An accurate understanding of soil heavy metal (HM) pollution characteristics and source apportionment, and a recognition of the major factors influencing ecological and human health risks (HHRs) are essential for soil HM pollution control and remediation. In this study, 212 surface soils (0-20 cm) and 15 profile soils (0-100 cm) were collected from cropland soils around an e-waste dismantling site in Taizhou city, Zhejiang Province, China. Spatial analysis was used to evaluate the pollution characteristics of HMs (Cd, Cu, Pb, Zn, Cr and Ni). Principal component analysis (PCA) and positive matrix factorization (PMF) were also conducted to quantify their source contributions. A modified source-oriented HHR assessment integrated source-oriented ecological risk and source-oriented HHR assessment was developed to describe the major factors that influenced HHR. Results showed that 94.81 %, 88.21 %, 36.79 % and 47.17 % of Cd, Cu, Pb and Zn, respectively, in surface soils exceeded their screening values in the soil environmental quality standard for agricultural soils (GB 15618-2018). Spatial analysis indicated that high values of Cd, Cu, Pb and Zn were distributed near the e-waste dismantling site. The results of PCA and PMF showed that the primary sources of HMs in the study area are e-waste dismantling activities, natural sources and atmospheric deposition, which contribute 27 %, 46 % and 27 % of HM pollutants, respectively. The results of source-oriented ecological risk and HHR assessment indicated that e-waste dismantling activities and natural sources were primary sources for ecological risk and HHR. However, source-oriented HHR assessment may underestimate the contribution of e-waste dismantling activities by ignoring HM pollution levels. The modified source-oriented HHR assessment highlights that e-waste dismantling activities were major factor that affect noncarcinogenic risk. This study could provide important data support for subsequent environmental remediation of soil HM pollution in cropland soils around e-waste dismantling sites.

Hg pollution in soils surrounding the Wanshan mercury mine (WMM), once the largest Hg-producing center in China, has been confirmed, neglecting other potential toxic elements (PTEs). Better understanding of the sources and transport pathways of soil PTEs remains insufficient. To response these limitations, eight soil PTEs (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) at two typical agricultural sites, namely AZ and WW that are located near and far from the WMM, respectively, were systemically investigated. The results showed that AZ exhibited significantly higher concentrations of all the PTEs in the surface soil than WW (p < 0.01). Hg and Cd were recognized as the priority control PTEs, with their average concentrations of 21.54 and 1.21 mg kg^-1 at AZ, and 15.79 and 0.48 mg kg^-1 at WW. Those affected PTEs tended to enrich in near-river areas. Atmospheric deposition contributed more to soil Hg than did regular irrigation, but these two sources could not explain the considerable soil Hg accumulation. Three sources, including natural sources, hydraulic transport (torrential floods and regular irrigation) and atmospheric deposition, were identified and quantified based on the positive matrix factorization model, statistical methods and various auxiliary information. Hydraulic transport (mainly torrential floods) dominated the soil Hg input, which could explain 83.8% and 69.8% of the soil Hg input at AZ and WW, respectively. Atmospheric deposition dominated the soil Cd input, explaining 44.3% and 59.9% of the soil Cd input at AZ and WW, respectively. More attention should be given to the safe utilization of agricultural land and long-term monitoring of atmospheric deposition of Hg and Cd. This study could provide insights to prevent PTE diffusion along the above dominant transportation pathways while developing similar mine regions.

