Effect of soluble phosphate and bentonite amendments on lead and cadmium bioavailability and bioaccessibility in a contaminated soil.

Effect of commonly used heavy metal immobilizing agents on risks of soil heavy metals has not been well investigated. In this work, a contaminated acidic soil (total Cd = 8.05, total Pb = 261 mg kg-1) was amended with soluble phosphate (P: 160 mg kg-1) and bentonite (3 g kg-1) and incubated for 360 d. The soil was then added to mouse feed at 1:9 soil: feed ratio (weight) and fed to mouse for 10 days, after which the liver, kidney and bone Pb and Cd concentrations were measured. The amended soils were extracted with SBRC and PBET to assay bioaccessibility, and extracted with DTPA to assess the environmental availability. The amendments did not affect the DTPA-Pb/Cd significantly (p > 0.05), while the Cd bioaccessibility in the gastric phase of the SBRC assay was reduced from 90.0 to 20.4 % for the bentonite amended treatment (p < 0.05). Kidney Pb and Cd concentrations of the mice fed with feed containing phosphate spiked soil was 80.2 and 66.0 % lower than the control mice fed with unamended soil (CK), respectively. Significant linear correlations were found between DTPA-extractable concentration and kidney concentrations for Pb/Cd. The effect of amendment on Pb/Cd bioavailability differed between the results calculated with different endpoints. The phosphate amendment resulted in 82.7 and 34.3 % lower Pb RBA compared with the unamended soil calculated with kidney and kidney+liver+bone Pb concentrations, respectively, and 68.8 and 49.7 % lower Cd RBA than the control with kidney and kidney+liver concentrations, respectively. However, no significant effect was observed with both amendments when the RBA was calculated with liver or bone Pb/Cd concentrations, or on Pb RBA with kidney, liver or bone metal concentrations. Results indicate the complex effect of amendments on organ, tissue and overall health risk of soil Pb/Cd to animal/human.

Cadmium and lead bioavailability to poultry fed with contaminated soil-spiked feed.

Geophagy is common for free-range chickens, however, the relative bioavailability (RBA) of heavy metals in contaminated soils consumed by chickens has not fully investigated. In this work, chickens were fed diets increasingly spiked with a contaminated soil (Cd = 105, Pb = 4840 mg kg-1; 3, 5, 10, 20 and 30 % of overall feed by weight), or Cd/Pb reagent spikes (from CdCl2 or Pb(Ac)2), for 23 d. After the study period, chicken liver, kidney, femur and gizzard samples were analyzed for Cd and Pb concentrations, and organ/tissue metal concentrations were used to calculate Cd and Pb RBA. Linear dose response curves (DRCs) were established for both Cd/Pb reagents-spiked and soil-spiked treatments. Femur Cd concentrations of soil-spiked treatments were two times of Cd-spiked treatments with similar feed Cd levels, while feed spiked with Cd or Pb also resulted in elevated Pb or Cd concentrations in some organ/tissues. Metal RBA was calculated using three different methods. Most Cd and Pb RBA values were in the range 50-70 %, with the chicken gizzard as a potential endpoint for bioaccessible Cd and Pb. Cadmium and Pb bioavailability values can help with more precise estimation of Cd and Pb accumulation in chicken following heavy metal-contaminated soil ingestion, with overall results helping to protect human health.

Fermentation affects heavy metal bioaccessibility in Chinese mantou.

