Research on the geochemical background values and evolution rules of lake sediments for heavy metals and nutrients in the Eastern China Plain from 1937 to 2017

Determination and application of soil heavy metal geochemical baseline in the southern region of Wushan County in the Yangtze River Basin, China

The geochemical baseline is an essential reference for distinguishing natural and anthropogenic environmental impacts. It is of great significance for evaluating the changes in chemical substance (element) content and concentration before and after human development, as well as the evolution of environmental quality. Using background values such as the "Background Values of Chinese Soil Elements" and expanding the research scale can easily lead to "over protection" or "under protection" when guiding pollution control and governance. The article takes Wushan County, Chongqing City, in the Yangtze River Basin, as an example to collect 100 surface soils and construct a heavy metal environmental geochemical baseline. Analysis shows that the average values of As, Hg, Co, Cd, Pb, Cu, Ni, Zn, and Mn in the soil of the study area are 14.06, 0.09, 19.39, 0.99, 31.01, 37.08, 47.77, 121.10, and 960.20 mg/kg, respectively; The ground accumulation index indicates that heavy metals are mainly pollution-free and lightly polluted, but Cd, Hg, Cu, Ni, Zn, and Mn have a certain proportion of moderate pollution (43, 7, 2, 3, 2, and 1 point, respectively). Hg and Ni each have 1 medium to strong pollution level soil site, while Cd has 6 strong pollution sites, 4 strong to extremely strong pollution sites, and 5 extremely strong pollution sites. Based on the cumulative frequency curve method, the geochemical baseline values of Hg, As, Co, Cd, Pb, Cu, Ni, Zn, and Mn were obtained as 0.06, 12.69, 16.47, 0.22, 30.15, 24.61, 34.54, 104.40 mg/kg, and 628.32 mg/kg, respectively. The constructed soil heavy metal environmental geochemical baseline determines the evaluation criteria for small-scale spatial areas, which can scientifically and accurately identify the current soil pollution status in the region.

Reliability assessment of using different heavy metals in remote sedimentary records to reconstruct historical pollution

Interpreting heavy metal variations in sedimentary records is an important approach to reconstruct historical pollution. However, few studies have investigated the reliability of using different heavy metals in sedimentary records for reconstructing historical pollution. This study retrieved sediment cores from two adjacent remote lakes in North China and investigated their temporal changes in excessive metal fluxes. Combined with a novel index of the ratio of atmospheric emissions of anthropogenic metals to background metal concentrations in lake sediments, the reliability and influencing factors of using eight metals (Cr, Co, Ni, Cu, As, Zn, Cd, and Pb) in sediments to reconstruct historical pollution were studied. (1) Vertical As variations in the sediments were controlled mainly by early diagenesis effects, although anthropogenic pollution might also have had an impact. Consequently, As profiles in lake sediment records are usually difficult to reflect historical pollution. (2) Among the eight metals, Zn, Cd, and Pb in both lakes have been affected considerably by anthropogenic pollution and insignificantly by natural factors. Their excessive flux variations in the two records were highly consistent with the historical trend of economic/industrial development. Relatively, these three metals can reliably reflect historical pollution. (3) Compared with Zn, Cd, and Pb, Cr, Co, Ni, and Cu in the two lakes have been relatively less affected by anthropogenic pollution. During the high anthropogenic metal emission period (post-∼1980), they could roughly reflect historical pollution in the region; however, during the low emission period (before ∼1980), they appeared to exhibit no signs of pollution. This suggests the complexity of using heavy metals in remote sediment records to reconstruct historical pollution. The importance of this study lies in its potential to provide guideline for the use of aquatic sediment records from relatively remote areas in reconstructing the history of metal pollution.

Exploring multi-media geochemical relationships in the southeastern Amazonian basin: A way forward to define source and background levels of potentially toxic elements in lake sediments

