Metal Contamination In Sediments Research Articles

An assessment of heavy metal contamination in the surface sediments of Ha Long Bay, Vietnam

Ha Long Bay is an attractive landscape and a center of dynamic economic activity; however, it is subject to negative impacts from tourism, activity in its harbor, mining, industry, and urbanization, which is evidenced by the presence of pollutants, including heavy metals, in surface sediment at the bay. To ascertain the extent of the anthropogenic impact, 48 surface sediment samples were collected and analyzed for grain size and the presence of heavy metals (Cu, Pb, Zn, As, Cd). Thirteen sediment types were identified in Ha Long Bay: sand, muddy sand, silty sand, sandy mud, mud, silt, sandy gravel, muddy sandy gravel, gravelly mud, gravelly muddy sand, slightly gravelly sandy mud, slightly gravelly sand, and sandy silt; of these, sandy silt and silty sand are the most common, while the others are less so. Regarding the concentration of heavy metals in the sediment, Cu concentration ranges from 3.80 to 41.72 mg/kg, with an average of 14.53 mg/kg; Pb ranges from 10.17 to 69.90 mg/kg, with an average of 30.39 mg/kg; Zn ranges from 6.34 to 119.21 mg/kg, with an average of 50.87 mg/kg; Cd ranges from 0.03 to 0.20 mg/kg, with an average of 0.08 mg/kg; As ranges from 1.78 to 13.71 mg/kg, with an average of 6.06 mg/kg. The concentrations of Cu, Pb, and As are higher than the Interim Sediment Quality Guideline (ISQG) levels at stations near the shoreline, and lower than the ISQG levels distributed throughout offshore stations.

Assessment of heavy metal contamination in the subsurface sediment of the southern coastal zone of Sfax, Tunisia

This work aims to establish an environmental assessment of the subsurface sediment of the Southern Coast of Sfax in Tunisia based on the chemical characterization of leachates of samples taken from ten stations along the zone, in accordance with the French standard X31–211. Results indicated rates in metallic trace elements (Pb, Cu, Cr, Cd, Ni, Zn, Fe and Hg) that exceeded the limits set by the Tunisian standard for environmental protection NT.106.002 concerning the discharge of effluents in the water environment. Findings prove the obvious contamination of the study zone due to the various polluting activities in its neighborhood. A more in-depth investigation program based on the results of this work can serve as a decision support tool for the implementation of an action plan and for the development of rehabilitation scenarios of the zone. The reclamation of the Southern coast of Sfax is necessary to reinforce the sustainability of the project of depollution and development of the northern coast of the city called Taparura that was realized in 2009.

Metal pollution assessment in surface sediments of Namak Lake, Iran.

Desiccation of the Namak Lake (NL) can result in the release of fine-grained dust contaminated with heavy metals, while there is little information available on the propagation of metals in the bed sediments of this lake. In this study, contamination of metals in the surface sediments of the NL was analyzed and the pollution status of sediments was assessed using geo-accumulation index (Igeo), enrichment factor (EF), the consensus-based sediment quality guidelines (CBSQGs), and mean probable effect concentration quotient (mPECQ). Results indicated that metal concentrations at the southern part were higher than at the middle and northern parts of the lake. Possible reasons are (i) pollution loads mainly entered the lake through the rivers at the west and northwest, but accumulated at the southern parts, (ii) hard layer of salt covering the bottom of the NL at the northern part suppresses adsorption of metals to the sediment, and (iii) the muddy nature of sediments at the southern part makes it easier for metals to be absorbed. EF results showed that sediments at the southern part of the lake were moderately enriched with lead (Pb). The low Igeo values suggested no pollution with the metals, and CBSQG values showed that the sediments of the NL were not toxic, while the mPECQ index suggested a toxicity probability of less than 25%. Cluster analysis classified the metals into two clusters. In general, the results showed that metal pollution in the surface sediments of NL was generally low although the concentration of Pb at the southern part of the lake was worrisome.

