Zn In Paddy Soils Research Articles

Spatial distribution and migration of lead and zinc and the influence of parent materials in typical paddy soils of Hunan Province, China.

This study aimed to investigate the distribution and migration characteristics of lead (Pb) and zinc (Zn) in paddy soils in Hunan Province, China. A total of 343 soil samples from 63 profiles were collected from typical regions. The concentration, spatial distribution, and migration behaviors of Pb and Zn in the paddy soils were examined. The results showed that (1) the concentration ranges of Pb and Zn in the surface layer were 17.62-114.07 mg/kg and 44.98-146.84 mg/kg, respectively. (2) The content was higher in the middle and lower reaches of the Xiangjiang River basin horizontally and exhibited shallow enrichment characteristics vertically. (3) Pb migration was weaker than Zn migration, and the parent material had the most significant influence on Pb and Zn content in the bottom soil layer. The research results will clarify the characteristics of Pb and Zn contents in paddy soils in Hunan Province, further understand the horizontal distribution and vertical migration and transformation characteristics of Pb and Zn contents in paddy soils, and provide basic data for scientific rice cultivation and safe food production.

A modified critical load assessment method of heavy metals in paddy soil at large scale

The environmental capacity of agro-ecosystem is the basis of sustainable development of agriculture, but this is hard to evaluate quantitatively due to complex input and output processes of heavy metals. Therefore, in this study, leaching of heavy metals based on PROFILE weathering model were integrated into the steady-state critical load (SSCL) of heavy metals. The results showed that the leaching rates of Hg, As, Cd, Cr, Pb, Cu and Zn in paddy soil were 0.08, 4.69, 0.22, 44.31, 18.13, 21.96 and 64.42 g/ha‧a, respectively, while the leaching rates were significantly correlated with pH, CaO, TFe2O3 and Corg.. Atmospheric deposition was the main input source of heavy metals in agricultural soil, while rice plant uptake and leaching were the main output pathways. The spatial distribution of SSCL were mainly affected by the content of heavy metals in soil, Aw (specific area of soil mineral), and ρ (bulk density). Values of SSCL hardly changed after about 40 years (Hg ≈ 0.02 kg/ha, As≈0.60 kg/ha, Cd ≈ 0.07 kg/ha, Cr ≈ 5.59 kg/ha, Pb ≈ 3.55 kg/ha, Cu ≈ 1.49 kg/ha and Zn ≈ 4.45 kg/ha). However, the sensitivity analysis indicated that soil leaching had 24.30%–27.90% positive effects on SSCL model. Based on the relationship among leaching, pH, standard limit and SSCL of heavy metals, the standard limit could be appropriately raised to cope with the increased human activities on the premise of the ecological capacity. Thus, the SSCL model provides a new insight for the establishment of environment management in agricultural soils.

Land-use conversion controls on the mobility of Zn in paddy soils revealed by stable Zn isotopes

Understanding Zn biogeochemical cycling is necessary for monitoring Zn supply for plants and life during land use conversion, which is critical for environmentally sustainable development. But little is known about how the conversion of paddy soil to abandoned land affects the Zn isotope signature. A comparative field observation was conducted in northeast Thailand to investigate the Zn isotope footprint of paddy soils and abandoned paddy soils (PL and NPL). Our results show that Zn (τZnint : 0.04) slightly retains on PL, but is lost from NPL (τZnint from − 0.81 to − 0.24) to the river during weathering. Compared to PL (Δ66Znparent-soil: −0.29 ‰), more 66Zn isotopes might enter the river when rice cultivation ceases in NPL (Δ66Znparent-soil from −0.26 ‰ to −0.47 ‰). Rice harvest and then root decay might result in heavy 66Zn isotopes accumulating at the topmost soil in PL (δ66Zn: 0.14 ‰) and short-term abandonment (1–2 years) in paddy soils (NPL1 δ66Zn: 0.18 ‰). The release of assimilated Zn, and then the high adsorption of Zn in the Fe-SOM-metal(loid)s ternary system positively contribute to the high [Zn] in PL, while this was not observed in NPL. Our findings provide a comprehensive insight into the Zn isotope signature in response to the conversion of land-use types, which is beneficial for understanding the terrestrial Zn geochemical cycle.

