Exploring the safe utilization strategy of calcareous agricultural land irrigated with wastewater for over 50 years

Accumulation and translocation of lead and cadmium in Lyophyllum decastes

Lyophyllum decastes (L. decastes) is a very precious edible mushroom. With simple structure, mushrooms have been proved to have the phenomenon of accumulating heavy metals. To investigate the accumulation and transfer of L. decastes to heavy metals and the effects of heavy metals on agronomic traits and yield, we used lead (Pb) and cadmium (Cd) inhibitory test for L. decastes. The results indicated that the addition of Pb and Cd affected the growth of aerial mycelium, and thus decreased the growth rate of mycelia. At a Cd concentration of 50 mg L-1, the mycelium reached its maximum tolerance concentration, but the maximum tolerance concentration of the mycelium had exceeded 1500 mg L-1. The addition of Pb and Cd led to the deterioration of agronomic traits and the decrease of yield. At the same concentration (20 mg kg-1), the negative effects of Cd on agronomic traits and yield were greater than that of Pb. The BAF values of the pileus and stipes under Pb treatments were < 1, which indicated that L. decastes was the bioexcluders of the elements Pb. The TF values were all greater than 1 under Cd treatments, indicated that the transfer ability of Cd was strong. This advancement has enhanced our knowledge of how heavy metals accumulate and distribute in mushrooms. The transfer ability of Cd was strong.

A review on As-contaminated soil remediation using waste biomass feedstock-based biochar and metal-modified biochar

Arsenic (As) is a carcinogen that threatens ecosystems and human health. Due to its high adsorption, and microporosity, biochar is widely available for soil remediation. This review significantly summarizes the current status of waste biomass feedstock-based biochar and metal-modified biochar for As-contaminated soil remediation. Firstly, this paper briefly describes the sources and hazards of As in soil, and secondly, lists eleven feedstocks for preparing biochar. Agricultural, domestic, and forestry wastes provide a plentiful source for biochar preparation. Single or multi-metal modifications such as iron (Fe), manganese (Mn), and cerium (Ce) can effectively improve the Arsenite [As(III)] and arsenate [As(V)] adsorption capacity of biochar. The primary mechanisms of As removal by waste biomass feedstock-based biochar and metal-modified biochar include ion exchange, electrostatic attraction, surface complexation, redox transformation, and H-bond formation. In conclusion, this review presents an in-depth discussion on both waste biomass feedstocks and metal modification, providing constructive suggestions for the future development of biochar to remediate As-contaminated soil.

Spatial insights into microplastics and heavy metals levels, and risks in wastewater irrigated surface soils of Okara, Pakistan: Microplastics sizes impacts on heavy metals distribution using structure equation model

Pakistan's freshwater shortage and climate events have caused soil nutrient leaching, prompting cities to adopt wastewater irrigation. This study investigates wastewater as a potential source of microplastics (MPs) and heavy metals (HMs), assessing contaminant levels in wastewater-irrigated surface soils (WISS) in district Okara, Pakistan. It further explores potential ecological and human health risks associated with HMs in soil and the impact of MPs on HMs distribution and physicochemical properties. The concentrations of HMs in WISS were within permissible limits (Cd: 0.48, Cu: 17.99, Zn: 29.73, Pb: 19.65, Fe: 8559.5), except for Mn, which was 182.94 mg/kg. MPs abundance ranged from 1850 to 5300 particles/kg, with the most common physical characteristics being fragment shapes (49.6%); black color (40.1%), and small sizes (<500 μm) many physical properties depicted association with HMs and MPs sizes. The structural equation model (SEM) showed a significant impact of MPs on HMs distribution, risk index, and pollution load index, but no significant relationship with physicochemical properties. The pollution indices for HMs in WISS indicated low ecological risk and negligible non-carcinogenic health risks were predicted for both adults and children. However, regular monitoring, enforcement of management and implementation plans, and remediation strategies for HMs and MPs in WISS are highly recommended.

