Influence of environmental factors on changes in the speciation of Pb and Cr in sediments of Wuliangsuhai Lake, during the ice-covered period

doi:10.21203/rs.3.rs-2861896/v1

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Influence of environmental factors on changes in the speciation of Pb and Cr in sediments of Wuliangsuhai Lake, during the ice-covered period

https://doi.org/10.21203/rs.3.rs-2861896/v1

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published 13 Mar, 2024

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Ecological pollution caused by heavy metals released by sediments is a worldwide concern. However, the effect of changes in sediment speciation on their release of heavy metals has not been adequately reported. This study analysed changes in the sediment speciation of Pb and Cr before and after a release experiment by varying the temperature, pH, and salinity of the water column. The results show that the release of Pb and Cr from sediments increases with increasing water temperature, mainly due to the conversion of the residual fraction of Pb to the Fe-Mn oxide fraction and Cr converting more residual fraction to the organic matter and sulfide fraction. The release of sediment Pb and Cr decreased with increasing pH, with Pb converting more acid extractable fraction to the residual fraction and Cr converting more organic matter and sulfide fraction to the residual fraction. In contrast, the release of Pb and Cr increased and then decreased with increasing salinity, with the acid extractable and residual fractions of Pb interconverting, and the organic matter and sulfide fraction and the residual fraction of Cr showing higher interconversion. For Pb, the acid extractable fraction was more susceptible to conversion to the residual fraction by environmental influences, whereas for Cr, the organic matter and sulfide fraction was susceptible to conversion to the residual fraction. This study highlights the influence of environmental factors on the sediment speciation of heavy metals, which can help reveal the transport and transformation of heavy metals in cold and arid lake sediments.

cold region

Wuliangsuhai Lake

speciation

sediments

heavy metals

environmental factors

Heavy metals are cumulative pollutants that pose potential long-term risks to humans and aquatic systems due to their toxicity, irreversibility, and bioconcentration in the food chain (Ikem et al., 2003; Wang and Zhang., 2018; Bing et al., 2019). Heavy metals can persist in the environment and disrupt the biochemical and physiological systems of plants, animals, and humans. Specifically, Pb can be absorbed by organisms through water, air, and nutrients and disrupt nucleic acid and protein formation, antioxidant enzyme activity, and cell membrane function (Yabe et al., 2015; Hu et al., 2016; Chen et al., 2019; Kataba et al., 2021; Kataba et al., 2021; Aytekin, 2022; Pham et al., 2022). Cr is the second most common metal contaminant in groundwater, soil, and sediments, and Cr occurs in two main oxidation states in surface water, as an immobile and less soluble Cr(III) under reducing conditions and as a mobile, toxic, and bioavailable Cr(VI) under oxidising conditions. Cr(VI) is a recognised human carcinogen that has a high environmental mobility and readily crosses biofilms (Rosa et al., 2017; Aharchaou et al., 2018; Chen et al., 2022; Kapoor et al., 2022). Cr inhibits both photosynthetic and respiratory processes to reduce oxygen in water systems, and also inhibits the uptake of water and minerals essential for the growth of submerged plants (Mathur et al., 2016; Mishra and Bharagava, 2016; Rahman and Singh, 2019).

The enrichment of sediments in heavy metals from water and suspended particulate matter can occur through processes such as adsorption, complexation, flocculation and sedimentation (Wang et al., 2023). Sediments act as a medium for land-based pollutants to enter water bodies and serve as an important habitat for aquatic organisms. Therefore, changes in sediment heavy metals should be monitored continuously in order to accurately assess the state of the water environment. Heavy metals in sediments enter the substrate through the food chain and their toxicity may be amplified by enrichment, directly or indirectly endangering human life and health (Li et al., 2023). Most importantly, heavy metals entering sediments undergo desorption and release under certain circumstances, disrupting the dynamic equilibrium of water bodies and causing secondary pollution. Therefore, riverbed sediments have a non-negligible role in the migration and transformation process of secondary pollutants in rivers (Qin and Tao, 2022). Factors such as water pH, dissolved oxygen, temperature, high salinity, high nitrogen levels, P content in overlying water, sediment redox potential, sulfides, and calcium content influence the release of heavy metals from sediments (Martín-Torre et al., 2015; Xu et al., 2017; Zhou et al., 2020). The results of relevant studies in China and abroad indicate that the potential ecological hazards and transportability of heavy metals can be better evaluated by analysing their speciation in sediments (Liu et al., 2021; Shi et al., 2022). The speciation of heavy metals in sediments can be divided into four categories: acid extractable (B1), Fe-Mn oxide combined (B2), organic matter and sulfide combined (B3), and residual (B4) fractions. The different heavy metal forms exhibit different geochemical behaviours in the aquatic environment because they have different biochemical reaction properties and their biological effectiveness and mobility vary (Bastami et al., 2018). When the environment changes, the release of heavy metals from sediments also changes.

