We investigated heavy metal contamination in soils and plants at polluted sites in China including some with heavy industries, metal mining, smelting and untreated wastewater irrigation areas. We report our main findings in this paper. The concentrations of heavy metals, including Cd and Zn, in the soils at the investigated sites were above the background levels, and generally exceeded the Government guidelines for metals in soil. The concentrations of metals in plants served to indicate the metal contamination status of the site, and also revealed the abilities of various plant species to take up and accumulate the metals from the soil. Substantial differences in the accumulation of heavy metals were observed among the plant species investigated. Polygonum hydropiper growing on contaminated soils in a sewage pond had accumulated 1061 mg kg(-1) of Zn in its shoots. Rumex acetosa L. growing near a smelter had accumulated more than 900 mg kg(-1) of Zn both in its shoots and roots. Therefore these species have potential for phytoremediation of metal-contaminated sites. Our results indicate the need to elucidate the dynamics of soil metal contamination of plants and the onward movement of metal contaminants into the food chain. Also our results indicate that the consumption of rice grown in paddy soils contaminated with Cd, Cr or Zn may pose a serious risk to human health, because from 24 to 22% of the total metal content in the rice biomass was concentrated in the rice grain. Platanus acerifolia growing on heavily contaminated soil accumulated only very low levels of heavy metals, and this mechanism for excluding metal uptake may have value in crop improvement. Sources of metal entering the environmental matrices studied included untreated wastewater, tailings or slurries and dust depositions from metal ore mining, and sewage sludge. Pb, Zn or Cd concentrations declined with the distance from metal smelter in accordance with a good exponential correlation (R2>0.9), and this shows that metal dust deposition is an important contributor to metal contamination of soils.

The sequential weight loss-on-ignition (WLOI) method for determination of organic and carbonate or inorganic carbon (C) content was evaluated on sediments from diverse sources with a great range of C contents. The sediments were collected from canal, wetland, river, estuary, lake, and marine sites. The organic and inorganic C contents of these samples ranged from 1 to 430 g kg( -1) and from 4 to 97 g kg( -1), respectively. Combinations of the combustion time and temperature and optimal weight ranges of representative samples were tested, and comparisons of the WLOI method with other methods, including dry combustion and wet combustion, were made. These methods were (1) use of the carbon-nitrogen-sulfur (CNS) autoanalyzer with normal and reduced temperatures for total and organic C, (2) thermogravimetry for both organic and inorganic C, (3) use of the CNS autoanalyzer after removal of inorganic (carbonate) C by fumigating samples with concentrated HCl for organic C, (4) Walkley-Black wet combustion method for organic C, and (5) pressure-calcimeter associated with subtraction method (total C minus inorganic C) for organic C determinations. The results of analyzing samples of sediments of diverse origins showed that the optimal combination of temperature and time of WLOI depended mostly on the sources of the analyzed sediment. The WLOI analysis of sediment samples for organic C from wetlands, canal, estuary, or river sites needed a relatively low temperature but that of sediment samples from lake and marine sites required a relatively high temperature. Overall, to obtain reliable analysis results of samples from widely varied sediment sources except marine sediments, 500°C for 12 h was optimal for organic C content determination, and 800°C for yet another 12 h was optimal for inorganic C content determination. The temperature could even be reduced to 475°C if only wetland and stream sediments were included, but for marine sediments, 550°C for 12 h was necessary. Precise C content determinations for most sediment sources could be obtained by WLOI when sample quantities ranged from 2.0 to 4.0 g. The WLOI method, when conducted properly, resulted in precise measurements of C contents in "standard samples" used for calibration, and these values were closely comparable to results obtained with other dry combustion methods (R (2) ≥ 0.96). We conclude that WLOI, which has advantages of simplicity, cost-effectiveness, and no waste disposal over other methods, can provide precise measurements of organic and inorganic C contents in sediments from a wide range of sources, but the selection of heating temperature and exposure time should be carefully considered based on sediment sources.

