Baoqing Shan

Historical records of heavy metal accumulation in sediments and the relationship with agricultural intensification in the Yangtze–Huaihe region, China

The extensive use of fertilizers on farmlands during the past several decades in China has led to a rapid deterioration of environmental water quality in recent years. An agricultural watershed with high-yield grain production and characterized by multipond systems in the Yangtze-Huaihe region of China was selected to establish the historic records of heavy metal pollution by (137)Cs-dated sediment cores. The experimental results indicated that the contents of most of the heavy metals investigated, such as Cd, Cr, Cu, Ni, Pb, and Zn, continuously increased in the multipond sediments throughout the past three decades. An inflection point appeared in the 1980s, prior to which all heavy metal contents showed little or no increase with time. Thereafter, the heavy metal contents increased dramatically due to the extensive application of phosphate fertilizers. The mean Cd content in 1980 was 0.13 microg/g which increased rapidly to 0.33 microg/g in 2004, but prior to 1980, the level was only 0.08 microg/g. Similar trends were also found for other heavy metals. The enrichment factor (EF) values indicated that Cd was not only the most anthropogenic metal in the multipond sediments but also aggravated anthropogenic impacts on the watershed environment during the past two decades. The high proportion of chemical reactive forms of Cd (10%-30%) implied a moderately high ecological risk. Our results clearly reveal that the extensive use of fertilizers has resulted in significant heavy metal pollution in this watershed, which threatens the water quality of the watershed and downstream water bodies.

Heavy metal sources and associated risk in response to agricultural intensification in the estuarine sediments of Chaohu Lake Valley, East China

In this study, the source and risk associated with heavy metals in the estuarine sediments of Chaohu Lake Valley in East China were studied. The results demonstrated that most metal contents (Cd, Pb and Zn) increased continuously from 0.21, 8.05 and 73.76 mg/kg in the substrate to 0.33, 17.20 and 100.22 mg/kg in the surface sediments on average, respectively, in all ten estuaries evaluated. In addition, the high proportion of chemically reactive forms of Cd (18.10-33.60%) implied a moderately high risk, while the risk associated with Pb and Zn was moderate in most estuaries. Enrichment factor (EF) and cluster analysis (CA) were conducted to assess the metal sources. The EF values of Cd, Pb and Zn (4.96, 3.68 and 2.25, respectively) indicated that they had accumulated in the estuarine sediments. Additionally, CA suggested that their primary sources were anthropogenic, namely the extensive use of fertilizers. Therefore, heavy metal pollution due to agricultural intensification in Chaohu Lake Valley should be taken into account during the formation of valley management strategies for the water environment.

Fraction distribution and risk assessment of heavy metals in sediments of Moshui Lake

To examine the status and risk of heavy metal pollution in urban lakes, in China, the distribution of several heavy metals (e.g., Cr, Cu, Ni, Pb, Zn) in the sediment of Moshui Lake, Hangyang District, Wuhan City, was characterized. The process of rapid urbanization and industrialization of the district was also studied to find out its relationship with the metal accumulation profile in the sediment. It was found that the total concentration of heavy metals in the sediment was higher than the severe effect level (SEL), at all sampling sites, except those in the riparian zone. The Cr and Cu maximum concentrations were 1,780 and 1,250 mg/kg, approximately 16 and 11 times as much as the SEL values, and they appeared as deep as 32 cm in one sample. The carbonate and exchangeable fractions of Zn were more than 50% of the total Zn content, resulting in very high risk according to the Risk Assessment Code (RAC). For Cu and Ni, a medium RAC value was found for carbonate and exchangeable fractions of 11%-20%. As sensitive indicators of contaminants in aquatic systems, heavy metals in the sediment reflect the outcome of regional urbanization, industrialization, and environmental management. With rapid urbanization, sedimentary Pb and Zn concentrations increased. The experimental results showed that high sedimentary heavy metal concentrations had resulted from rapid urbanization and industrialization, which would absolutely lead to substantial aquatic environmental decline in urban lakes.

Heavy metal contamination of overlying waters and bed sediments of Haihe Basin in China.

