In vitro model insights into the role of human gut microbiota on arsenic bioaccessibility and its speciation in soils

The bioaccessibility of arsenic and its speciation are two important factors in assessing human health risks exposure to contaminated soils. However, the effects of human gut microbiota on arsenic bioaccessibility and its speciation are not well characterized. In this study, an improved in vitro model was utilized to investigate the bioaccessibility of arsenic in the digestive tract and the role of human gut microbiota in the regulation of arsenic speciation. For all soils, arsenic bioaccessibility from the combined in vitro model showed that it was <40% in the gastric, small intestinal and colon phases. This finding demonstrated that the common bioaccessibility approach assuming 100% bioaccessibility would overestimate the human health risks posed by contaminated soils. Further to this, the study showed that arsenic bioaccessibility was 22% higher in the active colon phase than that in the sterile colon phase indicating that human colon microorganisms could induce arsenic release from the solid phase. Only inorganic arsenic was detected in the gastric and small intestinal phases, with arsenate [As(V)] being the dominant arsenic species (74%–87% of total arsenic). Arsenic speciation was significantly altered by the active colon microbiota, which resulted in the formation of methylated arsenic species, including monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)] with low toxicity, and a highly toxic arsenic species monomethylarsonous acid [MMA(III)]. Additionally, a high level of monomethylmonothioarsonic acid [MMMTA(V)] (up to 17% of total arsenic in the extraction solution) with unknown toxicological properties was also detected in the active colon phase. The formation of various organic arsenic species demonstrated that human colon microorganisms could actively metabolize inorganic arsenic into methylated arsenicals and methylated thioarsenicals. Such transformation should be considered when assessing the human health risks associated with oral exposure to soil

Field verification of low-level biochar applications as effective ameliorants to mitigate cadmium accumulation into Brassica campestris L from polluted soils

Introduction: Cadmium (Cd) has been recognized as a significant contributor to the pollution of farmland soils in China, and biochars have been reported to be effective in mitigating soil Cd pollution. However, most studies have been conducted in laboratory or greenhouse settings, not at a field scale, and the biochars used have been applied at unrealistically high amounts (>10 t/ha). Methods: In this research, three biochars: rice straw biochar (RSB), pig manure biochar (PMB) and rice husk biochar (RHB) were produced from readily available farm residues. Then the effects at low-level application (1.8 and 3.6 t/ha) on Cd were investigated in a field experiment cropped with rape (Brassica campestris L.). Results: Batch adsorption experiments indicated Cd adsorption capacity of three biochars followed the order of RSB (43.5 mg/g) > PMB (33.3 mg/g) > RHB (24.4 mg/g). Field experiment indicated biochar amendments could slightly change soil pH and cation exchange capacity (CEC); yet led to considerable and significant decreases in extractable Cd concentrations [reductions of: 43%–51% (PMB), 29%– 35% (RSB) and 17%–19% (RHB)]. Reduced extractable Cd correlated with lower Cd concentrations in rape plants. PMB and RSB were more effective in decreasing Cd phytoaccumulation into edible parts of rape (>68% reduction) than RHB. Discussion: Low-level application of PMB or RSB could efficiently decrease the phytoaccumulation of Cd from soils into crops. These results demonstrate the reality of biochar-based remediation solutions to contribute to the mitigation of diffuse Cd contamination in farmland. The results also highlight the need to trail biochars in the presence of the soil to be targeted for remediation

Enhanced bioremediation of aged polycyclic aromatic hydrocarbons in soil using immobilized microbial consortia combined with strengthening remediation strategies

Microbial biodegradation is considered as one of the most effective strategies for the remediation of soil contaminated with polycyclic aromatic hydrocarbons (PAHs). To improve the degradation efficiency of PAHs, PAH-degrading consortia combined with strengthening remediation strategies was used in this study. The PAH biodegrading performance of seven bacterial consortia constructed by different ratios of Mycobacterium gilvum MI, Mycobacterium sp. ZL7 and Rhodococcus rhodochrous Q3 was evaluated in an aqueous system containing phenanthrene, pyrene, benzo[a]pyrene and benzo[b]fluoranthene. Bacterial consortium H6 (Q3:ZL7:MI = 1:2:2) performed a high degrading efficiency of 59% in 8 days. The H6 was subsequently screened to explore its potential ability and performance to degrade aged PAHs in soils from a coking plant and the effects of strengthening strategies on the aged PAH degradation, including the addition of glucose or sodium dodecyl benzene sulfonate (SDBS) individually or as a mixture along immobilization of the inoculant on biochar. The highest degradation efficiencies, which were 15% and 60% for low-molecular-weight (LMW) PAHs and high-molecular-weight (HMW) PAHs, respectively, were observed in the treatment using immobilized microbial consortium H6 combined with the addition of glucose and SDBS after 24 days incubation. This study provides new insights and guidance for future remediation of aged PAH contaminated soils