Understanding geochemical source-sink relationships is an important aspect for developing background values of potentially toxic elements (PTEs) in a lake basin. This approach was studied in the Araguaia belt of Amazonia, Brazil. A total of 96 sediments (from 13 sediment core, low-altitude lateritic plateaus; LA2-LA14), 36 surface soils, and 19 catchment crusts/rocks were collected in 2022-2023 and chemical analysis of these samples was performed in the fine fraction (<177 μm) using XRF and ICP-MS. Results revealed that the PTEs concentration was significantly different (p < 0.05) between sediment, soil, and catchment rock, with more accentuated enrichment in rock followed by soils. The upper continental crust (UCC) normalization pattern shows that high enrichment of Fe, Ti, Ni, and Cr, and moderate enrichment of As, P and Cu in a few sediments, similar with catchment soils and crusts. Thus, the enrichment of PTEs in lake sediments is mainly controlled by dominant catchment lithology, whereby mafic and ultra-mafic bodies are the main source of Cr, Ni and Cu, whilst meta-mafic (Couto Magalhães Formation) rocks are a primary source of As. Principal component analysis (PCA) also supported a strong source-sink geochemical relationship. It identified the major bedrock geochemical signature Cr-Ni-Co as 'mafic rocks' and Al-Ti-Nb-Ga-Zr-Hf-U-Th as 'resistant minerals', and REE group, which were nearly similar between lake sediments, catchment soils, and crusts. Since the enrichment of PTEs is clarified by geogenic origin, these lake sediments are best suitable for establishing geochemical background (GB). This was calculated using a variety of methods, while the median ± 2 Median Absolute Deviation (mMAD) method was considered as most appropiate for this study. The new GB threshold values (estimated by mMAD) for As, Cu, Cr, Pb and Ni (most notably Cr and Ni) are significantly higher than those specified by the Brazilian CONAMA-L1 guidelines, as well as the regional GB values of Itacaiúnas River Watershed (IRW). Since these high values were already evidenced in catchment materials, the new GB threshold values should be considered as a more realistic reference value for anthropogenic risk assessment in the region. This is demonstrated by the results of the contamination factor (CF) of Cr and Ni in lake sediments, in which the CF values with respect to CONAMA limits and IRW GB values overestimated the contamination status. This finding made it clear that the site-specific GB values must be incorporated in the sediment quality guideline for improving contamination assessment and making any environmental decision of a given region.

Sedimentary environmental quality of a biosphere reserve estuary in southwestern Iberian Peninsula

The Huelva estuary is formed by the common mouths of the Odiel and Tinto Rivers, and inside this ecosystem is the biosphere reserve of the Odiel saltmarshes. This ecosystem has been historically affected by acid mine drainage (AMD) and by releases of pollutants from five phosphoric acid industrial plants and phosphogypsum (PG) waste stacks located in the area. This study carried out a comprehensive assessment of the environmental impact of the biosphere reserve of the Odiel saltmarshes. To this end, it was necessary to find a suitable sedimentary background (Piedras River in our case). To quantify this impact, several pollution indexes were used. According to the values reached by the indexes, this impact was classified as "serious" pollution for most trace elements, excepting the deepest layers, and "low-moderate" pollution for the 238U-series radionuclides, while no pollution for the 232Th-series and 40K radionuclides was found as expected.

Aging properties and cadmium remediation mechanism of biochar in sediment from phosphorus-rich water

Cadmium (Cd) is the main heavy metal pollutant in sediments from East China. The biochar-sediment nexus can provide carbon sequestration and pollution control. In this work, an in situ study was conducted to investigate the long-term effects and control mechanism of biochar and the effect of biochar aging on Cd stabilization in overlying water-pore water-sediment. The Cd2+ concentration in the overlying water was positively correlated with total nitrogen (0.960, P < 0.05), total organic carbon (0.983, P < 0.05), and total phosphorus (0.993, P < 0.01) in pore water. Biochar stabilized Cd2+ by increasing the pH and oxidation-reduction potential of the sediment environment and promoting the formation of Cd1.25Ca0.75(P2O7) on the biochar surface in sediment from phosphorus-rich water. These changes were closely related to the Brunauer-Emmett-Teller surface area and average pore size of the biochar. Within 60 days, the biochar in the sediment underwent aging, which was closely related to the preparation temperature of the biochar. The organic composition of biochar prepared at a low temperature (≤ 300 °C) and the surface structure of biochar prepared at a high temperature (≥ 500 °C) were altered. The biochar parameter changes were in the order of pore volume > Brunauer-Emmett-Teller surface area > pore size. Our results show that biochar modification can enhance the remediation capacity of biochar, but may be unfavorable to biochar anti-aging. This knowledge will support policymakers and researchers when exploring long-term biochar use in contamination control and strengthen future research.

Differentiating environmental scenarios to establish geochemical baseline values for heavy metals in soil: A case study of Hainan Island, China

Soil heavy metal distributions exhibit regional heterogeneity due to the complex characteristics of parent materials and soil formation processes, emphasizing the need for appropriate regional standards prior to assessing soil risks. This study focuses on Hainan Island and employs the Multi-purpose Regional Geochemical Survey dataset to establish heavy metal geochemical baseline and background values for soil using an iterative method. Geographical detector analysis reveals that parent materials are the primary factor influencing heavy metal distribution, followed by soil types and land use. Heavy metal geochemical baseline values are established for the island's three environments and administrative regions. Notably, a universal geochemical baseline value cannot adequately represent regional variations in heavy metal distribution, with parent materials playing a crucial role in various scenarios. Locally applicable values based on parent material are the most representative for Hainan Island. This study provides a reference framework for developing region-specific environmental baseline values for soil heavy metal assessments.