The exploration of heavy metals from the perspective of sediment speciation is essential for developing control strategies and methods to manage water quality in riverine areas at the catchment scale (Wang et al., 2021). Wuliangsuhai Lake is a typical eutrophic lake. For a long time, receding water from agricultural fields in the upper river-loop irrigation area has been flowing into Wuliangsuhai Lake through different drainage ditches, resulting in the declining water quality and inducing heavy metal enrichment and pollution in the watershed (Du et al., 2022). Wuliangsuhai Lake is located in the cold and arid region of northern China, and its freezing period is characterised by thicker ice (about 0.3–1.2 m), longer freezing period (about 6–7 months), and a large proportion of the lake water body (1/3–1/2). Moreover, the lake surface is covered by ice, which almost completely halts the process of reoxygenation by natural aeration. Consequently, the dissolved oxygen concentration reaches its lowest value, and the reducing environment is strengthened. Low water temperature directly affects the degradation of pollutants by microorganisms, and changes in the physicochemical properties of water bodies in the lake environment can lead to changes in the fate of heavy metals in the water environment (Zhao et al., 2018). Based on the above background, this paper aimed to investigate the effects of temperature, acidity, and salinity on changes in the fugitive forms of sediment Pb and Cr and to reveal the mechanism of environmental factors affecting the migration and transformation of sediment heavy metals. To this end, the release of Pb and Cr from sediments was estimated by changing the temperature, pH, and salinity of the overlying water body through simulation experiments, focusing on changes in the speciation of sediment Pb and Cr before and after the release.

Study area

The Wuliangsuhai Lake is located in the territory of Ulaat Qianqi, Bayannur City, Inner Mongolia Autonomous Region, with geographical coordinates between 40°36′–41°03′N and 108°43′–108°57′E. It is one of the eight major freshwater lakes in China, covering an area of approximately 325.31 km² with a storage capacity of approximately 2.5–3×10⁸ m³ (Yu et al., 2022). The average water depth is 2.16 m (measured in 2022) and the lake bottom is composed of sedimentary silt in the upper part and light yellow proto-silt in the lower part. Located in a cold, arid region, the region has a mean annual temperature of 7.5°C and precipitation of 225 mm. The region experiences five months of ice cover per year, with most precipitation occurring between June and September (Li et al., 2022). Wuliangsuhai Lake is a river track lake formed by the diversion of the Yellow River, which mainly covers the receding lakes of the farmland in the river-loop irrigation area, with serious eutrophication of the water body, accelerated marsh process, and serious water environmental issues.

Sampling

Water and surface sediment samples were collected using column samplers through GPS sampling at nine local sites in Wuliangsuhai Lake (Fig. 1). All samples were mixed and sealed in polyethylene bags and then immediately refrigerated at -4°C and transported to the laboratory for analysis (Luo et al., 2020).

Determination of total sediment Pb and Cr

Regarding sample processing, 0.3–0.4 g of the samples were weighed and placed in a Teflon crucible. A small amount of ultrapure water was added for moisture and 5 mL of superior pure hydrochloric acid was then added. Each sample was placed on an electric hot plate (130°C) and heated until the amount decreased to approximately 2–3 mL. It was then removed and cooled, and 10 mL (HClO₄:HNO₃ = 1:4), 5 mL hydrofluoric acid, and 10 mL superior pure nitric acid were added. It was moved to the electric hot plate, covered with a lid, heated, and decomposed until no black material remained in the crucible. The lid was opened, the white smoke of HClO₄ and steam were removed until the contents of the crucible became viscous and approximately 2 mL of liquid remained. A small amount of ultrapure water was added until white smoke appeared. Then, a small amount of water was added and when the white smoke was largely gone and the substance in the crucible became viscous, the crucible was removed and cooled, the liquid was transferred into a 25 ml test tube, the crucible was rinsed several times in small amounts, and the volume was fixed to 25 ml with UP water and left for measurement (Lv, 2018).

