Remobilization of trace metals from contaminated marine sediment in a simulated dynamic environment

Seagrass soils sequester up to half the metal emissions of one of the world's largest smelters

One of the world's largest smelters has been operating in South Australia since 1889, affecting environment and human health. Here we quantified the magnitude of Pb, Zn and Cd emissions from the smelter sequestered in the soil of an adjacent 110 km2Posidonia australis seagrass meadows. Seagrass core records show that the smelter contaminated the entire area with decreasing sequestration with increasing distance from contamination points. The soil accumulated ~1300 t of Pb, ~3450 t of Zn, and ~ 90 t of Cd since 1889, and sequestered the equivalent of ~20 % of Pb, and ~50 % of Zn and Cd cumulative smelter emissions since 1999, showing that seagrass can be significant, long-term sinks of metal pollution in highly contaminated environments. Conservation efforts should prioritize these seagrass meadows to avoid the potential release of pollutants from their soils following habitat loss, which could turn seagrasses from a sink to a source of pollution.

Mobilization of colloids during sediment resuspension and its effect on the release of heavy metals and dissolved organic matter

Natural colloids are important in mobilizing pollutants in aquatic environments. This study investigated the mobilization and aggregation of natural colloids during the sediment resuspension and re-sedimentation processes using nanoparticle tracking analysis. The metals and organic matter in overlying water were divided and examined in dissolved (<0.45 μm), colloidal (3 kDa - 0.45 μm), and truly dissolved (<3 kDa) forms. Excitation emission matrix-parallel factor analysis (EEM-PARAFAC) was used to characterize the dissolved organic matter (DOM). In overlying water, most natural colloids were < 200 nm before resuspension. An evident mobilization of colloids and an increase in colloid size were observed during resuspension. The formation of particles (>0.45 μm) and decreases of small colloids (<200 nm) indicated that resuspension promoted the aggregation of colloids. Mobilization of colloids was accompanied by increases in concentrations of Fe, Al, and organic carbon in colloidal fractions, which could be related to the formation of mineral-organic complexes under an oxic environment. The release of DOM from sediments mainly contributed to the truly dissolved humic-like fraction, and colloidal organic carbon accounted for, on average, 20 % of the total dissolved organic carbon (DOC). Fe and Al had the highest colloidal proportions as they are major compositions of inorganic colloids. Substantial removal of dissolved Al, Fe, Pb, and Zn occurred when colloids aggregated in the overlying water. Although the adsorption of suspended particles may also decrease the concentrations of dissolved metals, the increased proportions of colloidal metals indicated a possible role of colloids in this process. These findings provide insight into the behavior of colloids during the resuspension process and indicate that the aggregation of colloids could promote the removal of dissolved matter.

Metal enrichment evolution in marine sediments influenced by oxygen-deficient waters in a mineral loading zone, Atacama, Chile (27° S)

This study examines metal concentrations in sediments under the influence of the oxygen minimum zone of the SE-Pacific and the anthropogenic impact following industrialization in Caldera Bay (27° S), which is one of the main ore-loading ports in operation from 1849. ²¹⁰Pb and the CRS dating method were employed to estimate the age in two sediment cores sectioned at 1 cm. Metal concentrations from selected samples suggested clear impacts of industrial activities after ∼1860 on Cu, and moderate impacts on Fe, Pb, and Zn. Further, authigenic enrichment of nutrient type and redox-sensitive elements (Ni, Cd, Mo, and V) in ancient times was observed. This enrichment was related to low oxygen at the bottom and high productivity. As this condition varies over time, it could result in erroneous estimations of preindustrial values. Overall, we highlight the impact of natural processes on metal distribution in marine sediments during environmental assessments and regulations.

Identification of suspended particulate matters as the hotspot of polycyclic aromatic hydrocarbon degradation-related bacteria and genes in the Pearl River Estuary using metagenomic approaches

Bacterial degradation is unequivocally considered as an important way for the cleanup of polycyclic aromatic hydrocarbon (PAHs) in the aquatic environment. However, the diversity and distribution of PAH-degrading bacterial communities and PAH degradation-related genes (PAHDGs) in ambient environment need to be investigated. In this study, bacteria in the water of the Pearl River Estuary (PRE) were initially separated as the particle-attached bacteria (PAB) and free-living bacteria (FLB), and were further characterized using metagenomic approaches. Proteobacteria (80.1 %) was identified as the most abundant PAH-degrading phylum in the PRE water, followed by Bacteroidetes, Actinobacteria, and Firmicutes. A substantial difference in the community structure was observed between PAH-degrading PAB and FLB. Both of PAH-degrading bacteria and PAHDGs were enriched on the suspended particulate matters (SPMs), with the range of enrichment factor (EF) from 7.84 × 10⁴ to 6.64 × 10⁶ (PAH-degrading bacteria) and from 1.14 × 10³ to 1.76 × 10⁵ (PAHDGs). The levels of PAH-degrading bacteria 16 S rRNA genes and PAHDGs on the SPMs were both significantly correlated with those in the aqueous phase (AP) in the PRE water (p < 0.05), indicating a dynamic distribution of PAH-degrading bacteria between these two phases. The total PAH concentrations on the SPMs of the PRE water were also significantly correlated with the total PAHDG levels in the PAB (p < 0.05). Our results suggested that the SPMs could be the important compartment for the elimination of PAHs from the aquatic environment.

