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This study conducted a nationwide specific assessment of soil chromium (Cr) contamination status in 506 of China's industrial regions. The overall soil Cr concentrations were 0.74–37,967.33 mg/kg, and the soil Cr content in 4.15% of the regions exceeded the reference screening value (2500 mg/kg). Geochemical accumulation index (Igeo) and monomial potential ecological risk index (E) revealed Cr salt production and tanning were the primary control industries. The non-carcinogenic risks posed by Cr salt production and tanning industries were higher than the national average values, and children were the most vulnerable groups. The heavily polluted regions were mainly located at the Yangtze River Delta, the Bohai Rim, the Pearl River Delta, the Yangtze River Basin, and the Yellow River Basin. The Yangtze River Delta was further identified as the high priority control area based on the class distribution of Igeo and E. Regression analysis showed the soil Cr concentrations in industrial regions increased during 2002–2009 and then turned into a declining trend in 2009–2021. This paper gives detailed insights into soil Cr pollution status in industrial regions across China and the results may serve as references for formulating tailored control measures for different industries and areas. [ABSTRACT FROM AUTHOR]

Hexavalent chromium (Cr(VI)) waste produced by chrome plating activities pollutes the surrounding environment and harms human health. However, information about the chromium (Cr) pollution characteristics of actual electroplating sites is still lacking. In this study, the concentration, leachability and speciation of Cr in soils from a typical chrome plating site were analyzed. Our results showed that this site was severely contaminated by Cr (7.2 to 7735.2 mg/kg) and Cr(VI) reached the mean concentration of 138.7 mg/kg. The spatial distribution of Cr(VI) was related to the plating processes. Chrome plating and sewage treatment areas could be considered as the hot spots of contaminated sites. The vertical distribution of Cr(VI) was mainly affected by soil properties, where the loam layer retained and reduced a large amount of Cr(VI) due to its high content of iron minerals and finer particle fractions. Additionally, the chemical extraction results showed that Cr was mainly in non-residual fractions and the existence of Cr(VI) led to a high leaching toxicity based on the toxicity characteristic leaching procedure (TCLP) results. Moreover, X-ray photoelectron spectroscopy (XPS) results revealed the speciation of Cr in the long-term contaminated soils. A large amount of Cr(VI) was reduced into Cr(III) and mainly existed as Cr(OH)3 and Cr2O3. Furthermore, Cr(VI) tended to precipitate as CaCrO4 and persisted in soils. Therefore, it is necessary to find appropriate strategies to remediate these contaminated soils. Overall, these findings strengthen our understanding of Cr(VI) behaviors and lay a foundation for the future pollution investigation, ecological remediation and risk assessment of sites contaminated by electroplating. [ABSTRACT FROM AUTHOR]

Oxidation remediation is a commonly used technology for PAHs contaminated soil presently, but the overestimate of efficiency due to ongoing remediation by residual oxidants during extraction and testing has not been paid enough attention. In this study, persulfate was activated by Fe(II) to investigate the effects of residual oxidants on PAHs removal during detection process and the elimination effects of adding Na 2 SO 3 and extending sampling time on residual oxidants. Results verified that the residual oxidants removed PAHs in extraction process, making the results lower than the actual values: the detection recovery rate η of ∑PAHs and 3-6 ring PAHs ranged from 24.3% (25% Na 2 S 2 O 8 treatment) to 87.4% (5% Na 2 S 2 O 8 +4/4Fe2+ treatment), 20.1%-99.0%, 28.9%-87.9%, 20.8%-89.4%, and 18.6%-76.9%, respectively. After adding Na 2 SO 3 , the accuracy of detection results increased significantly: the η of ∑PAHs and 3-6 ring PAHs increased to 64.1%-96.5%, 58.8%-95.5%, 73.8%-114.4%, 60.6%-95.6%, and 45.4%-77.1%, respectively. After 49 days of adding oxidants, residual oxidants had no considerable effect on the detection of PAHs, indicating it was appropriate to start soil remediation verification sampling49 days after the remediation was completed. The observed results will help scientific evaluation of the remediation effects of chemical oxidation on organic contaminated soil. [Display omitted] [ABSTRACT FROM AUTHOR]

Cadmium (Cd) contamination in paddy soil has become a worldwide concern and severely endangered human health. Nano hydroxyapatite (n-HAP) is a practical material to manage paddy Cd pollution, but its dosage should not be excessive. Based on previous studies, we validated the effect of n-HAP pre-treatment on rice Cd uptake in pot and field experiments. The results indicated that n-HAP pre-treatment effectively restricted Cd translocation in the soil-rice system. In pot experiment, when soil n-HAP concentration was 5000 mg/kg, the Cd content in the grains of n-HAP pre-treated rice was 0.171 mg/kg, decreased by 29.3% compared with normal rice (0.242 mg/kg). In field experiment, when soil n-HAP concentration was 20,000 mg/kg, the Cd content in the grains of n-HAP pre-treated rice was 0.156 mg/kg, decreased by 35.3% compared with normal rice (0.241 mg/kg). The primary mechanism was that n-HAP pre-treatment altered the formation and composition of iron plaque and therefore enhanced the Cd binding ability of iron plaque. The available N and P content and urease activity in paddy field were increased. We further investigated the impact of n-HAP on the diversity and structure of paddy microbial communities. The Chao1 and Shannon diversity indices showed no significant difference. The relative abundance of Actinobacteria and Proteobacteria was significantly decreased by n-HAP, indicating that Cd pollution might be alleviated. Desulfobacterota , Gemmatimonadota , and Geobacteraceae were significantly enriched by n-HAP. The declining relative abundance of Basidiomycota and the increasing relative abundance of other fungal taxa also suggested that n-HAP could alleviate Cd toxicity in soil. [Display omitted] • n-HAP pre-treatment reduced Cd accumulation in rice grains effectively. • n-HAP pre-treatment restricted Cd translocation from root to stem by regulating iron plaque formation and composition. • n-HAP significantly increased available N, P content and urease activity in paddy field. • n-HAP did not significantly affect the abundance and diversity of paddy microbial communities but altered their structure. [ABSTRACT FROM AUTHOR]

Oxalic acid is the most abundant low molecular weight organic acid (LMWOA) in many environments and offers enormous prospects for treating Cr(VI) contamination. In this study, laboratory batch experiments were conducted to estimate the roles of oxalic acid in Cr(VI) removal by Penicillium oxalicum SL2. Oxalic acid changed the initial pH and provided a suitable condition for the growth of strain SL2 when the penicillium was applied to bioremediation of Cr(VI) contamination in alkaline soil. Gompertz model analysis indicated that initial pH affected the lag time of the growth curve of strain SL2. Scanning electron microscopy and scanning transmission X-ray microscopy analysis showed strain SL2 sufficiently contacted with contaminated soil and reduced Cr(VI) to Cr(III) in the hyphae. The results suggested that oxalic acid could enhance the bioremediation efficiency of strain SL2 though improving chromium bioleaching from the contaminated soil and strengthening Cr(VI) removal in the leaching solution. This study provided oxalic acid as a green reagent for stimulating Cr(VI) removal by strain SL2 and would expand knowledge on the roles of LMWOA in Cr(VI) bioremediation. [Display omitted] • Gompertz model could simulate the growth curve of strain SL2 under initial pH5 to pH9. • Growth of strain SL2 had a strong correlation with Cr(VI) removal. • Oxalic acid improved chromium bioleaching by strain SL2 from contaminated soil. • Oxalic acid enhanced Cr(VI) removal by strain SL2 in the leaching solution. [ABSTRACT FROM AUTHOR]