Effect of different fermentation methods on heavy metal bioaccessibilities in wheat flour is undetermined. In this work, gastric and gastrointestinal heavy metal bioaccessibility in wheat flour products (control-wheat dough, T1-mantou made with normally fermented dough, T2-mantou made with over-fermented dough and T3-mantou made with over-fermented dough + Na2CO3) made from two wheat flour samples (NX and QD) was assessed via a modified physiologically-based extraction test. Cadmium, Zn and Mn bioaccessibility in the gastric phase (GP) was greater than in the gastrointestinal phase (GIP), yet the opposite was observed for Cu (p < 0.05). Lead bioaccessibility in the GIP of the QD sample was 1.37-4.08 times greater than that in the GP, while only the control had greater bioaccessibility in the GIP than that in the GP (p < 0.05) for the NX sample. Treatments T2 and T3 had greater Cd, Cu, Zn and Mn bioaccessibilities than the control and T1 in the GP (p < 0.05). In the GIP, however, only T3 had greater Mn bioaccessibility than the control for the NX sample. Enhanced degradation of the heavy metal-phytate following over-fermentation may have led to greater heavy metal bioaccessibility. Results should help food processors reduce human absorption of excessive heavy metals present in wheat flour foods.

Heavy metal distribution in wheat plant components following foliar Cd application.

Atmospheric deposition of Cd, from anthropogenic activities, can be directly deposited onto and absorbed into wheat plants, yet, how foliar absorbed Cd is translocated in wheat plants is not well understood. A pot experiment investigated foliar Cd application on the accumulation and distribution of heavy metals in various wheat parts. Wheat was grown in a Cd/heavy metal contaminated soil, and from grain heading to the filling stage, 0, 10, 20, 30 and 40 mg kg-1 Cd solution was sprayed repeatedly on leaves (grain heads were covered). Foliar Cd application had no effect on grain yield and Cd concentration (3.01-3.51 mg kg-1 for all treatments), while increased flag leaf blade and sheath Cd concentrations by 1.06-2.77 and 0.00-0.66 times, respectively. Cadmium concentration in the center of the peduncle, from the 40 mg kg-1 Cd solution treatment, was 1.41 times that of the control (10.3 vs 7.30 mg kg-1). Foliar Cd application also increased Cd accumulation (concentration × mass) of the flag leaf blade and sheath. Rachis and grain Pb concentrations were reduced, while stem Pb concentration was increased by Cd application. Cadmium application negatively affected whole plant Ni accumulation and concentration of certain wheat parts; Ni absorption inhibition may have occurred in roots via the downward transport of Cd. Overall results implied that the predominant portion of foliar applied Cd was retained in leaves, while lesser portions migrated to peduncle or root and affected the absorption/distribution of other metals in wheat plants. These results are important for further discerning the mechanism of wheat grain Cd accumulation, especially when grain is raised in areas where atmospheric deposition of Cd (e.g., near smelting facilities) is an issue from an environmental and human health perspective.

Accumulation and speciation of arsenic in Eisenia fetida in sodium arsenite spiked soils - A dynamic interaction between soil and earthworms.

Arsenic (As) is a toxic metalloid that is a significant global pollutant of the environment and a persistent bioaccumulation carcinogen. Earthworms are frequently employed as sentinel organisms to investigate the bioavailability of As in contaminated soils. However, the process of As accumulation in earthworms and the mechanism of transformation of As species in their bodies are not well understood. The accumulation of As and variation of As species in the earthworms (Eisenia fetida) exposed to sodium arsenite (0, 20, and 80 mg kg-1 As) were investigated in this study. The total As concentration of earthworms in the three treatments at various sample times was dose-dependent on soil As content. After 56 days of exposure, the high concentration treatment had the highest total As content (772 ± 21 mg kg-1) in earthworms, followed by the low concentration treatment (579 ± 42 mg kg-1) and control (31 ± 1 mg kg-1). During 56 days, the proportion of trivalent As in earthworms increased from 70% to more than 90%, while pentavalent As decreased by 11-18%. On day 28, the sum of the four organic As species reached a maximum (<1%). Changes in soil As species and an increase in bioavailable As cause earthworms to accumulate more As. The total As in soil after 56 days of exposure was 9.51 ± 0.50, 25.6 ± 0.60, and 82.8 ± 0.28 mg kg-1, which was not significantly different from the total As in soil before the experiment. These findings are useful in assessing the risk of earthworm exposure to sodium arsenite in the soil.