The Haihe Basin is in an area of high population density and rapid economic development, and is one of the most polluted river basins in China. Examination of heavy metals (Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn) in overlying waters and surface sediments in rivers was conducted in the basins seven watersheds. Cd concentrations of overlying river waters exceeded Chinese environmental quality standard values for surface water (>0.010 mg/L) at 90% of stations. In surface river sediments, average concentrations of Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn in the basin were 0.364, 13.4, 81.9, 53.3, 435, 27.8, 20.0 and 256 mg/kg, respectively. Cd, Zn and Cu were the most anthropogenically enriched elements, as indicated by enrichment factor (EF) values>1.5; EF values were highest for these metals in the Zi Ya He (ZYH) and Zhang Wei He (ZWH) watersheds. Cd in surface river sediments showed a high potential ecological risk (PER) in the ZYH and ZWH watersheds. The comprehensive PER due to all studied metals was high at many stations, especially in the ZYH and ZWH watersheds. The results indicate that heavy metal contamination in the rivers of the Haihe Basin should be considered when developing basin management strategies for protecting the aquatic environment.

Heavy Metal Contamination in the Surface Sediments of Representative Limnetic Ecosystems in Eastern China

A comprehensive analysis of heavy metal pollution was conducted in the representative limnetic ecosystems of eastern China, which are subject to rapid economic development and population growth. The results demonstrated that the average contents with standard deviations of Cd, Cr, Cu, Ni, Pb and Zn in the surface sediments were 0.925 ± 0.936, 142 ± 46.8, 54.7 ± 29.1, 60.5 ± 21.6, 61.9 ± 36.0 and 192 ± 120 mg/kg dry wt., respectively, and that higher values were mainly observed in the southern portion of the study area, especially in the basins of Southeast Coastal Rivers (SCRB) and the Zhu River (ZRB). The six heavy metals in the surface sediments all had anthropogenic origins. In addition, the limnetic ecosystems, especially in the southern portion of the study area were found to be polluted by heavy metals, especially Cd. Overall, two hotspots of heavy metal pollution in the limnetic ecosystems of eastern China were found, one that consisted of the heavy pollution regions, SCRB and ZRB, and another composed of Cd pollution. These results indicate that heavy metal contamination, especially Cd, should be taken into account during development of management strategies to protect the aquatic environment in the limnetic ecosystems of eastern China, especially in the two aforementioned basins.

Size distribution and diffuse pollution impacts of PAHs in street dust in urban streams in the Yangtze River Delta

Particles of dust washed off streets by stormwater are an important pathway of polyaromatic hydrocarbons (PAHs) into urban streams. This article presented a comprehensive assessment of the size distribution of PAHs in street dust particles, the potential risks of the particles in urban streams, and the sources and sinks of PAHs in the stream network. This assessment was based on measurements of 16 PAHs from the USEPA priority list in street dust particles and river sediments in Xincheng, China. The content of total PAHs ranged from 1629 to 8986 microg/kg in street dust particles, where smaller particles have a higher concentrations. Approximately 55% of the total PAHs were associated with particles less than 250 microm which accounted for 40% of the total mass of street dust. The PAH quantities increased from 2.41 to 46.86 microg/m2 in the sequence of new residential, rising through main roads, old town residential, commercial and industrial areas. The sediments in stream reaches in town were found to be sinks for street dust particle PAHs. The research findings suggested that particle size, land use and the hydrological conditions in the stream network were the factors which most influenced the total loads of PAH in the receiving water bodies.

Pollutant loads of surface runoff in Wuhan City Zoo, an urban tourist area

The pollutant loads of surface runoff in an urban tourist area have been investigated for two years in the Wuhan City Zoo, China. Eight sampling sites, including two woodlands, three animal yards, two roofs and one road, were selected for sampling and study. The results indicate that pollutants ranked in a predictable order of decreasing load (e.g. animal yard > roof > woodland > road), with animal yards acting as the key pollution source in the zoo. Pollutants were transported mainly by particulate form in runoff. Particulate nitrogen and particulate phosphorous accounted on average for 61%, 78% of total pollutant, respectively, over 13 monitored rainfall events. These results indicate the treatment practices should be implemented to improve particulate nutrient removal. Analysis of the M(V) curve indicate that no first flush effect existed in the surface runoff from pervious areas (e.g. woodland, animal ground yard), whereas a first flush effect was evident in runoff from impervious surfaces (e.g. animal cement yard, roof, road).

