Distribution, contamination status and bioavailability of trace metals in surface sediments along the southwest coast of India

Pesticide and methylmercury fluxes to a marine protected region of Australia influenced by agricultural expansion

Estuarine environments provide diverse ecological services, including carbon burial and the sequestration of pollutants. Yet, urban expansion and anthropogenic activities can impact the ability of estuarine systems to retain and store pollutants, with unknown consequences for marine communities. Here, we present dated sediment cores from within the Solitarily Island Marine Park, a marine life sanctuary in Australia subject to runoff from a highly impacted catchment. We reveal historical accumulation rates of trace metals and pesticides likely associated with specific types of agricultural activities, including banana and blueberry production. Propiconazole and tebuconazole, fungicides highly reactive in marine habitats, were recorded in the sediment profile located at the site nearest the freshwater source. Furthermore, mercury content revealed elevated levels in the most recent sediments, up to 0.13 mg kg-1 in 1999, while methylmercury (MeHg) was detected ranging from 0.1 mg kg-1 in 2017 to 0.2 mg kg-1 in more recent sediments. Additionally, arsenic accumulation rates are shown here to have significantly increased from 19.1 mg m-2 year-1 in 1930 to 259.6 mg m-2 year-1 in 2020. These substances were found to be related to organic matter which was determined to be mostly of terrestrially derived sources, probably related to historical catchment deforestation, as indicated through δ13C and C:N molar ratios. This study highlights the importance in monitoring and evaluating agriculture-derived pollutant discharge to protected coastal regions and provides an initial dataset that may be used to monitor pollutant runoff in catchments impacted by expanding agricultural activities throughout Australia, and around the globe.

Tidal control of heavy metal loading in the nearshore of the northwestern Indian coast

Heavy metals accumulate in the marine food chain and their excessive amounts are hazardous to aquatic and human lives. The current study presents the role of ecosystem variables especially tides in deciding the presence of ten heavy metals (Fe, Zn, Cu, Co, Cr, Mn, Ni, V, Pb, and Cd) in seawater and copepods along the Indian west coast. The Indian northwestern coast is an industrial hub, where thousands of industries release enormous volumes of effluents, while the southwest coast has a far lower number of industries. Multiple surface seawater and zooplankton samples from eight selected marine outfall regions in the nearshore of the Indian west coast showed that Fe/Cd was generally the highest/lowest in seawater (av. 184 ± 12.40 μg L-1/ av. 0.01 ± 0.01 μg L-1) and copepods (av. 41,818 ± 2867 μg. g-1/ av. 0.2 ± 0.02 μg g-1). The heavy metals in seawater/copepods generally showed the order Fe/Fe > Zn/Zn > V/Mn > Cr/Cr > Pb/Cu > Ni/Ni > Cu/Pb > Mn/V > Co/Co > Cd/Cd. Contrary to expectations, despite being loaded with massive amounts of effluent from thousands of industries, most heavy metals in seawater on the northwestern Indian coast were not higher than on the southwestern coast. It is shown here that this feature is the result of the macro-tidal nature of the northwest Indian coast (av. 7 m tide), where tidal currents, sediment resuspension, and flushing are far more intense than in the southwest (av. 1 m tide), which reduce pollution levels. Yet, the marine pollution index and bioaccumulation factor of heavy metals in copepods was found highest along the northwestern Indian coast, which are important indicators to be considered when developing environmental management strategies for the area.

Metal contamination in the Ashtamudi Wetland ecosystem: Source identification, toxicological risk assessment of Ni, Cd, Cr, and Pb and remediation strategies