Interactions of Moisture Content, pH, and HA on the Immobilization of Pb and Zn in Paddy Soil Using Magnetic-chitosan Hydrochar

Interactions of Moisture Content, pH, and HA on the Immobilization of Pb and Zn in Paddy Soil Using Magnetic-chitosan Hydrochar

Experimental study on the movement of heavy metal Zn in paddy soil under different irrigation quota of reclaimed water

To reveal the mechanism of heavy metal Zn migration in the irrigated paddy field reclaimed water, this study investigated irrigation quota of 75, 150, 225 and 300 m3/hm2 for three consecutive years. The results showed that with the same irrigation quota, firstly the content of Zn, its variation and the rate of change in soil increased, and hereafter decreased with the increase of soil depth, and finally become stable of reclaimed water. Study results identified that when the irrigation quota was 75, 150, 225 and 300 m3/hm2, the average content of Zn in the soil reached the maximum with the value of 9.60, 12.10, 16.75 and 18.50 mg/kg respectively at the depth of 30 cm. The average content of Zn in soil found maximum values of 13.51, 16.01, 19.02 and 20.98 mg/kg, respectively on the 120th day of cultivation. This study also identified that the content of Zn, its variation and the rate of change increased with the increase of irrigation quota at the same soil depth. Additionally, when the soil depth or plant growth time was the same, the content of Zn, its variation and the rate of change increased with the increase of irrigation quota. However, at the soil depth of 30 cm, the content of Zn in the irrigation quota of 75, 150 and 225 m3/hm2 decreased by 48.11%, 34.59% and 9.46%. The fertility time of 120 days also decreased by 35.71%, 23.81% and 9.52% respectively compared to an irrigation quota of 300 m3/hm2. All the findings are explored by a nonlinear regression under different situations and timing. The mean value of the standard error between the statistical and measured value is found insignificant. However, the correlation coefficient is found greater than 0.9400 and statistically significant. Thus, the findings by nonlinear regression reflected the migration law of soil Zn duly with soil depth and plant growth time in the rice field. This study provided theoretical support for the comprehensive treatment and ecological restoration of heavy metals to the farmland soil in China.

Risk assessment, spatial distribution, and source identification of heavy metal(loid)s in paddy soils along the Zijiang River basin, in Hunan Province, China

This study aimed to reveal spatial distribution of As, Cd, Cr, Cu, Mn, Ni, Pb, Sb, V, and Zn in paddy soils in the Zijiang River basin and to evaluate its pollution status and potential ecological risks, and thus to provide basic information for rational utilization of paddy soils in the study area. The heavy metal(loid) concentrations in one hundred and thirty-five paddy soil samples (these samples were collected from the top 0–20 cm layer) were measured by inductively coupled plasma-optical emission spectrometry. The spatial distribution characteristics of the heavy metal(loid)s were depicted by the Ordinary Kriging interpolation analysis. The contamination degree and potential ecological risks of the heavy metal(loid)s in paddy soils were assessed by Nemerow’s comprehensive index, geoaccumulation index, potential ecological risk factor, and potential ecological risk index. The potential sources of the heavy metal(loid)s were deduced by Pearson’s correlation analysis, hierarchical cluster analysis, and principal component analysis. The mean concentrations of the heavy metal(loid)s decreased in the order of Mn > V ≈ Zn > Cr > Ni ≈ Pb > Cu ≈ Sb > As > Cd. Except for Cd and Sb, the mean concentrations of As, Cr, Cu, Mn, Ni, Pb, V, and Zn were close to the background reference values. The concentration of Cd in 94.8% of samples exceeded the soil quality standard value (grade II, 5.5 < pH < 6.5, GB 15618–1995). According to the assessments of pollution and potential ecological risks for the heavy metal(loid)s, 45.2% and 46.7% of samples were severely polluted and moderately polluted, respectively. The potential sources analysis indicated that Cd, Sb, and Zn mainly originated from agricultural, mining, and smelting activities; As, Cu, and Pb mainly originated from agricultural activities, while coal combustion by-products was another major source of these heavy metal(loid)s in paddy soils near the thermal power plant in the southwest corner of the study area; Cr, V, Mn, and Ni mainly originated from natural source. Cadmium and Sb are the main contaminants in paddy soils in the study area, and there are hot-spot pollution areas.

