Toxicity Of Halogenated Aromatic Hydrocarbons To Scenedesmus Obliquus And The QSAR Study

Halogenated aromatic hydrocarbons have been widely used in chemical industry as dyes, pesticides and so on, and consequently have a high potential to become environmental pollutants. These compounds have affected the growth of living beings and the health of people.48h acute toxicity and 8d chronic toxicity were determined by using Scenedesmus obliquus as tested organism. By using cell number and oxygen produced by photosynthesis as test endpoints separately, logarithms of the inverse median effective inhibition concentration after 48 h and 8 d, expressed as -lgEC_50(48h) and -lgEC_50(8d), were obtained from responsible concentration-effect curves. The values of-lgEC_50(48h) ranged from 2.61 for aniline to 4.57 forα-naphthol, and the values of -lgEC_50(8d) from 2.75 aniline to 4.76 forα-naphthol. The toxicity of halogenated aromatic hydrocarbons on Scenedesmus obliquus were affected by the substituents' kinds, quantity and position.The octanol/water partition coefficients(lgP) of 21 compounds were computed by Biobyte software. The electronic and spatial parameters were calculated by the Chem Office 2004 program. Various steps valence molecular connectivity index of 21 compounds were calculated according to their definition.Based on the experimental data and the structural parameters obtained, four methods were used to develop quantitative structure-activity relationship(QSAR) models for acute and chronic toxicity by using SPSS10.0 for windows software, including the octanol/water coefficients method, the quantum chemistry method, the molecular connectivity index method and the group contribution method. A series of models were obtained. These models were found to fit well.The acute and chronic toxicity of halogenated aromatic hydrocarbons on Scenedesmus obliquus were described by using the energy gap of molecular orbitals(ΔE) and lgP. Two models were obtained, for acute toxicity(R²=0.880), and for chronic toxicity(R²=0.892). The results showed the hydrophobicity and electrical parameters of the chemicals studied are important factors affecting toxicity.By using the molecular connectivity index method, two QSAR models were obtained, for acute toxicity(R²=0.938) and for chronic toxicity(R²=0.958). It is shown that the toxicity of chemicals was mainly related to the volume of molecular and the kinds, lengths, spatial structures of substituted groups and so on.By applying the group contribution method, two models were developed successfully. The toxicity contribution order of substituted groups was obtained:[C₆H_m]＞[NO₂]＞[B_r]＞[Cl]＞[CH₃]＞[OH]＞[NH_n].