This study examines the presence of potentially toxic elements (PTEs) in the surface sediments and water of the Ashtamudi wetland, a Ramsar site on India's southwest coast. The average concentration of PTEs in water(μg/L) and in sediments (mg/kg) follows the order Fe(147.89) > Zn(107.53) > Cu(5.73) > Pb(4.57) > Mn(4.41) > Ni(3.07) > Cr(2.98) > Cd(0.32) > Co(0.14) and Fe (37,311.91) > Mn (341.59) > Zn (147.97) > Cr (88.07) > Ni (74.24) > Cu (42.23) > Pb (30.84) > Co (15.61) > Cd (1.85) respectively. Contamination and ecological risk indices (e.g., EF, CF, Igeo, mCd, EI, RI, mHQ, TRI, PLI) reveal moderate to considerable ecological hazards and contamination. Health risk assessments identify elevated cancer risks associated with Ni, Cd, Pb, and Cr in high-contamination zones. Statistical tools (PCC, PCA, and HCA) elucidate pollution sources and sediment dynamics, showing that urban runoff and industrial discharge are the major contributors. In contrast to previous studies, this work integrates seasonal variations, advanced risk indices health risk assessments and remediation techniques, which are critical for sustainable management. The findings thus call for targeted remediation strategies to mitigate heavy metal contamination and safeguard the ecological integrity and public health of Ashtamudi Wetland.

Assessment of potentially toxic elements in sediment cores from reservoirs in the Upper Tiete River Basin, Brazil

This study evaluated concentrations of potentially toxic elements (PTEs)-As, Sb, Co, Cr, Zn, U, and Th-in sediment cores from the Jundiai and Taiaçupeba reservoirs in the Upper Tiete Water Basin, Sao Paulo, Brazil. These reservoirs are vital for supplying water to the São Paulo metropolitan area but face risks from agricultural and industrial activities. The research aimed to determine whether PTE enrichment in sediments is due to natural or anthropogenic factors, assess the influence of sediment geochemistry and grain size, and evaluate risks to public health and biota. Granulometric analysis and enrichment factors were used to interpret the results, with As, Cr, and Zn compared to sediment quality guidelines. Significant Zn contamination was found in the Taiaçupeba reservoir, exceeding the Probable Effects Level (PEL), suggesting mining-related contamination. This highlights the need for further research on Zn's spatial distribution, ecological risks, and bioavailability in the Taiaçupeba reservoir. Conversely, Sb, Co, Cr, U, and Th were linked to natural processes. Arsenic showed a local geologic anomaly in both reservoirs. This research emphasizes the importance of geochemistry as a critical tool for interpreting PTEs in trace element environmental monitoring. Geochemical parameters, including Hf, Ta, Sc, and K, and rare earth elements, were essential for understanding sedimentary dynamics and anthropogenic impacts. This approach enhances the effectiveness of PTE impact assessments and can be applied to other dam reservoirs worldwide.

The impact of organic carbon mineralization on pollution and toxicity of toxic metal in sediments: Yellow Sea and East China Sea study

Organic carbon mineralization is the main driving force of metal migration and transformation in sediments, greatly influencing the distribution, pollution degree, and toxicity of toxic metals. However, relevant research on this subject is still limited. In this study, the concentration of toxic metals (Cr, Cd, Cu, Pb, Zn, Co, Fe, Mn, Ni, As) in the solid and liquid phase (porewater) of sediments were measured, toxic metal pollution degree and toxicity of the Yellow Sea (YS) and the East China Sea (ECS) were assessed. Combined with the rate of organic carbon mineralization, the impact of organic carbon mineralization was analyzed. The results showed that Ni was slightly enriched and posed a certain ecological risk, and As was moderately enriched in the studied area, Pb was at a moderate pollution level in the studied area. Zn, Co, Mn, and Fe were at a moderate pollution level in the mud area of SYS and the west coastal area of ECS. Additionally, the total organic carbon mineralization rate (TCMR) in the ECS (5.12-18.04 mmol C m-2 d-1) was slightly higher than that in the YS (3.29-14.46 mmol C m-2 d-1) during spring. Moreover, organic carbon mineralization promotes metal enrichment, and the TCMR was significantly correlated with the pollution load index. Thus, TCMR can be used as an indicator to predict the degree of metal pollution. Furthermore, organic carbon mineralization promotes the mobilization of Cu from the solid phase to the liquid phase, while facilitating the transfer of Cr, Pb, Co, Ni, and Fe from the liquid phase to the solid phase. This process increases the potential risks of Cu and reduces the toxicity of Cr, Pb, Co, Ni, and Fe. Therefore, the impact of organic carbon mineralization should be considered in future assessments and predictions of toxic metal pollution and toxicity.

