Organic matter and pyritization relationship in recent sediments from a tropical and eutrophic bay

Assessment of anthropogenic pollution in Guanabara Bay (SE Brazil) through biogeochemical data and stable isotope mixing models

This work intends to identify pollution sources along the margins of Guanabara Bay (GB; SE Brazil) through a multiproxy approach and Bayesian stable isotopic mixture model (BSIMM). For this purpose, 33 surface sediment samples were collected and analyzed for granulometry, geochemistry (heavy metals, total organic carbon-TOC, stable isotopes of carbon and nitrogen-δ13C and δ15N, Rock-Eval pyrolysis parameters-REPP), and physicochemical parameters. Metal concentrations (E) dissolved in water (EW), adsorbed by organic matter (EOM) and by Mn hydroxides (EMn), and total extracted concentrations (ET) were analyzed. Sampling was conducted in 2018 after an oil spill from Reduc Oil Refinery. Potential Ecological risk index (PERI), based on metals, classified 85% of the analyzed stations as having moderate to considerable ecological risk. The metals with the potential to cause the highest ecological risk were CdW, CdOM, PbOM, and HgOM. The combination of BSIMM and REPP data was an effective proxy for oil spill detection by indicating the presence of polycyclic aromatic hydrocarbons (PAHs). Relatively high TOC contents suggested that the analyzed stations are eutrophicated environments. BSIMM discriminated three groups of stations with different sources of organic matter (OM), endorsing the result previously shown by the cluster analysis: (A) Niterói region, Botafogo marina, Glória marina, Fiscal and Fundão islands with diffuse sources of OM, including marine phytoplankton and material of continental origin from highly polluted rivers and domestic sewage; (B) region near Fundão and Governador islands and Mangue Channel outlet with OM (≃70%) supplied by highly polluted streams and a small contribution of PAHs; (C) Duque de Caxias and Botafogo-Urca inlet with significant contributions of PAHs, materials from C-3 plants and rivers polluted by urban sewage. Results of linear regressions in conjunction with BSIMM indicate that HgMn and PbOM mainly affect Group A's stations. Although the eastern margin of GB (Niterói; Group A) showed greater oceanic interaction than the other groups, it presented substantial concentrations of metals, potentially harmful (i.e., Hg and Pb) to marine biota and human health.

Geochemical fractionation of trace metals and ecological risk assessment of surface sediments in Sepetiba Bay, Brazil

The Sepetiba Bay (Southeast Brazil) is a known Cd- and Zn-contaminated site that received spills of a large slag pile leachate from a Zn smelter. With important harbors, Sepetiba Bay demands periodic dredging operations which affect the mobility of the metals. The main goal of this work was to assess metal mobility in sediments and its associated toxicity in a fictive dredging area, to evaluate the risks of the operation. To achieve this goal, 18 superficial sediment samples were collected and characterized for pH and Eh. Sediments were analyzed for grain size, organic carbon, and total nitrogen, and metal mobility was evaluated with a sequential extraction procedure, proposed by the European Community Bureau of Reference (BCR). The results demonstrate that Cd and Zn are mainly associated with the exchangeable fraction (mean concentrations 1.4 mg kg-1 and 149.4 mg kg-1, respectively) and reducible fractions (mean concentrations 0.3 mg kg-1 and 65.5 mg kg-1, respectively), while Fe, Cr, Cu, Ni, and Al were associated with the residual fraction. Metals in the residual fraction are probably associated with the mineral lattice of the sediment and should not represent an environmental risk for the biota. The application of the enrichment factor and three risk assessment indexes (Risk Assessment Code, Risky Pollution Index, and Bioavailability Risk Assessment Index) show that the sediments are considerably enriched in metals that constitute a relevant risk for the sediment biota. In the case of dredging operations, Cd and Zn should be released to the overlying waters and be available to organisms, threatening the whole ecosystem. The proposed approach was shown to be much more precise than what is frequently presented in the Environmental Impact Assessments that only consider the threshold limits of the legislation.