Coastal sediment heavy metal(loid) pollution under multifaceted anthropogenic stress: Insights based on geochemical baselines and source-related risks

Contamination and risk assessments generally ignore the potential bias in results caused by the variation of background values at different spatial scales due to the spatial heterogeneity of sediments. This study aims to perform quantitative source-ecological risk assessment via establishing geochemical baselines values (GBVs) of heavy metal(loid)s (HMs) in Daya Bay, China. Cumulative frequency distribution (CFD) curves determined the GBVs of 12.44 (Cu), 30.88 (Pb), 69.89 (Zn), 0.06 (Cd), 47.85 (Cr), 6.80 (As), and 0.056 mg kg-1 (Hg), which were comparable to the background values of Guangdong Province surface soils, and implied a potential terrestrial origin of the coastal sediments. Principal component analysis (PCA) and positive matrix factorization (PMF) identified three sources (F1: natural processes; F2: anthropogenic impacts; F3: specific sources) with contributions of 51.7%, 29.2%, and 19.1%, respectively. The source-specific risk assessment revealed an ecological risk contribution potential of 73.8% for the mixed anthropogenic sources (F2 + F3) and only 26.2% for natural processes. Cd and Hg were the priority management of metallic elements, occupying 63.5% and 72.5% of the contribution weights of F2 and F3, respectively, which showed multi-level pollution potentials and ecological risk levels. The spatial distribution patterns demonstrated the hotspot features of HM pollution, and priority concerns should be given to the management of marine traffic and industrial point source pollution in Daya Bay. The results of the study provide a scientific approach and perspective for pollution treatment and risk management in the coastal environment.

Uncertainties in Pollution and Risk Assessments of Heavy Metals in Lake Sediments Using Regional Background Soils in China

Background soils are frequently utilized as a surrogate to assess pollution levels and environmental risks of heavy metals in Chinese lakes. However, there remains a lack of understanding regarding the reliability and uncertainty of such assessments. Here, we determined heavy metals (As, Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn) in sediment cores from five rural lakes in North China to evaluate the reliability and uncertainty of the assessments using background soils by comparing them with assessments based on background sediments. Comparative studies reveal large uncertainties in the assessments using background soils. Among these metals, uncertainties for Hg and Cd are relatively large, whereas those for the other metals are minor. This discrepancy is due to the considerably higher natural variability of Hg and Cd in soils and sediments in comparison to the other metals. Generally, assessments utilizing background soils underestimate pollution levels and risks of Hg but overestimate those of Cd in these lakes. Despite limited human activities around the lakes, they still received a considerable influx of heavy metals via regional atmospheric transport. Assessments of the nine metals indicate moderate to considerable ecological risks in these lakes. The risks are contributed primarily (78-89%) by Hg and Cd. This study underscores the substantial uncertainties in assessing heavy metal pollution and risks using regional background soils and emphasizes the importance of controlling atmospheric emissions of Hg and Cd to mitigate pollution in rural and remote water bodies in China.

Risk assessment and source apportionment for metals in sediments of Kaptai Lake in Bangladesh using individual and synergistic indices and a receptor model

Metal enrichment in lake sediments originating from multiple sources can threaten both the aquatic ecosystem and human health. Therefore, assessment of the eco-environmental risks and potential sources of metals in the sediments is essential for effective lake management. Here, we analyzed the sediment metal contents of Kaptai Lake, the largest lake in Bangladesh for the first time with this study. The results indicated that only Cr and Ni contents among the metals studied exceeded the probable effect concentrations (PEC) at 25.42 % and 55.93 % of the sampling stations, respectively. All metals at most sampling stations showed low contamination and low ecological risk based on the individual indices (geoaccumulation index, contamination factor, ecological risk factor, enrichment factor and modified hazard quotient). There was no significant risk from the combined metals in the sediments of the lake according to the synergistic indices (toxic risk index, Nemerow risk index, ecological risk index, Nemerow pollution index and pollution load index). Organic matter and silt were significant sediment parameters that favored the accumulation of Cr, Fe, Cu, Pb and Mn. In the absolute principle component scores-multiple linear regression model (APCS-MLR), five potential sources of metals were identified in the sediments: Zn, Mn, Co and Cd mainly from natural sources and to a lesser extent from agricultural and aquacultural activities, Ni, Cr and Fe from parent materials, Pb and Cu mainly from natural sources and to a lesser extent from vehicle emissions, Hg and U from lithogenic sources, and As from natural sources. This study will improve our knowledge of the sedimentary metal contents of Kaptai Lake and provide helpful information for developing effective lake management and pollution control strategies.

