Arsenic In Sediments Research Articles

Extent of As(III) versus As(V) adsorption on iron (oxyhydr) oxides depends on the presence of vacancy cluster-like micropore sites: Insights into a seesaw effect

Iron (oxyhydr)oxides are ubiquitous in terrestrial environments and play a crucial role in controling the fate of arsenic in sediments and groundwater. Although there is evidence that different iron (oxyhydr)oxides have different affinities towards As(III) and As(V), it is still unclear why As(V) adsorption on some iron (oxyhydr)oxides is larger than As(III) adsorption, while it is opposite for other ones. In this study, six typical iron (oxyhydr)oxides are selected to evaluate their adsorption capacities for As(III) and As(V). The characteristics of these iron minerals such as morphology, arsenic adsorption species, and pore size distribution are carefully examined using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), positron annihilation lifetime (PAL) spectroscopy, and X-ray absorption spectroscopy (XAS). We confirm a seesaw effect occurred in different iron minerals for As(III) and As(V) immobilization, i.e., at pH 6.0, adsorption of As(V) on hematite (0.73 μmol m−2) and magnetite (0.33 μmol m−2) is higher than for As(III) (0.61 μmol m−2 and 0.27 μmol m−2, respectively), for goethite and lepidocrocite it is almost equal, while As(III) sorption on ferrihydrite (5.77 μmol m−2) and schwertmannite (28.41 μmol m−2) showed higher sorption than As(V) (1.53 μmol m−2 and 12.99 μmol m−2, respectively). PAL analysis demonstrates that ferrihydrite and schwertmannite have a large concentration of vacancy cluster-like micropores, significantly more than goethite and lepidocrocite, followed by hematite and magnetite. The difference of adsorption of As(III) and As(V) to different iron (oxyhydr)oxides is due to differences in the abundance of vacancy cluster-like micropore sites, which are conducive for smaller size As(III) immobilization but not for larger size of As(V). The findings of this study provide novel insights into a seesaw effect for As(III) and As(V) immobilization on naturally occurring iron mineral.

Bio-stabilization of arsenic in sediments by natural carbon-containing biomass: Performance and microbial metabolites

The development of sustainable methods for the control and bio-stabilization of arsenic in sediments, without generating secondary pollution, is an urgent technological need. In this study, we utilized three types of natural carbon-containing biomass (NCCB) to explore the stabilization of arsenic through the synergistic action of native sediment microbiomes. We also examined the metabolic pathways of microorganisms following the introduction of NCCB into high-arsenic sediments, aiming to elucidate the biological processes critical for arsenic bio-stabilization. Our findings indicate that humic acid (HA) and soil organic matter (SOM) are effective in preventing the leaching of As(III) from sediments, while fulvic acid (FA) and SOM can significantly reduce the leaching of As(V). Furthermore, the introduction of NCCB into the system altered the biological metabolic processes, with notable upregulation of metabolites such as 8-hydroxyondansetron, 1,2,3,5,6,8-hexathionane, and citric acid. These results hold promise for the application of these findings in the management of arsenic in natural sediments.

Arsenic Adsorption Isotherms of Sediments from Old Mining Area and Their Implications: A Case Study of the Ron Phibun Area, Thailand