Remediation of cadmium and lead polluted soil using thiol-modified biochar

Thiol-modified rice straw biochar (RS) was prepared by an esterification reaction with β-mercaptoethanol and used for the remediation of Cd and Pb polluted soils. Modified biochar was characterized through elemental analysis, BET analysis, FE-SEM, FT-IR and XPS. These analytical results revealed that thiol groups were successfully grafted onto the surface of the biochar and were involved in metal ion complexation. Batch sorption experiments indicated that Cd2+ and Pb2+ sorption onto RS described well by a pseudo second order kinetic model and a Langmuir isotherm. The maximum adsorption capacities for Cd2+ and Pb2+, in the single-metal systems, were 45.1 and 61.4 mg g−1, respectively. In the binary-metal systems, RS selectively adsorbed Cd2+ over Pb2+. Cd2+ and Pb2+ were removed mainly through surface complexation. In the soil incubation experiments (28 days), RS reduced the available Cd by 34.8–39.2 %; while, RS reduced the available Pb by 8.6 %–11.1 %. This research demonstrates RS as a potentially effective amendment for the remediation of heavy metal polluted soils

Field verification of low-level biochar applications as effective ameliorants to mitigate cadmium accumulation into Brassica campestris L from polluted soils

Introduction: Cadmium (Cd) has been recognized as a significant contributor to the pollution of farmland soils in China, and biochars have been reported to be effective in mitigating soil Cd pollution. However, most studies have been conducted in laboratory or greenhouse settings, not at a field scale, and the biochars used have been applied at unrealistically high amounts (&gt;10 t/ha).Methods: In this research, three biochars: rice straw biochar (RSB), pig manure biochar (PMB) and rice husk biochar (RHB) were produced from readily available farm residues. Then the effects at low-level application (1.8 and 3.6 t/ha) on Cd were investigated in a field experiment cropped with rape (Brassica campestris L.).Results: Batch adsorption experiments indicated Cd adsorption capacity of three biochars followed the order of RSB (43.5 mg/g) &gt; PMB (33.3 mg/g) &gt; RHB (24.4 mg/g). Field experiment indicated biochar amendments could slightly change soil pH and cation exchange capacity (CEC); yet led to considerable and significant decreases in extractable Cd concentrations [reductions of: 43%–51% (PMB), 29%–35% (RSB) and 17%–19% (RHB)]. Reduced extractable Cd correlated with lower Cd concentrations in rape plants. PMB and RSB were more effective in decreasing Cd phytoaccumulation into edible parts of rape (&gt;68% reduction) than RHB.Discussion: Low-level application of PMB or RSB could efficiently decrease the phytoaccumulation of Cd from soils into crops. These results demonstrate the reality of biochar-based remediation solutions to contribute to the mitigation of diffuse Cd contamination in farmland. The results also highlight the need to trail biochars in the presence of the soil to be targeted for remediation

Modest amendment of sewage sludge biochar to reduce the accumulation of cadmium into rice (Oryza sativa L.): A field study

Much research has considered the influence of biochars on the availability and phytoaccumulation of potentially toxic elements (PTEs) from soil. However, the vast majority of these studies use, what are arguably, unrealistic and unpractical amounts of biochar (10, 50 and even up to 100 t/ha). To offer a more realistic insight into the influence of biochar on PTE partitioning and phytoaccumulation, a field study, using modest rates of biochar application (1.5, 3.0 t/ha), was undertaken. Specifically, the research investigated the influence of sewage sludge biochar (SSBC) on the accumulation of Cd into rice (Oryza sativa L.) grown in Cd contaminated (0.82 ± 0.07 mg/kg) paddy soil. Results indicated, Cd concentrations in rice grains to significantly (p < 0.05) decrease from 1.35 ± 0.09 mg/kg in the control to 0.82 ± 0.07 mg/kg and 0.80 ± 0.21 mg/kg in the 1.5 t/ha and 3.0 t/ha treatments, respectively. Accordingly, the hazardous quotient (HQ) indices for Cd, associated with rice grain consumption, were also reduced by ∼40%. SSBC amendment significantly (p < 0.05) increased grain yields from 1.90 ± 0.08 g/plant in the control to 2.17 ± 0.30 g/plant and 3.40 ± 0.27 g/plant in the 1.5 t/ha and 3.0 t/ha treatments, respectively. Thus, the amendment of SSBC to contaminated paddy soils, even at low application rates, could be an effective approach to mitigate Cd accumulation into rice plants, to improve rice grain yields, and to thereby improve food security and protect public health

Enhanced biodegradation of PAHs in historically contaminated soil by M. gilvum inoculated biochar

