Vertical distribution of arsenic and bacterial communities in calcareous farmland amending by organic fertilizer and iron-oxidizing bacteria: Field experiment on concomitant remediation.

The migration and transformation mechanisms of arsenic (As) in soil environments necessitate an understanding of its influencing processes. Here, we investigate the subsurface biogeochemical transformation of As and iron (Fe) through amended in the top 20 cm with iron oxidizing bacteria (FeOB) and organic fertilizer (OF). Our comprehensive 400-day field study, conducted in a calcareous soil profile sectioned into 20 cm increments, involved analysis by sequential extraction and assessment of microbial properties. The results reveal that the introduction of additional OF increased the release ratio of As/Fe from the non-specific adsorption fraction (136.47 %) at the subsoil depth (40-60 cm), underscoring the importance of sampling at various depths and time points to accurately elucidate the form, instability, and migration of As within the profile. Examination of bacterial interaction networks indicated a disrupted initial niche in the bottom layer, resulting in a novel cooperative symbiosis. While the addition of FeOB did not lead to the dominance of specific bacterial species, it did enhance the relative abundance of As-tolerant Acidobacteria and Gemmatimonadetes in both surface (39.2 % and 38.76 %) and deeper soils (44.29 % and 23.73 %) compared to the control. Consequently, the amendment of FeOB in conjunction with OF facilitated the formation of poorly amorphous Fe (hydr)oxides in the soil, achieved through abiotic and biotic sequestration processes. Throughout the long-term remediation process, the migration coefficient of bioavailable As within the soil profile decreased, indicating that these practices did not exacerbate As mobilization. This study carries significant implications for enhancing biogeochemical cycling in As-contaminated Sierozem soils and exploring potential bioremediation strategies. ENVIRONMENTAL IMPLICATION: The long-term exposure of sewage irrigation has potential adverse effects on the local ecosystem, causing serious environmental problems. Microorganisms play a vital role in the migration and transformation of arsenic in calcareous soil in arid areas, which highlights the necessity of understanding its dynamics. The vertical distribution, microbial community and fate of arsenic in calcareous farmland soil profile in northwest China were studied through field experiments. The results of this work have certain significance for the remediation of arsenic-contaminated soil in arid areas, and provide new insights for the migration, transformation and remediation of arsenic in this kind of soil.

Arsenic and cadmium simultaneous immobilization in arid calcareous soil amended with iron-oxidizing bacteria and organic fertilizer.

Immobilization stands as the most widely adopted remediation technology for addressing heavy metal(loid) contamination in soil. However, it is crucial to acknowledge that this process does not eliminate pollutants; instead, it confines them, potentially leaving room for future mobilization. Presently, our comprehension of the temporal variations in the efficacy of immobilization, particularly in the context of its applicability to arid farmland, remains severely limited. To address this knowledge gap, our research delves deep into the roles of iron-oxidizing bacteria (FeOB) and organic fertilizer (OF) in the simultaneous immobilization of arsenic (As) and cadmium (Cd) in soils. We conducted laboratory incubation and field experiments to investigate these phenomena. When OF was combined with FeOB, a noteworthy transformation of available As and Cd into stable species, such as the residual state and combinations with Fe-Mn/Al oxides, was observed. This transformation coincided with changes in soil properties, including pH, Eh, soluble Fe, and dissolved organic carbon (DOC). Furthermore, we observed synergistic effects between available As and Cd when treated with bacteria and OF individually. The stabilization efficiency of As and Cd, as determined by the Toxicity Characteristic Leaching Procedure, reached its highest values at 33.39 % and 24.67 %, respectively, after 120 days. Nevertheless, the formation of iron­calcium complexes was disrupted due to pH fluctuations. Hence, long-term monitoring and model development are essential to enhance our understanding of the remediation process. The application of organic fertilizer and the use of FeOB in calcareous soil hold promise for the restoration of polluted soil and the maintenance of soil health by mitigating the instability of heavy metals(loid).

Response of trace elements in urban deposition to emissions in a northwestern river valley type city: 2010-2021.

Anthropogenic activities release significant quantities of trace elements into the atmosphere, which can infiltrate ecosystems through both wet and dry deposition, resulting in ecological harm. Although the current study focuses on the emission inventory and deposition of trace elements, their complex interactions remain insufficiently explored. In this study, we employ emission inventories and deposition data for eight TEs (Cr, Mn, Ni, Cu, Zn, As, Cd, Pb) in Lanzhou City to unveil the relationship between these two aspects. Emissions in Lanzhou can be roughly divided into two periods centered around 2017. Preceding 2017, industrial production constituted the primary source of TEs emissions except for As; coal combustion was the primary contributor to Cr, Mn, and As emissions; waste incineration played a significant role in As, Zn, and Cd emissions; biomass combustion influenced Cr and Cd emissions; and transportation sources were the predominant contributors to Pb and Cu emissions. With the establishment of waste-to-energy plants and the implementation of ultra-low emission retrofits, emissions from these sources decreased substantially after 2017. Consequently, emissions from industrial production emerged as the main source of TEs. The deposition concentrations of Cr, Mn, Ni, Cu, and Pb followed a similar trend to the emissions. However, Cd and As exhibited lower emissions and a less pronounced response relationship. Moreover, Zn concentrations fluctuated within a narrow range and showed a weaker response to emissions. The consistent changes in emissions and TEs deposition concentrations signify a shift in deposition pollution in Lanzhou city from Coal-fired pollution to that driven by transportation and industrial activities. Within this transition, the industrial production process offers significant potential for emission reduction. This insight provides a crucial foundation for managing TEs pollution and implementing strategies to prevent ecological risks.

Temporal distribution and accumulation pattern of cadmium and arsenic in the actual field calcareous soil-maize system, northwest China.

The contrasting chemical behaviors of two toxic elements, arsenic (As) and cadmium (Cd) in co-contamination calcareous soil and its absorption by crops have not been thoroughly explored, especially in the implementation of the measure of prohibiting the use of wastewater to irrigate farmland. We propose that the present environmental characteristics of ecologically fragile areas and appropriate restoration measures are critical determinant of soil remediation. In this study, the typical field farmland irrigated by industrial and domestic wastewater in the Chinese Loess Plateau for >50 years was selected. The results showed that after the sewage irrigation was stopped, the mean contents of Cd (7.09 mg/kg) and As (13.47 mg/kg) in the soil were still rising, which might be a potential input source. The average values of soil risk indices such as the potential ecological risk (PERI = 2394), pollution load index (PLI > 4 for 60 % of studied samples), and degree of contamination (Dc = 86.6) showed severe soil pollution in the study area. The decrease of soil pH, the loss of soil texture and calcium carbonate were found to be the reasons for the high chemical activity of Cd. The bioconcentration factors (< 0.2) and translocation factor (> 1.0) of Cd indicate that corn is an excluder plant and an ideal phytoremediation method. Thus, 20 % of studied samples were higher than maximum permitted levels of Cd in grain, indicating potential related health hazards. On the contrary, As was mainly adsorbed in calcareous soil, and its bioavailability was lower compared with Cd. The difference between DTPA extraction and sequential extraction may be due to the transformation of chemical forms, resulting in unstable fractions increased the bioavailability of toxic elements. Overall, the findings provide new insights for solutions to manage and repair farmlands under the post-wastewater irrigation period.