Although tin mining activities in the southern part of Thailand have been abandoned for more than 40 years, arsenic contamination in old tin-mining areas continues to pose a health risk. Fortunately, natural adsorption of arsenic by sediment has reduced the arsenic concentration in water to the maximum allowable level within a 10-kilometre radius of the mine sources. This article attempts to characterize the arsenic adsorption properties of sediment along a water creek which passes through the old tin-mine areas in Ron Phibun district, Nakhon Si Thammarat province, Thailand, where the contamination has been most severe. It was found that Fe tends to be associated with the adsorption capacity of arsenic in sediment. However, pH 4 and pH 7 did not associate with adsorption capacity. At pH 12, the solubility of arsenic increases, making it less likely to be adsorbed into the sediment and more likely to dissolve in water. For the adsorption isotherms of the sediment, the so-called ‘2-step Langmuir/Freundlich models’, with the advance of switching functions (Logistic or Arctan functions), were proposed. Then, based on the principle of parsimony, a stepwise model reduction approach was used to choose the optimal models. It was found that the isotherms were used successfully to describe the historical arsenic-contamination data of the past 14 years (2005 - 2019) and to predict future trends qualitatively. HIGHLIGHTS Two-step Langmuir/Freundlich models with the switching functions were proposed The historical arsenic-contamination data of the past 14 years (2005 - 2019) was examined The model described the historical arsenic-contamination data as a function of pH and metal-complex formation in sediment soils successfully GRAPHICAL ABSTRACT

Seasonal variations in spatial distribution, mobilization kinetic and toxicity risk of arsenic in sediments of Lake Taihu, China

This study investigated seasonal variations in spatial distribution, mobilization kinetic and toxicity risk of arsenic (As) in sediments of three representative ecological lakes in Lake Taihu. Results suggested that the bioavailability and mobility of As in sediments depended on the lake ecological types and seasonal changes. At the algal-type zones and macrophyte-type zones, elevated As concentrations were observed in April and July, while these occurred at the transition areas in July and October. The diffusion flux of soluble As ranged from 0.03 to 3.03 ng/cm2/d, indicating sediments acted as a source of As. Reductive dissolution of As-bearing iron/manganese-oxides was the key driver of sediment As remobilization. However, labile S(-II) caused by the degradations of algae and macrophytes buffered sediment As release at the algal-type and macrophyte-type zones. Furthermore, the resupply ratio was less than 1 at three ecological lakes, indicating the resupply As capacity of sediment solid phase was partially sustained case. The risk quotient values were higher than 1 at the algal-type zones and transition areas in July, thereby, the adverse effects of As should not be ignored. This suggested that it is urgently need to be specifically monitored and managed for As contamination in sediments across multi-ecological lakes.

Littoral sediment arsenic concentrations predict arsenic trophic transfer and human health risk in contaminated lakes.

Lake sediments store metal contaminants from historic pesticide and herbicide use and mining operations. Historical regional smelter operations in the Puget Sound lowlands have resulted in arsenic concentrations exceeding 200 μg As g-1 in urban lake sediments. Prior research has elucidated how sediment oxygen demand, warmer sediment temperatures, and alternating stratification and convective mixing in shallow lakes results in higher concentrations of arsenic in aquatic organisms when compared to deeper, seasonally stratified lakes with similar levels of arsenic pollution in profundal sediments. In this study we examine the trophic pathways for arsenic transfer through the aquatic food web of urban lakes in the Puget Sound lowlands, measuring C and N isotopes-to determine resource usage and trophic level-and total and inorganic arsenic in primary producers and primary and secondary consumers. Our results show higher levels of arsenic in periphyton than in other primary producers, and higher concentrations in snails than zooplankton or insect macroinvertebrates. In shallow lakes arsenic concentrations in littoral sediment are similar to deep profundal sediments due to arsenic remobilization, mixing, and redeposition, resulting in direct arsenic exposure to littoral benthic organisms such as periphyton and snails. The influence of littoral sediment on determining arsenic trophic transfer is evidenced by our results which show significant correlations between total arsenic in littoral sediment and total arsenic in periphyton, phytoplankton, zooplankton, snails, and fish across multiple lakes. We also found a consistent relationship between percent inorganic arsenic and trophic level (determined by δ15N) in lakes with different depths and mixing regimes. Cumulatively, these results combine to provide a strong empirical relationship between littoral sediment arsenic levels and inorganic arsenic in edible species that can be used to screen lakes for potential human health risk using an easy, inexpensive sampling and analysis method.