Determination of fugitive forms of Pb and Cr

The following method (Fig. 2) was applied to determine the four forms of sediment Pb and Cr. The content of the different chemical forms of heavy metals was extracted in a graded manner using the BCR (provided by the EC Bureau of Standards for Substances) step-by-step extraction method, with three parallel samples set up for each sample in the experiment and a blank sample set up for each step of the experiment for reference (Lv, 2018).

Evaluation of sediment Pb and Cr

Sediment Quality Gauging (SQG)

The sediment mass benchmark method is a method for evaluating the risk of heavy metal biotoxicity in sediments based on critical effect concentrations (TEL) and probable effect concentrations (PEL), where the TEL values for Cr and Pb are 37.3 mg·kg^− 1 and 35 mg·kg^− 1, respectively, and the PEL values are 90 mg·kg^− 1 and 91.3 mg·kg^− 1, respectively (Smith et al., 1996). Heavy metal concentrations less than the TEL are considered to pose biological risks. Toxic effects on organisms occur frequently at heavy metal concentrations greater than the PEL and occasionally at concentrations between the TEL and PEL (Zhang et al., 2019).

Single factor pollution index method (Cⁱ_f)

The Heavy Metal Single Factor Index is the ratio of measured levels of heavy metals (Cⁱ_s) to local background values (Cⁱ_n) and indicates the contamination status of heavy metals in surface sediments, which is calculated as:

Cⁱ_f=Cⁱ_s/Cⁱ_n

Based on Cⁱ_f results, pollution levels can be classified as follows: Cⁱ_f < 1, no pollution; 1 < Cⁱ_f < 3, light pollution; 3 < Cⁱ_f < 6, moderate pollution; Cⁱ_f ≥ 6, severe pollution (Sutherland, 2000; Meena et al., 2017; Kuang et al., 2018).

Ratio of secondary phase to primary phase distribution (RSP) method

Sediments can be divided into primary and secondary phases based on their geochemical origin and the source of the heavy metals within them. The residual fraction of heavy metals present in the primary mineral lattice is called the primary phase and the remaining heavy metal forms are called the secondary phase. The secondary phase of heavy metals is bioavailable, whereas the primary phase is not bioavailable. A method for determining the level of heavy metal contamination in sediments by the ratio of the total mass fraction of heavy metals in the secondary phase to the mass fraction of heavy metals in the primary phase is the secondary phase to primary phase distribution ratio method (Zhang et al., 2022). This method can be expressed as follows:

RSP_i=𝑆_i/P_i

where RSP_i is the degree of pollution of the ith heavy metal; S_i is the content of the secondary phase of the ith heavy metal in the sediments; and P_i is the content of the primary phase of the ith heavy metal in the sediments. According to RSP results, pollution levels can be classified as follows: 0༜RSP༜1, no pollution; 1༜RSP༜2, light pollution; 2༜RSP༜3, moderate pollution; RSP༞3, heavy pollution.

Risk Assessment Coding method

As B1 heavy metals are readily and directly bioavailable and are more hazardous, a risk assessment coding (RAC) method based on the ratio of B1 content to the total content can be used to evaluate the transport and bioavailability of heavy metals in sediments (Zhang et al., 2022). RAC can be calculated as follows:

RAC=(C_e/C_t)×100%

where C_e is the content of heavy metal B1 and C_t is the total content of heavy metals. According to RAC evaluation results, risks can be classified as follows: RAC < 1%, no risk; 1% <RAC < 10%, low risk; 11% <RAC < 30%, medium risk; 31% <RAC < 50%, high risk; RAC > 50%, very high risk.

