Heavy metal pollution in Mongolian-Manchurian grassland soil and effect of long-range dust transport by wind.

Grasslands provide a range of valuable ecosystem services, but they are also particularly fragile ecosystems easily threatened by human activities, such as long-term open-pit mining and related industrial activities. In grassland area, dust containing heavy metal(loid)s generated by mines may further migrate to remote places, but few studies have focused on the long-range transport of contaminants as an important pollution source. In the present study, one of the largest and most intact grassland ecosystems, the Mongolian-Manchurian steppe, was selected to investigate its pollution status and track potential sources. A total of 150 soil samples were collected to explore reginal distribution of nine heavy metal(loid)s that has potential risk in grassland. We conducted a combined multi-variant analysis of positive matrix factorization (PMF) and machine learning, which foregrounded the source of long-range transport of contaminants and inspired the hypothesis of a novel stochastic model to describe contaminants distribution. Results showed four different sources accounting for 44.44% (parent material), 20.28% (atmospheric deposition), 20.39% (farming), and 14.89% (transportation) of the total concentration, respectively. Factor 2 indicated that coal surface mining lead to a significant enrichment of As and Se with their concentration far above the global average level, which was different from other reported grassland areas. Machine learning results further confirmed that atmospheric and topographic features were their contamination controlling factors. The model results proposed that As, Se and Cu released by surface mining will be transported over long distance under prevailing monsoon, until finally deposited in the windward slope of mountain due to terrain obstruction. The long-range transport by wind and deposition of contaminants may be a prevailing phenomenon in temperate grassland, making it a pollution source that cannot be ignored. Evidence from this study reveals the urgency of precautions for fragile grassland ecosystems around industrial areas and provides a basis for its management and risk control policies.

Comprehensive assessment of soil and dust heavy metal(loid)s exposure scenarios at residential playgrounds in Beijing, China.

Small playgrounds situated within residential communities are popular recreational areas. However, heavy metal(loid)s (HMs) in soil or equipment dust may pose a public health risk. This study provides a comprehensive assessment of the health risk associated with HMs exposure at residential playgrounds in cities, a field that has not been thoroughly investigated previously. 70 soil and 70 equipment dust samples were collected from 30 urban and 40 suburban playgrounds in Beijing. Results indicated significant enrichment of Cu, As, and Ni in the soil with Enrichment Factors (EFs) >5 from both anthropogenic and lithogenic sources. Correlation analyses showed that the levels of Be, Cr, Mn, Co, Ni in soil and Be, Mn, As, Cd in dust were positively correlated with the distance to the nearest highway, with p-values < 0.01. Enrichment and correlation analyses contributed to a better understanding of the sources and transport pathways of HMs in urban environment. Based on a site-specific Conceptual Site Model (CSM), the carcinogenic risks (CRs) and Hazard Quotients (HQs) were quantified for residents as the ratio of HMs exposure to reference doses. Risk assessment indicated the mean predicted CR for children and adults exposed to soil was 3.75 × 10-6 and 5.29 × 10-6, respectively, while that at dust exposure scenarios was lower, at 2.47 × 10-6 and 3.49 × 10-6, respectively, all of which were at the upper end of U.S. EPA's acceptable criteria of 1 × 10-6 to 1 × 10-4. Among the HMs, As and Ni were identified as the priority control contaminants due to significant contribution to CRs. Furthermore, the spatial distribution revealed an increasing trend in health risk from the urban center to the suburbs. This study emphasizes the need for effective measures to mitigate potential health risk and enhance the safety of recreational areas, particularly for susceptible individuals.

Manganese stabilization in mine tailings by MgO-loaded rice husk biochar: Performance and mechanisms.

