Distribution and ecological risk assessment of heavy metals in sediments of Dajiuhu Lake Wetland in Shennongjia, China

The "Fe-S wheel": A new perspective on methylmercury production dynamics in subalpine peatlands

The cycling of iron (Fe) and sulfur (S) in peatland ecosystems plays a pivotal role in modulating methylmercury (MeHg) formation. This study integrates data on Fe and S fractions, geochemical factors, microbial communities, and statistical modeling to propose the novel "Fe-S wheel" conceptual framework. This framework explores the coupled cycling of Fe, S, and Hg in the Dajiuhu peatland (DJH), an exemplary natural laboratory in central China. Through this framework, we demonstrate that the "Fe-S wheel" exerts a strong direct inhibitory effect on MeHg formation. However, when the S/Fe molar ratio is less than 0.25, the "Fe-S wheel", influenced by microbial communities, can indirectly enhance MeHg generation by promoting humic acid-bound Hg. Conversely, when the S/Fe molar ratio exceeds 0.25, the "Fe-S wheel", under the influence of dissolved oxygen, suppresses MeHg formation by inhibiting strong-complexed Hg and sulfide-bound Hg. Global peatland data corroborate these findings, showing a significant negative correlation between the S/Fe ratio and MeHg concentrations. Given the uncertainties in the interaction and transformation mechanisms between Fe and S, the S/Fe molar ratio is likely to serve as a key parameter reflecting their coupled effects on MeHg. This study highlights the critical role of Fe and S interactions in regulating MeHg generation within peatland ecosystems.

Metal contamination in the Ashtamudi Wetland ecosystem: Source identification, toxicological risk assessment of Ni, Cd, Cr, and Pb and remediation strategies

This study examines the presence of potentially toxic elements (PTEs) in the surface sediments and water of the Ashtamudi wetland, a Ramsar site on India's southwest coast. The average concentration of PTEs in water(μg/L) and in sediments (mg/kg) follows the order Fe(147.89) > Zn(107.53) > Cu(5.73) > Pb(4.57) > Mn(4.41) > Ni(3.07) > Cr(2.98) > Cd(0.32) > Co(0.14) and Fe (37,311.91) > Mn (341.59) > Zn (147.97) > Cr (88.07) > Ni (74.24) > Cu (42.23) > Pb (30.84) > Co (15.61) > Cd (1.85) respectively. Contamination and ecological risk indices (e.g., EF, CF, Igeo, mCd, EI, RI, mHQ, TRI, PLI) reveal moderate to considerable ecological hazards and contamination. Health risk assessments identify elevated cancer risks associated with Ni, Cd, Pb, and Cr in high-contamination zones. Statistical tools (PCC, PCA, and HCA) elucidate pollution sources and sediment dynamics, showing that urban runoff and industrial discharge are the major contributors. In contrast to previous studies, this work integrates seasonal variations, advanced risk indices health risk assessments and remediation techniques, which are critical for sustainable management. The findings thus call for targeted remediation strategies to mitigate heavy metal contamination and safeguard the ecological integrity and public health of Ashtamudi Wetland.

Assessment of forest soil contamination by heavy metals in the Polish National Park near Warsaw

The forest ecosystems are essential for human well-being development and reduction of the risk of natural disasters. Maintaining forest growth and ecosystem services is dependent on soil sustainability. The content of heavy metals is the main parameter determining the degree of soil contamination and degradation. The objective of the study was to assess the extent of soil contamination and identify the sources of potential anomalies. The content of the cadmium, lead, manganese and chromium (using atomic emission spectroscopy with induction-coupled plasma), as well as granulometric composition, pH value and nitrogen and total carbon content, were conducted on soil samples taken from the surface layer (0-10 cm) in the protected area of the Kampinos National Park in Poland. The soil quality assessment was conducted by calculating indicators of contamination including the geo-accumulation index, contamination factor, degree of contamination, ecological risk of individual heavy metals and potential ecological risk index. The results exhibited that the tested soils were very acidic or acidic sands. The content of the determined elements did not exceed the permissible limits as outlined in Polish standards, which are 2 mg/kg, 100 mg/kg and 150 mg/kg for cadmium, lead and chromium, respectively. The indicators show differences in the degree of contamination of the surface soil layer in the studied area, which is predominantly uncontaminated by heavy metals. However, the geochemical index values equal 0.42, 0.71 and 0.98 for certain samples suggesting the anthropogenic impact on the soils of the Kampinos National Park. The pollution appears to have been generated by the metallurgical industry, heating and power plants in the Warsaw agglomeration and transport.

