Effect of metal-modified sewage sludge biochar tubule on immobilization of chromium in unsaturated soil: Groundwater table fluctuations induced by rainfall.

Many studies have studied biochar immobilizing chromium (Cr) in soil. However, few studies were conducted to reduce the environmental risks due to biochar aging in soil. In this study, we adopt FeCl3, MgCl2, and AlCl3 to activate sewage sludge to form modified biochar and produce biochar tubules. Then, the column experiments were carried out to study the effect of fluctuating groundwater table on Cr leaching behavior, total Cr, and fractions distribution with the insertion of biochar tubule. Results showed that the Cr immobilization performance was improved by metal-modification biochar, the biochar tubules can significantly decrease the Cr leaching amounts, retard the Cr downward migration in the soil, and there was a better effect with slightly Cr-contaminated soil. In addition, the immobilization effect is also impacted by the biochar's application mode and the hydrodynamic conditions. Detailedly, the Cr leaching amounts maximally decreased by 33.39%, the residual amounts maximally increased by 10.05% in the soil column, and the exchangeable (EX) and carbonates-bound (CB) fractions were maximally increased by 85.18%, 151.78% at the equal depth of soil column, respectively. BET, SEM-EDS, XRD, and FTIR analyses revealed that biochars' immobilization mechanisms on Cr involved reduction(predominately), physisorption, precipitation, and complexation. Risk assessment demonstrated that the sewage sludge biochar has very low environmental risk. This study indicates that the biochar tubule applied to immobilize Cr in soil has potential and provides new insights into reducing environmental risks due to biochar aging.

Multi-isotope identification of key hydrogeochemical processes and pollution pathways of groundwater in abandoned mining areas in Southwest China.

Acid mine drainage (AMD) is considered one of the serious environmental issues in the mining area. Understanding the key processes and pathways of hydrogeochemical evolution is critical for the effective control of AMD pollution. Hydrogeochemical analysis along with environmental isotope tracing was utilized to provide information regarding the hydrogeochemical process of groundwater pollution by using the multi-aquifer of abandoned Dashu pyrite in Southwest China as an example. Using the deuterium excess parameter d of groundwater and the results of 2H, 18O, and T analysis, the water-rock interaction intensity was determined. The distribution characteristics of d-T revealed that the groundwater primarily originated from the Quaternary reservoir platform groundwater and that there was a close hydraulic connection among the aquifers. The results of ion analysis and sulfur isotope tracing indicated that the sulfur in groundwater was primarily derived from gypsum dissolution, whereas the sulfur in mine water was primarily derived from pyrite oxidation. The results of the hydrogeochemical inversion indicated that mining activities altered the water level and flow conditions, promoted water-rock interactions, altered the hydrogeochemical process, and caused aquifer and mine water cross-contamination. The findings provide theoretical guidance for identifying the pollution sources and critical hydrogeochemical processes that affect groundwater in depleted mining areas of multi-aquifers and also provide technical support for developing water source control and prevention techniques.

Distribution Patterns of Microplastics Pollution in Urban Fresh Waters: A Case Study of Rivers in Chengdu, China.

Microplastics are widely found in oceans and rivers. In China, the research on microplastic pollution in inland urban fresh waters of China is insufficient. We studied microplastics in the surface waters of urban rivers in Chengdu, which is the largest city in western China. The concentration of microplastics in the analysis environment ranged from 5.00 to 10.5 items/L, and the average quantity was 8.82 items/L. The majority of the microplastics were transparent and took the form of fragments, particles, and fibers. Polyethylene terephthalate (PET) and polyamide (PA) were the dominant polymer types of the microplastics analyzed. Plastic particles ≤ 500 µm accounted for 69.8% of the total. This large proportion of small transparent microplastics in urban rivers in Chengdu is a potential threat to the growth of aquatic organisms and birds foraging from the river and may pose hazards to human health. Additionally, the correlation of microplastic content with population quantity and economic level was calculated by the Pearson coefficient method (p < 0.05), and the results showed that both have an important effect on the number of microplastics in rivers. This research provides a reference for understanding the level of microplastics in urban rivers in Chengdu and pollution control.

Effects of biochar addition on toxic element concentrations in plants: A meta-analysis.

Consuming food contaminated by toxic elements (TEs) could pose a substantial risk to human health. Recently, biochar has been extensively studied as an effective soil ameliorant in situ because of its ability to suppress the phytoavailability of TEs. However, despite the research interest, the effects of biochar applications to soil on different TE concentrations in different plant parts remain unclear. Here, we synthesize 1813 individual observations data collected from 97 articles to evaluate the effects of biochar addition on TE concentrations in plant parts. We found that (1) the experiment type, biochar feedstock and pyrolysis temperature all significantly decreased the TE concentration in plant parts; (2) the responses of Cd and Pb concentrations in edible and indirectly edible plant parts were significantly more sensitive to the effect of biochar than the Zn, Ni, Mn, Cr, Co and Cu concentrations; and (3) the biochar dosage and surface area, significantly influenced certain TE concentrations in plant tissues as determined via correlation analysis. Moreover, the only exception in this study was found for metalloid element (i.e., As) concentrations in plants, which were not significantly influenced by biochar addition. Overall, the effects of biochar on TE concentrations in plant tissues were negative, at least on average, and the central trends suggest that biochar has a considerable ability to mitigate the transfer of TEs to food, thereby reducing the associated health risks. Our results provide an initial quantitative determination of the effects of biochar addition on multifarious TEs in different plant parts as well as an assessment of the ability of biochar to reduce TE concentrations in plants.