Recalcification stabilizes cadmium but magnifies phosphorus limitation in wastewater-irrigated calcareous soil

Long-term wastewater irrigation leads to the loss of calcium carbonate (CaCO3) in the tillage layer of calcareous land, which irreversibly damages the soil's ability to retain cadmium (Cd). In this study, we selected calcareous agricultural soil irrigated with wastewater for over 50 years to examine the recalcification effects of sugar beet factory lime (SBFL) at doses of 0%, 2.5%, 5%, and 10%. We found that SBFL promoted Cd transformation in the soil from active exchangeable species to more stable carbonate-bonded and residual species, which the X-ray diffraction patterns also confirmed results that CdSO4 reduced while CdS and CaCdCO3 increased. Correspondingly, the soil bioavailable Cd concentration was significantly reduced by 65.6-84.7%. The Cd concentrations in maize roots and shoots were significantly reduced by 11.7-50.6% and 13.0-70.0%, respectively, thereby promoting maize growth. Nevertheless, SBFL also increased the proportion of plant-unavailable phosphorus (P) in Ca8-P and Ca10-P by 4.3-13.0% and 10.7-25.9%, respectively, reducing the plant-available P (Olsen P) content by 5.2-22.1%. Consequently, soil P-acquiring associated enzyme (alkaline phosphatase) activity and microbial (Proteobacteria, Bacteroidota, and Actinobacteria) community abundance significantly increased. Our findings showed that adding SBFL to wastewater-irrigated calcareous soil stabilized Cd, but exacerbated P limitation. Therefore, it is necessary to alleviate P limitations in the practice of recalcifying degraded calcareous land.

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.

Tradeoffs between pH, dissolved organic carbon, and mineral ions regulate cadmium uptake by Solanum hyperaccumulators in calcareous soil

Soil solution pH and dissolved organic carbon (DOC) influence cadmium (Cd) uptake by hyperaccumulators but their tradeoff in calcareous soils is unclear. This study investigated the mechanisms of Solanum nigrum L. and Solanum alatum Moench in calcareous soil using a combination of concentration gradient experiments (0.6-100 mg Cd kg-1) and soil solution composition analysis. The results showed that the soil solution pH of S. nigrum remained stable despite Cd stress. On average, the soil solution pH of S. alatum was 0.23 units higher than that of S. nigrum, although pH decreased significantly under high Cd stress. In addition, the concentrations of potassium (K) and calcium (Ca) in the soil solution of S. nigrum increased and decreased under low and high levels of Cd stress, respectively. In S. alatum, the K and Ca concentrations in the soil solution generally increased with increasing Cd stress levels. Moreover, the level of DOC in the soil solution of both plants was higher under Cd stress compared to the control, and a gradually increasing trend with Cd stress level was observed in S. alatum. Consequently, the bioconcentration factors of the roots (2.62-19.35) and shoots (1.20-9.59) of both plants were >1, while the translocation factors were <1, showing an obstacle of Solanum hyperaccumulators in transferring Cd into their aboveground parts. Redundancy analysis revealed that the Cd concentration in S. nigrum roots was significantly negatively correlated with the soil solutions of K and Ca. In contrast, Cd concentrations in S. alatum roots and shoots were significantly positively correlated with soil solution DOC, K, and Ca but negatively correlated with pH. Our results suggest that calcareous soil neutralizes the acidity of released protons but does not affect cation exchange, inhibiting DOC in assisting the translocation of Cd within plants.

Spatial and temporal distribution of heavy metals pollution and risk indices in surface sediments of Gomal Zam Dam Basin, Pakistan

Sediments were considered a sink and potential source of heavy metals in the aquatic system. For this purpose, the present study examined surface sediments for spatial and temporal variation of heavy metals pollution and risk indices in the Gomal Zam Dam Basin (GZDB), Pakistan. Sediment samples (n = 20) were collected from the GZDB, i.e., Gomal Zam Dam, its inlets, and outlets in the winter and summer seasons of 2020, and examined for heavy metals such as zinc (Zn), nickel (Ni), manganese (Mn), lead (Pb), chromium (Cr), copper (Cu), iron (Fe), and cobalt (Co) concentrations. Among GZDB, results showed that the Zhob River Inlet had a higher levels of heavy metals in both seasons. The results revealed that pollution load index values were < 1, observing no pollution in the aquatic system. The risk indices values revealed that sampling sites showed no or very low risk during the summer, 84% of samples showed no or very low risk during the winter, and the rest noted with reasonable risks. Winter season showed higher average values of contamination and risk indices than summer. Statistical analyses revealed that the heavy metals contaminations were mainly due to geogenic sources of rock weathering and ore deposits, with minor contributions from anthropic activities. This study recommends regular monitoring of temporal studies on heavy metals contamination in the water of the GZDB.