Investigating heavy metal pollution in Anzali coastal wetland sediments: A statistical approach to source identification

Pollution Load Index and Ecological Risk Assessment of Sediment Heavy Metals in Lake Edku, Egypt

Coastal lagoons, like lake Edku in north Egypt, are vital ecosystems that offer a wide variety of ecosystem services, including wildlife habitats. However, many are experiencing severe human impacts due to their proximity to urbanization. The main objectives of this study were to determine the concentrations of major and trace elements in lake Edku sediments, and to assess their ecological risk impacts based on Contamination Degree (Cd), Pollution Load Index (PLI), and Potential Ecological Risk Index (PERI). During March 2022, six sampling stations (S1 through S6) were established across the lake, and a total of 14 elements were analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES). Our analyses indicate that sediment collected from sampling stations near to sources of wastewater runoff is the most polluted. For example, S1, which is located near to wastewater discharge, had the highest concentration of Cr, Co, Ni, Cu, Zn, Cd, and Pb (90.9, 23.1, 58.7, 55.2, 81.4, 0.5, and 12.8 µg/g, respectively). Evaluating the sediment PERI revealed that sampling stations S1, S2, and S4 had moderate ecological risk (150 < average PERI < 300), indicating there is a negative environmental impact on the living organisms and water quality of lake Edku. Because lake Edku is important for biodiversity conservation, continuous monitoring of metal contamination should be a top priority, as well as improving the efficiency of wastewater treatment facilities to ensure removal of metals before discharging to coastal ecosystems.

Wetland shrinking and dust pollution in Khuzestan Iran: insights from sentinel-5 and MODIS satellites

Dust pollution is a major environmental issue that threatens public health and ecosystems. This study investigates the relationship between wetland area reduction and the intensification of dust pollution in southwestern Iran, utilizing satellite data from Landsat, Sentinel-5, and MODIS (2010-2022). High-resolution imagery from Google Earth Engine (GEE) was used to extract dust event frequency data, while Aerosol Optical Depth (AOD) and Absorbing Aerosol Index (AAI) were employed to monitor dust pollution levels. Normalized Difference Water Index (NDWI) analysis revealed that the Hoor Al-Azim and Shadegan wetlands experienced their driest conditions in 2010, 2011, 2021, and 2022. A strong inverse correlation was observed between wetland area and dust event frequency, with correlation coefficients of - 0.85 for Hoor Al-Azim and - 0.90 for Shadegan. When the area of Hoor Al-Azim dropped below 60 km2, dust events increased to 20-35 occurrences. Similarly, in Shadegan, dust events exceeded 20 when the wetland area fell below 100 km2. Wind rose analysis indicated that prevailing northeast and northwest winds, combined with dry conditions in northern parts of Shadegan, significantly contribute to dust formation. Furthermore, the study established a clear inverse relationship between wetland area reduction and the number of polluted days for both PM10 and PM2.5. For each 1 km2 decrease in wetland area, PM10 polluted days increased by 0.03, explaining 56% of the variation, while PM2.5 polluted days increased by 0.05, accounting for 64%. Principal Component Analysis (PCA) further demonstrated that wetland area changes explain 87.5% and 90.1% of the variance in PM10 and PM2.5 levels, respectively. These findings highlight the critical role of wetland preservation in mitigating dust pollution and improving air quality.

Sediment heavy metal speciation of Hirakud Reservoir-a Ramsar site in Mahanadi River in India

Heavy metal speciation is an important tool for the assessment of sediment quality. This work was conducted to investigate the geochemical occurrence, distribution, and spatial variability of sediment heavy metals in the Hirakud Reservoir (a Ramsar site) of the Mahanadi River in India. Estimation based on a single-extraction (speciation) method revealed the dominance of Fe-Mn-bound (39.33%) fractions suggesting the potential mobility of heavy metals. Co-dominance of residual (35.03%) and organic matter-sulfide (23.02%) fractions indicate lattice-bound associations of elements under natural conditions and suggest anthropogenic organic input contribution respectively. The heavy metals distribution was spatially affected (p < 0.05). While, Ag, Cd, Hg, and Mo displayed extremely severe enrichment (EF > 50) and very strong geo-accumulation conditions (Igeo > 5); Cd and Hg displayed very high ecological risk (ERF > 320). However, the contamination factor for all heavy metals except Cd and Hg showcased low contamination (CF < 1). The principal component and cluster analysis revealed that the source of Mn, Mo, Hg, and Ag was mainly from anthropogenic or biogenic origin. The Fe and Al however displayed signs of being derived from multiple sources. However, the risk assessment code (RAC) results suggest that As exhibited a medium to very high risk (11 < RAC < 30) of bio-availability. Thus, the results of this study can be used for the formulation of strategies for the reduction of anthropogenic loads, planning for sediment quality management, and regular monitoring to curb the rising pollution issues of the reservoir.