Chemical speciation and comprehensive risk assessment of metals in sediments from Nabq protectorate, the Red Sea using individual and synergistic indices

The study evaluates metal concentrations, distributions, contamination, risk, sources, fractionation, and mobility in Nabq Protectorate sediments, revealing a metal content order of Fe, Mn, Pb, Ni, and Cd. Metals are dominated by residual fractions, with Cd (83.70 %) > Ni (82.98 %) > Pb (80.96 %) > Fe (80.31 %) > Mn (76.65 %) reflecting the natural sources of investigated metals. Mn (23.35 %) was the most abundant mobile metal, and the sediments of the protectorate had low toxicity and moderate risk according to the synergistic indices (1 ≤ mRAC<10 and ERM; 5-10). The results from the proposed individual indices showed that Mn, Fe, and Pb are the most bioavailable (BIM 0.1-0.4), Cd, Mn, Ni, Fe, and Pb are of moderate mobility (MIM 0.1-0.4), and Cd is the most available (ARIM 5-10), with Cd posing the most ecological risk. The total hazard quotient (THQ) for child was greater than one, exposure to manganese through ingestion and skin contact while swimming may endanger human health.

Preliminary study of geochemical speciation of copper and nickel in coastal sediments in Surabaya, Indonesia

Surabaya is one of the big coastal cities in Indonesia with rapid municipal development. Thus, the investigation on the metal's geochemical speciation in the coastal sediment is required to assess the environmental quality by studying their mobility, bioavailability, and toxicity. This study is aimed at evaluating the condition of the Surabaya coast by assessing copper and nickel fractionations and total concentrations of both metals in sediments. Environmental assessments were performed by using geo-accumulation index (Igeo), contamination factor (CF), and pollution load index (PLI) for existing total heavy metal data and by using individual contamination factor (ICF) and risk assessment code (RAC) for metal fractionations. Copper speciation was observed geochemically in the fraction order of residual (9.21 - 40.08 mg/kg) > reducible (2.33 - 11.98 mg/kg) > oxidizable (0.75 - 22.71 mg/kg) > exchangeable (0.40 - 2.06 mg/kg), while the detected fraction order of nickel was residual (5.16 - 13.88 mg/kg) > exchangeable (2.33 - 5.95 mg/kg) > reducible (1.42 - 4.74 mg/kg) > oxidizable (1.62 - 3.88 mg/kg). Different fraction levels were found for nickel speciation wherein its exchangeable fraction was higher than copper, even though the residual fraction was dominant for both copper and nickel. The total metal concentrations of copper and nickel were found in the range of 13.5 - 66.1 mg/kg dry weight and 12.7 - 24.7 mg/kg dry weight, respectively. Despite the fact that almost all index values are detected low through total metal assessment, the port area is indicated to be in the moderate contamination category for copper. Through the assessment of metal fractionation, copper is classified into the low contamination and low-risk category, while nickel is categorized into the moderate contamination level and medium risk to the aquatic environment. Although the coast of Surabaya generally remains in the safe category for living habitat, certain sites had relatively high metal concentrations estimated to have originated from anthropogenic activities.

Portunus pelagicus (Linnaeus, 1758) as a Sentinel Species to Assess Trace Metal Occurrence: A Case Study of Kuwait Waters (Northwestern Arabian Gulf)

Heavy metal pollution can adversely impact marine life, such as crabs, which can accumulate it in different organs and potentially transfer and biomagnify along the food chain in aquatic ecosystems. This study aimed to examine the concentrations of heavy metals (Cd, Cu, Pb, and Zn) in sediment, water, and crab tissues (gills, hepatopancreas, and carapace) of the blue swimmer crab Portunus pelagicus in the coastal areas of Kuwait, northwestern Arabian Gulf. Samples were collected from Shuwaikh Port, Shuaiba Port, and Al-Khiran areas. The accumulation of metals in crabs were higher in the carapace > gill > digestive gland, and the highest metal concentration was found in crabs collected from Shuwaikh > Shuaiba > Al-Khiran. The metal concentrations in the sediments were in the order Zn > Cu > Pb > Cd. Zn was the highest metal concentration detected in marine water sampled from the Al-Khiran Area, whereas the lowest metal was Cd sampled in water from the Shuwaikh Area. The results of this study validate the marine crab P. pelagicus as a relevant sentinel and prospective bioindicator for evaluating heavy metal pollution in marine ecosystems.

