Study On Ecotoxicological Effects Of Chromium(Ⅵ) And Phenanthrene Combined Pollution On Soil Biont And Its Hazard Assessment Methods

With the rapid development of industrial production, all kinds of pollutants are released into the soil environment through various channels and coexist, which caused serious soil pollution.Among this, heavy metals and polycyclic aromatic hydrocarbons are two kinds of the main pollutants. Although these substances content is not high in the farmland, but in some contaminated sites, especially in industrial pollution area, the concentrations of heavy metals and polycyclic aromatic hydrocarbons are high. Now, most of the soil ecotoxicological research are focused on pesticides and heavy metal toxicity, rather than the chemical pollutants found in the industrial sites. On the other hand, most toxicology studies are focused on environmental toxicity effect of the single substance, which can’t reflect the joint effect of a variety of pollutants existed in soils. The reports about the joint effect of heavy metals and polycyclic aromatic hydrocarbons on soil biont are infrequent.Hence, in this study, higher plants, soil invertebrates and soil microbial enzyme were used as test experimental object to study the ecotoxicological effects of the single and combined pollution of chromium(VI)and phenanthrene, and their hazardous property. The localization model biont and biomarkers were selected in the biological toxicity research. The tested methods were improved according to the higher plant test and earthworm acute toxicity test listed in the OECD and soil enzyme test methods recorded in the literature. Different combination evaluation methods were chosen according to the characteristics of plants, animals and microbical enzymes. Suitable biological hazards classification evaluation methods for this study were put forward with referencing to relevant hazards evaluation methods. The results are showed as follows:1. The EC20 of chromium(VI)on stem length of mung beans, pterocladia tenuis and rice were 289.08 mg·kg-1, 247.93 mg·kg-1 and 549.93 mg·kg-1 and the EC20 of chromium(VI)on fresh weight of mung beans, pterocladia tenuis and rice were 334.49 mg·kg-1, 307.21 mg·kg-1 and550.92 mg·kg-1.The EC20 of phenanthrene on stem length of mung beans, pterocladia tenuis and rice were527.76 mg·kg-1, 425.57 mg·kg-1 and 628.03 mg·kg-1 and the EC20 of phenanthrene on fresh weight of mung beans, pterocladia tenuis and rice were 527.76 mg·kg-1, 425.57 mg·kg-1 and 628.03mg·kg-1.The EC20 of combined chromium(VI)and phenanthrene at the concentration ratio of 1:1 on stem length of mung beans, pterocladia tenuis and rice were 384.84 mg·kg-1, 346.56 mg·kg-1 and558.56 mg·kg-1;and 400.52 mg·kg-1, 410.92 mg·kg-1and 542.64 mg·kg-1 on fresh weight of mung beans, pterocladia tenuis and rice.Pterocladia tenuis was more sensitive than mung beans and rice at the pollution of chromium(VI)and phenanthrene.According to the additive index method, the combined effect of chromium( VI) and phenanthrene on the stem length and fresh weight overground of both mung beans and rice was synergy, while, antagonism on pterocladia tenuis.2. The 7 d-LC50 and 14 d-LC50 of chromium(VI)on Eisenia foetida were 259.98 mg·kg-1and241.13 mg·kg-1, respectively, and the 7 d-LC50 and 14 d-LC50 of phenanthrene on Eisenia foetida were 88.01 mg·kg-1 and 60.96 mg·kg-1.The 7 d-LC50 and 14 d-LC50 of chromium(VI)on Fridericia bulbosa were 24.33 mg·kg-1and21.43 mg·kg-1, respectively, and the 7 d-LC50 and 14 d-LC50 of phenanthrene on Fridericia bulbosa were 4.20 mg·kg-1 and 3.71 mg·kg-1.The 7 d-LC50 and 14 d-LC50 of combined chromium( VI) and phenanthrene at the concentration ratio of 4:1 on Eisenia foetida were 189.66 mg·kg-1 and 172.11 mg·kg-1; and the 7d-LC50 and 14 d-LC50 of their combined exposure at the concentration ratio of 6:1 on Fridericia bulbosa were 23.90 mg·kg-1 and 18.89 mg·kg-1.Fridericia bulbosa was more sensitive to the pollution of chromium(VI)and phenanthrene than Eisenia foetida.The combined effect of chromium(VI)and phenanthrene on Eisenia foetida were addition according to isobologram, but antagonism on Fridericia bulbosa.3. The EC10 and EC20 of chromium(VI)on soil catalase were 203.61mg·kg-1and 471.48mg·kg-1; the EC10 and EC20 of phenanthrene on soil catalase were 299.89 mg·kg-1 and more than800.00 mg·kg-1.The EC10 and EC20 of chromium(VI)on soil dehydrogenase were less than 50.00 mg·kg-1;the EC10 and EC20 of phenanthrene on soil dehydrogenase were 113.43 mg·kg-1and 223.49mg·kg-1.The EC10 and EC20 of combined chromium(VI)and phenanthrene at the concentration ratioof 1:1 on soil catalase were 116.14 mg·kg-1 and 349.28 mg·kg-1; and the EC10 and EC20 of their combined exposure at the concentration ratio of 1:1 on soil catalase were both less than 100.00mg·kg-1.Soil dehydrogenase was more sensitive to the pollution of chromium(VI)and phenanthrene than soil catalase.The combined effect of chromium(VI)and phenanthrene on both soil catalase and soil dehydrogenase were antagonism.4. The hazardous classification of single and combined pollution of chromium(VI)and phenanthrene on mung beans, pterocladia tenuis and rice was all low toxicity.The hazardous classification of chromium(VI)on Eisenia foetida was low toxicity, while medium toxicity on Fridericia bulbosa. The hazardous classification of phenanthrene on Eisenia foetida was medium toxicity, while higher toxicity on Fridericia bulbosa. The combined toxicity of chromium(VI)and phenanthrene on Eisenia foetida was low toxicity, while medium toxicity on Fridericia bulbosa.The hazardous classification of single and combined pollution of chromium( VI) and phenanthrene on soil catalase was low toxicity, while medium toxicity on soil dehydrogenase.