Analysis and assessment of heavy metals pollution in soils around a Pb and Zn smelter in Baoji City,Northwest China

Soil heavy metal pollution from mining activities is potentially harmful to human health through the food chain. In this study, a total of 43 soil samples were collected from a depth of 0–20 cm from fields close to a Pb and Zn smelter. The samples were used to: 1) analyze the pollution level of heavy metals (Pb, Zn, Cr, and Cu) and spatial distribution pattern; 2) evaluate the degree of accumulation and enrichment, potential ecological risk, and human health risk; and 3) perform source apportionment in Fengxiang County, Shaanxi Province of China. The results showed that the concentration ranged from 43.67 to 189.55, 131.43 to 239.53, 74.77 to 112.25, and 24.69 to 37.71 mg·kg^?1 for Pb, Zn, Cr, and Cu, respectively, and the mean concentration for Pb, Zn, Cr, and Cu was 129.46, 192.85, 91.98 and 31.67 mg·kg^?1, respectively. The concentrations were greater than the Shaanxi Province background values, while they were lower than the second-level limits of Environmental Quality Standard for Soils of China (EQSS). The spatial distribution of heavy metal contents showed a banded in soil except Cu. The spatial distribution pattern and pollution assessment indexes (I_geo, EF) indicated that the investigated metals had been accumulated in the study areas, and implied significant influences from anthropogenic activities, local meteorological situation, and soil properties. The ecological risk assessment showed that the risks were relatively low (RI<150). Compared with the exposure risk for adults, that for children was significantly greater. The ingestion of heavy metals in the soils by humans was the main exposure pathway compared with the dermal exposure. There may be a risk of noncarcinogenic adverse health effects (HQ < 1, 0.377 ≤ HI≤1.553) on children, but the adults were unlikely to experience obvious adverse health effects (HQ < 1, HI < 1). The carcinogenic risk of Cr for adults and children was at an unacceptable level. The carcinogenic and noncarcinogenic risks were in the order of children > adults. The correlation analysis showed that Pb, Cr, and Cu have identical anthropogenic and natural sources, while Zn has another identical source. This study could provide a basis for the sustainable management of this region by reducing metal inputs and to protect soils from long-term heavy metal accumulation.     

Computational study on the structural and optoelectronic properties of a carbazole-benzothiadiazole based conjugated oligomer with various alkyl side-chain lengths

The effect of the alkyl side-chain length on the structural and optoelectronic properties of poly[N-9′-heptadecanyl-27-carbazole-alt-55-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) conjugated oligomers have been studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The study was carried out by varying the length of alkyl side-chain attached to the nitrogen atom of the carbazole unit of the PCDTBT oligomers. The structural properties of the optimised oligomers were then studied by determining the bond-length alternation and dihedral angles (Φ) for various side-chain lengths. Total energy calculations for the determination of HOMO energy (E_HOMO), LUMO energy (E_LUMO), and fundamental energy gap (E_Gap) were performed using DFT at the B3LYP/6-31G(d), while the first singlet excitation energies (E_Opt) were calculated by TD-DFT also at the same level of theory. It was observed that there are no significant structural changes occurring as the alkyl chain lengths are varied. For the electronic properties, very small differences (i.e. ~0.01 eV) were observed for E_Gap and E_Opt while the exciton binding energies (E_B) were virtually the same. The results suggest that using shorter alkyl side-chains do not significantly affect the structural and optoelectronic properties of the carbazole-benzothiadiazole based polymer. The observations can aid future computational design studies of analogous systems by reducing large structures thus decreasing computational costs.     

Plant and soil intake by organic broilers reared in tree- or grass-covered plots as determined by means of n-alkanes and of acid-insoluble ash

Free-range birds such as organic broilers may ingest soil and plants during exploration. The estimation of such intakes is of great interest to quantify possible nutritional supplies and also to evaluate the risk of exposure to parasites or to environmental contaminants. Marker-based techniques are now available and would allow to quantify plant and, especially, soil intake in free-range birds, and this quantification was the aim of this study. Methodologically, the proportion of plants in diet intake was determined first using a method based on n-alkanes. Subsequently, the fraction of soil in the total intake was estimated with a second marker, acid-insoluble ash. This approach was carried out to estimate ingested amounts of plants and soil for five successive flocks of organic broilers, exploring grass-covered yards or those under trees, at two time points for each yard: 51 and 64 days of age. Each factor combination (yard type×period=flock number×age) was repeated on two different yards of 750 broilers each.The birds’ plant intake varied widely, especially on grass-covered yards. The proportion of plant intake was significantly higher on grass-covered plots than under trees and was also affected, but to a lesser extent, by age or flock number. The ingestion of plants would generally not exceed 11 g of DM daily, except two extreme outliers of nearly 30 g. The daily plant intake under trees tended to be lower and never exceeded 7 g of DM. The amount of ingested plants increased significantly for spring flocks. It increased slightly but significantly with age. The proportion of ingested soil was significantly higher under trees than on grass-covered yards. Dry soil intake was generally low with not more than 3 g per day. Only in adverse conditions – that is, older birds exploring yards under trees in winter – soil intake reached the extreme value of nearly 5 g. Broilers on yards under trees ingested significantly more soil than on grass-covered yards with least square means of, respectively, 2.1 and 1.1 g dry soil per day. These quantifications would allow us to evaluate the impact of plant and soil intake in the management of free-range broilers, especially for the management in organic farming systems. Nevertheless, under the two rearing conditions tested in the current study, the quite low proportions of soil intakes would represent a low risk for the safety of the produced food, unless the birds explore yards on heavily contaminated soil.     

Change of liver metabolism of 1,2-dibromoethane during simultaneous treatment with carbon tetrachloride

The combination of carbon tetrachloride (CCl₄) and 1,2-dibromoethane (DBE) in isolated rat hepatocytes led to a significant potentiation of both lipid peroxidation and of plasma membrane damage observed after a single treatment with CCl₄. Such a synergistic effect appeared to be related to the CCl₄-induced shift of DBE metabolism from the cytosolic conjugation with glutathione towards the microsomal transformation into toxic intermediates. In fact, CCl₄ significantly inactivated hepatocyte total GSH-transferase, i.e. the DBE detoxification pathway. Furthermore, while the microsomal metabolism of CCl₄ was not affected by the simultaneous presence of DBE, the amount of DBE reactive metabolities covalently bound to hepatocyte protein was significantly enhanced in the presence of CCl₄.     

Aphid Herbivory Drives Asymmetry in Carbon for Nutrient Exchange between Plants and an Arbuscular Mycorrhizal Fungus

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