Bioaccessibility, source and human health risk of Pb, Cd, Cu and Zn in windowsill dusts from an area affected by long-term Pb smelting.

Non-ferrous metal smelting results in heterogenous spatial distribution of potentially toxic metals (PTM) near smelters. In this work, windowsill dusts were collected from smelting (SA) and urban (UJ) sub-areas of Jiyuan (a city affected by >70 years of Pb smelting) to investigate PTM source and bioaccessibility. The <10 µm fraction of dusts were analyzed for total and bioaccessible Pb, Cd, Cu and Zn concentrations; bioaccessibility was analyzed by a three-stage assay (i.e., lung phase, gastric phase and gastrointestinal phase) using artificial lysosomal fluid (ALF, L phase) followed by simulated gastric and gastrointestinal fluids (G and GI phases). This assay mimicked the movement of particles phagocytosed by alveolar macrophages in the respiratory system, then transported up the oropharynx and subsequently swallowed and transported into the digestive system. Zinc had greater bioaccessible concentrations in L and GI phases than other metals, and the mean L phase bioaccessible PTM concentrations in SA were greater than in UJ. The mean L + GI phase bioaccessible concentrations of Pb, Cd, Cu and Zn in SA were 280, 79, 124 and 1458 mg kg-1, while those in UJ were 215, 54, 116 and 598 mg kg-1, respectively. The L phase extracted 87.7 to 98.8 % of PTM within the L + GI assay. Lead had a lower L + GI bioaccessibility than Cd, Cu and Zn (70-76 % vs. 82-92 %). Higher tolerable Cd carcinogenic risks based on bioaccessibility were found in SA sub-area than in UJ while no carcinogenic or non-carcinogenic risk was found for other metals. Lead isotopic ratios indicated that both Pb ore and smelting bottom ash contributed to dust Pb accumulation in SA, while coal burning, lead ore, Pb smelting bottom ash and diesel engine exhaust contributed to dust Pb accumulation in UJ. Overall, results indicated heterogenous distribution of PTM source and bioaccessibility in the vicinity of Pb smelters.

Metal contamination in soils and windowsill dusts: implication of multiple sources on dust metal accumulation within a city affected by Pb smelting.

The accumulation of total Pb, Cd, Cu, and Zn in soils (0-5 cm) and windowsill dust fractions (45-125, 10-45, and < 10 µm), and soil pollution indices (PI), were investigated in a long-term (~ 70 years) Pb smelter area and in the nearby urban city of Jiyuan, China. Principal component analysis (PCA) was utilized to identify metal contamination sources. Results showed that mean soil Pb, Cd, Cu, and Zn concentrations in the smelter area were 803, 13.8, 118, and 323 mg kg-1, while those of the urban area were 270, 7.95, 51.6, and 244 mg kg-1, respectively. Lead and Cd had greater soil PI than Cu and Zn. Lead concentrations in the 45-125, 10-45, and < 10-µm urban dust fractions ranged from 197.1 to 1953 (mean 1020), 202-3962 (2407), and 51.1-1258 (310.7) mg kg-1, while Cd concentrations ranged from 11.1 to 111 (49.2), 10.4-159 (64.3) and 21.5-131 (60.0) mg kg-1, respectively. Excessive Zn concentrations (5000-22,000 mg kg-1) in some urban dust samples were found at two sampling sites, while Zn concentrations were < 2600 mg kg-1 in all other samples. Based on PCA results, metal accumulation near the Pb smelter was dominated by smelting activities. The PCA results further suggested that mass vehicular transportation modes may be an important source of metals such as Cu and Zn in the urban area. Certain samples in both sub-areas had unsafe potential non-carcinogenic risks of Pb for children. These findings suggest that reducing environmentally relevant metal concentrations in this, and similar areas, will likely require a multi-faceted approach.