Interplay of legacy irrigation and nitrogen fertilizer inputs to spatial variability of arsenic and uranium within the deep vadose zone

The vadose zone is a reservoir for geogenic and anthropogenic contaminants. Nitrogen and water infiltration can affect biogeochemical processes in this zone, ultimately affecting groundwater quality. In this large-scale field study, we evaluated the input and occurrence of water and nitrogen species in the vadose zone of a public water supply wellhead protection (WHP) area (defined by a 50-year travel time to groundwater for public supply wells) and potential transport of nitrate, ammonium, arsenic, and uranium. Thirty-two deep cores were collected and grouped by irrigation practices: pivot (n = 20), gravity (n = 4) irrigated using groundwater, and non-irrigated (n = 8) sites. Beneath pivot-irrigated sites, sediment nitrate concentrations were significantly (p < 0.05) lower, while ammonium concentrations were significantly (p < 0.05) higher than under gravity sites. The spatial distribution of sediment arsenic and uranium was evaluated against estimated nitrogen and water loading beneath cropland. Irrigation practices were randomly distributed throughout the WHP area and presented a contrasting pattern of sediment arsenic and uranium occurrence. Sediment arsenic correlated with iron (r = 0.32, p < 0.05), uranium negatively correlated to sediment nitrate (r = −0.23, p < 0.05), and ammonium (r = −0.19 p < 0.05). This study reveals that irrigation water and nitrogen influx influence vadose zone geochemistry and mobilization of geogenic contaminants affecting groundwater quality beneath intensive agricultural systems.

Mineralogical Associations of Sedimentary Arsenic within a Contaminated Aquifer Determined through Thermal Treatment and Spectroscopy

Sedimentary arsenic (As) in the shallow aquifers of Bangladesh is enriched in finer-grained deposits that are rich in organic matter (OM), clays, and iron (Fe)-oxides. In Bangladesh, sediment color is a useful indicator of pore water As concentrations. The pore waters of orange sediments are usually associated with lower As concentrations (&lt;50 µg/L) owing to abundant Fe-oxides which sorb As. Using this color signal as a guide, spectroscopic measurements alongside thermal treatment were extensively utilized for analyzing the properties of both Fe-oxides and clay minerals. This study uses Fourier transform infrared (FTIR) and diffuse reflectance (DR) measurements along with thermal treatment to evaluate the solid-phase associations of As from sediment collected along the Meghna River in Bangladesh. The samples analyzed in this study were chosen to represent the various lithologies present at the study site and included riverbank sands (1 m depth), silt (6 m depth), aquifer sand (23 m depth), and a clay aquitard (37 m depth). The concentrations of sedimentary As and Fe were measured by X-ray fluorescence, and the spectroscopic measurements were taken on the samples prior to the thermal treatment. For the thermal treatment, sediment samples were placed in a preheated furnace at 600 °C for 3 h. The thermal treatment caused a deepening of reddish-brown hues in all samples, and the greatest change in color was observed in the finer-grained samples. The FTIR spectral analysis revealed that the clay minerals were composed primarily of illite, smectite, and kaolinite. The DR results indicate that the majority of Fe in sands was present as goethite; however, in the clay and silt samples, Fe was incorporated into the structure of clay minerals as Fe(II). The amount of structural Fe(II) was strongly positively correlated with the sedimentary As concentrations, which were highest in the finer-grained samples. After thermal treatment, the concentrations of As in the finer-grained samples decreased by an average of 40%, whereas the change in the As concentrations of the sand samples was negligible. These findings indicate that significant proportions of solid-phase As may be retained by OM and Fe(II)-bearing clay minerals.