The bioavailability and potential ecological risk of copper and zinc in river sediment are affected by seasonal variation and spatial distribution

River sediment is the ultimate sink for heavy metal pollution. Copper (Cu) and zinc (Zn) are consistently found at environmentally significant levels in sediments worldwide. We hypothesized that the bioavailability and potential ecological risk of Cu and Zn in river sediments may be affected by seasonal variations and spatial distribution. In this study, we tested our hypothesis using highly industrialized river sediments (Laojie River) as an example. The concentration of heavy metals, pollution indexes, and risk indexes were evaluated and multivariate statistical analyses were performed. We found that seasonal variations affect heavy metal contamination, pollution indexes, and potential ecological risk in sediments and this effect was more severe in the dry season. In addition, higher levels of metal contamination, pollution indexes, and potential ecological risk were observed midstream and downstream of the Laojie River. We found that Cu and Zn were the primary contaminants in Laojie River sediments and may originate from common anthropogenic sources. Analysis of the chemical fractions further revealed that Cu and Zn exhibited high mobility and potential bioavailability risk. In addition, a high percentage and amount of Cu and Zn were found in exchangeable fractions, suggesting they pose a great risk to aquatic organisms. Our results indicate that seasonal variations and spatial distribution affect the bioavailability and potential ecological risk of Cu and Zn in river sediments. These findings suggest that seasonal variations and spatial distribution are important parameters to consider for environmental monitoring and environmental management in aquatic environments.

Effectively reducing the bioavailability and leachability of heavy metals in sediment and improving sediment properties with a low-cost composite.

Heavy metal-contaminated sediment is a common environmental problem. In situ stabilization is an effective and low-cost method to remediate heavy metal-contaminated sediment. In this study, ared mud-based low-cost composite (RMM) was used to stabilize heavy metal-contaminated sediment. RMM was mixed with heavy metal-contaminated sediment at the doses of 0%, 1%, 3% and 5%. The CaCl2-extractable, DTPA-extractable, leachability (TCLP) and heavy metal fractions were analysed to evaluate the stabilization efficiency of RMM for heavy metals. The selected properties and microbial activities of the sediment were analysed to verify the safety of RMM to sediment. The results showed that RMM reduced the DTPA-, CaCl2- and TCLP-extractable heavy metals in sediment. At an RMM dose of 5%, DTPA-, CaCl2- and TCLP- extractable heavy metals were reduced by 7.60%, 72.34% and 69.24% for Pb; 18.20%, 76.7% and 23.57% for Cd; 32.7%, 96.50% and 49.64% for Zn; and 35.0%, 61.20% and 55.27% for Ni, respectively. TCLP- and DTPA-extractable Cu was reduced by 71.15% and 12.90%, respectively. In contrast, CaCl2-extractable Cu increased obviously after the application of RMM. RMM reduced the acid-soluble fraction of Zn by 6.99% and increased the residual fraction of Ni by 4.28%. However, the influence of RMM on the fractions of Pb, Cd and Cu was nonsignificant. In addition, the application of RMM increased the pH values of the sediment, and the microbial activity in the sediment was also obviously enhanced. These results indicated that RMM has great potential in the remediation of heavy metal-contaminated sediment.

The effects of urban vehicle traffic on heavy metal contamination in road sweeping waste and bottom sediments of retention tanks

