Assessing the Application of an Additive Model to Estimate Toxicity of a Complex Effluent

Abstract

A number of industries monitor levels of chemicals in their effluent, but few have undertaken prolonged biological monitoring of this wastewater. The focus of the present study was to determine whether past chemical data for effluent from a lead smelter could be used to estimate its past toxicity. Since the interactive effects of metals in effluents are often assumed to be additive, it was hypothesized that an additive model, 100/[sigma(metal concentration in effluent/EC50 for individual metal)], could be used to generate an EC50 from chemical data (where EC50 is the concentration of test material that affects 50% of the test organisms). To test the approach, a larval development toxicity test with the marine polychaete, Galeolaria caespitosa, was used to test 26 separate samples of effluent from a lead smelter, generating empirical EC50 values. EC50 values for each individual metal in the effluent were also generated using the larval development toxicity test. The concentrations of trace metals in each effluent sample were determined and, using the additive model, EC50 values were calculated. For the majority of effluent samples tested, the additive model underestimated toxicity, suggesting the presence of additional unidentified contaminants in the effluent samples. Additionally, a nonlinear rather than linear regression curve was found to best describe the relationship between the model and empirically derived EC50 values. This relationship was then used to estimate past trends in toxicity of the smelter effluent. Forty-eight percent of the variability in measured toxicity was explained by the model, with the model underestimating toxicity in the majority of samples.

New implications in the use of imposex as a suitable tool for tributyltin contamination: experimental induction in Hexaplex trunculus (Gastropoda, Muricidae) with different stressors

“…When pollutants occur together in the environment, they may interact in an additive manner, which is the most common one (Ross and Bidwell 2003), in a synergistic (Mu and Le Blanc 2004) or antagonistic way (Reish et al 1999). Furthermore, toxic compounds potentially act as endocrine disruptors, interfering with the endocrine system of organisms (Depledge and Billinghurst 1999).…”

The Toxicology of Chemical Mixtures Risk Assessment for Human and Ecological Receptors

“…Contaminants missed by chemical screening analyses or below the detection limit can contribute to toxicity (Ankley and Mount, 1996;Smolders et aL, 2003;Van Leeuwen et al, 1996). A component approach (additive HI) was shown to underestimate the toxicity of a lead smelter effluent due to metals or other toxicants in the mixture that were below detection limits; this underestimation was not due to interaction as an artificial mixture 59 iFcontaining the measured metals produced the predicted additive toxicity (Ross and Bidwell, 2003).…”

“…Toxicity of related chemicals or those having the same mode of action can be summed using additivity or dose addition (ECETOC, 2001;Escher and Hermens, 2002). Additivity has been confirmed in various species for PAHs, triazine congeners, BTEX (benzene, toluene, ethylbenzene and xylenes) and many metals (Ankley and Mount, 1996;Dyer et at, 2000;Faust et a!, 2000;Niederlehner eta!, 1998;Ross and Bidwell, 2003;Vighi and Calamari, 1996). Additivity occurs even when components are present below the individual chemical lowest observable effect concentrations (LOECs).…”

“…This method assumes that the only exposure to sediment dwelling organisms is through pore water; exposure is dependent on the organic carbon content of the sediment and the partitioning of the chemical to organic carbon (MacDonald et al, 2000;Villa et al, 2003). Marine aquatic and sediment organisms differ in sensitivity from freshwater; salinity increases the toxicity of organophosphate insecticides and some metals (Ross and Bidwell, 2003;Villa et al, 2003).…”