Adsorption and migration of heavy metals between sediments and overlying water in the Xinhe River in central China

Metal contamination, their ecological risk, and relationship with other variables in surface sediments of urban rivers in a big city in Asia: case study of Hanoi, Vietnam

Urban rivers are significantly impacted by anthropogenic pressure. This study presents the updated assessment of the concentrations of 11 metals and other variables (pH, total organic carbon (TOC) and nutrients (total nitrogen, total phosphorus, and total silica)) in the sediments of four urban rivers in inner Hanoi city, Vietnam, during the period 2020-2022. The mean concentrations of Fe, Zn, As, and Cr were higher than the permissible values of the Vietnam National technical regulation on the surface sediment quality. Moreover, Zn and Cr were at the severe effect level of the US EPA guidelines for sediment quality. The calculation of pollution indices (Igeo and EF) demonstrated that Mn, Ni, and Fe were from natural sources whereas other metals were from both anthropogenic and natural sources. The ecological risk index revealed that metals in Hanoi riverine sediments were classified at considerable ecological risk. High values of metals, TOC, and nutrients in the sediments of these urban rivers mostly originate from the accumulation of untreated urban wastewater that is enhanced by low river discharge. Our results may provide scientific base for better management decisions to ensure environmental protection and sustainable development of Hanoi city.

Effects of sediment resuspension and changes in water nutrient concentrations on the remobilization of lead from contaminated sediments in Klity Creek, Thailand

As Pb-containing sediments in Klity Creek have had negative impacts on the area for more than 20 years, the Supreme Court ordered the Pollution Control Department (PCD) of Thailand to remediate the site. In response to the court order, the PCD decided to reduce the contamination level by dredging the sediments of the creek. Therefore, this study is the first investigation to be conducted on the coupled effects of sediment resuspension caused by dredging and changes in water nutrient concentrations upon the remobilization of Pb from sediments into the water column. The Pb concentrations and speciation in both the water and sediments collected from upstream and downstream regions of the contaminated area were determined. The results showed that the total Pb concentrations in the water taken from all sampling sites in both the dry and wet seasons were lower than the national standard (50 μg/L), and a very low mobility index was found for Pb. The highest total Pb concentration in the sediments (6930 mg/kg) from the downstream site was 23.7- to 30.4-fold greater than those of the sediments collected from the upstream site. The predominant Pb species (organic and residual Pb fractions) in the sediments collected during the dry season were identified. However, carbonate- and Fe-Mn oxide-bound Pb fractions were mainly found in the sediments collected in the wet season. The diffusive gradients in thin films (DGT)-labile Pb concentrations, which reached 2.1 mg/L, indicated potential toxicity to aquatic organisms. A total of nine resuspension scenarios generalizing all changes in water nutrient concentrations in addition to sediment resuspension due to dredging were constructed. The results confirmed that sediment resuspension alone could remobilize Pb from the sediments into the water at levels from 0.06 to 16.9 μg/L. Sediment resuspension in water contaminated with 1 mg/L phosphate (PO₄^3-) led to the dissolution of 28.4-73.0 μg/L Pb in the water column. Nitrate (NO₃^-) did not significantly remobilize Pb from the sediments into the water. The high ionic strength and activity coefficient of PO₄^3- in the water were expected to cause the retention of dissolved Pb in the water and enhance the remobilization of Pb from the sediments due to the association of Pb with PO₄^3- in the water.

Chemical speciation and bioavailability of potentially toxic elements in surface sediment from the Huaihe River, Anhui Province, China

In order to understand the characteristics of speciation and ecological risk of potentially toxic element (PTE) pollution in the surface sediment of huaihe river (Anhui province), 23 surface sediment samples were collected. The occurrence characteristics of PTEs (As, Cr, Zn, Cu, Cd, Pb, Mn) were analyzed by modified continuous extraction method (BCR), and the pollution status and potential ecological risk of PTEs were comprehensively evaluated by Pollution Load Index (PLI), Geoaccumulation Index (Igeo), Enrichment Factor (EF) and the risk assessment code (RAC). Results showed that the total concentrations of As, Mn, Cd, Cr, Cu, Pb, and Zn in sediment were 14.98 ± 2.32, 936.02 ± 144.48, 0.32 ± 0.08, 161.73 ± 124.83, 40.44 ± 9.67, 15.46 ± 6.67, and 74.85 ± 26.43 mg/kg, respectively. The mean concentrations of PTEs with the increasing order of Zn < Mn < Cr < Pb < Cu < As < Cd. Most PTEs appeared to mainly associate with a dominant proportion of residual fraction suggesting lower mobility whereas Cd and Mn presented a relative higher exchangeable fraction indicating a great degree of bioavailability and easily ingested by aquatic organism. Results of pollution degree showed that 3 sampling sites belong to the pollution degree of strong pollution, and the other sampling sites belonged to the medium pollution level. The indexes EF revealed moderately enrichment of Cr, minor enrichment of Cd, Mn and As, no enrichment of Cu, Zn and Pb. The values of the Igeo and RAC demonstrated that Cd and Mn pose a high ecological risk, which deserves further attention.

Analysis and potential ecological risk assessment of heavy metals in surface sediments of the freshwater ecosystem in Zhenjiang City, China

Heavy metals contamination in freshwater ecosystems has drawn attention worldwide. It is necessary to investigate heavy metals content and assess their ecological risk in order to protect the aquatic ecosystems. In this study, we collected surface sediment samples from the freshwater ecosystem of the city of Zhenjiang, in China, in both winter and summer. Then, we analyzed the seasonal and spatial distribution patterns of lead (Pb), chromium (Cr), cadmium (Cd), zinc (Zn), and copper (Cu). The contamination factor (CF), enrichment factor (EF), geo-accumulation index (Igeo), and potential ecological risk (Eri) were jointly used to assess the pollution degree and the ecological risk posed to the freshwater ecosystem by the aforementioned elements. Multivariate statistical analysis, including Pearson’s correlation and principal component analysis and cluster analysis, were used to identify potential sources of the investigated metals in this research area. Study results showed that: (1) the average concentrations values were 1.81 mg/kg and 1.15 mg/kg for Cd, 55.3 mg/kg and 62.2 mg/kg for Cu, 88.0 mg/kg and 52.5 mg/kg for Cr, 27.3 mg/kg and 22.8 mg/kg for Pb, 87.0 mg/kg and 271 mg/kg for Zn, in winter and summer, respectively. Amongst the investigated elements, the average concentrations of Cd, Cu, Cr, and Pb, were above the local background values in winter, whereas, Cd, Cu and Zn concentrations were higher than the background values in Zhenjiang; (2) The CF and EF indicated that Cd had a high contamination degree and a significant enrichment compare to others investigated metals in the surface sediment of in this research area. (3) Cd posed moderate, considerable, or very high ecological risks in different sites, while the other elements (i.e., Cu, Cr, Pb, and Zn) presented a low degree of ecological risk. (4) Multivariate statistical analyses results indicated Pb, Cu, and Zn had similar geochemical characteristics, while, Cd and Cr had significant differences with the above elements. Therefore, Pb, Cu, and Zn probably originate from the same sources, while Cd and Cr might have mixed sources, including both natural sources and human activities. Overall, more attention should be paid to Cd for risk assessment in the current study area. The findings of this study provide fundamental information for the evaluation and management of the heavy metals investigated in the freshwater ecosystem of Zhenjiang.