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... Yi YL et al. (2010) discussed the changes in the content of different forms of mercury with an increase in culture time after exogenous mercury entered the soil with different water content. Tang XC et al. (2020) studied mercury speciation in wetland sediments with different water level gradients. However, no studies are available on the characteristics and influencing factors of mercury speciation in subsurface flow zones of loess, alluvial, and proluvial strata under hydrodynamic conditions. ...
... Meanwhile, main forms of mercury transformed from the iron and manganese oxidation state, strong organic state, and residual state in the loess into the residual and strong organic states in the tailings slag, silt, and sandy pebble layers. This occurred because the adhesion of active substances in soil (such as microorganisms) to mercury decreased during river water leaching and FeO-Hg was liable to decrease and be released under flooded and anoxic conditions (Tang XC, 2020). It can be seen from Table 5 and Table 6 that, under the excitation of hydrodynamic force, the order of the total mercury content and the content of the iron-manganese combined state, residual state, and strong organic form was transformed from the surface loess > the tailings, sandy pebble, and silt layers into the tailings, sandy pebble, and silt layers > the loess layer. ...
In order to study the migration and transformation mechanism of Hg content and occurrence form in subsurface flow zone of gold mining area in Loess Plateau and its influence on water environment, the field in-situ infiltration test and laboratory test were carried out in three typical sections of river-side loess, alluvial and proluvial strata in Tongguan gold mining area of Shaanxi Province, and the following results were obtained: (1) The source of Hg in subsurface flow zone is mainly caused by mineral processing activities; (2) the subsurface flow zone in the study area is in alkaline environment, and the residual state, iron and manganese oxidation state, strong organic state and humic acid state of mercury in loess are equally divided in dry and oxidizing environment; mercury in river alluvial or diluvial strata is mainly concentrated in silt, tailings and clayey silt soil layer, and mercury has certain stability, and the form of mercury in loess is easier to transform than the other two media; (3) under the flooding condition, most of mercury is trapped in the silt layer in the undercurrent zone where the sand and silt layers alternate with each other and the river water and groundwater are disjointed, and the migration capacity of mercury is far less than that of loess layer and alluvial layer with close hydraulic connection; (4) infiltration at the flood level accelerates the migration of pollutants to the ground; (5) the soil in the undercurrent zone is overloaded and has seriously exceeded the standard. Although the groundwater monitoring results are safe this time, relevant enterprises or departments should continue to pay attention to improving the gold extraction process, especially vigorously rectify the small workshops for illegal gold extraction and the substandard discharge of the three wastes, and intensify efforts to solve the geological environmental problems of mines left over from history. At present, the occurrence form of mercury in the undercurrent zone is relatively stable, but the water and soil layers have been polluted. The risk of disjointed groundwater pollution can not be ignored while giving priority to the treatment of loess and river alluvial landform areas with close hydraulic links. The research results will provide a scientific basis for water conservancy departments to groundwater prevention and control in water-deficient areas of the Loess Plateau.
... Samples from S14 were collected from the only outlet of the Caohai Wetland. The change of water ow rate causes PFASs to be absorbed and intercepted by a large amount of vegetation along with the suspended solids (Tang et al. 2020). And the speci c reasons need to be further con rmed. ...
The Caohai Wetland is located in a region of karst within the Yunnan-Guizhou Plateau, and serves as an important nature reserve for migratory birds. It is therefore of considerable ecological value in China. The presence and concentration of per- and polyfluoroalkyl substances (PFASs) in the wetland were unknown prior to this investigation. This study documents the occurrence, distribution, and ecological risks of 16 PFASs in the Caohai Wetland. The analysis showed that 11 PFASs were widely present in the Caohai Wetland; total concentrations (defined as the concentration of the total of all studied PFASs, ΣPFASs) ranged from 1.78 ng/L to 112.21 ng/L (mean 19.43 ng/L). Perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA) and potassium perfluorobutanesulfonate (PFBS) were the dominant forms in surface water, contributing 48.12%, 14.61%, and 11.59% to the total PFASs burden, respectively. Chlorinated polyfluoroalkyl ether sulfonic acid (F-53B) was also detected frequently and occurred at relatively high concentrations (0.14–1.48 ng/L, mean 0.48 ng/L). In the absence of point sources, high PFASs concentrations occurred inside a nearby town, resulting from anthropogenic activities. Risk assessment revealed that both individual and combined PFASs pose a relatively low risk to aquatic organisms at the present time. However, long-term monitoring of PFASs in the Caohai Wetland is needed given the potential of PFASs to be biomagnified and the extremely important ecological value of the Caohai Wetland.