Source apportionment of heavy metals and their effects on the species diversity of plant communities in the Caizi Lake wetland, China

This study investigated the effects of heavy metals on the species diversity of the Xinjian Dyke Wetland, an ecosystem where reclaimed farmlands are being transformed back into wetlands through the introduction of indigenous plants. The sources of soil heavy metals were analyzed, and correlation analyses were conducted to assess the relationships between heavy metal content and biodiversity indices. The results indicated that (1) the mean contents of Hg, Cd, Cu, Zn, As, Cr, and Pb were higher than the control values, with the content of Hg, Cd, Cu, and Zn exceeding the national standard; (2) the soil heavy metals mainly came from pesticides, chemical fertilizer, transportation, sewage irrigation, and the soil matrix; and (3) Hg and As were not significantly correlated with the diversity indices, but there was a highly positive correlation for Cu, Cr, and Pb, and a significant negative correlation for Zn and Cd. Collectively, our findings indicated that heavy metals have different effects on the plant species diversity inXinjian Dyke reconstruction area. The ecological restoration of wetlands from reclaimed farmlands should reasonably increase tolerant species and maximize the ecological niche differentiation of the species. Moreover, functionally redundant species should not be planted.

The significance of applying different factors for the evaluation of sediment contamination by toxic elements and estimation of the ecological risk

The optimized three-step sequential extraction procedure for the fractionation of micro- and macroelements, was conducted to determine fractional characteristics of PTEs (potentially toxic elements) in surface sediments of rivers in the Vlasina watershed. The sequential extraction results, which enable the evaluation of mobility of the studied elements, have indicated that Zn, Ni, Cu, Cr, and As can be considered slightly mobile, whereas Pb, Mn, Cd, and Co were regarded as possibly mobile elements. Lead was dominantly bounded (specifically adsorbed or co-precipitated) to iron and manganese oxides (up to 80%) and may be released by reduction. Since the content of the exchangeable fraction (F1) is an indicator for anthropogenic impact on the aquatic environment, a low percentage (0-8%) of studied toxic elements in this fraction indicated that these elements have lithogenic origin in most sampling locations in the area of study. Except for Pb, the substantial positive correlations between Al and other elements showed that studied elements came primarily from terrigenous sources. Although the values obtained for the risk assessment code (RAC) indicated a slightly increased mobility of some elements (up to 22.44%), the values of the modified risk assessment code (mRAC), which include toxic effects on the environment, showed there is no danger of pollution by studied elements (all values were < 1%). Our recommendation is to use mRAC instead of RAC in ecochemical studies and assessment of the degree of sediment and soil pollution, because mRAC includes toxic effects of elements. Based on ATI values, river sediments show no toxic to a low toxic degree. Even though obtained results indicate that there was no considerable risk for river water contamination, the ecological risk for Fe and Pb should be monitored in the future.

Metagenomes from Coastal Sediments of Kuwait: Insights into the Microbiome, Metabolic Functions and Resistome

Coastal sediments in the proximity of wastewater and emergency outfalls are often sinks of pharmaceutical compounds and other organic and inorganic contaminants that are likely to affect the microbial community. The metabolites of these contaminants affect microbial diversity and their metabolic processes, resulting in undesirable effects on ecosystem functioning, thus necessitating the need to understand their composition and functions. In the present investigation, we studied the metagenomes of 12 coastal surface sediments through whole genome shot-gun sequencing. Taxonomic binning of the genes predicted about 86% as bacteria, 1% as archaea, >0.001% as viruses and Eukaryota, and 12% as other communities. The dominant bacterial, archaeal, and fungal genera were Woeseia, Nitrosopumilus, and Rhizophagus, respectively. The most prevalent viral families were Myoviridae and Siphoviridae, and the T4 virus was the most dominant bacteriophage. The unigenes further aligned to 26 clusters of orthologous genes (COGs) and five carbohydrate-active enzymes (CAZy) classes. Glycoside hydrolases (GH) and glycoside transferase (GT) were the highest-recorded CAzymes. The Kyoto Encyclopedia of Genes and Genomes (KEGG) level 3 functions were subjugated by purine metabolism > ABC transporters > oxidative phosphorylation > two-component system > pyrimidine metabolism > pyruvate metabolism > quorum sensing > carbon fixation pathways > ribosomes > and glyoxalate and dicarboxylate metabolism. Sequences allying with plasmids, integrons, insertion sequences and antibiotic-resistance genes were also observed. Both the taxonomies and functional abundances exhibited variation in relative abundances, with limited spatial variability (ANOVA p > 0.05; ANOSIM-0.05, p > 0.05). This study underlines the dominant microbial communities and functional genes in the marine sediments of Kuwait as a baseline for future biomonitoring programs.