Soil micronutrient pools and their transfer to paddy-crops in semi-arid agro-ecosystems, Central India

Irrigation is a key component of crop productivity, environmental protection and sustainable agriculture. To understand this, paddy-crops and soil samples were collected from rainfed (RFS) and irrigated (IRS) soils of semi-arid agro-ecosystems, Central India. The objectives of the current study were to (1) determine total concentrations of Cu, Fe, Mn and Zn in paddy-soils and paddy-crops, (2) chemical fractionation of operationally defined pools of Cu, Fe, Mn and Zn content in paddy-soils. Total micronutrient concentrations followed the order as: Fe > Mn > Zn > Cu with higher values in RFS paddy-soils. High residual fraction indicated the existence of micronutrients within mineral lattice structure, which resulted in low to moderate mobility factor (MF) of Cu, Fe, and Zn in the paddy-soils. The high Mn concentrations in non-residual fractions resulted in MF more than 50%. The transfer factors of total micronutrients (TFTM) showed high transfer of Zn and Mn to paddy-crops. The high TFEMF (transfer factor of exchangeable micronutrient fractions) of Cu and Fe revealed significant accumulation in paddy-roots. Paddy-grains differed significantly (P < 0.05) in total micronutrient content with high values in IRS agro-ecosystems. The correlation and multiple linear regression analyses showed control of micronutrient fractions on availability, uptake, transfer and translocation in paddy-crops through root system.

Effects of organic matter fraction and compositional changes on distribution of cadmium and zinc in long-term polluted paddy soils

Soil particulate organic matter (POM) has rapid turnover and metal enrichment, but the interactions between organic matter (OM) and metals have not been well studied. The present study aimed to investigate changes in the OM concentration and composition of the POM fraction and their corresponding effects on metal distribution and extractability in long-term polluted paddy soils. Soil 2000–53 μm POM size fractions had higher contents of C–H and C=O bonds, C–H/C=O ratios and concentrations of fulvic acid (FA), humic acid (HA), cadmium (Cd) and zinc (Zn) than the bulk soils. Cadmium and Zn stocks in soil POM fractions were 24.5–27.9% and 7.12–16.7%, respectively, and were more readily EDTA-extractable. Compared with the control soil, the 2000–250 μm POM size fractions had higher organic carbon concentrations and C/N ratios in the polluted soils. However, there were no significant differences in the contents in C–H and C=O bonds or C–H/C=O ratios of POM fractions among the control, slightly and highly polluted soils. In accordance with the lower contents of C=O bonds and FA and HA concentrations, the Cd and Zn concentrations in 250–53 μm POM size fractions were lower than those in 2000–250 μm POM size fractions. Enrichment of Cd in POM fractions increased with increasing soil pollution level. These results support the view that changes in the OM concentration and the size and composition of POM fractions play a key role in determining the distribution of Cd and Zn in paddy soils.

The respective effects of soil heavy metal fractions by sequential extraction procedure and soil properties on the accumulation of heavy metals in rice grains and brassicas.

This study was carried out to examine heavy metal accumulation in rice grains and brassicas and to identify the different controls, such as soil properties and soil heavy metal fractions obtained by the Community Bureau of Reference (BCR) sequential extraction, in their accumulation. In Guangdong Province, South China, rice grain and brassica samples, along with their rhizospheric soil, were collected from fields on the basis of distance downstream from electroplating factories, whose wastewater was used for irrigation. The results showed that long-term irrigation using the electroplating effluent has not only enriched the rhizospheric soil with Cd, Cr, Cu, and Zn but has also increased their mobility and bioavailability. The average concentrations of Cd and Cr in rice grains and brassicas from closest to the electroplating factories were significantly higher than those from the control areas. Results from hybrid redundancy analysis (hRDA) and redundancy analysis (RDA) showed that the BCR fractions of soil heavy metals could explain 29.0 and 46.5% of total eigenvalue for heavy metal concentrations in rice grains and brassicas, respectively, while soil properties could only explain 11.1 and 33.4%, respectively. This indicated that heavy metal fractions exerted more control upon their concentrations in rice grains and brassicas than soil properties. In terms of metal interaction, an increase of residual Zn in paddy soil or a decrease of acid soluble Cd in the brassica soil could enhance the accumulation of Cd, Cu, Cr, and Pb in both rice grains and brassicas, respectively, while the reducible or oxidizable Cd in soil could enhance the plants' accumulation of Cr and Pb. The RDA showed an inhibition effect of sand content and CFO on the accumulation of heavy metals in rice grains and brassicas. Moreover, multiple stepwise linear regression could offer prediction for Cd, Cu, Cr, and Zn concentrations in the two crops by soil heavy metal fractions and soil properties.