Effects of exogenous additives on wheat Cd accumulation, soil Cd availability and physicochemical properties in Cd-contaminated agricultural soils: A meta-analysis.

Cadmium (Cd) contamination in wheat is a serious issue. The application of exogenous additives can effectively inhibit Cd bioavailability in soil and decrease Cd accumulation in wheat. However, a comprehensive and quantitative analysis of how additives affect wheat Cd accumulation, wheat yield, soil Cd availability, and soil properties is lacking. We conducted a meta-analysis of 65 peer-reviewed papers published before April 2021 to investigate how additives application affects Cd accumulation in wheat and soil Cd availability. The results indicated that most additives application decreased the diethylenetriaminepentaacetic acid extractable-Cd content (5.27-56.33%) in the soil, and wheat grain and root Cd concentrations (0.03-129.87% and 0.42-52.84%, respectively); the pH values of wheat-grown soil and the properties of the additives affected the reduction percentage. Overall, most wheat-grown soils were calcareous soil (42 peer-reviewed papers); in calcareous soil, the magnitude of the Cd reduction in wheat grain was the highest under treatments with clay minerals (129.87%) due to clay modification, followed by composite (75.36%) and phosphorus materials (73.55%). Moreover, most additives application increased wheat grain yield by 0.03-51.84%, which was attributed to the positive effects of additives on wheat antioxidant capacity, photosynthesis, respiration, and nutrient uptake. Additives application increased the pH value of acidic wheat soil, and positively affected the electrical conductivity, cation exchange capacity, and organic carbon content of the wheat grown soil. In addition, regression analysis showed that soil available Cd was negatively correlated with the pH value with additives application in acidic soil (r2 = 0.43), while a non-significant correlation was observed in neutral and calcareous wheat soils (r2 = 0.017 and 0.016, respectively). The results of this study can assist in the selection, modification, and utilisation of additives to remediate Cd-contaminated wheat soils.

Lead smelting alters wheat flour heavy metal concentrations and health risks.

Wheat (Triticum aestivum L.) flour consumption may be a major source of human metal intake, especially when wheat is cultivated in metal-contaminated soils. This work investigated Cd, Cu, Pb, and Zn distribution in whole wheat flour, wheat flour, and wheat bran when grown in an area polluted by Pb smelting. Wheat product heavy metal concentrations were analyzed, and the (non)carcinogenic risks were assessed. Mean Cd, Cu, Pb, and Zn concentrations in whole wheat flour were 0.38, 3.83, 0.48, and 29.3 mg kg-1 , respectively; those in flour were only slightly reduced. The ratios between noncarcinogenic average daily dose of whole wheat flour and wheat flour consumption ranged from 1.06 to 3.76, with Pb having the greatest values compared with other metals. For children, the average hazard quotients (HQs) of whole wheat flour consumption of Cd, Cu, Pb, and Zn were 4.19, 1.06, 1.53, and 1.07; those for wheat flour consumption were 3.81, 0.68, 0.70, and 0.98, respectively. The HQs of adults were less than those of children. Overall results indicated that consumption of wheat products may lead to health concerns in the heavy metal contaminated area, yet when wheat flour rather than whole wheat flour is consumed, only the human health risk from Pb ingestion is reduced. Altering or removing human edible crops in the most contaminated areas should be considered.

Atmospheric deposition of arsenic, cadmium, copper, lead, and zinc near an operating and an abandoned lead smelter.