Factors affecting the release of heavy metals

Temperature

Eighteen sediment samples (dry samples) were accurately weighed at (1.0000 ± 0.0005) g each, and placed in 50 mL triangular flasks. Three parallel samples were set up for a total of 6 groups, at 5°C, 15°C, 25°C, 35°C, and 45°C. In a constant temperature water bath shaker (SHZ-82), 20 mL (pH = 7, salinity 1.5 g/l) of the solution was added in turn. The solution was shaken for 24 h (25°C, 200 r∙min^− 1), then centrifuged for 20 min (4000 r∙min^− 1) on a benchtop low-speed centrifuge (TDZ4-WS), and filtered. The supernatant was removed and pH was adjusted to 2, and Cr and Pb in the supernatant were determined (Lv, 2018).

pH

According to the pH monitoring data of the waters of Wuliangsuhai Lake, the pH of the water body ranged from 4.0 to 10.8, and the mean values of pH in winter, spring, summer, and autumn were 8.7, 9.0, 8.2, and 8.4, respectively. pH values indicated that the water environment of Wuliangsuhai Lake is neutral-alkaline (Zhao et al., 2022). Therefore, Pb and Cr simulations were carried out at pH 4, 5, 6, 7, 8, and 9. Eighteen sediment samples (dry samples) of (1.0000 ± 0.0005) g each were accurately weighed and placed in 50 mL triangular flasks, and three parallel samples were set up in six groups. Solutions (20 mL) of pH 4, 5, 6, 7, 8, and 9 (salinity 1.5 g/l) prepared with HCl and NaOH were added in turn and shaken on a constant temperature water bath shaker (SHZ-82) for 24 h (25°C, 200 r∙min^− 1), then centrifuged for 20 min (4000 r∙min^− 1) on a benchtop low-speed centrifuge (TDZ4-WS), and filtered. The supernatant was removed and pH was adjusted to 2, and Cr and Pb in the supernatant were determined (Lv, 2018).

Salinity

Eighteen sediment samples (dry samples) were accurately weighed at (1.0000 ± 0.0005) g each, placed in 50 mL triangular flasks. Three parallel samples were set up for a total of six groups, and 20 mL of solutions (pH = 7) with salinities of 0.5, 1.5, 2.5, 3.5, 4.5, and 5.0 g∙L^− 1 (measured) prepared with NaCl were added sequentially (Qifeng Zhang & Xiaohong Shi et al., 2022), shaken on a constant temperature water bath shaker (SHZ-82) for 24 h (25°C, 200 r∙min^− 1), centrifuged on a benchtop low-speed centrifuge (TDZ4-WS) for 20 min (4000 r∙min^− 1), and filtered. The supernatant removed and acidified to pH = 2. Then, Cr and Pb in the supernatant were determined (Lv, 2018).

Total sediment heavy metals and speciation

The total amount of Pb in the ice-covered sediments of Wuliangsuhai Lake (Fig. 3) ranged from 11.17 mg/kg to 24.25 mg/kg, with an average of 18.60 mg/kg, and the total amount of Cr ranged from 42.26 mg/kg to 69.68 mg/kg, with an average of 58.60 mg/kg. Regarding Pb in the sediments of Wuliangsuhai Lake during the ice-covered period, the average contents of B1, B2, B3, and B4 were 0.05 ± 0.04 mg/kg, 5.77 ± 4.46 mg/kg, 5.69 ± 2.21 mg/kg, and 7.09 ± 2.22 mg/kg, accounting for 0.27%, 29.06%, 32.16%, and 38.50% of the total, respectively. Regarding Cr, the average contents of B1, B2, B3, and B4 were 2.51 ± 0.54 mg/kg, 2.01 ± 1.47 mg/kg, 6.37 ± 1.84 mg/kg, and 47.71 ± 8.16 mg/kg, accounting for 4.40%, 3.42%, 10.93%, and 81.25% of the total, respectively. Overall, the secondary phases (B1 + B2 + B3) of Pb and Cr in the ice-covered sediments of Wuliangsuhai Lake reached 61.95% and 18.75%, with B3 dominating the secondary phases of both Pb and Cr.