Study of biological indicators of heavy metal pollution in sediments and plants of Hoor-Al-Azim wetland

Wetland ecosystems are vulnerable to various environmental pollutants. In southwest Iran, the presence of significant wetlands alongside multiple oil facilities has led to serious biological issues for these ecosystems. This study was conducted in 2022 to investigate biological indicators of heavy metal pollution in the sediments and plants of the Hoor-al-Azim wetland. A total of 10 samples of sediments and the plant species Typha latifolia were collected. Heavy metals consist of Pb, Hg, Ni, Cu, and Cd were measured. The contamination level of sediments was assessed using contamination factor (CF) and ecological risk (ER) indices, while the transfer of pollution to native plant species was evaluated through transfer factor (TF) and bioaccumulation factor (BCF) indices. Results indicated that in sediment samples, Cd had the lowest average concentration (0.052 mg/kg) and Ni had the highest (147 mg/kg). In plant samples, Cd also showed the lowest concentration (0.086 mg/kg), while Hg had the highest (43.6 mg/kg). Pb and Ni levels were significantly elevated compared to other metals. The CF and ER indices revealed that Ni and Pb posed the greatest pollution levels and ecological risks. The TF index indicated that lead had the highest biological pollution potential (1.06). The average BCF values for lead, nickel, and copper were 0.05, 0.053, and 0.12, respectively. Overall, sediment pollution levels in the wetlands near oil facilities are concerning. Therefore, implementing environmental management strategies, including bioremediation, is crucial to mitigate pollution impacts.

Analysis of PAHs content, source identification and ecological risk assessment in surface sediments from the Caspian Sea

The concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in surface sediments were investigated in the southern Caspian Sea. The results revealed that the total PAHs in sediments varied from 6.53 to 170.6 ng·g- 1, with an average of 60.59 ng·g- 1. The methods of diagnostic ratio and Principal Component Analysis (PCA) were applied to explore the sources of PAHs in the sediments and the results indicated that they had both petrogenic and pyrogenic origins. The ecological risk induced by PAHs in this area was evaluated using sediments quality guidelines (SQGs) criteria and Risk Quotient (RQ) index. SQG ranges for PAHs such as Acenaphthylene (Acy), Acenaphthene (Ace) and Fluorene (F) in the Lisar transect were found at a moderate toxicity level. The RQ∑PAHs index suggested a low ecological risk in the studied stations. Based on the results of the Toxic Equivalent (TEQ) approach, PAHs did not pose carcinogenic risks.

Potential risk of heavy metals release in sediments and soils of the Yellow River Basin (Henan section): A perspective on bioavailability and bioaccessibility

The ecology of watersheds plays an important role in regulating regional climate and human activities. The sediment-soil system in the middle and lower reaches of the Yellow River Basin (Henan section) was explored. The spatial distribution characteristics of heavy metals (HMs) showed that tributaries, which are affected by anthropogenic activities, contain higher concentrations of HMs than the main channel. Sequential extraction experiments indicated that Cd had the strongest potential to be released, followed by Mn. In vitro simulation experiments showed that gastric and pulmonary fluids rendered these two orders of magnitude more bioaccessible compared to sweat. Moreover, Cd exhibited the highest bioaccessibility in both gastric and lung fluids. When bioaccessibility was considered in the evaluation of health risks, more than 82 % of reductions in non-carcinogenic and carcinogenic risk indices were observed in children and adults. A positive matrix factorization model was utilized to determine the potential sources of HMs: industrial sources, natural sources, and mixed agricultural and transportation sources were identified as the three main sources of HMs in sediments and soils. In addition, mining activities were also an HMs source in sediments.

Assessment of potentially toxic element contamination in wetland sediments of Boracay Island, Philippines

Boracay Island, Philippines, famous for its white sand beaches, has wetlands increasingly threatened by human activities. This study evaluated the ecological state of Boracay Island's wetlands and assessed the consequences of anthropogenic activities on sediment quality. Results showed that sediments from Wetland Nos. 3 and 4 have higher concentrations of potentially toxic elements (PTEs) than Wetland No. 1. Comparative analysis with other Southeast Asian wetlands revealed that Boracay's sediments contain the highest average values of As, Cd, Cu, Ni, Zn. Enrichment factor values suggest that the moderate enrichment of Cd, Cr, Cu, Mo, Pb, and Zn in the wetland sediments can be attributed to anthropogenic activities on the island. Elevated concentrations of Cr, Cu, and Zn above interim sediment quality guidelines indicate occasional adverse biological effects on aquatic biota. These findings provide a crucial baseline for future pollution monitoring and highlight the need for ongoing conservation efforts in Boracay's wetlands.