Groundwater is a primary source of water for nearly half of the world’s population. Its quality has become as important as its quantity, as serious groundwater pollution has been identified in many regions and countries of the world. The contaminants in groundwater generally have two sources: one is the geogenic origin and the other is human activities. The contaminants in groundwater can seriously affect human health, inducing a number of waterborne diseases. This book attempts to provide a platform for researchers, policymakers, and engineers to share their latest thoughts and findings on groundwater quality and public health, as well as novel methods for dealing with groundwater pollution. The chapters published in this book include the latest research results by world-renowned researchers, whose findings can benefit researchers, engineers, policymakers, and government officials in future groundwater quality research and policy-making. This book focuses on understanding the relationship between groundwater quality and public health, and the current state of knowledge on the links between geological/geochemical processes and human health across the world. The factors that accelerate or decelerate geological/geochemical processes, thus affecting human health, are also considered.
In order to study the occurrence form, vertical migration and transformation and the potential ecological risk of Hg in the disjointed hyporheic zone in the gold mining area is investigated. Through field investigation, in-situ test, and test analysis, the results show that: (1) the form of mercury in the original stratum where the river water-groundwater hydraulic connection is disconnected is mainly in the residual state, accounting for 77.78% of the total mercury; (2) after the water content increases or the water level changes, the various forms of occurrence in the soil surface layer decrease, and the residual state is still the main form; the main forms of mercury in the sand and pebble layer are diversified, including the residual state, strong organic state and humic acid state; (3) the mercury content in the subsurface zone in winter is higher than that in summer; (4) although the mercury content in groundwater has not been detected, the potential ecological risk of mercury in the disjointed Hyporheic zone near the river in the study area is much higher than the extreme ecological hazard threshold, which has a value of 320. The risk of groundwater pollution caused by mercury during the long-term runoff of the river is higher than that during the flood period. Therefore, relevant departments need to rectify the river as soon as possible, from the source to reduce the ecological risk of heavy metals to groundwater. The results will provide a scientific basis for groundwater control.
In this study, selected heavy metals (Hg, As, Cd, Pb, Cr, Cu and Zn) in the lake water and sediments from the Caohai wetland, which is a valuable state reserve for migrant birds in China, were investigated to assess the spatial distribution, sources, bioavailability and ecological risks. The results suggested that most of the higher concentrations were found in the eastern region of the lakeshore. The concentration factor (CF) revealed that Hg, Cd and Zn were present from moderate risk levels to considerable risk levels in this study; thus, based on the high pollution load index (PLI) values, the Caohai wetland can be considered polluted. According to the associated effects-range classification, Cd may present substantial environmental hazards. An investigation of the chemical speciation suggested that Cd and Zn were unstable across most of the sites, which implied a higher risk of quick desorption and release. Principal component analysis (PCA) indicated that the heavy metal contamination originated from both natural and anthropogenic sources.
As highly developing urbanized and industrialized processes, wetland ecosystems are subject to natural and man-induced change through physical, chemical and energetic processes. Heavy metal pollution situation is more serious increasingly, water birds whose life history is in wetlands are at high risk both lethal and sub-lethal effects, as their body burdens increase. It is costly and time-consuming to determine environmental quality by examining concentrations of metals in very many organisms, thus indicator species and indicator tissues must be selected. Biological monitoring is thought to be satisfactory way to quantify heavy metal abundance and bioavailability. Waterbirds populations may serve as sentinel species for natural and man-made toxicological problems in the environment.