Heavy Metal(loid) Levels in Paddy Soils and Brown Rice in Korea

There is an increasing concern over heavy metal(loid) contamination of soil in agricultural areas including paddy soils. This study was conducted to monitor the background levels of heavy metal(loid)s, arsenic (As), cadmium (Cd), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn) in major rice growing soils and its accumulation in brown rice in Korea. The samples were collected from 82 sites nationwide in the year 2012. The mean and range values of As, Cd, Cu, Hg, Ni, Pb, and Zn in paddy soils were 4.41 (0.16-18.9), 0.25(0.04-0.82), 13.24 (3.46-27.8), 0.047 (0.01-0.20), 13.60 (3.78-35.0), 21.31 (8.47-36.7), and 54.10 (19.19-103.0) mg kg-1, respectively. This result indicated that the heavy metal(loid) levels in all sampled paddy soils are within the permissible limits of the Korean Soil Environment Conservation Act. The mean and range values of As, Cd, Cu, Hg, Ni, Pb, and Zn in brown rice were 0.146 (0.04-0.38), 0.024 (0.003-0.141), 4.27(1.26-16.98), 0.0024 (0.001-0.008), 0.345 (0.04-2.77), 0.113 (0.04-0.197), and 22.64 (14.1-35.1) mg kg -1 , respectively. The mean and range BCF (bioconcentration factor) values of As, Cd, Cu, Hg, Ni, Pb, and Zn in brown rice were 0.101 (0.01-0.91), 0.121 (0.01-0.70), 0.399 (0.05-2.60), 0.061 (0.016-0.180), 0.033 (0.004-0.44), 0.005 (0.003-0.013), and 0.473 (0.19-1.07), respectively, with Zn showing the highest. The results show that the levels of all metal(loid)s in all sampled brown rice are generally within the acceptable limit for human consumption.

폐금속광산 하류 논토양의 중금속에 대한 인체흡수도 평가

BACKGROUND: For the heavy metal cotamination sites, it is very important to estimate the human bioavailability quotients for heavy metals in paddy soils released from mine tailings, which is a major source of contamination in Korea, and to assess the human health risks of heavy metals. METHODS AND RESULTS: This experiment was carried out to investigate the human bioavailability quotient of the heavy metals in paddy soils below part of the closed metalliferous mine. For estimating the human bioavailability quotients for heavy metals, 30 paddy soils below part of the closed mine were collected, and analyzed for Cd, Cu, Pb, Zn, and As using simple bioavailability extraction test(SBET). The quantities of Cd, Cu, Pb, Zn and As extracted from paddy soils below part of the mine by using the SBET analysis were 28.1, 17.3, 34.1, 14.6 and 2.3% respectively. Specially, the maximum values of Cd, Pb and Zn were 73.3, 81.5 and 58.1% of human bioavailability quotient, respectively, and varied considerably among the sampling sites. The human bioavailability quotient of Cd, Cu, Pb and Zn in soils near the closed mine showed significant positive correlation among soil pH value, O.M. and Ex. Ca. contents, while it correlated negatively between soil Ex. K and Ex. Mg contents in paddy soils. Also, its of Cd, Cu, Pb and Zn in paddy soils showed significant positive correlation with 0.1M HCl extractable and total contents, while in soils, it correlated negatively with As content in soil near the closed mine. CONCLUSION: The results of the simple bioavailability extraction test (SBET) indicate that regular ingestion of soils by the local population could be closed a potential health threat due to long-term heavy metals exposure in these mine areas.