Leachable metal in abandoned mine tailings may be toxic to vegetation, affecting effective ecological restoration. In this study, MRB was synthesized through MgCl2·6H2O wet impregnation followed by duplicate slow pyrolysis. Manganese tailings were mixed with MRB, rice husk biochar (RB), and MgO at a dosage of 0-5%, followed by 90-day incubation. Toxicity characteristic leaching procedure and sequential leaching were used to analyze the leachability and species of Mn in tailings, while a stabilization mechanism was proposed with the support of the characterization of the tailings before and after amendment. Results suggested MRB addition significantly decreased leachable Mn by 63.8%, reducing from 59.88 mg/L to 21.68 mg/L, while only a 14.39% reduction was achieved by rice husk biochar (RB). The sharp decline of leachable Mn after 90-day mixing was contributed by the transformation from labile to stable fractions. A microporous biochar matrix along with the uniform dispersion of MgO active component were both responsible for the better Mn stabilization. Only less than 10% of the variation in substrate pH was observed with the increase of MgO loading or incubation time. Linear correlation analyses indicated substrate pH's strongl negative relationship with leachable Mn and moderately positive relationship with residual fraction. Characterization results revealed that MRB exhibited different stabilization mechanisms in mine tailings, where Mn was likely to be stabilized by direct interaction with active MgO or indirect alkaline precipitation to form stable MgMn2O4, Mn(CH3COO)2, and MnO(OH)2. This work validated the promoting potential of recycling agricultural biomass waste for the amendment of manganese mine tailings.

Spatial distribution of lead contamination in soil and equipment dust at children's playgrounds in Beijing, China.

Lead contamination is widespread across China, posing a serious public health concern. In quantifying child lead exposure, established health risk assessment (HRA) approaches often take into account residential soil lead levels. However, this may not constitute a significant exposure source for children in urban mainland China, where the population mainly dwell in high-rise buildings without back or front yards. In this setting, children's playgrounds may represent a more probable exposure source. The present study analyzed lead levels in settled dust on playground equipment and in surficial soils at 71 playgrounds in Beijing, China. Our results reveal that the average playground dust lead concentration was 80.5 mg/kg, more than twice the average soil lead concentration of 36.2 mg/kg. It was found that there are differences in statistical and spatial distributions for lead in playground dust and soils. Lead levels in equipment dust were largely consistent across Beijing, with elevated levels detected at locations in the main city area, the newly developed Tongzhou District, and the rural counties. Whereas average soil lead concentrations were higher at playgrounds in the main city area than other areas of Beijing. Statistical analysis suggests that the lead content in dust and soil may derive from different natural and anthropogenic sources. Equipment dust lead may be associated with long-distance atmospheric transportation and deposition. Whereas lead in soil is more likely to be associated with local traffic. This study also found that, in certain areas of Beijing, the risk of blood lead levels (BLLs) exceeding safe levels was up to 6 times higher when based on dust exposure than when based on playground soil exposure. The results of this study suggests that HRA undertaken for children in urban mainland China should pay closer attention to children's playgrounds as a lead exposure source, and, in particular, playground equipment dust.

Lead-based paint remains a major public health concern: A critical review of global production, trade, use, exposure, health risk, and implications.

Human exposure to lead (Pb) is a growing global public health concern. Elevated blood lead is thought to cause the mental retardation of >0.6 million children globally each year, and has recently been attributed to ~18% of all-cause mortality in the US. Due to the severe health risk, the international community, led by the United Nations Environment Programme (UNEP) and the World Health Organization (WHO), is actively supporting the global phase-out of lead-based paint by 2020. However, there are many significant hurdles on the way to achieving this goal. In light of the importance of the lead-based paint issue, and the urgency of achieving the 2020 phase-out goal, this review provides critical insights from the existing scientific literature on lead-based paint, and offers a comprehensive perspective on the overall issue. The global production and international trade of lead-based paints across Asia, Africa, Latin America, and Europe are critically discussed - revealing that lead-based paints are still widely used in many low and middle-income developing countries, and that the production and trade of lead-based paint is still wide-spread globally. In India, as well as many south-east Asian, African, Latin American and European countries, lead concentrations in paints often exceed 10,000 mg/kg. This will certainly pose a serious global threat to public health from surfaces painted with these products for many decades to come. The sources and pathways of exposure are further described to shed light on the associated health risk and socioeconomic costs. Finally, the review offers an overview of the potential intervention and abatement strategies for lead-based paints. In particular, it was found that there is a general lack of consensus on the definition of lead based paint; and, strengthening regulatory oversight, public awareness, and industry acceptance are vital in combating the global issue of lead based paint.

Assessing long-term stability of cadmium and lead in a soil washing residue amended with MgO-based binders using quantitative accelerated ageing.