Composition and vertical distribution of organic matter in Central Indian Ocean sediment cores

This study aimed to investigate the quality and quantity of organic matter (OM) using biochemical components (protein, carbohydrate and lipids) in the sediment cores collected from the Central Indian Ocean (CIOB) under the program Equatorial Indian Ocean Process Study Dynamics and Biogeochemistry (EIOPS). Total organic carbon (TOC) and biochemical parameters (carbohydrate, lipid, protein, Tannin and lignin) were determined in core I and core II, respectively. Total carbohydrates varied from 4.66 to 2557.32 mg/kg (average 459.31 mg/kg) and 142.23 to 821.56 mg/kg (average 380.01 mg/kg) in core I and II, respectively. In core I, PRT varied from 70.95 to 107.05 mg/kg, and the minimum and maximum content of CHO was 143.23 and 822.56 mg/kg. The maximum and minimum concentrations of BPC in core II were 786.32 and 381.07 at 0-10 cm depth, respectively, which corresponded to the concentrations of PRT, CHO, LPD, and Tannin. The results showed that PRT was statistically significant with the TOC and negatively correlated with the LPD and CHO, while LPD was highly significant with clay and silt grains. In most of the samples, the ratio of LPD to CHO ratio was > 1, which indicated higher productivity of benthic organisms inhabiting the CIOB.

Role of marine algal blooms in the release of arsenic at the sediment-seawater interface: Evidence from microcosm experiments

Algal blooms can aggravate arsenic (As) release from sediments and thus pose a pollution risk in the marine environment. However, the driving mechanism of algal blooms on sedimentary As cycling remains unclear. This study undertakes the first comprehensive examination of As release mechanisms under algal bloom conditions based on the evidence provided by temporal and depth profile changes of As species in the overlying water column, porewater and sediment, as well as As-related functional genes over the course of a 30-day incubation experiment using algal addition. The higher rate of increase of dissolved total As (dTAs) concentrations in a high biomass algal group (HAG) than an experimental control group (CG) suggested that algal degradation promoted the release of sedimentary As. The solid phase in all experimental groups remained rich in As(V), while in porewater As(III) and As(V) were the dominant As species during the initial rapid and subsequent slow degradation phases of organic matter, respectively, indicating that microbial reduction of As(V) and Fe(III) controlled the release of As during these two periods. A pronounced increase in arrA gene copies, and not a corresponding increase in the Geobacter copies, in HAG relative to CG supported the notion that algal blooms promoted microbial As(V) reduction. Additionally, the lower concentration of dissolved As(III) and cumulative dTAs flux in the sterilized-HAG treatment than in the sterilized-CG one further suggested that geochemically-mediated processes were not the main pathways of As release. Finally, it is estimated that summer algal blooms in the Changjiang Estuary can cause the release of 1440 kg of sedimentary As into the overlying water.

Sediment quality and environmental risk assessment in a Mediterranean coastal system using geochemical and multivariate statistical analyses: the case of Boughrara Lagoon (southeastern Tunisia)

Coastal ecosystems are the most vulnerable to natural and anthropogenic pressures which should be assessed using various chemical and ecological indicators. Our study aims to provide practical monitoring of anthropogenic pressures related to metal discharges in coastal waters for identifying potential ecological deterioration. The spatial variability of various chemical elements concentrations and their main sources were determined in the surficial sediments of a Mediterranean coastal area submitted to high anthropogenic pressure, the semi-enclosed Boughrara Lagoon located in southeastern Tunisia, by conducting several geochemical and multi-elemental analyses. The grain size and the geochemical analyses both suggested a marine influence of the sediment inputs in the north of the area (near Ajim channel), whereas continental and aeolian features dominated the sedimentary inputs in the southwestern lagoon. This last area was also characterized by the highest concentrations of metals, in particular Pb (4.45-173.33 ppm), Mn (68.45-1469.27 ppm), Cu (7.64-134.26 ppm), Zn (28.74-244.79 ppm), Cd (0.11-2.23 ppm), Fe (0.5-4.9%), and Al (0.7-3.2%). By referring to background crustal values and the contamination factor calculations (CF), the lagoon is considered as highly polluted for Cd, Pb, and Fe (3 < CF < 6). Three possible sources of pollution were identified: phosphogypsum effluents (P, Al, Cu, and Cd), the ex-Pb mine (Pb and Zn), and the cliff weathering and streams input from the red clay quarry (Fe). Furthermore, pyrite precipitation was identified for the first time in the Boughrara lagoon, suggesting the occurrence of anoxic conditions in this lagoon.