Investigation of Potential Drivers of Elevated Uranium Prevalence in Indian Groundwaters with a Unified Speciation Model

Elevated uranium (U) (>WHO limit of 30 μg L^-1) in Indian groundwaters is primarily considered geogenic, but the specific mineralogical sources and mechanisms for U mobilization are poorly understood. In this contribution, statistical and geochemical analyses of well-constrained metadata of Indian groundwater quality (n = 342 of 8543) were performed to identify key parameters and processes that influence U concentrations. For geochemical predictions, a unified speciation model was developed from a carefully compiled and updated thermodynamic database of inorganic, organic (Stockholm Humic model), and surface complexation reactions and associated constants. Critical U contamination was found at shallow depths (<100 m) within the Indo-Gangetic plain, as determined by bivariate nonparametric Kendall's Tau_b and probability-based association tests. Analysis of aquifer redox states, multivariate hierarchical clusters, and principal components indicated that U contamination was predominant not just in oxic but mixed (oxic-anoxic) aquifers under high Fe, Mn, and SO₄ concentrations, presumably due to U release from dissolution of Fe/Mn oxides or Fe sulfides and silicate weathering. Most groundwaters were undersaturated with respect to relevant U-bearing solids despite being supersaturated with respect to atmospheric CO₂ (average pCO₂ of reported dissolved inorganic carbonate (DIC) data = 10^-1.57 atm). Yet, dissolved U did not appear to be mass limited, as predicted solubilities from reported sediment concentrations of U were ∼3 orders of magnitude higher. Integration of surface complexation models of U on typical aquifer adsorbents, ferrihydrite, goethite, and manganese dioxide, was necessary to explain dissolved U concentrations. Uranium contamination probabilities with increasing dissolved Ca and Mn exhibited minima at equilibrium solubilities of calcite [∼50 mg L^-1] and rhodochrosite [∼0.14 mg L^-1], respectively, at an average groundwater pH of ∼7.5. A potential indirect control of such U-free carbonate solids on U mobilization was suggested. For locations (n = 37) where dissolved organic carbon was also reported, organic complexes of U contributed negligibly to dominant U speciation at the groundwater pH. Overall, the unified model suggested competitive dissolution-precipitation and adsorption-desorption controls on U speciation. The model provides a quantitative framework that can be extended to understand dominant mobilization mechanisms of geogenic U in aquifers worldwide after suitable modifications to the relevant aquifer parameters.

Bioaccumulation and human health risk assessment of some heavy metals in sediments, Sparus aurata and Salicornia europaea in Güllük Lagoon, the south of Aegean Sea

In the current study, it was aimed to determine the sediment in Sparus aurata (Linnaeus 1758) tissues and Salicornia europaea L. Cu, Zn Fe, Hg, Cd, Pb and Mn concentration distributions in Güllük Lagoon which is located in the south of Aegean Sea and under the influence of anthropogenic activities by means of metal pollution and health indices and to investigate the effects of these metals on public health. The concentration range of Cu, Zn, Fe, Hg, Cd, Pb and Mn in sediment samples was determined as 12.16-26.00, 1.62-2.03, 7.77-8.36, 7.52-16.15, 0.071-0.40, 7.99-13.74 and 12.11-12.63 mg kg^-1, respectively. Cu and Hg concentrations in sediment were found to be higher than sediment quality guidelines standards. In addition, according to the enrichment factor (EF), Hg, Cd and Cu were found to show above moderate enrichment. Cu, Zn, Fe, Hg, Cd and Mn concentrations in S. aurata muscle tissue were 1.31 ± 2.30, 1.01 ± 0.24, 3.43 ± 0.75, 2.79 ± 0.85, 0.01 ± 0.01 and 1.80 ± 1.12 mg kg^-1, respectively. S. europaea heavy metals (HMs) concentrations were determined as Cu = 10.97 ± 3.20, Zn = 0.74 ± 0.62, Fe = 5.69 ± 0.22, Hg = 9.62 ± 8.84, Cd = 0.53 ± 0.33, Pb = 0.22 ± 0.26 and Mn = 8.61 ± 0.14 mg kg^-1. It was seen that Hg in S. aurata muscle tissue and Hg in S. europaea concentrations exceeded the limit values determined for consumption purposes. Target hazard quotient (THQ) and total target hazard quotient (TTHQ) values were found to be < 1 for S. aurata and S. europaea. When all these results were considered, it was determined that the metals that could pose a potential ecological and health risk were Hg, Cd and Cu in the study area.