Contamination and vertical distribution of As, Cd, Cr, Cu, Pb, Tl, and Zn in paddy soil irrigated with untreated leachate from tailings retention ponds

The contamination and vertical distribution of As, Cd, Cr, Cu, Pb, Tl, and Zn in paddy soil irrigated with untreated leachate from the tailings retention pond were investigated. As, Cr, Cu, and Zn were slightly contaminated in the surface soil and hence their vertical distribution was not obvious. However, Cd and Pb were highly contaminated in the surface soil, while their concentrations decreased with depth, being negatively correlated with pH and positively with total organic matter. Tl was considerably contaminated in the surface soil and a V-shaped vertical distribution was observed where the concentration increased to a maximum at about 30 cm depth and decreased thereafter. The findings revealed that the regular irrigation with untreated leachate from the tailings retention ponds could cause considerable contamination of Cd, Pb, and Tl, and thus tailings should be stringently treated before disposal to minimize their potential environmental impacts on the surroundings.

Heavy metal pollution and potential health risk assessment of white rice around mine areas in Hunan Province, China

To assess the pollution situation and human health risks, the concentrations of heavy metals Pb, Cd, Cu, and Zn in paddy soils and white rice around seven mining-affected areas in Hunan Province were analyzed. The ranges of concentrations of Pb (23.9–1595.8 mg kg−1), Cd (0.3–9.5 mg kg−1), Cu (31.2–321.5 mg kg−1) and Zn (56.1–3478.9 mg kg−1) in all paddy soils were significantly higher than Hunan background values and even exceeded the maximum permissible concentrations for paddy soil quality recommended by the Ministry of Environmental Protection of China. The geoaccumulation index (I- geo ) showed that Cd (1.42–6.33) was the predominant pollutant in all paddy soils, while Zn was the least important element. The concentrations of Pb, Cd, Cu, and Zn in white rice ranged from 0.18 to 0.72 mg kg−1, 0.10 to 1.32 mg kg−1, 3.83 to 5.95 mg kg−1, and 8.64 to 18.18 mg kg−1, respectively. Human health risk, associated with these heavy metals, was assessed based on hazard quotients (HQ) and hazard indexes (HI) for adults through consumption of white rice. HQ values of heavy metals (except for Cd) in most of mining-affected areas were below 1.0, while the HI of all heavy metals in all mine areas was higher than 1.0, the maximum acceptable level, suggesting that consumption of such contaminated white rice was a health risk. Except for the Leng Shui-Jiang mine area, Cd was the major contributor to the risk in the mine areas through white rice consumption, amounting to over 67 % of the HI, while Zn was a minimal contributor compared to the other metals.

Paddy soil heavy metal contamination and uptake in rice plants from the adjacent area of Barapukuria coal mine, northwest Bangladesh

This study was carried out to estimate the heavy metal contamination in paddy soil and subsoil and uptake by rice plants collected from Barapukuria coal mine area of Bangladesh. The mean contents of As, Cr, Cu, Mn, Ni, Pb, and Zn in paddy soil and subsoil exceed the world averages, and the observed soils are moderately to extremely polluted with inputs from mining activities. Correlation and regression model analyses suggest that pH and TOC have distinct effect on the availability of observed metals in soils. Sequential extraction of paddy soil and subsoil samples demonstrate that the mobility of heavy metals increases in the order of Cu > Zn > Pb > Fe > Cr > Ni > Mn > As. The uptake of metals in rice root is much higher than those in straw and rice grains. Arsenic, Cr, and Pb uptake in rice grains are 6.87-, 1.58-, and 5.26-fold higher than the maximum permissible concentration which shows a tendency of transformation of these elements from contaminated soil to rice plants.

Optimum Nutrient Rate and Nutritional Constraints in Tuber Crops Growing in Ultisol of India with Special Emphasis on Tannia

Tuber crops are generally grown in marginal lands with low native soil fertility. In India, laterite soils (acidic Ultisols) are the major soils for tropical tuber crops and are poor in innate fertility. Among tropical tuber crops, some have adapted to poor soils, such as cassava, whereas others such as tannia (Xanthosoma sagittifolium L.) cannot establish well in these soils and may manifest nutritional disorders, which ultimately result in the complete devastation of the crop. Therefore, we investigated the effects from a preliminary rate trial (PRT) and nutrient-omission pot trial (NOPT) using maize as a test crop and a NOPT with tannia to determine the optimum nutrient rate and limiting nutrients, as well as nutritional problems affecting the growth and yield of tannia. Each experiment was laid out in a complete randomized design with three replications and was conducted for both garden and paddy soils. The PRT revealed that the optimum nutrient requirements for the soils were different, with garden soils requiring nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), boron (B), zinc (Zn), and molybdenum (Mo) at 200, 60, 160, 70, 60, 50, 4, 8, and 0.8 kg ha−1, respectively, and paddy soil requiring twice these rates. The NOPT indicated that in addition to N, P, K, B, and Mo in both garden and paddy soils, Ca and Zn in paddy soils and S in garden soils were the constraining nutrients. The NOPT carried out with tannia indicated that the main nutritional problem was subsoil acidity-induced multinutrient deficiencies involving K, Ca, and Mg.