Distribution, sources, and contamination evaluation of heavy metals in surface sediments of the Qizhou Island sea area in Hainan, China

Coastal areas are regions of active interaction between the sea and land and are highly sensitive to changes in heavy metal contamination caused by natural and anthropogenic activities. The contents of heavy metals in 80 surface sediments in the Qizhou Island sea area in the northeast of Hainan Island were determined to assess the contamination status, spatial distribution, sources, and ecological risks. The results indicate that the main factors influencing the distribution patterns and contents of heavy metals are hydrodynamic conditions and sources of materials. The accumulation of Cd and Pb in the sediments is attributed to the combined effects of natural sources and anthropogenic input. In addition to widespread anthropogenic influence, the enrichment of Cd in the southeastern outer shelf area of the study region may be controlled by biogenic carbonate rocks or enhanced input of near-source materials during the late Pleistocene low sea level period.

Mechanisms and controlling factors of heavy metals removal by electroflocculation in estuarine environments

Estuaries play a crucial role in preventing the influx of metals from rivers into seas, thereby offering potential insights for the water purification industry. This study seeks to identify the key parameters (including pH, electricity conductivity (EC), and Eh) influencing the removal efficiency of Mn, Zn, Cu, Co, and Ni during natural and electro-flocculation processes in the Siahroud River estuary. The experiments were conducted in three stages, each representing varying salinity levels and voltage conditions, to determine the most effective parameters for metal removal. The findings revealed that heavy metal flocculation rates were highest at lower salinities (0.5 to 1.5 PSU), with no significant improvement in contaminant removal observed with increasing voltage. Electro-flocculation efficiency was found to be more dependent on Eh. Overall, the flocculation processes reduced the annual total dissolved metal content from 14.84 to 6.46 tons, underscoring the potential of this method in water quality management.

Origin and comprehensive risk assessment of heavy metals in surface sediments along the Caspian Sea

Metal concentrations (Cu, Zn, Cr, Fe, As, Pb, Ni, V, and Co) in surface sediments were determined in the southern Caspian Sea. Sediment pollution was investigated using geochemical index such as Enrichment Factor (EF) and ecological risk indices like modified Hazard Quotient (mHQ) and Toxic Risk Index (TRI). The highest calculated geochemical index was observed in sediments near the cities of Chalus and Ramsar, which are highly polluted due to human activities. The ecological potential indices indicated that Ni contents in all the studied stations would impose harmful effects on aquatic organisms, while other metals had a low risk. Principal component and cluster analyses suggested that As and Pb emanated from anthropogenic sources, and other metals probably originated from lithogenic sources.

Hydrochemistry and trace metals in water and sediments in forest coastal wetlands influenced by tidal regime in the middle Río de la Plata estuary, Argentina

Coastal wetland ecosystems are of utmost importance in regulating the mobility and distribution of elements in water and sediments, being the flooding by tidal events a recurrent process that strongly controls the hydrodynamics of the system. The aim of this work is to assess the control of the tidal regime and anthropogenic influence on the dynamics of some trace metals in water and sediments in the Punta Lara Natural Reserve situated in the Río de la Plata littoral. For that purpose, relationship between tidal flows, surface water and groundwater was evaluated. Also, hydrochemistry was analyzed based on the study of major ions and trace metals, being the presence of high concentrations of elements in groundwater, such as Fe and Mn, probably favoured by redox processes associated with organic matter decomposition in the water - sediment interaction. Sediments in the wetland register deficient to minimal enrichment in most of the studied trace metals despite the numerous contributions that the Río de la Plata receives in relation to dissolved and particulate trace metals from diverse anthropogenic contributions. Despite that, there is a moderate enrichment in Pb and Cr in the surface sediments of the wetland. The data analyzed within the natural reserve in relation to the chemical composition of the water and sediments of the coastal wetland showed the strong influence of the tidal regime over the area.

Receptor model-based sources and risk assessment of metals in sediment of the coastal construction-oriented aquatic system in Bangladesh

Metal pollution in sediment from construction areas raises ecological and health concerns, yet source-based sediment pollution in Bangladesh remains understudied. Our investigation focused on fifteen locations in the Kohelia River and the coastal regions near the Matarbari projects (Matarbari Power Plant, Matarbari Deep Seaport), assessing metal concentrations' sources and impacts on ecology and human well-being. Sediment quality indices indicated high Cd and Cr contamination, with sites near Matarbari projects being the most polluted. The positive matrix factorization model identified three anthropogenic sources and mixed sources. Matarbari projects contributed significantly to As (67.9 %), Mn (50.25 %), Cd (48.35 %), and Cr (41.0 %), while ship-breaking yards contributed Fe (58.0 %), Zn (55.5 %), Pb (53.8 %), and Cu (36.1 %). Ecological indices showed different impacts on aquatic life from metal pollution, but cancer risk levels stayed below the threshold set by the US Environmental Protection Agency. These findings underscore the need for targeted measures to address metal pollution.