Ecological risk assessment of trace metals in sediments and their effect on benthic organisms from the south coast of Zhejiang province, China

To explore the ecological risks of trace metals in sediments and their relationship with benthic organisms, 12 trace metals were analyzed and the macrobenthos were identified in the sediments collected from the south coast of Zhejiang province which belongs to the East China Sea. Spatially, the concentrations of most trace metals were high in the estuary, except for Ba and Sr. There was no obvious enrichment for trace metals, except that the concentration of Cd slightly exceeded the coastal background. The ecological risks calculated by the concentrations of Cr, Cd, Cu, Zn, Pb, and Ni in sediments showed that the methods based on sediment quality guidelines could judge the ecological risk more intuitively than the methods based on background value (PN, PLI, RI). The significant correlations between ecological risks and benthos density and biomass revealed the negative impact of trace metals at high concentrations on macrobenthic survival in sediments.

Spatial co-occurrence patterns of benthic microbial assemblage in response to trace metals in the Atacama Desert Coastline

Taxonomic and functional microbial communities may respond differently to anthropogenic coastal impacts, but ecological quality monitoring assessments using environmental DNA and RNA (eDNA/eRNA) in response to pollution are poorly understood. In the present study, we investigated the utility of the co-occurrence network approach's to comprehensively explore both structure and potential functions of benthic marine microbial communities and their responses to Cu and Fe fractioning from two sediment deposition coastal zones of northern Chile via 16S rRNA gene metabarcoding. The results revealed substantial differences in the microbial communities, with the predominance of two distinct module hubs based on study zone. This indicates that habitat influences microbial co-occurrence networks. Indeed, the discriminant analysis allowed us to identify keystone taxa with significant differences in eDNA and eRNA comparison between sampled zones, revealing that Beggiatoaceae, Carnobacteriaceae, and Nitrosococcaceae were the primary representatives from Off Loa, whereas Enterobacteriaceae, Corynebacteriaceae, Latescibacteraceae, and Clostridiaceae were the families responsible for the observed changes in Mejillones Bay. The quantitative evidence from the multivariate analyses supports that the benthic microbial assemblages' features were linked to specific environments associated with Cu and Fe fractions, mainly in the Bay. Furthermore, the predicted functional microbial structure suggested that transporters and DNA repair allow the communities to respond to metals and endure the interacting variable environmental factors like dissolved oxygen, temperature, and salinity. Moreover, some active taxa recovered are associated with anthropogenic impact, potentially harboring antibiotic resistance and other threats in the coastal zone. Overall, the method of scoping eRNA in parallel with eDNA applied here has the capacity to significantly enhance the spatial and functional understanding of real-time microbial assemblages and, in turn, would have the potential to increase the acuity of biomonitoring programs key to responding to immediate management needs for the marine environment.

Health risk of consuming Sphoeroides spp. from the Navachiste Lagoon complex due to its trace metals and organochlorine pesticides content

The Navachiste complex (NAV) is impacted by neighbored human activities and is located in the southwestern coastal zone of the Gulf of California. The study determines the trace metal (TM) and organochlorine pesticides (OCP) health risk content in the edible tissue of Sphoeroides spp. from NAV. The daily intakes (EDI), target hazard quotient (THQ), hazard index (HI), and carcinogenic and non-carcinogenic risks were calculated. Twenty OCP and seven TM were detected. Cd, Cu, Fe, Mn, Pb, and Zn were above MRLs. The γ‒Chlordane was the most frequent OCP. The highest average concentration was for α‒HCH, followed by γ‒chlordane. With the high ratios of γ‒HCH, p, p'‒ DDD and p, p'‒DDD, and the absence of p, p'‒ DDT, the higher ratios for dieldrin and endrin than for aldrin, α‒ chlordane, γ‒chlordane, heptachlor, and heptachlor epoxide indicates historical contamination. In contrast, the residual products of methoxychlor, endosulfan, and its isomers indicate endosulfan's recent use. The TM EDI, THQ > 1 (at 120 g day-1), and the ILCR (> 1 × 10-6) were above minimum levels, showing a high-risk potential for cancer development in the long term.