The inoculation of rice straw biochar with PAH-degrading Mycobacterium gilvum (1.27 × 1011 ± 1.24 × 1010 cell g−1), and the subsequent amendment of this composite material to PAHs contaminated (677 mg kg−1) coke plant soil, was conducted in order to investigate if would enhance PAHs biodegradation in soils. The microbe-biochar composite showed superior degradation capacity for phenanthrene, fluoranthene and pyrene. Phenanthrene loss in the microbe-biochar composite, free cell alone and biochar alone treatments was, respectively, 62.6 ± 3.2%, 47.3 ± 4.1% and non-significant (P > 0.05); whereas for fluoranthene loss it was 52.1 ± 2.3%; non-significant (P > 0.05) and non-significant (P > 0.05); and for pyrene loss it was 62.1 ± 0.9%; 19.7 ± 6.5% and 13.5 ± 2.8%. It was hypothesized that the improved remediation was underpinned by i) biochar enhanced mass transfer of PAHs from the soil to the carbonaceous biochar “sink”, and ii) the subsequent degradation of the PAHs by the immobilized M. gilvum. To test this mechanism, a surfactant (Brij 30; 20 mg g−1 soil), was added to impede PAHs mass transfer to biochar and sorption. The surfactant increased solution phase PAH concentrations and significantly (P < 0.05) reduced PAH degradation in the biochar immobilized M. gilvum treatments; indicating the enhanced degradation occurred between the immobilized M. gilvum and biochar sorbed PAHs

Adsorptive Removal of Heavy Metal from Acidic Wastewater with Biochar Produced from Anaerobically Digested Residues: Kinetics and Surface Complexation Modeling

In this study, the adsorptive characteristics of biochar generated from anaerobically digested garden wastes (AD-char) were investigated. Metal adsorption onto AD-chars reached equilibrium in 48 h; the adsorption capacity of Cu2+ by AD-char was 182 μmol g-1, which was higher than that of Zn2+ (35.3 μmol g-1) and Mn2+ (60.7 μmol g-1). The metal adsorption was well described by the pseudo second-order kinetic and Langmuir isotherm models. pKinta1, pKinta2, and pkCu for AD-char, which described surface protonation reactions and complexation with Cu2+, were 5.75, -10.20, and -4.70, respectively, as optimized by the surface complexation model. Cu2+ adsorption onto AD-char increased with increasing pH to < 8.6, which suggests that the presence of surface alkaline functional groups can be attributed to the metal adsorption capacity of biochar. This study concluded that converting anaerobically digested food and garden wastes into biochar could be an efficient method of treating municipal solid waste and producing metal adsorbents for environmental remediation

Metal removal with two biochars made from municipal organic waste: adsorptive characterization and surface complexation modeling

<div><p>The adsorptive characteristics of biochar produced from garden green waste (S-char) and a mixture of food waste and garden green waste (FS-char) were investigated. Adsorption of Cu²⁺, Zn²⁺, and Mn²⁺ onto the two biochars reached equilibrium within 48 hours. The metal adsorption was effectively described by the pseudo-second-order kinetic and Freundlich isotherm models which suggest heterogeneous chemisorption. The initial solution pH influenced adsorption of Zn²⁺ and Mn²⁺ but not of Cu²⁺. Simulation via a surface complexation model showed that the fraction of XOCu⁺ adsorbed onto biochar was increased with increasing pH until it reached the adsorption maximum at pH 8.5, while the endpoint for the maximum of XOMn⁺ was higher than pH 12.</p></div

Carcinogenic potential of soils contaminated with polycyclic aromatic hydrocarbons (PAHs) in Xiamen metropolis, China

Xiamen is one of China's most rapidly developing metropolises. The objectives of the present study were: (1) to establish the levels and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in soil across the Xiamen metropolis, (2) to evaluate the extent to which PAH concentrations were elevated in the high urbanization area (HUA) of the island and how these compared with those in the low urbanization area (LUA) of the mainland, and (3) to evaluate the PAH hazard based upon their Carcinogenic Potential (CP), defined as toxicity equivalence of ?PAHs. Twenty two alternative relative carcinogenic potency schemes were used and compared. Results demonstrated PAH concentrations to be greatly elevated across the entire metropolis. Significantly, the most enriched compounds represented the greatest concern with respect to carcinogenicity. The CP of more than 25% of the industrial samples from the island surpassed the Canadian guidance threshold value (600 µg kg) for an excess lifetime cancer risk (ELCR) of 1 in 10 . While soil samples from the remaining land uses on the island were all below this threshold, PAH levels in soil were nonetheless elevated (enrichment factors of between 4.1 ± 1.9 and 16.3 ± 12.4 in the HUA, and between 1.3 ± 0.7 and 10.8 ± 4.4 in the LUA). Results relating to agricultural locations on the island indicated 75% of the samples in HUA and 28% of the samples in LUA to be above the USEPA guidance value for BaP (15 µg kg). Given the exceptionally high population density on the island there is a need for further research to evaluate multiple pathway PAH exposure risks