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The concentration addition (CA) and the independent action (IA) models are widely used for predicting mixture toxicity based on its composition and individual component dose–response profiles. However, the prediction based on these models may be inaccurate due to interaction among mixture components. In this work, the nature and prevalence of non-additive effects were explored for binary, ternary and quaternary mixtures composed of hydrophobic organic compounds (HOCs). The toxicity of each individual component and mixture was determined using the Vibrio fischeri bioluminescence inhibition assay. For each combination of chemicals specified by the 2 n factorial design, the percent deviation of the predicted toxic effect from the measured value was used to characterize mixtures as synergistic (positive deviation) and antagonistic (negative deviation). An arbitrary classification scheme was proposed based on the magnitude of deviation (d) as: additive (⩽10%, class-I) and moderately (10< d ⩽30%, class-II), highly (30< d ⩽50%, class-III) and very highly (>50%, class-IV) antagonistic/synergistic. Naphthalene, n-butanol, o-xylene, catechol and p-cresol led to synergism in mixtures while 1, 2, 4-trimethylbenzene and 1, 3-dimethylnaphthalene contributed to antagonism. Most of the mixtures depicted additive or antagonistic effect. Synergism was prominent in some of the mixtures, such as, pulp and paper, textile dyes, and a mixture composed of polynuclear aromatic hydrocarbons. The organic chemical industry mixture depicted the highest abundance of antagonism and least synergism. Mixture toxicity was found to depend on partition coefficient, molecular connectivity index and relative concentration of the components. [Copyright &y& Elsevier]

Abstract: The toxicity of 14 industrially relevant organic chemicals was determined using freshly grown Vibrio fischeri bioluminescence inhibition assay. The results were compared to lyophilized V. fischeri, 96h fish, 48h Daphnia magna and 95h green algae bioassays. Reliability of octanol–water partition coefficient (K ow), and first order simple and valence molecular connectivity index (1 χ, 1 χ v) based regression models for predicting toxicity to V. fischeri was studied. Correlations were obtained between freshly grown V. fischeri data (Log(EC50)) and Log(K ow), molecular connectivity indices (1χ, 1 χ v), energy of the highest occupied (E HOMO) and lowest unoccupied (E LUMO) molecular orbitals, and their difference (E LUMO − E HOMO). A good match was observed between V. fischeri assay conducted with freshly grown and lyophilized culture (r 2 =0.90). Good correlations (r 2 >0.95) were obtained with all the other bioassays after excluding compounds with Log(K ow) less than 2.0. Available regression models based on Log(K ow) and 1 χ v yielded lower toxicity values. V. fischeri bioassay showed fairly good correlation with Log(K ow), 1 χ and 1 χ v (r 2 >0.75) but poor correlation with E HOMO, E LUMO and (E LUMO − E HOMO) in presence of polar compounds. E HOMO and E LUMO values are affected by polarity and can be used along with Log(K ow) and 1 χ v for generating better predictive models. [Copyright &y& Elsevier]

Abstract: Evaluation of biological effects using a rapid, sensitive and cost effective method can indicate specific information on toxicity/ecotoxicity. Since assays based on animals, plants and algae are expensive, time consuming and require large sample volume, recent studies have emphasized the benefits of rapid, reproducible and cost effective bacterial assays for toxicity screening and assessment. This review focuses on a bacterial assay, i.e., Vibrio fischeri bioluminescence inhibition assay, which is often chosen as the first test in a test battery based on speed and cost consideration. The test protocol is simple and was originally applied for aqueous phase samples or extracts. The versatility of the assay has increased with subsequent modification, i.e., the kinetic assay for turbid and colored samples and the solid phase test for analyzing sediment toxicity. Researchers have reported the Vibrio fischeri bioluminescence assay as the most sensitive across a wide range of chemicals compared to other bacterial assays such as nitrification inhibition, respirometry, ATP luminescence and enzyme inhibition. This assay shows good correlations with other standard acute toxicity assays and is reported to detect toxicity across a wide spectrum of toxicants. [Copyright &y& Elsevier]