Purpose The aim of this study was to assess phosphorusretention (P ret ) capacities via P adsorption (P ads ) and desorption (P des ) by sediments collected from six different sources associated with various origins, physical, and chemical characteristics. Materials and methods Sediment samples were collected in the State of Florida, the USA, from estuary, marine, wetland, canal, river, and lake, respectively. Phosphorus adsorption and desorption for each sediment were evaluated in three types of ambient water, i.e., marine, wetland, and canal, with different rates of phosphate added and then desorbed by chloride (Cl − ). Capacities in adsorption and desorption of P by various sediments were evaluated with different isotherm models to compare their potentials and stabilities in P retention. Results and discussion Sediments from the canal and lake had the greatest native adsorbed P and the highest zero equilibrium P concentration. Sediment from the estuary had the highest P adsorption and followed by those from wetland and marine origins, respectively. Phosphorus desorption from sediments by replacing exchangeable P with Cl − (20 mmol L −1 KCl) was obtained from an excellent fit of the data by an exponential growth model of desorption kinetics. The fractions of retained P (P ret =P ads −P des ) were as high as 85-98% in the studied sediments, which displayed strong P retention capacities by all these sediments.Conclusions High capacities to retain P by sediments from estuary and wetland may play a critical role in buffering some chemical and ecological changes and benefit aquatic eco-environments by preventing P rapid release to the overlying water column.

The recent trend of an increase in the concentration of greenhouse gases (GHGs) in the atmosphere has led to an ele-vated concern and urgency to adopt measures for carbon (C) sequestration to mitigate the climate change. Among all GHGs, carbon dioxide (CO2) is the most important one which occurs in the greatest concentration and has the strong-est radiative forcing among all. Reducing the release of CO2 to the atmosphere through “green energy” technologies or fossil fuel energy alternatives, such as wind, solar and hydraulic energies, is a major challenge. However, removal of atmospheric CO2 by terrestrial ecosystems via C sequestration and converting the sequestered C into the soil organic C has provided a great opportunity for shifting GHG emission to mitigate the climate change. Soil is an ideal reservoir for storage of organic C since soil organic C has been depleted due to land misuse and inappropriate management through the long history. To optimize the efficiency of C sequestration in agriculture, cropping systems, such as crop rotation, intercropping, cover cropping, etc., play a critical role by influencing optimal yield, total increased C sequestered with biomass, and that remained in the soil. As matter of fact, soil C sequestration is a multiple purpose strategy. It restores degraded soils, enhances the land productivity, improves the diversity, protects the environment and reduces the enrichment of atmospheric CO2, hence shifts emission of GHGs and mitigates climate change

A pot experiment was conducted to study the influence of elemental sulphur (S) on solubility of soil Pb, Zn and Cd and uptake by maize (Zea mays L.). Two rates of elemental sulphur (S) applied at 0 (S 0 ) and 200 (S 200 À 1 soil, respectively. The result showed that with S application at 200 mmol S kg À 1 , soil pH decreased about 0.3 unit and the solubility of the Zn and Cd was significantly increased, but the solubility of Pb had no significant influence. The concentration of Pb, Zn and Cd in maize shoots and roots were increased with increasing rates of heavy metals. However, the concentration of Zn and Cd in shoots and roots were higher with application of S rather than without S but no significant difference was found for Pb. The highest concentration of Zn in the shoots was 2.3 times higher with application of S rather than without at the same rate of Zn, 200 mg kg. Plant biomass was also significantly affected by the application of S and of heavy metals. With heavy metal addition, the shoot and root biomass were decreased with the rates of those of heavy metals increased either with or without application of S. However, the shoot biomass was significantly decreased with S application at the same rate of heavy metals except that with Zn addition. The removal of Cd and Pb by maize uptake and accumulation with application of S had no significant increase compared to that without, but the removal Zn by maize uptake from the soil increased by application of S, 90.9 Ag plant À 1 contrast to 25.7 Ag plant À 1 at Zn 200 within a growth period of only 40 days. D