Identification of anthropogenic source of Pb and Cd within two tropical seagrass species in South China: Insight from Pb and Cd isotopes

Seagrass beds are susceptible to deterioration and heavy metals represent a crucial impact factor. The accumulation of heavy metal in two tropical seagrass species were studied in South China in this study and multiple methods were used to identify the heavy metal sources. E. acoroides (Enhalus acoroides) and T. hemperichii (Thalassia hemperichii) belong to the genus of Enhalus and Thalassia in the Hydrocharitaceae family, respectively. Heavy metal concentrations in the two seagrasses followed the order of Cr > Zn > Cu > Ni > As > Pb > Co > Cd based on the whole plant, and their bioconcentration factors were 31.8 ± 29.3 (Cr), 5.7 ± 1.3 (Zn), 7.0 ± 3.8 (Cu), 3.0 ± 1.9 (Ni), 1.2 ± 0.3 (As), 1.7 ± 0.9 (Pb), 9.1 ± 11.1 (Co) and 2.8 ± 0.6 (Cd), indicating the intense enrichment in Co and Cr within the two seagrasses. The two seagrasses were prone to accumulate all the listed heavy metals (except for As in E. acoroides), especially Co (BCFs of 1124) and Cr (BCFs of 2689) in the aboveground parts, and the belowground parts of both seagrasses also accumulated most metals (BCFs of 27) excluding Co and Pb. The Pb isotopic ratios (mean 208Pb/204Pb, 207Pb/204Pb and 206Pb/204Pb values of 38.2054, 15.5000 and 18.3240, respectively) and Cd isotopic compositions (δ114/110Cd values ranging from -0.09‰ to 0.58‰) within seagrasses indicated the anthropogenic sources of Pb and Cd including coal combustion, traffic emissions and agricultural activities. This study described the absorption characteristics of E. acoroides and T. hemperichii to some heavy metals, and further demonstrated the successful utilization of Pb and Cd isotopes as discerning markers to trace anthropogenic origins of heavy metals (mainly Pb and Cd) in seagrasses. Pb and Cd isotopes can mutually verify and be helpful to understand more information in pollution sources and improve the reliability of conclusion deduced from concentrations or a single isotope.

Effect of redox potential on the heavy metals binding phases in estuarine sediment: Case study of the Musa Estuary

Heavy metals (HMs) exist in various chemical forms in marine sediments, and environmental factors like the redox potential (Eh) can affect labile-bound HMs, harming aquatic life and human health. This study utilized the Tessier sequential extraction to investigate how Eh affects the binding forms of elements, including Cd, Co, Cu, Ni, Pb, Zn, Fe, and Mn. The results revealed that decreasing Eh from 120 to 50 mV resulted in the release of weakly bound forms of Cd, Co, Ni, Pb, and Zn into the water, some of which were re-adsorbed by the residual fraction as Eh decreased further to -150 mV. Manganese was consistently bound to FeMn oxides, while Cu and Fe were predominantly associated with the more stable binding phase. Based on EF, Igeo, and CF, sediment was only polluted by As nearby an industrial zone, while water pollution indices indicated significant HMs contamination in all water samples.

Development and application of novel risk indices for assessing heavy metal pollution in aquatic sediments

This study presents the development of a new sediment individual risk index (SIRI) and sediment complex risk index (SCRI) to assess heavy metal pollution in Anzali Wetland sediments. SIRI incorporates total metal concentrations, bioavailability, and sediment quality guidelines. SCRI, derived through principal component analysis (PCA), integrates SIRI for a comprehensive risk assessment. The newly developed indices were systematically classified. Results showed varying risk levels with SIRI values of Zn, Cr, Cu, Pb, Ni, As, Cd, and Hg as 0.82, 1.32, 0.98, 0.71, 1.41, 1.37, 0.79, and 0.79, respectively. Pb, Cd, and Hg posed very low risk, Cu and Zn posed low risk, and Cr, Ni, and As posed moderate risk. SCRI yielded an index value of 1.02, indicating a moderate level of risk for the studied stations. Pearson correlation analysis validated SCRI with a highly significant and strong correlation coefficient (0.923) with metal bioavailability, serving as a risk indicator.