Heavy metal concentrations and speciation in riverine sediments and the risks posed in three urban belts in the Haihe Basin

Heavy metal (Cr, Cu, Ni, Pb, and Zn) pollution and the risks posed by the heavy metals in riverine sediments in a mountainous urban-belt area (MB), a mountain-plain urban-belt area (MPB), and a plain urban-belt area (PB) in the Haihe Basin, China, were assessed. The enrichment factors indicated that the sediments were more polluted with Cu and Zn than with the other metals, especially in the MPB. The sediments in the MPB were strongly affected by Cu and Zn inputs from anthropogenic sources. The risk assessment codes and individual contamination factors showed that Zn was mobile and posed ecological risks, the exchangeable fractions being 21.1%, 21.2%, and 19.2% of the total Zn concentrations in the samples from the MB, MPB, and PB, respectively. Cr, Cu, and Zn in the sediments from the MPB were potentially highly bioavailable because the non-residual fractions were 56.2%, 54.9%, and 56.5%, respectively, of the total concentrations. The potential risks posed by the heavy metals (determined from the chemical fractions of the heavy metals) in the different areas generally decreased in the order MPB > MB > PB. Pictorial representation of cluster analysis results showed that urbanization development level could cause Cr and Zn pollution in the urban riverine sediments to become more severe.

Comparison of cadmium and lead sorption by Phyllostachys pubescens biochar produced under a low-oxygen pyrolysis atmosphere

Phyllostachys pubescens (PP) biochars produced under a low oxygen pyrolysis atmosphere (oxygen content 1-4%) were prepared as sorbents for investigating the mechanisms of cadmium and lead sorption. A low-oxygen pyrolysis atmosphere increased biochar ash and specific surface area, promoting heavy metal precipitation and complexation. The maximum sorption capacity (Qm) of Pb2+ obtained from the Langmuir model was 67.4mg·g-1, while Qm of Cd2+ was 14.7mg·g-1. The contribution of each mechanism varied with increasing oxygen content at a low pyrolysis temperature. Mineral precipitation with Pb2+ was the predominant mechanism for Pb2+ removal and the contribution proportion significantly increased from 17.2% to 71.7% as pyrolysis oxygen atmosphere increased from 0% to 4%. The results showed that cadmium sorption primarily involved coordination with π electrons, at 54.1-82.6% of the total adsorption capacity. The PP biochar shows potential for application in removing heavy metal contaminants, especially Pb2+.

Assessment of Preparation Methods for Organic Phosphorus Analysis in Phosphorus-Polluted Fe/Al-Rich Haihe River Sediments Using Solution 31P-NMR

Fe/Al-rich river sediments that were highly polluted with phosphorus (P) were used in tests to determine the optimum preparation techniques for measuring organic P (Po) using solution 31P nuclear magnetic resonance spectroscopy (31P-NMR). The optimum pre-treatment, extraction time, sediment to solution ratio and sodium hydroxide-ethylenediaminetetraacetic acid (NaOH-EDTA) extractant solution composition were determined. The total P and Po recovery rates were higher from freeze- and air-dried samples than from fresh samples. An extraction time of 16 h was adequate for extracting Po, and a shorter or longer extraction time led to lower recoveries of total P and Po, or led to the degradation of Po. An ideal P recovery rate and good-quality NMR spectra were obtained at a sediment:solution ratio of 1∶10, showing that this ratio is ideal for extracting Po. An extractant solution of 0.25 M NaOH and 50 mM EDTA was found to be more appropriate than either NaOH on its own, or a more concentrated NaOH-EDTA mixture for 31P-NMR analysis, as this combination minimized interference from paramagnetic ions and was appropriate for the detected range of Po concentrations. The most appropriate preparation method for Po analysis, therefore, was to extract the freeze-dried and ground sediment sample with a 0.25 M NaOH and 50 mM EDTA solution at a sediment:solution ratio of 1∶10, for 16 h, by shaking. As lyophilization of the NaOH-EDTA extracts proved to be an optimal pre-concentration method for Po analysis in the river sediment, the extract was lyophilized as soon as possible, and analyzed by 31P-NMR.