삼보광산 수계 하천수질 및 퇴적토의 오염도 평가

BACKGROUND: Mine drainage from metal mining districts is a well-recognized source of environmental contamination. Oxidation of metal sulfides in mines, mine dumps and tailing impoundments produces acidic, metal-rich waters that can contaminate the local surface water and soil. METHODS AND RESULTS: This experiment was carried out to investigate the pollution assessment of heavy metal on the water quality of mine drainage, paddy soils and sediment in lower watershed affected by mine drainage of the Sambo mine. The average concentrations of dissolved Cd (0.018∼0.035 mg/L) in mine drainage discharged from the main waste rock dumps(WRD) was higher than the water quality standards (0.01 mg/L) for agricultural water in Korea. Also, the average concentrations of dissolved Zn, Fe and Mn were higher than those of recommended maximum concentrations (Zn 2.0, Fe 5.0, Mn 0.2 mg/L) of trace metal in irrigation water proposed by FAO (1994). The average contents of Pb and Zn in paddy soils was higher than those of standard level for soil contamination(Pb 200, Zn 300 mg/kg) in agricultural soil by Soil Environmental Conservation Act in Korea. Also, the concentrations of Cd, Pb and Zn in sediment were higher than those of standard level for soil contamination (Cd 10, Pb 400, Zn 600 mg/L) in waterway soil by Soil Environmental Conservation Act in Korea. The enrichment factor (EFc) of heavy metals in stream sediments were in the order as Cd>Pb>Zn> As>Cu>Cr>Ni. Also, the geoaccumulation index (Igeo) of heavy metals in stream sediments were in the order as Zn>Cd>Pb>Cu>As>Cr>Ni, specially, the geoaccumulation index (Igeo) of Zn (Igeo 3.1∼6.2) were relatively higher than that of other metals in sediment. CONCLUSION(s): The results indicate that stream water and sediment were affected by mine drainage discharged from the Sambo mine at least to a distance of 1 km downstream (SN-1, SN-2) of the mine water discharge point.

Chemical fractionation of seven heavy metals (Cd, Cu, Fe, Mn, Ni, Pb, and Zn) in selected paddy soils of Iran

The content and fractionation of seven heavy metals (Cd, Cu, Fe, Mn, Ni, Pb, and Zn) were determined in 28 surface soil samples (0–20 cm) of agricultural topsoil from Isfahan Province in central Iran. The order of abundance of metals in the soils was Fe (1240.4 mg kg−1) > Mn (95.7 mg kg−1) > Pb (51.6 mg kg−1) > Zn (23.8 mg kg−1) > Ni (13.4 mg kg−1) > Cu (7.0 mg kg−1) > Cd (2.8 mg kg−1). Iron, Mn, Ni, Pb, and Zn existed in paddy soils mainly in Fe-Mn oxides (53.6 %, 65.2 %, 40.4 %, 40.8 %, 53.3 %, respectively), whereas Cu and Cd occurred essentially as residual mineral phase (41.4 %) and carbonate (36.1 %), respectively. The mobile and bioavailable fractions of Cd, Cu, Fe, Mn, Ni, Pb, and Zn in paddy soils averaged 48.8, 20.8, 0.79, 29.2, 28.5, 41.1, and 24.8 %, respectively, which suggests that the mobility and bioavailability of the seven metals probably decline in the following order: Cd > Pb > Mn ≥ Ni > Zn > Cu ≫ Fe, suggesting greater contribution of anthropogenic Cd. As Cd in soil is easily accumulated by plants through the root system, the concentration of Cd in these paddy soils could be a concern to human health.