Atmospheric deposition samples were collected over 15 mo at several locations near an operating smelter and an abandoned Pb smelter to investigate the contribution of Pb smelting to depositional fluxes and potential local air quality degradation. Samples were analyzed for As, Cd, Cu, Pb, and Zn and subjected to scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS). Concentrations of Cd and Pb at both sites were greater than at the control site (p < .05), and significant correlations existed between Cd and Pb concentrations at both sites (p < .05). Monthly depositional flux variations at both sites were similar, with greater deposition during cold and dry periods. Heavy metal(loid)s deposition during these periods was correlated with wind speed. Greater Cd depositional flux differences were found between the smelter and control sites compared with other elements. The SEM images suggested that some particles at the operating smelter site were from Pb smelting material. However, most particles at both sites had no characteristics of smelting, suggesting reactions occurred between the smelter-emitted particles and soil components. The EDS results indicated that atmospheric deposition from both sites had lower Pb concentrations than smelting material or ash. The main atmospheric deposition source at the operating and abandoned sites was likely from the resuspension of heavy metal(loid)-enriched soil particles. Greater risk of air pollution from historical Pb smelting facilities exists years after closing down. Reducing soil wind erosional losses may help reduce heavy metal(loid)s dispersion across environments.

Lead source and bioaccessibility in windowsill dusts within a Pb smelting-affected area.

Windowsill, heavy metal-containing dust samples, collected at different building heights, may provide some insight into both source and human health risk. Windowsill dust samples were collected from the 1st to 9th floor (1.4-23.2 m above ground) near a lead smelter (1 km to the smelter) and in urban areas (4.2-7.3 km to the smelter) and separated into <10, 10-45 and 45-125 µm size fractions. Samples were extracted with artificial lysosomal fluid (ALF) and the physiologically based extraction test (PBET) (<10 µm fractions only), subjected to scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDS) and Pb isotopic analysis. Greater Pb concentrations were found in 10-45 µm fraction than the other size fractions; at the PX site, dust Pb concentrations increased with windowsill height, while an opposite trend was found at other sites. Isotopic analysis and SEM-EDS results supported this contention. Higher floor samples collected near the smelter were more affected by lead smelting than lower floor samples; lower floor samples collected at urban sites were more affected by resuspended Pb-laden particles from the ground than higher floors. The Pb bioaccessible fraction (BAF) in the ALF and PBET ranged between 68.9-90.1 and 1.3-17.0%, respectively; urban samples had greater BAF values than samples collected near the smelter. This, first of its kind investigation regarding Pb in dusts at different building heights, provides further insight for reducing human health risks within Pb smelter vicinities.

Cadmium, copper, lead and zinc accumulation in wild plant species near a lead smelter.

Smelting activities have been shown to increase the likelihood of environmental heavy metal accumulation and bioaccumulation potential within relative proximity to smelter sites. This investigation focused specifically on cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) accumulation in 43 wild plant species and corresponding soils near a Pb smelting contaminated area. Soils in the study area had elevated Cd, Cu, Pb and Zn concentrations, with pollution indices ranked as Cd > Pb > Cu > Zn. Aboveground plant heavy metal concentrations ranked Pb > Zn > Cd > Cu, with plants having greater bioconcentration factor (BCF) values for Cd than for Pb, Cu and Zn. Plant Cd BCF averaged 1.42, while Pb, Cu and Zn averaged 0.128, 0.256 and 0.560, respectively. The greatest Cd BCF value was 5.40 for Dendranthema indicum; Cd accumulation for this species has not been reported previously. The greatest shoot Cd concentration (66.5 mg kg-1) was found in Viola verecunda. Significant correlations existed between plant shoot Cd and Pb concentrations and soil total and DTPA-extractable Cd and Pb. Plant species with greater heavy metal accumulation could potentially be used for phytoextraction in the study area, while those having less accumulation potentially being used to reduce heavy metal flow into the food chain, reducing the health risks associated with elevated heavy metal soil contamination.

Cadmium foliar application affects wheat Cd, Cu, Pb and Zn accumulation.