Microbial community shift under exposure of dredged sediments from a eutrophic bay

Microbial communities occur in almost every habitat. To evaluate the homeostasis disruption of in situ microbiomes, dredged sediments from Guanabara Bay-Brazil (GB) were mixed with sediments from outside of the bay (D) in three different proportions (25%, 50%, and 75%) which we called GBD25, GBD50, and GBD75. Grain size, TOC, and metals-as indicators of complex contamination-dehydrogenase (DHA) and esterase enzymes (EST)-as indicators of microbial community availability-were determined. Microbial community composition was addressed by amplifying the 16S rRNA gene for DGGE analysis and sequencing using MiSeq platform (Illumina).We applied the quality ratio index (QR) to the GB, D, and every GBD mixture to integrate geochemical parameters with our microbiome data. QR indicated high environmental risk for GB and every GBD mixture, and low risk for D. The community shifted from aerobic to anaerobic profile, consistent with the characteristics of GB. Sample D was dominated by JTB255 marine benthic group, related to low impacted areas. Milano-WF1B-44 was the most representative of GB, often found in anaerobic and sulfur enriched environments. In GBD, the denitrifying sulfur-oxidizing bacteria, Sulfurovum, was the most representative, typically found in suboxic or anoxic niches. The canonical correspondence analysis was able to explain 60% of the community composition variation and exhibit the decrease of environmental quality as the contamination increases. Physiological and taxonomic shifts of the microbial assemblage in sediments were inferred by QR, which was suitable to determine sediment risk. The study produced sufficient information to improve the dredging plan and management.

Effects of aeration on the suspended matter from a tropical and eutrophic estuary

A comprehensive understanding of the complex biogeochemical interactions between organic matter and persistent contaminants in the suspended matter is vital for eco-efficient estuary recovery. However, little is known regarding aeration effects in suspended particulate aggregates. Therefore, this study aimed to investigate the effects of aeration on the suspended matter from a Tropical and Eutrophic estuarine environment. Anoxic water with 60 g/L of suspended particulate matter (SPM) was collected from Guanabara Bay, Rio de Janeiro, Brazil, transferred to experimental boxes and aerated for 61 days. SPM aggregates monitoring included abiotic variables measurements and, determination of total organic matter (TOM), biopolymers composition, bacterial activity, trace metals, and polycyclic aromatic hydrocarbons (PAHs) concentrations. The aeration enhanced dissolved oxygen (DO) concentration and the redox potential (Eh). However, from days 0 to 61 the predominant bacterial activities were denitrification and fermentation. Electron transport system activity increased after day 10, and aerobic activity was detected after day 19. In summary, aeration increased aerobic bacterial activity, lipids (LIP) and trace metal concentrations, although diminished protein/carbohydrate ratio and PAH concentration. Trace metals concentration (Ni, Pb, Cu, Cr, Mn, and Fe) were the highest on day 19 when the pH was 5.9. Copper presented toxic values (Cu > 20.0 μg/g). The pH showed a strong negative correlation with Eh (r = -0.94; p < 0.001). Acidic environment (pH ≤ 5.9) in marine ecosystems with high loads of toxic trace metals is unsafe for biota. Therefore, managers must be aware of the environmental and biological risks of introducing the aeration technique into a eutrophic marine environment.

Nickel and iron partitioning between clay minerals, Fe-oxides and Fe-sulfides in lagoon sediments from New Caledonia