Diffuse pollution formed during a surface runoff on paved surfaces is a source of heavy metals (HMs) of various origin. This research study indicates the connection between bottom sediments of retention tanks located on urban streams and road sweeping wastes (RSW) that migrate during surface runoff to the stormwater drainage systems with discharge to the retention tanks. Moreover, we test the primary sources of HMs in RSW by analysing the mechanical wastes (MW) produced by vehicles in order to track the relationship between car parts and HMs deposited in the retention tanks receiving the surface runoff from streets. To identify the origin of HMs diverse source tracking approaches were used: statistical methods, Pb isotope ratios, and the flag element ratio approach. MW presented a very high HMs content (max observed values in mg/kg d.w.: 10477-Zn, 3512-Cu, 412-Pb, 3.35-Cd, 226-Ni, and 633-Cr), while for RSW the HMs content was similar to the bottom sediments. The total carcinogenic risk raises concerns due to the Cr content. The source of Zn was tyre wear and traffic. Ni, Cr, Fe, and Cd were correlated to Zn and shared a common/similar origin. PCA suggested that Cu features quasi-independent behaviour. The Pb isotopic ratios of RSW indicated Pb enrichment originating from coal combustion, while the gasoline and diesel source of Pb was excluded. The Pb isotopic ratios characteristic for MW were in within the following ranges: 1.152–1.165 (206Pb/207Pb), 2.050–2.085 (208Pb/206Pb), and 2.350–2.418 (208Pb/207Pb). The complex analysis of HMs origin confirmed the motorization origin of HMs: Zn, Cr, Ni, and Cd, except Pb (coal combustion as the main source) and Cu (non-uniform origin). The results of various source tracking methods were coherent, but Pb isotope ratios alone brought important information allowing to link Pb in sediments to the atmospheric deposition of coal combustion products.

Assessment of heavy metal contamination in surface sediments in the western Taiwan Strait

The concentrations of the heavy metals Cu, Pb, Zn, As, Cr, Co, and Ni of a total of 187 surface sediment samples collected from the western Taiwan Strait were analyzed. The distribution characteristics and degree of contamination of these elements were investigated. The mean concentrations of Cu, Pb, Zn, As, Cr, Co, and Ni in the surface sediments of the study area were 10.2 mg/kg, 18.3 mg/kg, 51.7 mg/kg, 7.5 mg/kg, 38.7 mg/kg, 8.0 mg/kg, and 16.5 mg/kg, respectively. The heavy metals in the study area were mainly from natural sources. The regional pollution load index (PLIzone) was 0.64, indicating that there was no contamination, and an area with a relatively high PLIzone was found in the northern part of the study area. Furthermore, the impacts of the rapid development of Fujian's marine economy on the marine environment in the past decade should be further compared and analyzed.

Metal(loid) contamination in water, sediment, epilithic periphyton and fish in three interconnected ecosystems and health risk assessment through intake of fish cooked in Indian style.

Samples of water, sediment and epilithic periphyton (EP) were collected from a lake (Dimna, DL), an intermediate canal (IC), and a river (Subarnarekha River, SR) to compare the pollution status of an urban ecosystem, and the concentrations of metal(loid) s were determined. Water characteristics were analysed by the water quality index (WQI). Sediment pollution was assessed using the ecological risk index (ERI). Accumulation of metal(loid) s in EP was determined by using bioaccumulation factor (BAF) and biota-sediment accumulation factor (BSAF). The result showed that the DL was least polluted (WQI = 30.39) and SR (WQI = 90.13) was the most polluted ecosystem. Sediment analysis revealed that Ni, Cr and Cd are the significant pollutants, especially in SR. The THQ value for fish dishes cooked in Indian style was found higher than that of raw fish, suggesting calculations considering the cooking process can provide better results. Health risk assessment shows that people inhabiting DL are vulnerable to Cr and Cu exposure, whereas people inhabiting IC and SR are susceptible to As and Co exposure due to the consumption of cooked fish. Moreover, for a developing country like India, it is important to upgrade the assessment methods and include regular monitoring of interconnecting ecosystems for the safeguard of human and ecological health.

Potential Ecological Risk Assessment of Heavy Metals Contamination in Surface Sediments of Ikpoba River, Southern Nigeria

The potential ecological risk assessment of heavy metals contamination in surface sediments of Ikpoba River, Edo State was estimated in this study after assessment of heavy metal concentrations in surface sediments from seven stations of the study area. Heavy metals were analyzed in the sediments using Atomic Absorption Spectrophotometer. The index of geo-accumulation for the metals (Lead (Pb); Iron (Fe); Nickel (Ni) and Copper (Cu)) studied were less than zero showing that the stations sampled were unpolluted with heavy metals. Contamination factor followed same pattern. Generally, there was a low potential ecological risk for heavy metal contamination to sediment dwelling organisms. However, station 4 (Capitol) was moderately contaminated and extremely enriched with Cu. Heavy metal values in this study were below the EPA limits for sediments except station 4 which was heavily polluted with Cu following the EPA guidelines. Regular monitoring and assessment of pollution load of Ikpoba River is recommended.

