In soil ecosystems, chemicals are often found as mixtures. Therefore, the toxicity data generated by single toxicity tests are inadequate for assessing the potential risk of complex mixtures of chemicals for soil ecosystems. In the present study, the mixture toxicity of copper and manganese on the reproduction of Paronychiurus kimi were assessed using a Toxic Unit approach (1TU=EC50). The concentrations of each metal in the mixture were summed as follows: TUmixture = CCu/EC50 of Cu + CMn/EC50 of Mn, where CMetal are the concentrations of copper and manganese in the mixture. From the Sum TU based dose-response relationships, sum of a toxicunit (TU50) at 50% reduction for the mixture (EC50mix) was calculated. The binary mixture toxicity was defined as being concentration additiv (EC50mix=1TU) or as being more or less than additive (EC50mix<1TU or 1>TU, respectively). Also, values of the mixture (TUi) at i% reduction found were predicted to get more insight regarding the relationship between mixture toxicity and various effect levels (ranging from EC10 to EC90). The toxicities of copper and manganese mixtures were less than additive at the EC10 level, whereas more than additive at the EC90 level. These findings imply that the effect levels are important for determining the toxicity of metal mixtures.

In this study, the effects of single and binary heavy metals toxicity on the growth and phosphorus removal ability of Bacillus sp.. known as be a phosphorus-removing microorganism, were quantitatively evaluated. Cd, Cu, Zn, Pb, Ni were used as heavy metals. As a result of analysis of variance of the half of inhibition concentration and half of effective concentration for each single heavy metal treatment group, the inhibitory effect on the growth of Bacillus sp. was Ni < P b < Z n < Cu < C d. A nd the inhibitory effect on phosphorus removal by Bacillus s p. w as N i < Pb < Z n < Cu < C d. When analyzing the correlation between growth inhibition and phosphorus removal efficiency of a single heavy metal treatment group, a negative correlation was found (R2 = 0.815), and a positive correlation was found when the correlation between IC50 and EC50 was analyzed (R2 = 0.959). In all binary heavy metal treatment groups, the interaction was an antagonistic effect when evaluated using the additive toxicity index method. This paper is considered to be basic data on the toxic effects of heavy metals when phosphorus is removed using phosphorus removal microorganisms in wastewater.

The objective of this research was to evaluate the toxicity of the industial xenobiotic Aroclor 1248 (A) and natural origin substances~elemental sulfur (S80) and oleic acid (OA) and their binary mixtures to V. fischeri bioluminescence during the prolonged exposure time (up to 60 min). The bioluminescence quenching test was used to determine the toxic effects. Full factorial experiment design and multiple regression analysis and the comparison of binary mixture effect with the sum of effects of individual chemicals were used for the evaluation of combined effects of toxicants. The analysis of general trend of mixture toxicity to bioluminescence showed that mixture toxic effects were reversible up to 60 min. Data analysis revealed different joint effects, which were depended on mixture composition. S80 enhanced toxic effect of A and acted additively with synergistic interaction. Hydrophobic OA in mixture with A acted antagonistically and in mixture with sulfur caused an additive effect with antagonistic component of interaction. It was concluded that low concentrations of natural toxic substances present in environmental samples as mixtures of chemicals can define the toxicodynamic character of industrial xenobiotics.