Pollution, fractionation, and mobility of Pb, Cd, Cu, and Zn in garden and paddy soils from a Pb/Zn mining area

This study was conducted to investigate the pollution load index, fraction distributions, and mobility of Pb, Cd, Cu, and Zn in garden and paddy soils collected from a Pb/Zn mine in Chenzhou City, China. The samples were analyzed using Leleyter and Probst's sequential extraction procedures. Total metal concentrations including Pb, Cd, Cu, and Zn exceeded the maximum permissible limits for soils set by the Ministry of Environmental Protection of China, and the order of the pollution index was Cd > Zn > Pb > Cu, indicating that the soils from both sites seriously suffered from heavy metal pollution, especially Cd. The sums of metal fractions were in agreement with the total contents of heavy metals. However, there were significant differences in fraction distributions of heavy metals in garden and paddy soils. The residual fractions of heavy metals were the predominant form with 43.0% for Pb, 32.3% for Cd, 33.5% for Cu, and 44.2% for Zn in garden soil, while 51.6% for Pb, 40.4% for Cd, 40.3% for Cu, and 40.9% for Zn in paddy soil. Furthermore, the proportions of water-soluble and exchangeable fractions extracted by the selected analytical methods were the lowest among all fractions. On the basis of the speciation of heavy metals, the mobility factor values of heavy metals have the following order: Cd (25.2-19.8%) > Cu (22.6-6.3%) > Zn (9.6-6.0%) > Pb (6.7-2.5%) in both contaminated soils.

Simulation of retention and transport of copper, lead and zinc in a paddy soil of the Red River Delta, Vietnam

Heavy metal (HM) contaminations in the topsoil around handicraft villages with non-ferrous heavy metal recycling in the Red River Delta can impose serious threats to the subsoil as well as to the groundwater quality. This feature is very important for paddy soils due to relatively high leaching rates and the dissolution of Fe–Mn oxides under reducing conditions which can accelerate the amount of HM translocated to the subsoil and groundwater. The transport of Cu, Pb and Zn in paddy soils was simulated by numerical modeling of non-equilibrium solute transport with an adaptation of the Hydrus-1D model. For the simulation, a water layer on the soil surface was included, from which HM can infiltrate into the soil depending on the soil hydraulic properties. Sorption coefficients, obtained from batch experiments were used as input data for the simulations. Calculated leaching rates were compared with the binding forms of HM in the samples. The simulations show that leaching rates decrease in the order: Zn > Cu > Pb. This order is confirmed by the results of sequential extractions. Under constant flooded conditions at a water table of 20 cm, Cu, Pb and Zn were estimated to reach the soil depth of 1 m within 470, 495 and 370 days, respectively, emphasizing that reactive pollutants can reach groundwater in a relatively short time. A change of the water layer from 1 to 30 cm can accelerate the leaching rate of HM up to 36%. The hard pan layer was observed to induce a hysteresis in hydraulic conductivity and slow down the movement of HM. Uncertainties in modeling arise as several parameters in the simulation can be determined only with significant errors. However, Hydrus-1D is a suitable tool for simulation of the transport of HM in paddy soils.

Status of trace elements in paddy soil and sediment in Taihu Lake region.

Thirteen paddy soil profiles and river sediments which are sources of irrigation water were collected around the Taihu Lake, and the trace elements were estimated. The content of La and Ce in paddy soil and sediment were 39.3 and 68.6 mg/kg soil and 36.9 and 65.1 mg/kg soil, being within the range of background values. The values for Pb, Cu, Ni, Cr, Co, Mn, Zn, Se in paddy soil were 23.3, 27.8, 25.5, 63.5, 10.2, 386, 68.7 and 0.25 mg/kg soil respectively, all below the national permission level. There was a decline of Zn in paddy soil. Some of the river sediments were seriously polluted. The river in Yangjin site was most contaminated with 5.47 g Cu/kg and 7.4 g Zn/kg. The high concentration of Pb and Ni also was observed in this sediment. River in Weitang, Huashi, Xinzhuang and Meiyan were contaminated with Pb, Cu and Ni to some extent. Zn, Cu and Pb were the main pollutants in present experiment sites. The fast development of village/township industries have caused severe environmental pollution in the Taihu Lake region, especially irrigation river sediments. Se content in plant and seed was 0.04 and 0.03 mg/kg respectively, showed Se-deficiency in paddy soil in the Taihu Lake region.