Organochlorine pesticides (OCPs) were typical persistent organic pollutants that posed great hazards and high risks in soil. In this study, a peanut shell biochar-loaded nano zero-valent iron (BC/nZVI) material was prepared in combination with soil indigenous microorganisms to enhance the degradation of α-hexachlorocyclohexane(α-HCH) and γ-hexachlorocyclohexane(γ-HCH) in water and soil. The effects of BC/nZVI on indigenous microorganisms in soil were investigated based on the changes in redox potential and dehydrogenase activity in the soil. The results showed as follows: (1) The specific surface area of peanut shell biochar loaded with nano-zero-valent iron was large, and the nano-zero-valent iron particles were evenly distributed on the peanut shell biochar; (2) peanut shell BC/nZVI had a good degradation effect on α-HCH and γ-HCH in water, with degradation rates of 64.18% for α-HCH and 91.87% for γ-HCH in 24 h; (3) peanut shell BC/nZVI also had a good degradation effect on α-HCH and γ-HCH in soil, and the degradation rates of α-HCH and γ-HCH in the 1% BC/nZVI reached 55.2% and 85.4%, second only to 1% zero-valent iron. The degradation rate was the fastest from 0 to 7 days, while the soil oxidation-reduction potential (ORP) increased sharply. (4) The addition of BC/nZVI to the soil resulted in a significant increase in dehydrogenase activity, which further promoted the degradation of HCHs; the amount of HCHs degradation was significantly negatively correlated with dehydrogenase activity. This study provides a remediation strategy for HCH-contaminated sites, reducing the human health risk of HCHs in the soil while helping to improve the soil and increase the activity of soil microorganisms.

The excessive nitrogen and phosphorus discharged into the water environment will cause water eutrophication and thus disrupt the water ecosystem and even exert biological toxicities. In this study, the absorption removal of nitrogen and phosphorus from the anaerobic tank in an anaerobic–anoxic/nitrifying system using four different kinds of biowaste-reclaimed biochars were investigated and compared. The effects of temperature and pH on nutrient adsorption removal were further investigated. The four kinds of biochar were successfully prepared and well characterized using a scanning electron microscope, fourier transform infrared spectroscopy, X-ray diffraction and Brunner−Emmet−Teller methods. Generally, there was no significant change in chemical oxygen demand (COD) and NH₄⁺-N removal efficiencies when treated by the different biochars, while the activated sludge biochar (ASB) displayed the highest total phosphorus (TP) removal efficiency. The initial TP concentrations (<40 mg/L) displayed no remarkable effects on the TP adsorption removal, while the increase of temperature generally enhanced TP and NH₄⁺-N adsorptions on the ASB. Besides, the increase of pH significantly promoted NH₄⁺-N removal but depressed TP removal. Moreover, the adsorption process of TP by the ASB complies with the secondary kinetic model, suggesting the chemical precipitation and physical electrostatic interaction mechanisms of TP adsorption removal. However, the adsorption of NH₄⁺-N conformed to the inner-particle diffusion model, indicating that the NH₄⁺-N adsorption was mainly involved with pore diffusions in the particles.

Phosphate-solubilizing fungi (PSF) are commonly employed in the bioremediation of lead contamination through the production of organic acids. However, the secretion of organic acids by PSF is typically affected by various environmental factors. This study investigated the Pb removal process by typical PSF A. niger and P. chrysogenum under different Mn ²⁺ concentrations (0–30 mg/L). The different concentrations of Mn ²⁺ can significantly influence the Pb toxicity tolerance of PSF. PSF A. niger exhibits a stable Pb removal ratio of >99% under different Mn ²⁺ concentrations, much higher than P. chrysogenum <90%. The high concentrations of Mn ²⁺ (15 and 30 mg/L) both inhibited the secretion of organic acids by A. niger and P. chrysogenum . However, 7.5 mg/L Mn ²⁺ can significantly increase the secretion of oxalic acid by A. niger and promote the formation of lead oxalate and pyromorphite. Only 2.25% Pb ²⁺ is released again from the immobilized Pb minerals. Meanwhile, PSF has the highest pyruvate dehydrogenase (PDH) enzyme activities of 31.53 and 17.23 nmol/min/g in 7.5 mg/L Mn ²⁺ treatment. Compared with P. chrysogenum , A. niger is more effective in removing and stabilizing Pb cations. Controlling the appropriate Mn ²⁺ concentration can further improve the Pb bioremediation by PSF.