Human-induced sediment degradation of Burullus lagoon, Nile Delta, Egypt: Heavy metals pollution status and potential ecological risk

Heavy metals contamination level and their ecological risk of the Burullus lagoon were estimated using four cores and twelve surficial sediment samples. The distributions maps of Fe, Mn, Zn, Hg, Cu, and Pb indicate an increase toward drains areas, whereas Cd rises toward the Boughaz El-Burullus. The geoaccumulation index (I_geo) and contamination factor (CF) for heavy metal displayed the following order: Cd > Zn > Fe > Cu > Pb > Mn > Hg. The degree of contamination (C_d) indicates a considerable degree of contamination for 81.25% of the studied stations, and the pollution load index (PLI) suggested deterioration in 100% of sediments. Regarding the potential ecological risk (RI), the metals were arranged as: Cd > Hg > Cu > Pb > Zn, with considerable risk at the eastern part. According to sediment quality guidelines (SQGs), Zn concentrations suggest frequently adverse impacts on biota while Cu and Cd indicating an occasional adverse impact. Periodic monitoring of heavy metals in aquatic organisms is recommended to assess their toxic risk.

Study of trace metal contamination and ecological risk assessment in the sediments of a tropical river estuary, Southwestern India

The present study aims to assess the extent of trace metal pollution in the sediments of Sita-Swarna estuary, west coast of India, and investigate their possible ecological risk on the aquatic environment. The sediment cores were analyzed for sand, silt, clay, organic carbon, and trace metals (Al, Fe, Mn, As, Cd, Co, Zn, Pb, Ni, Cr, and Cu) at 2-cm intervals. The study revealed that sediments have deposited in relatively violent to very violent hydrodynamic energy conditions. Factor analysis indicated that the metal distribution is mainly controlled by Fe-Mn oxyhydroxides and organic carbon. Further, the geochemical approach, pollution indices, and statistical evaluation revealed moderate pollution in the catchment. From an ecotoxicological perspective, the estimated risk index (RI) value was found to less than 150, indicating low risk for aquatic life. Thus, this baseline study would help to adopt strategies in pollution control and protect the fragile marine environment.

Adsorption-desorption behavior of heavy metals in aquatic environments: Influence of sediment, water and metal ionic properties

Limited knowledge of the combined effects of water and sediment properties and metal ionic characteristics on the solid-liquid partitioning of heavy metals constrains the effective management of urban waterways. This study investigated the synergistic influence of key water, sediment and ionic properties on the adsorption-desorption behavior of weakly-bound heavy metals. Field study results indicated that clay minerals are unlikely to adsorb heavy metals in the weakly-bound fraction of sediments (e.g., r = -0.37, kaolinite vs. Cd), whilst dissociation of metal-phosphates can increase metal solubility (e.g., r = 0.61, dissolved phosphorus vs. Zn). High salinity favors solubility of weakly-bound metals due to cation exchange (e.g., r = 0.60, conductivity vs. Cr). Dissolved organic matter does not favor metal solubility (e.g., r = -0.002, DOC vs. Pb) due to salt-induced flocculation. Laboratory study revealed that water pH and salinity dictate metal partitioning due to ionic properties of Ca²⁺ and H⁺. Selectivity for particulate phase increased in the order Cu>Pb>Ni>Zn, generally following the softness (2.89, 3.58, 2.82, 2.34, respectively) of the metal ions. Desorption followed the order Ni>Zn>Pb>Cu, which was attributed to decreased hydrolysis constant (pK1 = 9.4, 9.6, 7.8, 7.5, respectively). The study outcomes provide fundamental knowledge for understanding the mobility and potential ecotoxicological impacts of heavy metals in aquatic ecosystems.