Bioaccumulation and changes of trace metals over the last two decades in marine organisms from Guangdong coastal regions, South China

Trace metal (Cr, Ni, Cu, Zn, Cd and Pb) exposures, distribution and bioaccumulation were investigated in marine organisms from Guangdong coastal regions, South China. The results showed that all of the selected metals were observed in marine organisms with a predomination of Cu and Zn. The metal exposure levels exhibited obvious variations between species with the decreasing order of crab>shellfish>shrimp>fish. The higher metals enrichment seen in shellfish and crab species primarily attributed to their living habits and the higher sediment background values of trace metals. Endpoint bioaccumulation factor (BAF_fd) was used to characterize the bioaccumulation potentials of marine organisms to trace metals, of which Cu and Zn were the most accumulated elements. The exposure of trace metals in the cultured organisms was far lower than those in wild marine organisms, which is probably due to the effect of growth dilution. Comparisons with previous studies demonstrated that the concentration profiles of most trace metals declined over the last one to two decades, except Cu, that increased indistinctively.

An Ex-Situ Immobilization Experiment with Zn, Pb, and Cu in Dredged Marine Sediments from Bohai Bay, China

The remediation of dredged marine sediments contaminated by metals has drawn increasing attention globally. Immobilization was regarded as a promising method for reducing adverse impacts on marine ecosystems. In this study, kaolinite and limestone were used as amendments to immobilize Zn, Pb, and Cu in dredged marine sediments, which were collected from the coastal zone adjacent to Tianjin Port in Bohai Bay. The sequential extraction procedure was applied to identify the mobility of metals and, further, to evaluate the immobilization effect of the amendments. The physical–chemical properties of the sediments, such as the pH, electrical conductivity (EC), salinity, and total organic carbon (TOC), were also measured to better understand their influence on the three metals’ mobility. The results of the sequential extraction procedure indicated that the mobile fractions of the metals were converted into relatively stable fractions because of the two amendments. In addition, the EC, salinity, and TOC decreased moderately, while no obvious variations in the pH of the sediments were observed with the addition of kaolinite and limestone. It was confirmed that both kaolinite and limestone can effectively reduce the mobility and bioavailability of metals, particularly Zn, and limestone generally has a better immobilization effect, compared with kaolinite.

Effect of Acidic Industrial Effluent Release on Microbial Diversity and Trace Metal Dynamics During Resuspension of Coastal Sediment

Both industrial effluent discharge and the resuspension of contaminated marine sediments are important sources of trace metals in seawater which potentially affect marine ecosystems. The aim of this study was to evaluate the impact of the industrial wastewaters having acidic pH (2–3) and containing trace metals on microbial diversity in the coastal ecosystem of the Gulf of Gabès (Tunisia, southern Mediterranean Sea) subjected to resuspension events of marine sediments. Four trace elements (As, Cd, U, and V) were monitored during 10-day sediment resuspension experiments. The highest enrichment in the seawater dissolved phase was observed for Cd followed by U, V, and As. Cd remobilization was improved by indigenous microbial community, while U release was mainly abiotic. Acidic effluent addition impacted both trace metal distribution and microbial diversity, particularly that of the abundant phylum Bacteroidetes. Members of the order Saprospirales were enriched from sediment in natural seawater (initial pH > 8), while the family Flavobacteriaceae was favored by acidified seawater (initial pH < 8). Some Flavobacteriaceae members were identified as dominant species in both initial sediment and experiments with acidic wastewater, in which their relative abundance increased with increasing dissolved Cd levels. It could be therefore possible to consider them as bioindicators of metal pollution and/or acidification in marine ecosystems.

Seasonal variations and relationships between environmental parameters and heavy metal concentrations in tissues of Crassostrea species and in its ambience from the tropical estuaries

This study aimed to evaluate the relationship between physicochemical parameters and heavy metal (Cu, Ni, Pb, and Cd) concentrations from sediment, seawater, and its accumulation in tissues of oyster species (Crassostrea madrasensis and C. gryphoides) from the three sites (Chicalim Bay (CB), Nerul Creek (NC), Chapora Bay (ChB)) along the Goa coast (India). Results showed enrichment of Cu and Ni in sediment exceeding the effect range low (ERL) level. The higher concentrations of Cu and Ni in sediments and in suspended particulate matter (SPM) from all the study sites are indicative of severe contamination of estuarine and associated habitats. Moreover, particulate Ni (at all the sites), Cu (at NC and ChB), Pb (at NC), and Cd (at CB and NC) concentrations were recorded more than its total loadings in surface sediment. Concentration of Cu and Cd in oyster tissue was several folds higher than its concentration in ambience. Further, this study showed that the levels of metal in oysters and their ambient environment were higher during the monsoon season. Hence, the consumption of oysters needs to be considered carefully with respect to the health hazards posed by the elevated levels of metal contaminants in certain seasons. The present study concludes that metals associated with the particulate matter in water column are the main source of metal accumulation in oyster. It is also suggested that concentration of metal pollutants in coastal and estuarine water bodies should be monitored regularly to ensure the acceptable limits of metal concentrations.