From the results of the sediment quality benchmark method (Fig. 4), the values of Pb in the sediments of the Wuliangsuhai Lake during the freezing period (January) were lower than the TEL and PEL values, indicating that Pb has essentially no toxic effects on organisms in the lake. In contrast, Cr exceeded the TEL value, but the values were lower than the PEL value at all sampling points, indicating potential toxicity. The single factor pollution index method showed light pollution of both Pb and Cr. The results of the two evaluation methods are somewhat different and comprehensive. The contamination of Pb and Cr was further analysed according to their morphology, based on the evaluation of Pb and Cr in the ice-covered sediments of Wuliangsuhai Lake using the RSP method. The results showed that the ratio of the secondary phase to the primary phase of Cr was less than 1, indicating no contamination, while the ratio of Pb was greater than 1, indicating generally light contamination and even moderate contamination at some sampling sites. The RAC method showed that the ratio of the acid extractable content of Cr to the total heavy metal content was greater than 1, which indicates that Cr is more likely to migrate and be absorbed and used by organisms. Therefore, Cr poses a certain risk.

The results of the RAC method showed that Pb does not pose risks, which means that the content of B1 in Pb is within the safe range. Nevertheless, the results of the RSP method showed generally light contamination of Pb, with moderate contamination at some individual sites, which proves that the proportion of the secondary phase is larger than that of the primary phase. Therefore, the ratio was greater than 1 and fell within the range of contamination. The RSP results for Cr were opposite to the RAC results, indicating that although the B1 content was higher, the proportion of the secondary phase remained smaller than the proportion of the primary phase. Combining the results of the total and morphological evaluation methods, both Pb and Cr have a certain risk of release, with Cr mainly having a high B1 content and Pb mainly having a high B1 + B2 + B3 content. Therefore, their risk levels deserve further attention.

Changes in sediment heavy metal speciation under different environmental changes

Temperature variations

Changes in the external environment, including temperature, pH and salinity, influence changes in the speciation of heavy metals in the sediments.

Pb and Cr were released under different temperature conditions at 5°C, 15°C, 25°C, 35°C, and 45°C (Fig. 5), respectively, and the release of Pb increased by 0.17 mg/g with temperature increasing from 5°C to 45°C. The total percentage of B1 + B2 + B3 increased by 2.06%. In particular, the percentage change of B2 was the largest, increasing by 1.70%, whereas that of B4 decreased by 2.06%. Under the condition of increasing temperature, the amount of Cr released rapidly increased, increasing by 1.99 mg/g from 5℃ to 45℃. The total proportion of B1 + B2 + B3 increased by 9.86%. In particular, the proportion of B3 increased by 6.62%, whereas that of B4 decreased by 9.86%.

pH changes

Pb and Cr releases were simulated at pH 4, 5, 6, 7, 8, and 9 respectively (Fig. 6).

Pb release exhibited a steady decline, decreasing by 0.31 mg/g from pH = 4 to pH = 9. more B1 + B2 + B3 transformed to B4, and the percentage of B1 + B2 + B3 decreased by 33.29%. Cr release decreased rapidly by 1.97 mg/g from pH = 4 to pH = 5 and by 0.63 mg/g from pH = 5 to pH = 9. More B1 + B2 + B3 was converted to B4 before and after the release, and the total B1 + B2 + B3 decreased by 9%. The percentage of total B1 + B2 + B3 decreased by 9%, with the percentage of B3 decreasing by 7.58%.

Salinity changes

Changes in the release and morphology of Pb and Cr were observed under various salinity conditions (Fig. 7).