Beyond the geological origin of sediment arsenic in groundwater systems: arsenic redux by redox

Beyond the geological origin of sediment arsenic in groundwater systems: arsenic redux by redox

Warning system for potential releases of chemical warfare agents from dumped munition in the Baltic Sea

The research aimed to determine the scale of the potential contamination of the southern Baltic by substances from dumped chemical weapons, in the context of applying a strategy for detecting the potential releases of toxic materials. The research included the analysis of total arsenic in sediments, macrophytobenthos, fish, and yperite with derivatives and arsenoorganic compounds in sediments and as an integral part of the warning system the threshold values for arsenic in these matrices were set. Arsenic concentrations in sediments ranged from 11 to 18 mg kg−1 with an increase to 30 mg kg−1 in layers dated to 1940–1960, what was accompanied by the detection of triphenylarsine (600 mg kg−1). The presence of yperite or arsenoorganic-related chemical warfare agents was not confirmed in other areas. Arsenic ranged from 0.14 to 1.46 mg kg−1 in fish and from 0.8 to 3 mg kg−1 in macrophytobenthos.

Micropore sites in ferrihydrite are responsible for its higher affinity towards As(III) relative to As(V)

Poorly-crystalline ferrihydrite is ubiquitous in the environment and contributes to controlling the fate of arsenic in sediments and soils. Although there is evidence that ferrihydrite has a higher affinity towards As(III) relative to As(V), little is known about how and why As(III) is readily immobilized by ferrihydrite. In this study, ferrihydrite was employed to evaluate the As(III) and As(V) adsorption behavior. The properties of ferrihydrite such as morphology, pore size distribution, arsenic adsorption species, and adsorption energies of arsenic at different sites were carefully examined using TEM-EDS mapping, positron annihilation lifetime (PAL) spectroscopy, X-ray absorption spectroscopy (XAS), N2 adsorption isotherms, and theoretical calculations of density function theory (DFT). Batch adsorption experiments revealed that the maximum adsorption of As(III) (839.7 μmol g−1) on ferrihydrite, fitted by Langmuir model, was considerably larger than that of As(V) (372.4 μmol g−1). PAL characterization and pore size distribution analysis demonstrated that ferrihydrite had an abundance of vacancy cluster-like micropores, which consisted of 10–20 atom deficiencies (V10-20). The calculated hydrated ion size of As(III) species (4.22 Å) at pH 6.0 was smaller than the size of As(V) (5.90 Å). The higher As(III) adsorption to ferrihydrite was attributed to its surface adsorption sites as well as its abundant micropore adsorption sites, which are available only to As(III) due to their size matching well with the size of the ferrihydrite micropores, thus significantly contributing to greater As(III) immobilization.

Arsenic Occurrence and Cycling in the Aquatic Environment: A Comparison between Freshwater and Seawater

Owing to the toxicity and adverse effects of arsenic on human health, its levels in aquatic environments are among the most serious threats to humans globally. To improve our understanding of its occurrence and cycling in aquatic environments, herein we review the concentration, speciation, and distribution of arsenic in freshwater, seawater, and sediments. Many natural processes, such as rock weathering and geothermal activities, contribute to the background arsenic concentrations in the natural environment, whereas metal mining and smelting are anthropogenic sources of arsenic in the water. The high solubility and mobility of arsenic in aquatic environments affects its global cycling. Furthermore, the biological processes in the aquatic environment are discussed, especially the possible microbe-mediated reactions of arsenic in sediments. In addition, various environmental factors, such as redox conditions, pH, and salinity, which influence the transformation of arsenic species, are summarized. Finally, the differences between freshwater and seawater with reference to the concentration as well as speciation and distribution patterns of arsenic are addressed. This review provides deep insights into arsenic occurrence and cycling between freshwater and seawater aquatic environments, which can more accurately distinguish the risks of arsenic in different water environments, and provides theoretical guidance for the prevention and control of arsenic risks.