Unveiling the role of bioturbation on bacterial activity in metal-contaminated sediments

The processes permeating the relationships between bioturbation and microorganisms remain poorly understood due to the difficulty of traditional techniques in quantifying their two- and three-dimensional aspects. We used cutting-edge technologies to address the macro- and microorganisms' interactions under metal-contamination. Bioturbation (mucus-lined gallery perimeter, mucus-lined gallery surface area, and gallery water volume) positively influence the carbohydrate consumption rate by the bacterial consortium, elevating bacterial metabolic activity, despite metal-contamination. Synchrotron-based 2D-μXRF revealed that the mucous lining by marine worm during bioturbation as the primary carbon source enhances metal immobilization by bacterial biofilm, improving the bacterial metabolic activity. Bioturbation thus can positively affect bacterial consortium that can use the mucus as a carbon source, which enhances the resistance to metals through biofilm formation in metal-contaminated sediments.

Heavy metal contamination in water, sediments and Planiliza subviridis tissue in the Donan River, Indonesia

Heavy metals like cadmium (Cd) and lead (Pb) are pollutants that are toxic, difficult to decompose and accumulate in biota. One of the biota that lives in the waters is mullet fish. This fish is demersal, has a relatively long life period, has a specific tolerance to the aquatic environment and highly consumable in Indonesia. Therefore need to know the metal content of Cd and Pb in water, sediments and mullet fish and their relationship in Indonesia. The study used a survey method with purposive random sampling at four stations, three replications. The study was conducted from June to November 2019. Analysis of data was descriptive, F-test and correlation. The results showed that the heavy metal content of Cd and Pb between stations in the water media, sediment and in mullet fish there was a significant difference. The highest Cd and Pb were showed in station III, coming from the oil industry, domestic waste and transportation activities. The heavy metal content of Cd and Pb in water, sediment and mullet fish (Planiliza subviridis) in the Donan River, Cilacap shows results exceeding the allowed threshold and danger to human health.

Use of embedded Chelex chelating resin and sediment toxicity bioassays with medaka embryos to determine the bioavailability and toxicity of lead-contaminated sediment

The aquatic sediment acts as a reservoir for multiple sources of pollutants including toxic metals. Most analytical methods used for estimating the bioavailability of sediment heavy metals have not been biologically validated by correlation with an aquatic organism's response. A reliable whole-sediment contacting toxicity assay using vertebrate species is lacking and the exposure routes for sediment metals are unclear. This study established a novel bio-analytical approach involving the Chelex-100 resin detection system and sediment toxicity assessment with embryo-larval stages of medaka fish (Oryzias latipes) to evaluate the bioavailability and toxicity of lead (Pb) contamination in sediment to fish. Treated fish exposed to the Pb-spiked artificial sediment with whole-sediment exposure showed more dose-dependent toxic responses than those from pore- or overlying-water exposure extracted from the same sediment. The Chelex-100 resin-extractable Pb content was highly correlated with mortality, total malformation and Pb bioaccumulation in medaka embryos or hatchlings from Pb-spiked sediment at environmentally relevant concentrations. The environmental sediment with higher contents of clay or organic carbon showed lower potency of releasing Pb from sediment to overlying water, as compared to those observed with artificial sediment. Our results suggest that the bio-analytical method can be practically applied in situ to evaluate the adverse effect of heavy metal-contaminated sediment on the aquatic ecosystem.