Cadmium is toxic to plants, easily reaching unsafe levels for animal and human consumption. A greenhouse experiment investigated the effect of foliar-applied Cd on the accumulation and distribution of Cd, Zn, Cu and Pb in wheat (Triticum aestivum) grown in heavy metal-contaminated soil. Cadmium solutions (0, 10, 20, 30 and 40 mg L-1) were repeatedly sprayed on entire aboveground wheat plants during heading stage to medium milk development stage. Plant sample analyses after harvest indicated that both the biomass yield and grain yield were negatively affected by Cd application (p < 0.05); compared to controls, leaf and grain Cd concentrations increased 187-547% and 26.3-91.8%, respectively. However, grain Cd accumulation (concentration × yield) was not affected by Cd treatments (p > 0.05). Stem, leaf and glume Zn concentrations increased by less than 31%, while grain Zn concentrations were negatively affected by Cd treatments (3.4-34.4% lower than the control). Grain Cu concentrations were also negatively affected by Cd treatments, while grain Pb concentrations were similar between treatments. The antagonistic effect of Cd on grain Zn accumulation may mainly be due to competition for transporters and binding compounds in wheat leaves and stems. Preventing excess Cd from entering aboveground plant tissues should lessen negative plant and potentially animal/human health effects.

Lead smelting effects heavy metal concentrations in soils, wheat, and potentially humans.

Cadmium, Cu, Pb and Zn concentrations and distribution in soil, wheat, and the potential for human heavy metal accumulation near a Pb smelting affected area were investigated. Farm land soil, wheat grain and scalp hair samples were collected from three villages (named QD, GF and BS) with increasing distance from a large Pb smelter in China. Soil Cd and Pb concentrations exceeded national standards 46-100% of the time, depending on location. Soil and wheat grain Cd, Cu, Pb and Zn concentrations increased as distance to the smelter decreased. Similarly, greater Cd, Cu and Pb concentrations were present in human scalp hair for those residents living closest to the smelter. Decreasing trends existed for hair-to-wheat grain ratios for Cd and Pb as distance to the smelter increased. Results suggest that as distance to the smelter decreases, human heavy metal absorption via the consumption of metal-contaminated food products (e.g., wheat) increases.

Inhalation bioaccessibility of Cd, Cu, Pb and Zn and speciation of Pb in particulate matter fractions from areas with different pollution characteristics in Henan Province, China.

Windowsill particulate matter (PM) samples were collected from an area near large lead-smelting facilities in Jiyuan (JP), the urban area of Jiyuan (JU) and the peri-urban area of Mianchi (MC) in Henan, China to investigate the concentration and inhalation bioaccessibility of Cd, Cu, Pb and Zn. The <10 µm portions of the samples were extracted with simulated lung fluid to assess the in vitro inhalation bioaccessibility. Lower concentrations of heavy metals were found in the MC samples than in the JP and the JU samples. The average concentrations of Pb, Cd and Cu in the portions of the same size are in the order of JP samples > JU samples > MC samples. For Pb, Cd and Zn, the maximum inhalation bioaccessibility fraction values are all found in the MC samples, which ranged 3.87-8.79%, while those of the JP and the JU samples are <2%. The Pb speciation analysis with X-ray absorption spectrometry indicate mineral bound Pb, PbS and Pb3(PO4)2 are the predominant Pb species in the JP samples; for the JU sample, organic bound Pb is the predominant Pb species in the 45-125 µm portion, while mineral bound Pb is the predominant Pb species in the 10-45 µm portion; for the MC samples, organic bound Pb is the predominant Pb species, followed by PbS. The results indicate that there is significant accumulation of Pb, Cd, Cu and Zn associated with PM in the area near the lead smelter and in the urban area of Jiyuan, especially Pb and Cd, however, the inhalation bioaccessibility of these metals in samples from the lead smelting impacted area is low, this may be due to the higher proportion of less soluble species of the metals in the samples from this area. However, organic matter bound Pb found in some samples has higher bioaccessibility than other Pb species.

Spatial distribution of smelter emission heavy metals on farmland soil.