The key role of biogenic arsenic sulfides in the removal of soluble arsenic and propagation of arsenic mineralizing communities

Biogeochemical processes govern the transport and availability of arsenic in sediments. However, little is known about the transition from indigenous communities to cultivable consortia when exposed to high arsenic concentrations. Such cultivable communities could be exploited for arsenic bioremediation of waste streams and polluted sites. Thus, it is crucial to understand the dynamics and selective pressures that shape the communities during the development of customized bacterial consortia. First, from the arsenic partitioning of two sediments with high arsenic concentrations, we found that up to 55% of arsenic was bioavailable because it was associated with the soluble, carbonate, and ionically exchangeable fractions. Next, we prepared sediment enrichment cultures under arsenate- and sulfate-reducing conditions to precipitate arsenic sulfide biominerals and analyze the communities. The produced biominerals were used as the inoculum to develop bacterial consortia via successive transfers. Tracking of the 16S rRNA gene in the fresh sediments, sediment enrichments, biogenic minerals, and bacterial consortia revealed differences in the bacterial communities. Removing the sediment caused a substantial decrease in diversity and shifts toward the dominance of the Firmicutes phylum to the detriment of Proteobacteria. In agreement with the 16S rRNA gene results, the sequencing of the arrA gene confirmed the presence of phylotypes closely related to Desulfosporosinus sp. Y5 (100% similarity), highlighting the pivotal role of this genus in the removal of soluble arsenic. Here, we demonstrated for the first time that besides being important as arsenic sinks, the biogenic arsenic sulfide minerals are reservoirs of arsenic resistant/respiring bacteria and can be used to culture them.

Sediment pollution: An assessment of anthropogenic and geogenic trace element contributions along the central Algerian coast

Sediment cores from the central Algerian coast were collected to investigate the distribution, sources and risk of trace metals. The local geochemical background of metals was defined from the core S collected in an uncontaminated area of the coast. The anthropogenic inputs in Algiers Bay elevated Ag, Cd, Pb and Zn concentrations as their maximum were 3.1, 3, 2.1 and 1.8 times the background values, respectively. Meanwhile, increased contents of Arsenic (up to 21.1 mg/kg) were detected in all sites. Correlations and PCA suggest that lithogenic sources controlled metal deposition, while most sediment arsenic was agriculture-derived. Organic matter acted as a sink or source for some trace metals. According to EFs, the study area showed slight to moderate enrichment with respect to Ag, As, Pb, Cd, Zn and Cu, whereas they remained uncontaminated with Cr, V, Co and Ni. This study provides a needed baseline for future environmental investigations.

Identification of Microcrustaceans as Potential Bioindicators of Arsenic in Tropical Water Bodies.

We investigated microcrustaceans inhabiting arsenic contaminated and non-contaminated freshwater to identify potential bioindicators of arsenic contamination in the tropical freshwater of Matehuala in northern Mexico. We collected water, sediment, and zooplankton, at five sampling points during three sampling campaigns. We determined water temperature, pH, electrical conductivity, dissolved oxygen, alkalinity, salinity, and total arsenic concentration in water. Additionally, we determined total arsenic and arsenic speciation in sediment samples. We identified microcrustaceans and determined abundance, richness, and Shannon Index. We also investigated relationships and correlations between physiochemical and ecological variables. Results showed that arsenic concentrations in freshwater ranged from 0.001 to 53.23mg/L, while total arsenic in sediments ranged from 10.37 to 2472.84mg/kg as As + 5. Six microcrustacean species were found in highly and moderately contaminated water (Latonopsis australis, Eucyclops chihuahuensis, Acanthocyclops americanus, Pleuroxus (Picripleuroxus) quasidenticulatus, Macrocyclops albidus, and Paracyclops chiltoni), while five species were found in arsenic-free water (Simocephalus punctatus, Alona glabra, Eucyclops leptacanthus, M. albidus, and P. quasidenticulatus). An inverse relationship was observed between microcrustacean richness and arsenic. However, the scope of the data did not allow for a strong and significant correlation. Nevertheless, among the species inhabiting As-free water, S. punctatus showed potential to be further tested as a bioindicator of As contamination in Matehuala. Identification of potential bioindicators could help monitor water quality and increase understanding of the incorporation and toxicity of As in freshwater-sensitive and freshwater-metallotolerant microcrustaceans, which, in turn, might help us to understand As incorporation in the food web.