Assessment of potential toxic elements in soils, sediments, and vegetation in the surroundings of Anapa, Russia

The study presented here reports the concentration of major, trace, and rare earth elements in soil, sediments, and vegetation samples collected from 13 locations around Anapa City located on the northern coast of the Black Sea in Russia. The neutron activation analysis technique has been used to fulfill this objective. Along with this, the bioconcentration and translocation factors were calculated. Overall, the content of 31 elements was detected in soil and sediments while 20 elements were determined in three types of vegetation: macroalgae (Cystoseira sp. and Ulva sp.), aquatic plants (Phragmites australis), and sea grass (Zostera sp.). The quantified concentration followed the order soil > sediment > vegetation. The phytotoxic levels for Zn, V, Mn, and Fe have been quantified as the highest. Bromine was the most abundant and accumulated in Phragmites australis. Based on the results obtained from this investigation, there is a possibility of contamination in the study area.

Analysis of heavy metals in sediments with different particle sizes and influencing factors in a mining area in Hunan Province

Heavy metals mainly exist on the surface of sediment particles and are transported using particulate matter as carriers. Therefore, the particle size of sediment particles can affect the adsorption, release, and migration of heavy metals. This study aim to investigate the distribution characteristics and chemical fraction of Cd, Pb, and As contents in sediments of different particle sizes using the BCR method, and to determine the key factors affecting the distribution of heavy metals through mineralogical methods such as XRD and EDS. The results revealed that the overall content of various forms of heavy metals increases with the decrease of particle size, mainly presents in fine particles. The mineralogical analysis results indicated that fine particles predominantly contained clay minerals such as chlorite and illite and coarse particles mainly include primary minerals. Due to the mining areas in the middle-upstream, Cd, Pb and As were primarily associated with galena, sphalerite and pyrite, respectively. The distribution of heavy metals is jointly influenced by sediment particle size and sediment material composition.

Physiological and Cellular Ultrastructural Responses of Sesuvium portulacastrum under Cd Stress Grown Hydroponically

This study aimed to investigate the physiological and cellular mechanisms of Sesuvium portulacastrum under heavy metal stress to evaluate possible tolerance and adaptation mechanisms in a metal-polluted environment. The physiological and cellular ultrastructural responses of S. portulacastrum were studied hydroponically under exposure to a range of cadmium (Cd) concentrations (50 µM to 600 µM) for 28 days. The activity of antioxidant enzymes like catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD), changes in chlorophyll, and cellular ultrastructural content were examined. There was no significant difference in chlorophyll content in the leaf under the stress of 300 μM, but 400 μM and 600 μM Cd stress showed significantly decreased chlorophyll content. The SOD activity indicates an increase under the Cd stress of 100 μM for leaves, 300 μM for stems, and 50 μM for roots; after that, the SOD activity gradually decreased with increasing Cd concentrations. But POD activity was considerably increased with increasing Cd stress. CAT activity showed a gradual increase in concentrations until 300 μM of Cd stress and then decreased sharply in roots, stems, and leaf tissues. Cd stress had a considerable impact on the structure of the roots, stems, and leaves cells, such as distorted and thinner cell walls and the deformation of chloroplasts, mitochondria, and other organelles. Therefore, the increased number of nucleolus in the cell nucleus suggests that cells may be able to maintain their protein synthesis in a stressful environment. This study concludes that SOD is the dominant antioxidant enzyme activity during low Cd toxicity (<100 μM), while POD is the dominant enzyme activity during higher Cd toxicity (>100 μM).

Pollution status and risk assessment of heavy metals in the sediment of a historically contaminated lake treated by oxidation pond in China

Sediment plays an important role in controlling biogeochemical cycling of heavy metals in aquatic environment. The Ya-Er Lake is a typical lake which was historically contaminated by heavy metals in Hubei province, China. After industries surrounding the Ya-Er Lake being shut down, oxidation pond treatment and dredging program were conducted for pollution management since 1970s. To date, the Ya-Er Lake has been used for aquaculture for several decades. However, the status of heavy metal levels and ecological risks in this lake remains unclear. Herein, concentrations, chemical fractions, and risk assessment of heavy metals were investigated in the Ya-Er Lake sediment. Results showed that concentrations of heavy metals in the Ya-Er Lake sediment were higher than other reported lake systems, suggesting that heavy metal pollution in the Ya-Er Lake is still serious. Relatively higher proportions of carbonates bound form of Cd and Ni indicated high-risk potential of these two heavy metals, and Cd and Ni should be listed as the primary heavy metal pollutants in the Ya-Er Lake according to the results of potential ecological risk index (PERI) and sediment quality guidelines (SQGs). The risk assessment code (RAC) analysis showed that Ni and Cd poses higher bioavailability and mitigation potential, and may affect the Ya-Er Lake ecosystem and downstream aquatic environment. These findings reflected that oxidation pond treatment and dredging sediment to near place are not effective to control heavy metal pollution, and a long-term ecological risk is still posed to surrounding aquatic environment. Our study provides scientific basis on pollution control and management in aquatic system contaminated by heavy metals.