This work was conducted to explore heavy metal pollution in soils in an area near lead smelters in Jiyuan City, which is one of the main lead production areas in China. Altogether, 88 topsoil samples (0-20 cm) were collected from farmlands near the Yuguang lead smelting facilities; the sampling sites were 1570 to 6388 m to the main stack of the Yuguang. Analysis of the samples indicated that (i) the ranges of total Cd and Pb concentrations were 0.81-4.30 and 64.5-435 mg kg-1, respectively, mean pollution indices (concentration in soil/background value, PI) were 32.8 and 9.11, respectively, and the concentrations of total Cu, Zn, and Ni were slightly higher than the background values. Mean concentrations of DTPA-extractable Cd and Pb were 0.752 and 58.7 mg kg-1, respectively. (ii) The total concentrations of Cd, Pb and Pb/Cd ratios of samples decreased as the distance to the main stack of the Yuguang increased. Abnormal variations of these trends suggested these parameters of certain samples were affected by pollution sources other than the Yuguang. (iii) Judged by the results of this work, the area of the heavy metal-polluted land in Jiyuan was much greater than 115 km2, a value reported by an earlier investigation. These results indicate that the soil in the study area was polluted by Cd and Pb emissions from more than one polluting sources, the variation of Cd, Pb concentration and Pb/Cd ratios of samples to the distance of the pollution source can be potentially used for pollution source identification.

Influence of phosphate amendment and zinc foliar application on heavy metal accumulation in wheat and on soil extractability impacted by a lead smelter near Jiyuan, China.

Higher concentrations of Pb and Cd in wheat grains harvested in several lead-smelting-polluted areas in northern China have been reported. This field experiment was conducted to investigate the effect of phosphate amendment and Zn foliar application on the accumulation of Pb and Cd in wheat grains grown in a lead-smelting impacted area in Jiyuan in northern China. The soil (total Pb and Cd are 261 and 2.65 mg kg-1, respectively) was amended with superphosphate at P:Pb ratios (mol:mol) of 1.90 or 2.57 either during wheat (Triticum aestivum L.) planting or a split of 60% of the phosphate applied at planting, with remaining 40% applied at the jointing stage. Zn was sprayed on the canopy of the wheat plants at the jointing stage. The phosphate amendment resulted in lower DTPA (diethylene triamine pentaacetic acid)-extractable Pb (1.39-10.7% lower than the control) and Cd (0.040-7.12%) in the soil. No significant effect of split application of phosphate was found on Pb and Cd availability in soil; however, higher rates of P resulted in lower Pb and Cd availabilities in the soil. Grain Pb (5.41-21.5% lower than the control), Cd (3.62-6.76%), and Zn (4.29-9.02%) concentrations were negatively affected by the phosphate application, with higher rates of phosphate resulting in lower grain heavy metal concentrations. Foliar application had no statistically significant influence on Pb and Cd concentrations in the grain (p > 0.05). Although Pb and Cd concentrations in wheat grains were reduced by the phosphate application, their concentrations were still much higher than the maximum permissible concentrations for wheat in the national standards of China. The results suggest that it is feasible to reduce wheat grain concentrations of Pb and Cd in Pb-smelting-polluted areas in northern China by soil application of superphosphate; however, the split application of the phosphate and the foliar application of Zn compounds do not have substantial impact on reducing accumulation of Pb and Cd in the wheat grains.

Repeated phytoextraction of metal contaminated calcareous soil by hyperaccumulator Sedum plumbizincicola.

