Shiwei Ai

Spatial distribution and source identification of heavy metals in soils under different land uses in a sewage irrigation region, northwest China

PurposeHeavy metal pollution is of major concern due to its potential threat to ecosystem safety and human health. To give a valuable insight into the status of heavy metal pollution in a sewage irrigation region in northwest China, this paper thoroughly studied the spatial distribution and possible source of heavy metals in soils under different land uses.Materials and methodsSoil samples were collected from arable lands (maize field, orchard, and paddy field) and nonarable lands (village and barren hill) from a sewage irrigation region, northwest China. The concentrations of Cd, Cr, Cu, Mn, Ni, Pb, and Zn in the soils, together with soil pH, soil organic matter (SOM), and soil particle size distribution, were detected. GIS-based approach was employed to construct the spatial distribution maps of heavy metals, and multivariate analysis was used to identify their possible source.Results and discussionAlthough elevated concentrations of Zn, Pb, and Cu are detected, Cd is the priority pollutant in the soils. Land use, location, and SOM are crucial factors affecting metal distribution in the soils. Metal concentrations in different land uses arrange in the order of orchard > paddy field/maize field > village > barren hill. The area within the basin of Dongdagou stream presents the most pollution, whereas the northeast side far from the stream is the least. Irrigation water both from Dongdagou stream and the Yellow River are deemed as primary sources of Cd, Zn, Pb, and Cu. Besides, agrichemical application particularly contributes to metal accumulation in orchard soils, and Cd and Zn partially derive from atmospheric deposition. Nickel and Mn predominately originate from the soils.ConclusionsWhen studying metal pollution in soils, land use should be taken into account because of its important roles in determining metal concentrations. In the study area, arable lands are more likely to be polluted by Cd, Zn, Pb, and Cu than nonarable lands via sewage irrigation; moreover, agrichemical application and atmospheric deposition also should be held responsible for metal accumulation in the soils.

Assessment of the bioavailability, bioaccessibility and transfer of heavy metals in the soil-grain-human systems near a mining and smelting area in NW China

Elucidating the transfer behaviour of heavy metals from soils to grains and ultimately to humans is of great significance for both human health risk assessment and pollution control. In this study, the bioavailability of heavy metals (Cd, Cu, Pb, Zn, Cr and Ni) in farmland soils and bioaccessibility in grains (spring wheat, maize and rice) were determined to elaborate transfer dynamics in the soil-grain-human systems near a mining and smelting area in the Dongdagou watershed, Baiyin district, Gansu province, NW China. The results showed that Cd, Cu, Pb and Zn concentrations in soils were elevated compared to background levels, while Cr and Ni concentrations were relatively low throughout the region. High levels of bioavailable soil Cd were found using both EDTA and CH3COOH extraction methods. Mean concentrations of Cd, Pb and Zn in spring wheat grains and the Cd and Cr concentrations in maize grains exceeded the relevant maximum levels for pollutants according to the Chinese national standards for food safety. Except for Ni (41.90%) and Pb (31.39%), heavy metal bioaccessibility was relatively low in grains, ranging from 10.80% (Cd) to 17.18% (Zn). CH3COOH-extracted Cd, Pb and Ni, EDTA-extracted Zn, and total Cu in soils were the best indices for evaluation of uptake in grains (R2=0.54-0.91, p<0.001). Internal exposure doses of Cd and Ni in humans from spring wheat grain consumption was predicted by the linear correlations between bioaccessible and total metal concentrations (R2=0.61 and 0.67; p<0.001). The results from this study provide sufficient data and theoretical support for the use of these methods for local pollution prevention and control.