Land use Land cover of the Burullus Lake shoreline (Egypt) and health risk assessment of metal-contaminated sediments

The mean concentrations of heavy metals in the sediments of Burullus Lake shoreline follow a descending order of Mn > Fe > Zn > Co > Cu > Cd > Ni > Pb > Cr. Where concentrations of Cd indicated that 100% of samples were higher than the limits of SQGs and the reverse to Cr that its concentration is within those limits. The mean probable effect level quotient mPELq and mean effect range median quotient mERMq showed 73 and 76% probability of toxic effects in the south-western side of the Lake. Calculation of HI showed hazard degree for Cd in site 7 and sites 4, 6 and 7 for Co and 4 and 5 for Mn in case of adults. While it represents hazard in all sites for Co and Mn except 2 and 3 for Cd in case of Child. Carcinogenic risk assessment gives an indication that the only expected pathway that may cause carcinogenic impacts to the children in the studied sites is from ingestion, while in adults, the chance of exposure pathways increases. Although the chance of risk is higher to a child than those of adults as expected from the comparison of its range.

Types, occurrence, and distribution of microplastics and metals contamination in sediments from south west of Kerkennah archipelago, Tunisia.

Microplastics (MPs) are one of the most significant solid waste pollutants in the marine environment and accumulate in sediments around worldwide. In this study, the pollution level, the type, occurrence, and distribution of MPs in sediments from the southwestern Kerkennah archipelago, Tunisia, were investigated. Sediment samples were collected from 20 adjacent sites through three "lines L1, L2, and L3." MPs were separated from sediment by density flotation (NaCl, 1.2gcm-3) and characterized in terms of shape, size, and color using microscope. The accumulation of toxic chemicals such as trace metals on microplastics was measured by atomic absorption microwave-assisted acid extraction. Polymer types were identified using FTIR-ATR spectroscopy. This study showed that microplastics were found in all samples, which emphasized that their extensive distribution throughout three lines by an average abundance of "MPs" was 611 items/m2. Among the shape categories of plastic particles, fiber and fragment were the most dominant frequent shapes (94%). The more frequent colors found were white (52.7%) and transparent (35.1%). Regarding the sizes, the microplastics below 1mm were the most common accounting for 97% of all plastics. Results of trace metals Zn, Cu, Pb, Cr, and Ni in sediments with concentrations were reported as 3.48μg/g, 0.41μg/g, 0.38μg/g, 0.33μg/g, and 0.12μg/g, respectively. Graphical abstract.

Assessment of the Effects of Sediment-Associated Metals and Metalloids on Mangrove Macroinvertebrate Assemblages

Although much previous research effort has examined the impacts of metal contamination on macrobenthic assemblages in subtidal sediments, little attention has been directed at macroinvertebrate responses in intertidal mangrove habitats. Thus, in order to assess the unique responses of mangrove macroinvertebrate assemblages to sediment metal(loid) contamination, total, normalised and bioavailable metal(loid)s (Mn, Pb, Cr, Cd, As, Se, Co, Ni, Zn and Cu) were assessed within and between four mangrove locations in Lake Macquarie, NSW, Australia, and compared to resident macroinvertebrate assemblages over two sampling occasions. Mangrove biomass and physicochemical properties of sediment are known to influence macroinvertebrate assemblages, and as such, were also assessed to account for any potential confounding effect on macroinvertebrate assemblage composition. Significant differences in total and bioavailable metal(loid) contamination were found between and within locations and were consistent over time. Sediments at contaminated locations presented a high risk to biota with bioavailable concentrations of Pb, Cd, Zn found to exceed sediment quality guidelines and concentrations of Se capable of adverse impacts to biota. Macroinvertebrate assemblage composition varied with metal(loid) contamination loads present at study locations. Metal(loid) contamination was significantly correlated with macroinvertebrate assemblages over two sampling periods. Further analysis revealed that 71% of macroinvertebrate assemblage composition could best be explained by a combination of five variables namely, bioavailable Mn, Zn, and Se, number of mangrove seedlings and mean mangrove biomass. Rather than tolerant polychaetes dominating metal(loid)-contaminated sediments (as is found generally in subtidal sediments), polychaetes in intertidal mangroves appeared to be relatively sensitive to metal(loid) stress. Further, decapod crustaceans in the family, Varunidae, and gastropod molluscs, in the family, Amphibolidae, were found to be metal-sensitive taxa and may be employed in future studies as indicator taxa of sediment metal(loid)-related impacts in south-eastern Australian mangrove forests.