The effects on juvenile rainbow trout survival, growth, food consumption, and food conversion efficiency from dietborne exposures to inorganic arsenic (arsenite, arsenate) and to the organoarsenicals monomethylarsonate (MMA), dimethylarsinate (DMA), and arsenobetaine (AsB) were investigated in two experiments: (1) a 28-d exposure using live diets of oligochaete worms separately exposed via water to these five arsenic compounds and (2) a 56-d exposure using pellet diets prepared from commercial fish food to which arsenite, MMA, or DMA were added. In the live diet experiment, the degree to which worms could be contaminated with the organoarsenicals was limited by toxicity to the worms and other experimental constraints, so that their toxicity relative to inorganic arsenic could not be fully established, but AsB was concluded to have low toxicity, consistent with published results for mammals. For the pellet diet experiment, MMA and DMA were found to be at least an order of magnitude less toxic than inorganic As on the basis of concentration in the diet, as well as much less toxic on the basis of accumulation in the fish. The need to consider speciation in aquatic risk assessments for arsenic was further demonstrated by tissue analyses of three macroinvertebrate species from a mining-impacted stream, which showed large variations in both total arsenic and the relative amounts of inorganic and organic arsenic. Additionally, although effects of arsenic on trout appear to be well correlated with inorganic arsenic, worms were found to be more sensitive to waterborne DMA than to inorganic arsenic, showing that low toxicity of organoarsenicals cannot be assumed for all aquatic organisms. Various difficulties in evaluating and applying studies on dietborne exposures and fish growth are also discussed.
The accumulation and redistribution of heavy metals in soil in a water-level fluctuation zone (WLFZ) can create ecological risks to reservoirs and reduce river health. Little is known about how heavy metals are accumulated and redistributed in the WLFZ of reservoirs with a high background value of the heavy metal in soil. The site chosen for this case study is the Nuozhadu mega reservoir in the upper Mekong River Basin, which is held back by a dam with a height exceeding 250 m. Five sampling transects were established around the reservoir. Each transect contained three vertical sampling lines representing three land-use types: forest, farmland, and rubber plantations. Soil samples were collected both in the WLFZ and in the infralittoral reference zone (IRZ), and the concentrations of the heavy metals Zn, Cr, Ni, Cu, Mn, and Fe (%) were measured in these samples. We found that the average concentrations of each of these heavy metals were higher in the WLFZ than in the IRZ. The land-use types, especially the rubber plantations and farmlands, determine the redistribution of the heavy metals in the soil of the WLFZ. The heavy metals Cu, Mn, and Ni increased with increasing elevation within the WLFZ, but the metals Cr and Zn decreased with elevation. The results of analysis of variance indicate that the soil properties had certain differences under different land-use types and inundation durations at various elevations, which partly determined the accumulation and redistribution of heavy metals in the WLFZ. We suggest that long-term monitoring of the concentration of heavy metals is needed for soil and water management in the WLFZ of the Nuozhadu reservoir.
Mangrove sediments act as natural biogeochemical reactors, modifying metals partitioning after their deposition. The objectives of the present study were: to determine distribution and partitioning of metals (Fe, Mn, Ni, Cr, Cu, Co and As) in sediments and pore-waters of Can Gio Mangrove; and to assess their ecological risks based on Risk Assessment Code. Three cores were collected within a mudflat, beneath Avicennia alba and Rhizophora apiculata stands. We suggest that most metals had a natural origin, being deposited in the mangrove mainly as oxyhydroxides derived from the upstream lateritic soils. This hypothesis could be supported by the high proportion of metals in the residual fraction (mean values (%): 71.9, 30.7, 80.7, 80.9, 67.9, 53.4 and 66.5 for Fe, Mn, Ni, Cr, Cu, Co, and As respectively, in the mudflat). The enrichment of mangrove-derived organic matter from the mudflat to the Rhizophora stand (i.e. up to 4.6% of TOC) played a key role in controlling metals partitioning. We suggest that dissolution of Fe and Mn oxyhydroxides in reducing condition during decomposition of organic matter may be a major source of dissolved metals in pore-waters. Only Mn exhibited a potential high risk to the ecosystem. Most metals stocks in the sediments were higher in the Avicennia stand than the Rhizophora stand, possibly because of enhanced dissolution of metal bearing phases beneath later one. In a context of enhanced mangrove forests destruction, this study provides insights on the effects of perturbation and oxidation of sediments on metal release to the environment.