A field study on the dynamic uptake and transfer of heavy metals in Chinese cabbage and radish in weak alkaline soils

Vegetables and crops can take up heavy metals when grown on polluted lands. The concentrations and dynamic uptake of heavy metals vary at different growth points for different vegetables. In order to assess the safe consumption of vegetables in weak alkaline farmlands, Chinese cabbage and radish were planted on the farmlands of Baiyin (polluted site) and Liujiaxia (relatively unpolluted site). Firstly, the growth processes of two vegetables were recorded. The growth curves of the two vegetables observed a slow growth at the beginning, an exponential growth period, and a plateau towards the end. Maximum concentrations of copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd) were presented at the slow growth period and showed a downtrend except the radish shoot. The concentrations of heavy metals (Cu, Zn, and Cd) in vegetables of Baiyin were higher than those of Liujiaxia. In the meanwhile, the uptake contents continued to increase during the growth or halted at maximum at a certain stage. The maximum uptake rates were found on the maturity except for the shoot of radish which took place at the exponential growth stages of root. The sigmoid model could simulate the dynamic processes of growth and heavy metals uptake of Chinese cabbage and radish. Conclusively, heavy metals have higher bioaccumulation tendency for roots in Chinese cabbage and for shoots in radish.

Long-term heavy metal pollution varied female reproduction investment in free-living anura, Bufo raddei

Environment contamination is known to affect the growth, reproduction, and even mortality of anuran species, and hence modulate their life history traits. Although knowledge of the ability of amphibians to cope with harsh environments has gained ongoing research, the reproductive strategy of free-living amphibians subjected to long-term heavy metal pollution is largely unknown. This study aimed to explore the variation in the life history traits, including age structure, maturation age, reproductive investment, and reproduction trade-off, in female Bufo raddei, a widespread anuran in Baiyin (BY) in northwest of China, subjected to sublethal heavy metal pollution. B. raddei collected from Liujiaxia (LJX), a relatively unpolluted area, were used as control. Skeletochronological analysis revealed variation in the average breeding age of females: more than 70% of females from BY began to breed 1 year before the toads collected from LJX. Females from BY tended to prioritize reproduction over survival and invested more in their first reproductive event. Further, females in BY with a high fluctuating asymmetry index showed a relatively lower reproductive investment. For trade-off in offspring number and size, BY population optimize larger clutch sizes with smaller egg size compared with population in LJX. Changes in female reproductive investment caused by heavy metal pollution might ultimately alter the structural stability of amphibian population.

A field study on heavy metals phytoattenuation potential of monocropping and intercropping of maize and/or legumes in weakly alkaline soils

ABSTRACT The study focused on the phytoattenuation effects of monocropping and intercropping of maize (Zea mays) and/or legumes on Cu, Zn, Pb, and Cd in weakly alkaline soils. Nine growth stages of monocropping maize were chosen to study the dynamic process of extraction of heavy metals. The total content of heavy metals extracted by the aerial part of monocropped maize increased in a sigmoidal pattern over the effective accumulative temperature. The biggest biomass, highest extraction content, and lowest heavy metals bioaccumulation level occurred at physiological maturity. Among the different planting patterns, including monocropping and intercropping of maize and/or soybean (Glycine max), pea (Pisum sativum), and alfalfa (Medicago sativa), the extraction efficiency of Cu, Zn, Pb, and Cd varied greatly. Only intercropping of maize and soybean yielded relatively higher extraction efficiency for the four metals with no significant difference in the total biomass. Moreover, the heavy metals concentrations in dry biomass from all the planting patterns in the present study were within Chinas national legal thresholds for fodder use. Therefore, slightly polluted alkaline soils can be safely used through monocropping and intercropping of maize and/or legumes for a range of purposes. In particular, this study indicated that intercropping improves soil ecosystems polluted by heavy metals compared with monocropping.

Sperm Morphology and Motility of Bufo raddei Under Long-Term Environmental Heavy Metal Stress

The present study aimed to investigate the effects of environmental heavy metals on sperm morphology and motility of Bufo raddei. We collected B. raddei from Baiyin (BY) and Liujiaxia (LJX); BY is an area heavily polluted by heavy metals, while LJX is a relatively unpolluted area. Significant accumulations of copper, zinc, lead and cadmium were observed in B. raddei from BY, together with relatively smaller sperm size and higher sperm abnormality rate. Unexpectedly, sperm velocity, percentages of sperm motility and viability of B. raddei from BY were significantly higher than those from LJX. Similarly, when sperm was suspended in heavy metal solutions, sperm velocity, percentages of sperm motility and viability significantly increased compared with those suspended in distilled water. These results indicate that environmental heavy metal stress may decrease sperm size, meanwhile enhance sperm motility through increasing the ratio of head length to total sperm length of B. raddei.