Improving the efficiency of machine learning in simulating sedimentary heavy metal contamination by coupling preposing feature selection methods

Sediment cores were collected from Taihu Lake in China. The chronology was determined by radionuclide. Heavy metals and magnetic properties of each core slice were assessed, respectively. The concentrations of most heavy metals in sediments surged at 20 cm from the surface, accompanying the increase in the concentrations of single-domain magnetic particles. This may be resulted from the influence of anthropic activities on the lake's environment after the 1970s. Two feature selection methods, random forest (RF) and maximal information coefficient (MIC), were combined with support vector machine (SVM) model to simulate heavy metals, with the inclusion of selected magnetic and physicochemical parameters. Compared with the modeling results obtained with the full set of parameters, a reasonable simulation performance was obtained with RF and MIC. RF performed better than MIC by increasing the R² of simulation models for Cd, Cr, Cu, Pb, and Sb. For heavy metals with high ecological risks (As, Cd, Cr, Hg, Pb, Sb), the correlation coefficients for observed and predicted data ranged from 0.73 to 0.97 with only 14-27% of the parameters selected by RF as input variables. The RF-RBF-SVM enabled heavy metal predictions based on the magnetic properties of the lake sediments.

Potentially toxic elements in lake sediments in China: Spatial distribution, ecological risks, and influencing factors

Potentially toxic elements (PTEs) pollution in lake sediments is a serious threat to the ecological safety of lake water and human health, owing to anthropogenic activities. Studies on the distribution of pollution, the differences in lake types, and the influencing factors in China as a whole are lacking. This study collected data on PTEs (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in Chinese lake sediments published from 2005 to 2021, and aimed to evaluate pollution levels and spatial distribution characteristics of PTEs in lake sediments, differences in pollution in different types of lakes, and influencing factors. The results showed that (1) All metals in the lake sediments accumulated to different degrees, when compared to the background values. (2) The lake type pollution levels were ranked: urban lakes > reservoirs > plateau lakes > natural lakes. (3) The geoaccumulation and potential ecological risk indexes both indicated that Cd and Hg are the main pollutants, and that the overall ecological risk level of lake sediments in China is high. (4) The degree of economic and population growth is highly correlated with the concentrations of eight PTEs; the amount of fertilizer and pesticide used in agricultural activities are the main factors affecting As and Hg; industrial activities and traffic pollution emissions are the predominant factors affecting Cu and Ni. (5) In the interaction detection analysis, the Cr content was mainly influenced by natural factors; Cd, Pb, and Zn contents were affected more by human activities. This study provides a reference for understanding the current status and influencing factors of PTE pollution in Chinese lakes.

Sediment organic carbon dynamics response to land use change in diverse watershed anthropogenic activities

Sediment organic carbon (SOC) is a precious archive that synthesizes anthropogenic processes that remove geochemical fluxes from watersheds. However, the scarcity of inspection about the dynamic mechanisms of anthropogenic activities on SOC limits understanding into how key human factors drive carbon dynamics. Here, four typical basins with similar natural but significantly diverse human contexts (high-moderate-low disturbance: XJ-ZS and YJ-LS) were selected to reconstruct sedimentation rates (SR) and SOC dynamics nearly a century based on 200-cm corers. A partial least squares path model (PLS-PM) was used to establish successive (70 years) and multiple anthropogenic data (population, agriculture, land use, etc.) quantification methods for SOC. Intensified anthropogenic disturbances shifted all SR from pre-stable to post-1960s fluctuating increases (total coefficient: high: 0.63 < low: 0.47 < medium: 0.45). Although land use change was co-critical driver of SOC variations, their trend and extent differed under the dams and other disturbances (SOC mutated in high-moderate but stable in low). For high basin, land use changes increased (0.12) but dams reduced (-0.10) the downstream SOC. Furthermore, SOC mutation corresponded to soil erosion due to urbanization in both periods A and B. For moderate, SOC was reversed with the increase in afforestation and cropland (-0.19) due to the forest excitation effect and deep ploughing, which corresponded to the drought in phase B and the anthropogenic ecological project in A. For low, the increase in SOC corresponded to the Great Leap Forward deforestation in period B and the reed sweep in A, which suggested the minor land change substantially affected (0.16) SOC in fragile environments. Overall, SOC dynamics revealed that anthropogenic activities affected terrestrial and aquatic ecosystems for near the centenary, especially land use. This is constructive for agroforestry management and reservoir construction, consistent with expectations like upstream carbon sequestration and downstream carbon stabilization.