Enhanced electrokinetic remediation (EKR) for heavy metal-contaminated sediments focusing on treatment of generated effluents from EKR and recovery of EDTA.

Electrokinetic remediation (EKR) is one of the most successful remediation techniques to treat the sediments contaminated with heavy metals. EDTA is the most widely used enhancing agent to improve the transport process in EKR. But often the generated effluents from EKR contains a high concentration of heavy metals, which cannot be disposed of without treatment. The major objective of this study includes the estimation of optimal concentration of chelating agent EDTA, followed by treatment of contaminated sediments by EKR technique for heavy metal removal. The effluents generated from EKR were further studied for recovery and reuse of EDTA and for safe discharge of heavy metals. The optimum concentration of EDTA was found as 0.05M with a solid-to-liquid ratio as 1:10. When fresh EDTA was used as enhancing agent the average removal of heavy metals obtained as 74.8% with EKR, whereas the application of recovered EDTA in treatment process in first, second, and third cycle showed the slight reduction of heavy metals of about 71.1%, 63.5%, and 52.1%, respectively. The heavy metal removal by recovered EDTA was effective in reduction of heavy metals up to three cycles of re-use while reducing the ecological risk in sediments. PRACTITIONER POINTS: Treatment of contaminated sediments with heavy metals achieved by electrokinetic remediation (EKR) technique enhanced with EDTA. The recovery of EDTA and heavy metal reduction from the generated effluents during EKR treatment were performed by the addition of FeCl3 and Na2 PO4, and optimized concentration was evaluated. This study found that the use of recovered EDTA in EKR treatment has effectively reduced the risk associated with heavy metals.

Heavy metal contamination in water, sediments, and fauna of selected areas along the Kenyan coastline

Abstract. Mwatsahu SH, Wanjau R, Tole M, Munga D. 2020. Heavy metal contamination in water, sediments, and fauna of selected areas along the Kenyan coastline. Ocean Life 4: 37-47. Every year millions of tons of industrial waste and municipal sewage are dumped into the world’s oceans as rivers carrying agricultural wastes discharge their waters into the ocean. The Mombasa inshore (Kilindini and Portreiz) waters and Sabaki/Malindi bay, Kenyan coastline, complex are characterized by rapid urbanization and industrial activities, including shipping, agriculture, and tourism. As a result, the coastal fauna, sediments, and seawater are polluted with heavy metals, raw sewage, and organochlorine pesticides. Heavy metals such as Cadmium (Cd), Copper (Cu), Chromium (Cr), Lead (Pb), Iron (Fe), Manganese (Mn), Mercury (Hg), and Zinc (Zn) have threshold limits (USEPA) above which they are toxic. The aim of this study was to assess the levels of heavy metals Cd, Cu, Cr, Fe, Mn, Hg, and Zn in selected areas along the Kenyan Coastline. The analysis was done during the dry and wet seasons. The levels of the heavy metals were determined using Atomic Absorption spectro-photometry flameless Atomic Absorption Spectrophotometry (Mercury cold vapor), and Energy Dispersive X-ray fluorescence. The levels of the metals were as follows: In sediments, Hg: nd, Cr: nd, Cu: 9.912-40.412 µg/g, Fe: 3,195.667-35,435.981 µg/g, Mn: 135.467-228.780 µg/g, Zn: 54.700 -181.725 µg/g. Biota: Hg: nd, Cr: nd, Cu: 43.963-229843 µg/g, Mn: 29.770-486.611 µg/g, Fe: 379.853-35,277.752 µg/g, Zn: 99.476-872.852 µg/g, Cd: nd, Pb: 135.407-833.111 µg/g. Sea water: Cr: 0.015-0.026 µg/mL, Fe: 0.062-16.524 µg/mL, Cu: 0.010-0.033 µg/mL, Zn: 0.028-0.066 µg/mL, Pb: 0.006-0.010 µg/mL. Cd and Hg levels were not detected in seawater, sediments, and fauna. In contrast, Cr was not detected in sediments and fauna but had levels above USEPA guidelines at Kilindini, Malindi Bay, and Sabaki estuary sites. Cu had levels above USEPA guidelines at Sabaki in the water and sediments at most sites. Pb levels were above USEPA guidelines at most sites of the Kenyan Coastline, while Zn levels indicated moderate pollution in seawater, sediments, and fauna. These findings indicated that seawater sediments and fauna from the Kenyan Coastline are moderately polluted with Cu, Pb, and Zn according to USEPA guidelines. It is recommended that regular assessments of pollution levels be done and measures put in place to prevent increased pollution of the Kenyan Coastline.