The release of Pb increased by 0.31 mg/L with salinity increasing from 0.5 mg/L to 1.5 mg/L, but it decreased by 0.45 mg/L with salinity increasing from 1.5 mg/L to 5.0 mg/L. The percentage of B1 + B2 + B3 decreased by 19.83%. In particular, the percentage of B1 decreased by 11.25% and that of B4 increased by 19.83%. With the increase of salinity, the release of Pb increased first and then decreased until an equilibrium state after salinity reached 1.5 mg/L. The percentage of B1 + B2 + B3 increased before salinity reached 1.5 mg/L and then decreased. The percentage of B4 decreased until the salinity was 1.5 mg/L, after which it increased. The release of Pb increased by 1.59 mg/L from a salinity of 0.5 mg/L to 2.5 mg/L, decreased by 1.09 mg/L from 2.5 mg/L to 5.0 mg/L, and decreased by 1.09 mg/L from 0.5 mg/L to 2.5 mg/L. More B4 was converted to B1 + B2 + B3 at a salinity of 2.5 mg/L. B1 + B2 + B3 increased by 4.56%, with B3 particularly increasing by 2.59%. More B1 + B2 + B3 was converted to B4 with salinity increasing from 2.5 mg/L to 5.0 mg/L (B1 + B2 + B3 decreased by 2.69%). The release of Cr presented an inflection point at a salinity of 2.5 mg/L, rising and then falling. The proportion of total B1 + B2 + B3 in Cr increased up to a salinity of 2.5 mg/L, after which it decreased.

There is a close and complex relationship between the fate and physicochemical properties of heavy metals, with temperature, pH, and salinity all affecting the fate of heavy metals (Zhou et al., 2022). Therefore, the relationship between sediment heavy metal morphology and water temperature, pH, and salinity was analysed. The results showed that temperature has a significant positive correlation with the B1 and B2 contents of Pb and a negative correlation with the B4 content. The B1 and B3 contents of Cr were positively correlated with temperature and the B4 content was negatively correlated with temperature. The B4 content of Pb was positively correlated with pH, whereas those of B1 and B3, were negatively correlated with pH. The B2 and B4 contents of Cr were positively correlated with pH. The B4 content of Pb was positively correlated with pH, and those of B1 and B3 were negatively correlated with pH. The B2 and B4 contents of Cr were positively correlated with pH, and the remaining fractions were negatively correlated with pH. Salinity had a stronger effect on the B4 content of Pb, and all of them were significantly positively correlated, whereas the contents of other fractions were significantly negatively correlated.

In general, sorption is exothermic, with elevated temperatures favouring the desorption of metal ions from particulate matter (Wu et al., 2021). Under normal conditions, the residual fraction of heavy metals is the most stable and the soluble form is most readily released into the overlying water, with other species likely to be released by chemical reactions. With increasing temperature, the rate of reaction is accelerated and the DO concentration as well as carbonate and hydroxide dissolution rates in water increase. As a result, the rate of metal release from the sediments into the overlying water is increased for the water-soluble, carbonate, and exchangeable fractions (Li et al., 2013). With increasing temperature, more B4 converts to B1 + B2 + B3.

In general, the release of heavy metals from particulate matter decreases with increasing pH. Low pH conditions lead to the dissolution of carbonates and hydroxides, and the competing effects of H⁺ also increase the desorption of metal ions. For specific adsorption by ligand exchange, the degree of desorption of specifically adsorbed anions is enhanced over a wide pH range, as both H⁺ and OH⁻ can react with hydration groups on the surface of metal hydrate oxides (Wu et al., 2021). In an acidic environment, the release rate decreases rapidly with increasing pH and the turning point is generally between pH = 4 and 5. In neutral and basic environments, the release rate of heavy metals is low. This is mainly because the release of heavy metals in acidic environments is probably due to resolution and precipitation, whereas in alkaline environments, it is generally believed to be due to the decomposition of organic matter, which re-releases heavy metals bound to it (Chen and Zhou, 1992). B1 is mainly an exchangeable sorbent ion and a carbonate bound form, which is the most sensitive to environmental changes and can be released under acidic and neutral conditions. It is most sensitive to environmental changes and can be released under acidic and neutral conditions and can be directly bioavailable (Li et al., 2018). With the process of water alkalinisation, the B1 + B2 + B3 of heavy metals Pb and Cr in sediments transformed towards B4, with more alkaline environments having higher residual fraction and higher stability.

