Diagenesis and bioavailability of mercury in the contaminated sediments of Ulhas Estuary, India

Sequential extraction of Hg was performed in a core collected from intertidal area in Ulhas Estuary in order to characterize the downward distribution and diagenetic behavior of Hg in a polluted estuary. Concentration of total Hg ranged between 0.46 and 6.40 μg g⁻¹ with significant decrease in surficial sediment as a result of closing of two Hg-cell based chlor-alkali plants. Results of sequential extraction showed that >65% Hg was strongly bound to organo-sulphur and inorganic sulphide species that are not bioavailable. Flux of only 18.8% of Hg was found compared to its value deposited on sediment–water interface. Hence, it is concluded that there is no significant diagenetic remobilization of Hg in Ulhas Estuary. This core also has been analyzed for ²¹⁰Pb geochronology. The estimated sedimentation rate is 0.31 cm y⁻¹ in the present sampling region.     

The influence of physicochemical parameters on bioavailability and bioaccessibility of heavy metals in sediments of the intertidal zone of Asaluyeh region,Persian Gulf,Iran

In this research, we have worked on the evaluation of heavy metal contamination in the sediments taken from the intertidal zone of Asaluyeh region using Modified Community Bureau of Reference sequential extraction method (mBCR), the simplified bioaccessibility extraction test (SBET), and calculated enrichment factor (EF). Also, potential influencing factors including sediment characteristics that may affect the heavy metals bioavailability and bioaccessibility were investigated. mBCR extraction analysis indicated that among the metals, Mn, Zn, V, Cu, and Cd exhibit relatively higher mobility, while Ti, Pb, Cr, and Ni occur mainly in the residual fractions. Based on the mean values, the bioaccessibility of metals decreased in the order: Mn (50.01%)>Cd (46.26%)>Zn (14.61%)>V (13.97%)>Pb (10.88%)>Ni (9.2%)>Ti (8.43%)>Cr (6.66%)>Cu (6.23%). The obtained results from the principal component analysis (PCA), EF and mBCR extraction showed that most anthropogenic-derived metals with higher solubility are more bioaccessible compared to those of natural origin. Multiple linear regression analysis demonstrated that the main physicochemical variables of the sediment influencing the bioaccessibility of metals include cation exchange capacity (CEC), pH, and particle size fraction.     

Variation and correlations of selected heavy metals in sediment and aquatic plants in Tasik Chini,Malaysia

This paper aims to determine the correlation between Cd, Cu and Pb concentration in the sediment and in five aquatic plants sampled during wet, normal and dry seasons. Analyses of the sediment showed that concentrations of exchangeable Cd and Cd after acid reduction were higher during the wet season (October) than on other sampling dates with mean values of 0.18 and 0.29 μg g⁻¹, respectively. The concentration of Cu in the organic oxidation phase was higher in the normal season (January) than on other sampling dates with a mean value of 11.1 μg g⁻¹. The concentrations of exchangeable Pb and that in the residual phase were higher during the wet season than on other sampling dates with mean values of 1.05 and 9.18 μg g⁻¹, respectively. Cd and Pb concentrations in the leaves, stems and roots varied between sampling dates with a reduced concentration during dry season (July) and the highest metal concentrations (Cd and Pb) during wet season. There were positive correlations between Cd and Cu concentrations in the plant tissues (leaves, stems and roots) of most aquatic plants in the acid reduction fraction. Conversely, there was no positive correlation between Pb concentration in the plant tissues of all aquatic plants and the acid reduction fraction of the sediment.     

Relationship of metal content and bioavailability with benthic macrofauna in Camamu Bay (Bahia, Brazil)

Camamu Bay (Bahia, Brazil) is an Environmental Protected Area with mangroves of economic and ecological importance. The objective of this study was to elucidate, through the distribution of the benthic macrofauna and its relationships with trace metals and bioavailabilty, if the current quality of the mangrove sediments of Camamu Bay is acceptable for the protection of aquatic life. Seven sampling stations were selected as representative of the meso-littoral region of Camamu Bay. It was found 581 macrobenthic organisms distributed in 38 species. The highest values of metals occurred at stations located in areas that influenced by barite extraction, while the lowest concentrations were found in areas with relatively lower anthropogenic influence. Analysis of acid volatile sulphide and simultaneously extracted metals showed the occurrence of the ratio SEM/AVS >1, indicative of possible bioavailability of metals, at only one station. The results suggested that Camamu Bay is a nearly pristine area.     

Bioavailability of dissolved organic phosphorus compounds to typical harmful dinoflagellate Prorocentrum donghaiense Lu

The bioavailability of dissolved organic phosphorus (DOP) compounds to harmful alga Prorocentrum donghaiense Lu and its alkaline phosphatase activity (APA) were studied. Results showed that P. donghaiense could utilize the test DOP compounds such as glucose-6-phosphate (G-6-P), adenosine triphosphate (ATP) and ribonucleic acid (RNA) to sustain its growth. Nutrition between the test DOP compounds and orthophosphate was comparable. P. donghaiense could utilize intracellular phosphorus to sustain growth under depletion of dissolved phosphorus. Variation of APA in different test DOP compounds was addressed; the controlling mechanism of APA in different DOP media was discussed.     

Determination of Free Nickel Ion Concentrations Using the Ion Exchange Technique: Application to Aqueous Mining and Municipal Effluents

Free metal ion concentration is generally considered a useful indicator of a metal’s bioavailability and ecotoxicity to aquatic biota. This article reports the speciation of nickel in mining and municipal effluents from Sudbury (Ontario, Canada), and also in model solutions containing a fully characterized laurentian fulvic acid (LFA) at environmentally relevant concentrations. A column ion exchange technique (IET) using a cation exchange resin (Dowex 50W-X8) was applied to determine free nickel ion concentrations. In model solutions, reasonable correlation was found between the predictions of an equilibrium-based computer speciation code, Windermere Humic Aqueous Model (WHAM) VI, and the results obtained by IET at low nickel-to-fulvic acid ratios. However at higher mole ratios, the WHAM VI predicted higher free nickel ion concentrations than IET. Only three out of six effluent samples showed reasonable agreement between the IET and the WHAM VI results, indicating the need for further development of IET for application to effluent waters.     