Most studies on the phytoextraction of cadmium (Cd) and zinc (Zn) by the hyperaccumulator Sedum plumbizincicola (S. plumbizincicola) have been conducted in metal contaminated acidic and neutral soils. However, little information is available on phytoremediation of calcareous soils. Two experiments were conducted to investigate the phytoextraction efficiency of S. plumbizincicola in a contaminated calcareous soil in He'nan province, north China. In a field experiment there was no significant decrease in shoot biomass production or metal (Cd and Zn) concentration in the shoots after three successive repeated phytoextractions. Repeated phytoextraction had no significant effect on the percentage distribution of Cd or Zn fractions in the soil even though the soil total Cd and Zn concentrations decreased by 32.8 and 19.7%, respectively. In a pot experiment the shoot biomass production and Zn and Cd uptake by S. plumbizincicola increased significantly with growth in metal contaminated calcareous soil amended with organic fertilizer, perlite and vermiculite. The results indicate that S. plumbizincicola can maintain sustainable uptake of Cd and Zn from the calcareous soil and enhancement of soil fertility and structure will significantly increase the phytoextraction efficiency.

Heavy metal and metalloid concentrations in components of 25 wheat (Triticum aestivum) varieties in the vicinity of lead smelters in Henan province, China.

Soil contamination and human impacts have been reported in the vicinity of lead (Pb) smelters in Henan, China. However, no information is available on crop uptake of soil contaminants near these smelters. Grains, glume, rachis, and stem/leaf samples of 25 wheat (Triticum aestivum) varieties were collected from a small, smelter-impacted agricultural area of Beishe Village, Henan Province, and were analyzed for arsenic (As), cadmium (Cd), copper (Cu), Pb, and zinc (Zn) concentrations. The study aim was to evaluate the level of contaminant uptake in wheat and ostensibly observe if specific varieties of wheat were more susceptible to uptake. The mean concentrations of As, Cd, Cu, Pb, and Zn in whole grain flour were 0.0915, 0.192, 3.22, 0.280, and 32.5 mg kg(-1), respectively. Grain concentrations of all 25 varieties for Cd as well as 16 varieties for Pb exceeded the maximum permissible concentrations (MPC) for consumption. Mean pollution indexes (MPI) (element concentration of wheat grain/MPC for As, Cd or Pb) of the grains varied 0.562-2.15. As, Pb, and Cd contributed 5.22, 40.0, and 54.8 % to the MPI for all 25 varieties, respectively. This survey highlights Cd and Pb contamination of wheat grains in the vicinity of lead smelters in Henan Province, and likely other farm villages in the area. Further work is needed to examine uptake and contamination of other crops and vegetables impacted from the lead smelters in Henan Province and the absorption of toxic elements from food sources by local inhabitants.

Immobilization of lead in soil influenced by soluble phosphate and calcium: lead speciation evidence.

We investigated the effect of soluble Ca on the speciation of Pb in phosphate-amended soils. A calcareous soil was amended in sequence with soluble phosphate (0 and 299 mg kg P), calcium nitrate (0, 200, and 400 mg kg Ca), and/or lead nitrate (0 and 1000 mg kg Pb) and incubated for 50 d. Extractable Ca was relatively similar across all samples, with a minor reduction in Ca release for treatments amended with P possibly from the formation of Ca-phosphate minerals. Olsen-P extractability from P-added treatments was highest in the non-Pb-amended soils and was about 40% lower when Pb was added as a result of Pb-phosphate formation. In the absence of P, diethylene triamine pentaacetic acid (DTPA)-Pb extractability increased with increasing Ca amendment; however, in the P-amended treatments, DTPA-Pb decreased with increasing Ca addition. X-ray absorption spectroscopy results of the Pb spiked soils indicate that adsorbed Pb is the primary phase (up to 92%) in non-P-amended soils with minor distribution to hydrocerussite and Pb-phosphate phases. In the P-amended treatments, Pb speciation shifted to Pb-phosphate [chloropyromorphite and Pb(PO)] (42-48%) and adsorbed Pb (44-50%). As Ca concentration increased in the P-amended soils, Pb-phosphate speciation moved from combined chloropyromorphite and Pb(PO) (0 mg kg Ca) to exclusively chloropyromorphite. The study demonstrates that soluble Ca enhances Pb immobilization with P amendments.