Heavy metals are one among the toxic chemicals and accumulation in sediments and plants has been posing serious health impacts. Wetlands aid as kidneys of the landscape and help in remediation through uptake of nutrients, heavy metals and other contaminants. The analyses of macrophytes and sediment samples help in evaluating pollution status in aquatic environment. In this study concentration of six heavy metals (Cadmium (Cd), Chromium (Cr), Copper (Cu), Nickel (Ni), Lead (Pb) and Zinc (Zn)) were assessed in sediment and dominant macrophyte samples collected from Bellandur Lake, largest Lake of Bangalore, India. Sediment samples reveal of heavy metals in the inlet regions and shore samples. The accumulation of metals in sediments were in the order of Zn > Cu > Cr > Pb > Ni > Cd. All metals exceeded the critical limits of metals in the sediment. Concentration of different metals in the macrophyte samples ranked as: Cr > Cu > Zn > Pb > Ni > Cd. Chromium and Copper were found to be more than critical range. Typha angustata had the higher accumulation of all metals except chromium.
The distribution characteristics of mercury fractions at the site near a pesticide plant was investigated, with the total mercury concentrations ranging from 0.0250 to 44.3 mg kg⁻¹. The mercury bound to organic matter and residual mercury were the main fractions, and the most mobile fractions accounted for only 5.9%–9.7%, indicating a relatively low degree of potential risk. The relationships between mercury fractions and soil physicochemical properties were analysed. The results demonstrated that organic matter was one of the most important factors in soil fraction distribution, and both OM and soil pH appeared to have a significant influence on the Fe/Mn oxides of mercury. Together with the methodology of partial correlation analysis, the concept and model of delayed geochemical hazard (DGH) was introduced to reveal the potential transformation paths and chain reactions among different mercury fractions and therefore to have a better understanding of risk development. The results showed that the site may be classified as a low-risk site of mercury DGH with a probability of 10.5%, but it had an easy trend in mercury DGH development due to low critical points of DGH burst. In summary, this study provides a methodology for site risk assessment in terms of static risk and risk development.
In this study, heavy metals contamination in surface sediments of northwest Persian Gulf was investigated and a new index was formulated for assessing severity of heavy metal pollution in aquatic environments. The surface sediment samples were collected from 45 stations. The concentrations of 8 metals (Fe, Cu, Zn, Cr, Ni, Pb, Cd and V) were analyzed. According to the results of potential ecological risk index (RI), pollution load index (PLI) and modified degree of contamination (mCD), based on the average shale, considerable and intense pollution of heavy metals in sediments of study area was not observed. Based on the sediments quality guidelines the concentration of Ni at whole study area has frequently adverse biological effect on aquatic organisms. The mean effects range-median quotient indicated that surface sediments in the vicinity of petrochemical zone and Bahrekan pier with 49% probability of toxicity can be risky for the biota. The Consequence of the cluster analysis and principal component analysis/factor analysis indicated that Fe, Cu, Zn and Cr are mainly originated from natural sources and Ni, Pb, Cd and V are mostly derived from anthropogenic sources. Results of introduced index in this research (Contamination Severity Index) demonstrated that pollution of heavy metals in sediments at several sites is very intense. Assessment of results illustrated that proposed index is more reliable and logical compared with other investigated indices for evaluating heavy metals pollution in sediments of aquatic environments.