Mercury speciation in sediments at a municipal sewage sludge marine disposal site

Mercury speciation was performed in excess activated sewage sludge (ASS) and in marine sediments collected at the AAS disposal site off the Mediterranean coast of Israel in order to characterize the spatial and vertical distribution of different mercury species and assess their environmental impact. Total Hg (HgT) concentrations ranged between 0.19 and 1003ng/g at the polluted stations and 5.7 and 72.8ng/g at the background station, while the average concentration in ASS was 1181+/-273ng/g. Only at the polluted stations did HgT concentrations decrease exponentially with sediment depth, reaching background values at 16-20cm, the vertical distribution resulting from mixing of natural sediment with ASS solids and bioturbation by large populations of polycheates. Average Methyl Hg (MeHg) concentration in ASS was 39.7+/-7.1ng/g, ca. 3% of the HgT concentration, while the background concentrations ranged between 0.1 and 0.61ng/g. MeHg concentrations in surficial polluted sediments were 0.7-5.9ng/g (ca. 0.5% of the HgT) and decreased vertically, similar to HgT. A positive correlation between MeHg and Hg only at the polluted stations, higher MeHg concentrations at the surface of the sediment and not below the redoxline, and no seasonality in the concentrations suggest that the MeHg originated from the ASS and not from in situ methylation. By doing selective extractions, we found that ca. 80% of the total Hg in ASS and polluted sediments was strongly bound to amorphous organo-sulfur and to inorganic sulfide species that are not bioavailable. The fractions with potential bioaccessible Hg had maximal concentrations in the range in which biotic effects should be expected. Therefore, although no bioaccumulation was found in the biota in the area, the concentration in the polluted sediments are not negligible and should be carefully monitored.     

Dissolved iron(III) speciation in the high latitude North Atlantic Ocean

On voyages in the Iceland Basin in 2007 and 2009, we observed low (ca. 0.1 nM) total dissolved iron concentrations [dFe] in surface waters (<150 m), which increased with depth to ca. 0.2–0.9 nM. The surface water [dFe] was low due to low atmospheric Fe inputs combined with biological uptake, with Fe regeneration from microbial degradation of settling biogenic particles supplying dFe at depth. The organic ligand concentrations [L_T] in the surface waters ranged between 0.4 and 0.5 nM, with conditional stability constants (log K′_FeL) between 22.6 and 22.7. Furthermore, [L_T] was in excess of [dFe] throughout the water column, and dFe was therefore largely complexed by organic ligands (>99%). The ratio of [L_T]/[dFe] was used to analyse trends in Fe speciation. Enhanced and variable [L_T]/[dFe] ratios ranging between 1.6 and 5.8 were observed in surface waters; the ratio decreased with depth to a more constant [L_T]/[dFe] ratio in deep waters. In the Iceland Basin and Rockall Trough, enhanced [L_T]/[dFe] ratios in surface waters resulted from decreases in [dFe], likely reflecting the conditions of Fe limitation of the phytoplankton community in the surface waters of the Iceland Basin and the high productivity in the Rockall Trough.Below the surface mixed layer, the observed increase in [dFe] resulted in a decrease of the [L_T]/[dFe] ratios (1.2–2.6) with depth. This indicated that the Fe binding ligand sites became occupied and even almost saturated at enhanced [dFe] in the deeper waters. Furthermore, our results showed a quasi-steady state in deep waters between dissolved organic Fe ligands and dFe, reflecting a balance between Fe removal by scavenging and Fe supply by remineralisation of biogenic particles with stabilisation through ligands.     

Dynamics and sources of dissolved organic carbon during phytoplankton bloom in hypereutrophic Lake Taihu (China)

To establish the influence of phytoplankton blooms on the dynamics and sources of dissolved organic carbon (DOC) in Lake Taihu, the concentrations and stable carbon isotope values (δ¹³C) of DOC and particulate organic carbon (POC) were analyzed, along with environmental factors, including water temperature, chlorophyll a (Chl a) concentration, phytoplankton community and total bacterial abundance, from March to August 2013 at five sites in Lake Taihu. Significant differences were observed in the DOC concentrations and δ¹³C_DOC values at the sampling sites. On average, the proportion of DOC in the total organic carbon (TOC) pool ranged from 30% ± 10% to 81% ± 7%. POC was positively associated with both Chl a concentration and cyanobacteria biomass, suggesting that cyanobacteria blooms contribute to the POC pool in Lake Taihu. Depleted ¹³C in DOC relative to POC was observed in August, indicating that DOC was partially derived from POC in August. However, Chl a explained only 40% of the variation in DOC in the entirety of Lake Taihu, and at two sites far from the estuary, the contribution of allochthonous carbon was less than 50% in August. These results suggested a greater influence of allochthonous sources on the DOC pool. Moreover, the biodegradability of DOC was further determined by the total dissolved carbohydrates to DOC ratio (TCHO/DOC), specific UV absorbance (SUVA₂₅₄), and the concentrations of bioavailable DOC (BDOC). On average, 17% of the variation in DOC was attributable to the BDOC pool, and the BDOC concentration correlated positively with Chl a, cyanobacteria biomass, and total bacterial abundance, suggesting that cyanobacteria–derived DOC is biodegradable and is preferentially utilized by bacteria.