In aqueous solutions with increased salinity, alkali and alkaline earth metal ions can displace adsorbed heavy metal ions, thus leading to an increase in the release of heavy metals (Li et al., 2013). Therefore, the release of Pb and Cr in sediments increases with increasing salinity. In this study, the release of Pb and Cr in sediments first increased and then decreased with increasing salinity. The reason for this is that in the process of heavy metal release, with the release of heavy metals, other anions, organic particles and other soluble substances present in the sediment that co-precipitate with the heavy metals are likely to be leached out. When the process is carried out to a certain extent, heavy metal ions released in the aqueous phase will undergo physicochemical changes including complexation, adsorption, and co-precipitation with the leached substances, or occur as colloidal hydroxides The heavy metal concentration in the water-soluble state begins to decrease again until an equilibrium is established and the heavy metal concentration no longer changes (Lv et al., 2017). With increasing salinity, B4 of Pb and Cr in the sediment converts towards B1 + B2 + B3, and B1 + B2 + B3 converts towards B4 after reaching the inflection point.

Overall, the levels of Pb and Cr contamination in the sediments of Wuliangsuhai Lake were mild. In particular, Cr poses some risks and is transportable, with some risk of release. The sediment release of Pb and Cr is positively correlated with the increase in temperature, and the Fe-Mn oxide fraction of Pb changes the most significantly with increasing temperature, whereas the organic matter and sulfide fraction of Cr fraction shows the most significant changes. Changes in the release of sediment Pb and Cr were negatively correlated with the pH of the water column. The percentages of the acid extractable fraction of Pb, and the organic matter and sulfide fraction of Cr significantly changed with changes in the pH of the water column. Organic matter and sulfide changed the most significantly under the change of water column pH. the water column alkalinised and the acid extractable and organic matter and sulfide fractions of Pb and Cr transformed into the residual fraction. The release of heavy metals Cr and Pb increased with salinity and then decreased until equilibrium, indicating that the acid extractable was more likely to be converted to the residual fraction by under environmental influences. For Cr, the organic matter and sulfide fraction easily converted to residual fraction.

Author contributions

Material preparation, data collection, and analysis were performed by Yunxi Zhao. The frst draft of the manuscript was written by Yunxi Zhao and Shengnan Zhao, and all authors commented on previous versions of the manuscript. All authors read and approved the fnal manuscript.

Acknowledgements

This work was supported by the National Natural Science Foundation of China [grant numbers 52060022 and 52260028]; the National Key R&D Program of China [grant numbers 2017YFE0114800 and 2019YFC0409204]. The Inner Mongolia Autonomous Region Science and Technology Plan (2021GG0089).

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No competing interests reported.

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Influence of environmental factors on changes in the speciation of Pb and Cr in sediments of Wuliangsuhai Lake, during the ice-covered period

Status:

Journal Publication

Version 1

Abstract

Figures

Introduction

Materials and methods

Study area

Sampling

Determination of total sediment Pb and Cr

Determination of fugitive forms of Pb and Cr

Evaluation of sediment Pb and Cr

Sediment Quality Gauging (SQG)

Single factor pollution index method (Cⁱ_f)

Ratio of secondary phase to primary phase distribution (RSP) method

Risk Assessment Coding method

Factors affecting the release of heavy metals

Temperature

pH

Salinity

Results

Total sediment heavy metals and speciation

Changes in sediment heavy metal speciation under different environmental changes

Temperature variations

pH changes

Salinity changes

Discussion

Conclusions

Declarations

References

Additional Declarations

Status:

Journal Publication

Version 1

Influence of environmental factors on changes in the speciation of Pb and Cr in sediments of Wuliangsuhai Lake, during the ice-covered period

Status:

Journal Publication

Version 1

Abstract

Figures

Introduction

Materials and methods

Study area

Sampling

Determination of total sediment Pb and Cr

Determination of fugitive forms of Pb and Cr

Evaluation of sediment Pb and Cr

Sediment Quality Gauging (SQG)

Single factor pollution index method (Cif)

Ratio of secondary phase to primary phase distribution (RSP) method

Risk Assessment Coding method

Factors affecting the release of heavy metals

Temperature

pH

Salinity

Results

Total sediment heavy metals and speciation

Changes in sediment heavy metal speciation under different environmental changes

Temperature variations

pH changes

Salinity changes

Discussion

Conclusions

Declarations

References

Additional Declarations

Status:

Journal Publication

Version 1

Single factor pollution index method (Cⁱ_f)