Assessing Seasonal Variability, Trend, Distribution and Degree of Heavy Metal Contamination in Urban Lake Sediment, Malaysia

Assessing Seasonal Variability, Trend, Distribution and Degree of Heavy Metal Contamination in Urban Lake Sediment, Malaysia

Heavy metals contamination in seawater, sediments and seashells of the Gulf of Suez, Egypt

A comprehensive environmental assessment of the Abu Zenima coast, Egypt, was done by evaluating the heavy metal pollutant levels in sediments, marine seashells, and seawater. Environmental parameters as the geoaccumulation index, contamination factor, enrichment factor, soil pollution index and potential ecological risk index proved that the study area was very severely enriched with Cd, severely enriched with Pb, and moderately enriched with Zn. However, these pollutant levels were still lower than some standardized reference values. Furthermore, the bioaccumulation index indicated that gastropod shells had greater ability to concentrate Fe, Cd, Ni and Zn than pelecypod shells, which may be attributable to the shape of the gastropod shell. Regarding the seawater samples, Pb, Cd, Cu, and Fe levels were higher than their average oceanic metal concentrations. Moreover, the average concentrations of heavy metals in the studied area, especially those of Pb, Cd, and Zn, were higher than those the coasts of Rosetta, Kazakhstan, Russia, southeast India, and the North Adriatic Sea. The main sources of these pollutants were anthropogenic sources such as gypsum and manganese factories, kaolin deposits, sewage, industrial wastes, urban runoff and irrigation.

Trace metal contamination in sediment in the Mhlathuze Estuary, northern KwaZulu-Natal, South Africa: effects on the macrobenthic community

Mhlathuze Estuary constitutes one of the ecological most important estuaries in southern Africa and is regarded as an estuary of high conservation importance. The ongoing expansion of the adjacent industrialized Richards Bay Harbour increases the risk of metal pollution to the estuary. This study provides insight into the extent and sources of trace metal contamination using pollution indices and sediment quality guidelines and the effect on macrobenthic habitat quality. Sediment samples for sediment metal and macrobenthic analysis were collected quarterly during 2016–2017 at five sites in the estuary using a marine-grade Zabalocki grab. Metal concentrations were determined using an ICP-OES. Sediment metal concentrations were consistently highest in the subtidal mudflats and lowest in marine sand at the mouth of the estuary. Concentrations of all metals displayed significant differences between sites (P < 0.05). Pollution indices indicated moderate enrichment of Cr at all sites, although the mean pollution load index showed the estuary to be unpolluted. Comparison with sediment quality guidelines revealed that concentrations of Ni and Cr were potentially toxic to biota. Using multivariate analysis, metal concentrations appeared not to significantly affect the macrobenthic community. The multi-metric biotic index M-AMBI proved to be a robust tool in the habitat quality assessment of the estuary. The continuing use of M-AMBI as a biomonitoring tool for ecological management of the estuary is advocated.