In the tropics, continental weathering and erosion are major sources of trace metals towards estuaries and lagoons, where early diagenesis of sediments may influence their mobility and bioavailability. Determining trace metals speciation in tropical sedimentary settings is thus needed to assess their long-term fate and potential threat to fragile coastal ecosystems. In this study, we determined Fe, Ni and S speciation across a shore-to-reef gradient in sediments from the New Caledonia lagoon that receive mixed contribution from lateritic (iron-oxyhydroxides and clay minerals), volcano-sedimentary (silicates) and marine (carbonate) sources. Sulfur K-edge XANES data indicated a major contribution of pyrite (FeS₂) to S speciation close to the shore. However, this contribution was found to dramatically decrease across the shore-to-reef gradient, S mainly occurring as sulfate close to the coral reef. In contrast, Fe and Ni K-edge XANES and EXAFS data indicated a minor contribution of pyrite to Fe and Ni speciation, and this contribution could be evidenced only close to the shore. The major fractions of Fe and Ni across the shore-to-reef gradient were found to occur as Ni- and Fe-bearing clay minerals consisting of smectite (~nontronite), glauconite and two types of serpentines (chrysotile and greenalite/berthierine). Among these clay minerals, greenalite/berthierine, glauconite and possibly smectite, were considered as authigenic. The low contribution of pyrite to trace metals speciation compared to clay minerals is interpreted as a result of (1) a reduced formation rate due to the low amounts of organic carbon compared to the Fe pool and (2) repeated re-oxidation events upon re-suspension of the sediments top layers due to the specific context of shallow lagoon waters. This study thus suggests that green clay authigenesis could represent a key process in the biogeochemical cycling of trace metals that are delivered to lagoon ecosystems upon continental erosion and weathering.

Microbial community activity in response to multiple contaminant exposure: a feasible tool for sediment quality assessment

Sediments represent complex mixtures and the impacts of their physical and chemical processes on biota are important for assessing potential health risks. We aimed to rank sediment samples from Guanabara Bay by developing an algorithm (quality ratio-QR), focusing on key sediment parameters (fine grain size, total organic carbon (TOC), metal concentrations) and enzymatic activities (dehydrogenase (DHA-energy production into cell) and esterases (EST-hydrolase organic matter outside the cell membrane)) of in situ microbial communities. Our QR is supported by quantitative information and significant correlations between geochemical and microbial processes. The QR is a function of the dependent term DHA/EST and the geochemical term (TOC×∑CF)/fine-grained sediment, where ∑CF is the sum of contamination factors (ratio between actual and background metal concentrations). We could rank our sampling sites into three risk classes based on QR: low, medium, and high. Our findings suggest altered homeostasis due to the development of contamination resistance. We applied a sensitivity analysis, using Brazilian law for sediment quality assessment, to calibrate our risk index. Our QR is suitable for measuring the potential health risk of any sediment, especially in developing countries with serious technical limitations, since its evaluated parameters are cheap, fast, and easy to obtain.

An alternative approach to bioaccumulation assessment of methyl-Hg, total-Hg, Cd, Pb, Zn in bivalve Anomalocardia brasiliana from Rio de Janeiro bays

We present an alternative approach for establishing in situ bioaccumulation assessment of methyl-Hg (MeHg), total-Hg, Cd, Pb and Zn in bivalve Anomalocardia brasiliana from four bays of Rio de Janeiro presenting varying degrees of eutrophication, acid volatile sulfides (2-55 μmol g^-1), simultaneously extracted metals (SEM) and total metals (TM) in sediments. Using metal concentrations of composite samples from three size classes of bivalve and their incorporation rates (IR = metal concentration / total length), which depend on exposure time, we calculated asymptotic IR and respective consequent metal concentrations. Both IR and the metal concentration presented inverse relationships with total length (excepting MeHg) and bay contamination. Lead and zinc concentrations were above Brazilian legal criteria in the most anoxic and contaminated bay, suggesting significant metal bioavailability (SEM/TM between 8% and 63%).

Sulfide influence on metal behavior in a polluted southern Mediterranean lagoon: implications for management

The degree of pyritization and degree of trace metal pyritization (DTMP) were investigated in sediments from Ghar El Melh Lagoon (northern Tunisia) in order to study metal deposition. A sediment core and 28 samples were thus taken in summer 2008, and metals and sulfate were analyzed in pore water/pyrite. Acid-volatile sulfide and metals were simultaneously extracted from these two fractions and the role of pyrite in the metal cycling studied. To examine pyrite presence and mineralogical form in sediments, X-ray diffraction of the washed and decarbonated sediment was performed along with scanning electron microscopy. Results showed that pyrite is present in fromboidal and euhedral forms. Thermodynamic calculation highlighted the formation of metallic sulfides and the co-precipitation of metals with iron sulfides. The DTMP increases with depth, indicating that these metals are either sequestered as sulfides or that they co-precipitate with pyrite into the deep sediment.