Modeling and prediction for the acute toxicity of pesticide mixtures to the freshwater luminescent bacterium Vibrio qinghaiensis sp.-Q67

In China, water pollution by pesticide mixtures has constituted a serious environmental problem due to potential toxicity and bioaccumulation. But few pesticide combinations have exactly similar and dissimilar mechanisms of action. For this purpose, in tests with the freshwater luminescent bacterium （Vibrio qinghaiensis sp.-Q67）, ten pesticides, including three herbicides and seven insecticides, were selected as test substances. Concentration response analysis was performed for ten individual substances, and for mixtures containing all ten substances in twelve different concentration ratios （based on UDCR and EECR methods）. The observed mixture toxicity was compared with predictions by the two models, concentration addition （CA） and independent action （IA）. The toxicity of the tested mixtures showed a good agreement with those predicted by the concept of CA except four UDCR mixtures： UD10-2, UD10-4, UD10-8 and UD10-10. To examine the influence of imidacloprid in the four UDCR mixtures （UD10-2, UD10-4, UD10-8, UD10-10）, it was removed from the ten-pesticide mixtures and the remaining nine chemicals were combined at the same relative proportions based on the UDCR method （UD9-2, UD9-4, UD9-8, UD9-10）. There was not significant departure from CA for the scattered points with the nine remaining pesticides omitting imidacloprid. Thus, imidacloprid may significantly influence the other pesticides due to its properties.

Toxicity Measurement of Halogeno-benzene against Vibrio Qinghaiensis (Q67) and Their 2D,3D-QSAR Study

Toxicities （–lgEC50） of 16 halogeno-benzenes against vibrio qinghaiensis （Q67） were measured systematically, and their 2D-QSAR model （R2=0.875, q2=0.821） was established, which included two parameters： averaged polarizability （α） and total energy （TE）. The proposed model indicated that the toxicities of this kind of compounds were proportionate to α, i.e., their toxicities were relative to the molecular volume. Furthermore, 3D-QSAR model （R2=0.929, q2=0.712） of –lgEC50 was proposed by using comparative molecular force field （CoMFA） based on the molecular simulation. To our interest, 3D-QSAR model suggested that the hydrophobicity of substituents was the dominating factor for the toxicities, the electrostatic effect was the secondly important, and the steric field gave the least contribution. Comparably, the prediction ability of the 3D-QSAR model is slightly more advantageous than that of 2D-QSAR, and they can be used complementally in the toxicity description of this kind of compounds.

Toxicity (-lgEC_(50)) Measurement of the Fluorobenzene Derivants against Vibrio Qinghaiensis (Q67) and Their 2D,3D-QSAR Study

Toxicities （-lgEC50） of 16 fluorobenzene derivants against vibrio qinghaiensis （Q67） were measured systematically,and their quantum chemistry parameters were calculated at the B3LYP/6-311G＊＊ level. Based on the experimental toxicity data and quantum chemistry parameters,2D-QSAR model was proposed,which was validated by variance inflation factors （VIF）,t-value and cross-validation method. At the mean time,comparative molecular force field （CoMFA） based on molecular simulation was used to investigate the toxicity of fluorobenzene derivants. Furthermore,the intoxicating mechanism of fluorobenzene derivants was discussed. To our interest,2D-QSAR and CoMFA models exhibit good prediction ability,with which the toxicity of similar compounds can be predicted. Finally,toxicities （-lgEC50） of 12 fluorobenzene derivants against vibrio qinghaiensis （Q67） were predicted with these models.

Leaching toxicity characteristics of municipal solid waste incineration bottom ash

The continuously increasing production of municipal solid waste incineration bottom ash （MSWIBA） has promoted its utilization as construction material and raised environmental concern. The physico-chemical properties and leaching behavior of MSWIBA were studied, and ecotoxicological testing using a luminescent bacterium bioassay was performed to assess the ecological pollution risks associated with its leached constituents. The MSWIBA was leached by two types of leachants, H2SO4/HNO3 and HAc solution, at different liquid to solid ratios and contact times. The concentrations of heavy metals and anions in the leachates were analyzed. Multi- variate statistical analyses, including principle component analysis, Pearson＇s correlation analysis and hierarchical cluster analysis, were used to evaluate the contributions of the constituents to the toxicity （ECso） of the MSWIBA leachate. The statistical analyses of the ecotoxicological results showed that the Ba, Cr, Cu, Pb, F and total organic carbon （TOC） concentrations were closely correlated with the ECso value, and these substances were the main contributors to the ecotoxicity of the MSWIBA leachate. In addition, the cluster of these variables indicated similar leaching behaviors. Overall, the research demonstrated that the ecotoxicological risks resulting from MSWIBA leaching could be assessed before its utilization, which provides crucial information for the adaptation of MSWIBA as alternative materials.