Occurrence and behavior of arsenic in groundwater-aquifer system of irrigated areas.

Groundwater arsenic pollution has received much attention worldwide for decades as a serious threat to public health, but the mechanisms responsible for arsenic mobilization are not fully understood. Groundwater and bore drilling sediment samples from Qiji county, a small geographical agricultural area with endemic arsenicosis, are collected for demonstrating the occurrence and speciation of arsenic in groundwater and sediments, and arsenic release between solid-liquid phase influenced by human activities. Results show that arsenic concentrations in groundwater vary from 5 μg/L to 19.6 μg/L, with 80% exceeding the maximum permissible limits required by WHO (10 μg/L) for drinking water and therefore constituting a health risk for humans. In a weak oxidizing environment (oxidation-reduction potential (ORP): 12.9 mV-151 mV), inorganic As(V) accounts for 85% of total dissolved As, which to some extent alleviates the harm of As pollution on humans. Total As content in the sediments is in the range of 6.98 mg/kg and 14.34 mg/kg (median of 10.71 mg/kg), three times higher than the average value of many countries. Sequential chemical leaching indicates that 11% of arsenic in sediments is labile bound and may be closely related to the arsenic in groundwater. Additionally, irrigation intensity contributes to arsenic release with diverse As3+/As5+ by dissolving weakly bound arsenic rapidly. Subsequently part of As(III) is oxidized to As(V). Competitive and/or alkaline desorption of As(V), which had been adsorbed by FeMn (hydrous)-oxides and carbonates in the unsaturated zone and the aquifer, exerts a significant role in releasing arsenic into the groundwater. Our study indicates that systematic management and regulation of irrigation intensity are required to prevent further deterioration of groundwater resources.

Migration characteristics of arsenic in sediments under the influence of cascade reservoirs in Lancang River basin

Cascade hydropower development in the Lancang River (LCR) Basin has a complex and far-reaching impact on river ecosystem, which has always been the focus of international attention. In this study, diffusive gradients in thin films (DGT) technique was used to study the reactivation of arsenic (As) in the sediments of Xiaowan (XW) and Nuozhadu (NZD) cascade dams in LCR. Pearson correlation analysis and Redundancy Analysis (RDA) were used to evaluate the bioavailability and spatial distribution characteristics of As. The results showed that the vertical variation of As in DGT at different sampling points presented different activation trends. The content of DGT-labile As (CDGT-As) in NZD Reservoir (36.21 ng/ml) was less than that in XW Reservoir (47.26 ng/ml). However, the difference of total content of As between the two reservoirs was relatively small. The results showed that the development of cascade reservoirs had no significant impact on total As, but had a great impact on DGT-labile As. The diffusion fluxes of the two reservoirs indicated that most of the sediments in the reservoir area were the source of As. Similar distribution characteristics and correlation analysis indicated that the migration mechanism of As was related to Iron (Fe) and manganese (Mn). In addition, on the basis of the results, the sources of As in sediments had certain spatial differences: cascade dam projects had significant accumulation and interception effects on As in the sediments, and at the same time strengthened the role of regional sediment, and this role reduced the risk of As release in downstream NZD Reservoir.

Human-induced arsenic pollution modeling in surface waters - An integrated approach using machine learning algorithms and environmental factors

