on the basis of oxygen concentration to predict LC50 values. We conclude that dissolved oxygen concentration is an important environmental factor in the assessment of photo-induced toxicity of anthracene to fish.