Estuarine sediment resuspension and acidification: Release behaviour of contaminants under different oxidation levels and acid sources

Carbon dioxide (CO₂) Capture and Storage (CCS) is a technology to reduce the emissions of this gas to the atmosphere by sequestering it in geological formations. In the case of offshore storage, unexpected CO₂ leakages will acidify the marine environment. Reductions of the pH might be also caused by anthropogenic activities or natural events such as acid spills and dredging operations or storms and floods. Changes in the pH of the marine environment will trigger the mobilisation of elements trapped in contaminated shallow sediments with unclear redox boundary. Trace element (As, Cd, Cr, Cu, Ni, Pb and Zn) release from anoxic and oxic estuarine sediment is analysed and modelled under different laboratory acidification conditions using HNO₃ (l) and CO₂ (g): acidification at pH = 6.5 as worst-case scenario in events of CO₂ leakages and acid spills, and acidification at pH = 7.0 as a seawater scenario under CO₂ leakages, acid spills, as well as sediment resuspension. The prediction of metal leaching behaviour appear to require sediment specific and site specific tools. In the present work it is demonstrated that the proposed three in-series reactions model predicts the process kinetics of the studied elements under different simulated environmental conditions (oxidation levels and acid sources). Differences between HNO₃ and CO₂ acidification are analysed through the influence of the CO₂ gas on the ionic competition of the medium. The acidification with CO₂ provokes higher released concentrations from the oxic sediment than from the anoxic sediment, except in the case of Zn, which influences the release of the other studied elements. Slight acidification can endanger the aquatic environment through an important mobilisation of contaminants. The obtained prediction of the contaminant release from sediment (kinetic parameters and maximum concentrations) can contribute to the exposure assessment stage for risk management and preincidental planning in accidental CO₂ leakages and chemical spills scenarios.

Geochemical fractionation and pollution assessment of Zn, Cu, and Fe in surface sediments from Shadegan Wildlife Refuge, southwest of Iran

This research focuses on the fractionation and distribution patterns of heavy metals (Zn, Cu, and Fe) in surficial sediments collected from Shadegan Wildlife Refuge, the biggest wetland in southern part of Iran, to provide an overall classification for the sources of metals in the study area using a sequential extraction method. For this purpose, a four-step sequential extraction technique was applied to define the partitioning of the metals into different geochemical phases of the sediment. The results illustrated that the average total level of Zn, Cu, and Fe in surface sediments were 55.20 ± 16.04, 22.86 ± 5.68, and 25,979.01 ± 6917.91 μg/g dw, respectively. On the average, the chemical partitioning of all metals in most stations was in the order of residual >oxidizable-organic > acid-reducible > exchangeable. In the same way, the results of calculated geochemical indices revealed that Cu, Zn, and Fe concentrations are mainly influenced by lithogenic origins. Compared with consensus-based SQGs, Cu was likely to result in occasionally harmful biological effects on the biota.

The impact of submarine copper mine tailing disposal from the 1970s on Repparfjorden, northern Norway

We investigate the state of sedimentological environment and contaminant status of Repparfjorden (N Norway) impacted by submarine disposal of mine tailings during the 1970s using sedimentological and geochemical properties of seventeen sediment cores. The impact of tailings disposal is mainly restricted to the inner fjord where the discharge occurred. Sediment cores retrieved from the inner fjord contain layers of mine tailings up to 9-cm thick, 3-9cm below the seafloor. Spreading of the tailing-related metal Cu and particles is limited to the inner fjord and to a 2cm layer in one core from the outer fjord. Two interrelated factors, fjord morphology and sedimentation rate, controlled the distribution of contaminant-laden tailings in the fjord. The mobility of Cu from buried contaminated sediments to the sediment-water interface in the inner fjord indicates that benthic communities have been continuously exposed to elevated Cu concentrations for nearly four decades.

Geochemical partitioning and pollution assessment of Ni and V as indicator of oil pollution in surface sediments from Shadegan wildlife refuge, Iran

The total concentrations and chemical partitioning of Ni, V and Fe have been assessed in surface sediments from 160 sites along the Shadegan wildlife refuge. The results showed that the average total level of Ni, V and Fe in surface sediments were 45.08±12.09, 25.25±20.8 and 25,979.01±6917.91μg/g dw, respectively. On the average, the chemical speciation of Ni, V and Fe in most stations were in the order of residual>oxidisable-organic>acid-reducible>exchangeable. In all fractions, the residual was accounted the highest proportion for the metals analyzed. Among the non-residual phases, the proportion of heavy metals in organic matter fraction was higher than other phases collected from all locations. The comparison between measured values in this study and some fresh water sediment quality guidelines indicated that the levels of nickel would be expected to sporadically cause harmful biological impacts on biota in the Shadegan wildlife refuge.