铅锌冶炼区农田土壤中多环芳烃污染特征、源解析和风险评价

采用快速溶剂萃取(ASE)、凝胶渗透色谱净化(GPC)协同高效液相色谱(HPLC)检测方法,分析贵州省典型铅锌冶炼区赫章县41个表层农田土壤样品中16种优控多环芳烃(PAHs)的含量水平,并对其污染特征、来源和生态风险进行了分析.结果表明:典型铅锌冶炼区妈姑镇农田土壤∑PAHs的含量范围为196~11592μg·kg~(-1),算术均值和中位值分别为1500μg·kg~(-1)和780μg·kg~(-1),妈姑镇高含量的∑PAHs积累可能与当地长时间的铅锌冶炼活动有关.PAHs组分特征表现出以2~3环和4环多环芳烃为主.根据荷兰土壤干预值,妈姑镇农田土壤96.6%受到了不同程度的污染,其中,轻微污染、中度污染和重度污染所占比例分别为31.0%、24.1%和41.5%.研究区域PAHs的主要来源为煤和生物质的不完全燃烧及石油源.妈姑镇的新厂村、何家冲村、平桥组、拱桥村及赫章县的达依乡采样点土壤中PAHs的TEQBap10超过了荷兰土壤干预值规定的TEQBap10限值33.0μg·kg~(-1),说明赫章县、尤其是赫章县典型铅锌冶炼区妈姑镇农田土壤已受到PAHs的污染,存在潜在的生态风险.     

Physiological and biochemical characteristic of Miscanthus × giganteus grown in heavy metal – oil sludge co-contaminated soil

The effect of oil sludge and zinc, present in soil both separately and as a mixture on the physiological and biochemical parameters of Miscanthus × giganteus plant was examined in a pot experiment. The opposite effect of pollutants on the accumulation of plant biomass was established: in comparison with uncontaminated control the oil sludge increased, and Zn reduced the root and shoot biomass. Oil sludge had an inhibitory effect on the plant photosynthetic apparatus, which intensified in the presence of Zn. The specific antioxidant response of M. × giganteus to the presence of both pollutants was a marked increase in the activity of superoxide dismutase (mostly owing to oil sludge) and glutathione-S-transferase (mostly owing to zinc) in the shoots. The participation of glutathione-S-transferase in the detoxification of both the organic and the inorganic pollutants was assumed. Zn inhibited the activity of laccase-like oxidase, whereas oil sludge promoted laccase and ascorbate oxidase activities. This finding suggests that these enzymes play a part in the oxidative detoxification of the organic pollutаnt. With both pollutants used jointly, Zn accumulation in the roots increased 6-fold, leading to increase in the efficiency of soil clean-up from the metal. In turn, Zn did not significantly affect the soil clean-up from oil sludge. This study shows for the first time the effect of co-contamination of soil with oil sludge and Zn on the physiological and biochemical characteristics of the bioenergetic plant M. × giganteus. The data obtained are important for understanding the mechanisms of phytoremediation with this plant.     

Coprecipitation mechanisms of Zn by birnessite formation and its mineralogy under neutral pH conditions

Birnessite (δ-Mn(IV)O₂) is a great manganese (Mn) adsorbent for dissolved divalent metals. In this study, we investigated the coprecipitation mechanism of δ-MnO₂ in the presence of Zn(II) and an oxidizing agent (sodium hypochlorite) under two neutral pH values (6.0 and 7.5). The mineralogical characteristics and Zn–Mn mixed products were compared with simple surface complexation by adsorption modeling and structural analysis. Batch coprecipitation experiments at different Zn/Mn molar ratios showed a Langmuir-type isotherm at pH 6.0, which was similar to the result of adsorption experiments at pH 6.0 and 7.5. X-ray diffraction and X-ray absorption fine structure analysis revealed triple-corner-sharing inner-sphere complexation on the vacant sites was the dominant Zn sorption mechanism on δ-MnO₂ under these experimental conditions. A coprecipitation experiment at pH 6.0 produced some hetaerolite (ZnMn(III)₂O₄) and manganite (γ-Mn(III)OOH), but only at low Zn/Mn molar ratios (< 1). These secondary precipitates disappeared because of crystal dissolution at higher Zn/Mn molar ratios because they were thermodynamically unstable. Woodruffite (ZnMn(IV)₃O₇•2H₂O) was produced in the coprecipitation experiment at pH 7.5 with a high Zn/Mn molar ratio of 5. This resulted in a Brunauer–Emmett–Teller (BET)-type sorption isotherm, in which formation was explained by transformation of the crystalline structure of δ-MnO₂ to a tunnel structure. Our experiments demonstrate that abiotic coprecipitation reactions can induce Zn–Mn compound formation on the δ-MnO₂ surface, and that the pH is an important controlling factor for the crystalline structures and thermodynamic stabilities.