In recent years, assessment of sediment contamination by heavy metals, i.e., arsenic, has attracted the interest of scientists worldwide. The present study provides a new methodology to better understand the factors influencing surface water vulnerability to arsenic pollution by two advanced machine learning algorithms including boosted regression trees (BRT) and random forest (RF). Based on the sediment quality guidelines (Effects range low) polluted and non-polluted arsenic sediment samples were defined with concentrations >8 ppm and <8 ppm, respectively. Different conditioning factors such as topographical, lithology, erosion, hydrological, and anthropogenic factors were acquired to model surface waters' vulnerability to arsenic. We trained and validated the models using 70 and 30% of both polluted and non-polluted samples, respectively, and generated surface vulnerability maps. To verify the maps to arsenic pollution, the receiver operating characteristics (ROC) curve was implemented. The results approved the acceptable performance of the RF and BRT algorithms with an area under ROC values of 85% and 75.6%, respectively. Further, the findings showed higher importance of precipitation, slope aspect, distance from residential areas, and slope length in arsenic pollution in the modeling process. Erosion, lithology, and land use maps were introduced as the least important factors. The introduced methodology can be used to define the most vulnerable areas to arsenic pollution in advance and implement proper remediation actions to reduce the damages.

Assessment of sediment arsenic and iron occurrence and leaching potential in a potable water treatment plant wastewater stabilization pond system

Wastewater stabilization ponds (WSPs) are commonly used to reduce wastewater metal(loid) concentrations from drinking water treatment plants (DWTPs) through sedimentation. However, this results in increased sediment concentrations that can be released back into the overlying water. Thus, our goal was to evaluate the WSP metal(loid)s occurrence and leaching potential. Currently, a Saskatchewan based DWTP’s WSP system was investigated given historically elevated effluent As and Fe concentrations. The WSP consists of five ponds that were sampled on six occasions in 2019 and 2020. In addition, sediments were used in laboratory-based experiments to determine their leaching potential. Overall, the sediments were found to contain elevated concentrations of As and Fe of 25 to 400 mg/kg and 10 000 to 45 000 mg/kg, respectively. Leaching experiments indicated that the pond sediments could potentially release As and Fe with log Kd values ranging from 2.21 to 4.31 L/kg, whereas Fe ranged from 3.32 to 5.53 L/kg.

Trends and environmental factors of arsenic in sediments from the five lake ecoregions, China.

The behavior and risk of arsenic (As) closely relate to its geochemical fractionation and environmental factors in sediments. The soluble (F1), reducible (F2), oxidizable (F3), and residual fraction (F4) of As were extracted in the sediments from Lake Hulun, Wuliangsuhai, and Dalinor of Inner Mongolia Plateau. Coupled with lakes from Eastern and Northeast Plain, Yunnan-Guizhou and Qinghai-Tibetan Plateau, the responses of As fractions to environmental conditions were investigated according to the spatial distribution of As fractionations in five lake ecoregions at a national scale of China. Generally, F1 was more sensitive to environmental changes, and the pH presented significantly negative effects on the amount of soluble As, while water depth played an important role in regulating the distribution of the fraction F2 and F4. The As pools in surface lake sediments presented a latitudinal zonation due to the gradient effects of climate and anthropogenic activities on nutrient decomposition, and their influence on the capacity of sediments holding As. This work indicated that nutrients played a coordinating role in regulating the impacts of climate and environmental factors on As fractionation in aquatic environments.

Comparison of the effects of competitive adsorption and reductive dissolution on migration of arsenic in lake sediment

ABSTRACT Arsenic-contaminated sediment of Lake Yangzonghai (Yunnan province, China) and its overlying water was used to investigate the effects of phosphate ion (PO4 3−) and microbial activity on the migration of arsenic in the sediment. The results showed that the competitive adsorption of PO4 3− was the primary factor for the release of arsenic from the sediment to the overlying water, while microbial activity played a minor role in promoting the reductive dissolution of iron/arsenic (hydro) oxides. The reductive dissolution of ferrous ion (Fe2+) occurred in the initial stage, and partly contributed to the increase of arsenic concentration in the overlying water. The increase of PO4 3− concentration in the overlying water enhanced the mobility and biological toxicity of the arsenic in the sediment. After PO4 3− in the overlying water was depleted, arsenic in the overlying water could be adsorbed and precipitated again by iron salts, resulting in the decrease of arsenic concentration in the overlying water. The study implies that among those arsenic-contaminated lakes, eutrophication will aggravate the risks of secondary pollution of arsenic.