A soil washing residue (SWR) (containing 90% clay, cadmium (Cd2+) of 132 mg/kg, lead (Pb2+) of 3410 mg/kg) was stabilized with MgO (M) and MgO + bioapatite (MB) respectively at a dosage of 5% in w/w. The stability of the metals in original and amended SWRs was assessed after immediate treatment and using a laboratory accelerated ageing method simulating 26, 52, 78 and 104 years in field conditions. The dissolved Cd2+ and Pb2+ from the SWR in Toxicity Characteristic Leaching Procedure (TCLP) leachates significantly reduced (by 96.84-99.06%) by both amendments after immediate treatment. The stabilization remained effective within simulated 26 years as the TCLP leached Cd2+ and Pb2+ kept below regulatory levels. This immobilization was mainly due to the increased non-bioavailable Cd2+ and Pb2+ from sequential extraction tests in SWR by the amendments. At simulated 52 years, the TCLP leached Cd2+ from M and MB exceeded regulatory level by 106% and 1% respectively. Large amounts of Cd2+ and Pb2+ were leached out by 36.74-48.18% regardless of the treatments at simulated 104 years. Although bioapatite can significantly aid the stabilization of metals by MgO, the stabilization effectiveness for both treatments diminished at simulated 52 years and from 52 to 104 years.

Sulfur-modified rice husk biochar: A green method for the remediation of mercury contaminated soil.

Mercury (Hg) contamination of surface soils has increased by ~86Giga grams due to anthropogenic activities. There is an urgent need to find new, effective and preferably 'green' remediation technologies to protect human health and the environment. Sulfur-modification of sorbents can greatly enhance Hg sorption capacity - by forming low solubility HgS (cinnabar). However, S-modified sorbents are not considered suitable for soil remediation due to the economic cost and secondary environmental impacts of sorbents such as granulated activated carbon (GAC), and the toxicity of S-modifiers such as thiol compounds. It was previously found that if biochar is used as an alternative to GAC then the overall environmental impact can be significantly reduced. However, due to a lack of experimental evidence, the practicality of S-modified biochar remains uncertain. The present study was undertaken to provide a proof-of-concept for the 'green' remediation of Hg contaminated soils with rice husk biochar modified with non-toxic elemental S. It was found that the S modification process increased the biochar S content from 0.2% to 13.04% via surface deposition or volume pore filling. This increased the biochar's Hg2+ adsorptive capacity (Qmax) by ~73%, to 67.11mg/g. To assess the performance of S-modified rice husk biochar for soil remediation it was applied to a high 1000mg/kg Hg2+ contaminated soil. Treatment dosages of 1%, 2% and 5% (dry wt.) were found to reduce freely available Hg in TCLP (toxicity characterization leaching procedure) leachates by 95.4%, 97.4% and 99.3%, respectively, compared to untreated soil. In comparison, unmodified rice husk biochar reduced Hg concentrations by 94.9%, 94.9% and 95.2% when applied at the same treatment dosage rates, respectively. This study has revealed that S-modified rice husk biochar has potential to stabilize Hg as a 'green' method for the remediation of contaminated soils.

Biochar application for the remediation of heavy metal polluted land: A review of in situ field trials.

Polluted land is a global issue, especially for developing countries. It has been reported that soil amendment with biochar may reduce the bioavailability of a wide range of contaminants, including heavy metal(loids), potentially reclaiming contaminated soils for agricultural use. However, there have been only limited reports on the in situ application of biochar at the field scale. This review was devoted to providing preliminary scientific evidence from these field trials, based on a review of 29 publications involving field applications of biochar in 8 different countries. The data show that biochar's effectiveness in reducing the impacts of pollution depends on a myriad of factors in the field, including the application time period, site-specific factors (e.g. climate, biochar dosage rate, and mixing depth), biochar feedstock type, and biochar properties. The results of this review indicate that biochar application can potentially reduce contaminant bioavailability in the field; for instance, a significant decrease (control normalized mean value=0.55) in the Cd enrichment of rice crops was observed. It was found that the use of biochar may help increase crop yields on polluted land, and thus reduce the amount of mineral fertilizer used in the field. However, in order to maximize the benefits of biochar addition, farmers need to accept that the dosage rates of mineral fertilizers should be reduced. This review also revealed that the effectiveness of biochar in mitigating pollution may decrease with time due to ageing factors, such as leaching of biochar alkalinity.