Trace element accumulation and elutriate toxicity in surface sediment in northern Tunisia (Tunis Gulf, southern Mediterranean)

Spatial distribution, contamination assessment and potential ecological risk of some trace metals in the surface sediments of the Gulf of Tunis, North Tunisia

To evaluate the trace metals contamination status in the Gulf of Tunis, forty one sediment samples were analyzed using different approaches. According to certain contamination and ecological risk indices (Contamination Factor, Geoaccumulation index and Ecological risk index), Hg has the highest contamination level while pollution by Ni, Pb, Cd and Cr was absent. The highest concentrations of trace metals were found in sediments collected from the offshore and coastal areas located opposite the main exchange points with the gulf particularly, the Mejerda and Meliane Rivers, the Khalij Channel, Ghar El Melh and El Malah lagoons, Tunis Lake and Sebkhat Ariana. However, further ecological indices (Potential ecological risk index, Toxic unit and Mean effect-range median quotient) and comparison with sediment quality guidelines suggest that in addition to Mercury, Cr, Pb and Ni concentrations are detrimental to biota in both the offshore and areas near to the exchange points with the gulf. Moreover, in these areas the results from sequential extraction and individual contamination factor calculation pointed to the mobility and bioavailability of Cr, Pb and Ni.

Ecological quality status of the NE sector of the Guanabara Bay (Brazil): A case of living benthic foraminiferal resilience

The ecological quality status of the NE region of the Guanabara Bay (SE Brazil), one of the most important Brazilian embayments, is evaluated. For this purpose, sediment samples from in the inner of the Guanabara Bay (GB) were collected and analyzed (grain-size, mineralogy, geochemistry and living foraminifera). In this study, it is hypothesized that the potentially toxic elements (PTEs) concentrations, in solution and associated with organic matter (_OMPTEs, potential nutrient source), may represent two potential pathways to impact benthic foraminifers. A multiproxy approach applied to complex statistical analyses and ecological indexes shows that the study area is, in general, eutrophic (with high organic matter and low oxygen content), polluted by PTEs and oil. As a consequence, foraminifera are not abundant and their assemblages are poorly diversified and dominated by some stress-tolerant species (i.e., Ammonia tepida, Quinqueloculina seminula, Cribroelphidium excavatum). The results allow us to identify a set of species sensitive to eutrophication and _OMPTEs. Factors such as the increase of organic matter contents and _OMPTEs and, in particular of Zn, Cd and Pb, the oxygen depletion and the presence of oil, altogether contribute to a marked reduction in the abundance and diversity of foraminifera. Ammonia-Elphidium Index and the Foram Stress Index confirm that the NE zone of GB is, in general, "heavily polluted", with "poor ecological quality status" and experiences suboxic to anoxic conditions. In light of it, special attention from public authorities and policymakers is required in order to take immediate actions to enable its environmental recovery.

Inorganic and organic characterization of Santa Lucía salt mine peloid for quality evaluations

Santa Lucía peloid is a sediment used in pelotherapy in Cuban primary health care services. Therefore, in addition to physicochemical regulated parameters, other analyses are required to complement their physicochemical characterization and understand potential element mobility, radiological risk, and toxicity as well as likely bioactive compounds present in Santa Lucía peloid. For these purposes, inorganic and organic elements and compounds were considered to evaluate Santa Lucía peloid's quality. This was accomplished through an integral approach that included (1) determination of physicochemical parameters (pH, electrical conductivity, oxidation-reduction potential, temperature, dissolved oxygen, elemental C, H, and N analyses, organic matter, and hexane removable substances content); (2) determination of total concentration of elements with biological and toxicological importance (i.e., Na, K, Ca, Mg, Fe, Mn, Cr, Cu, Ni, Pb, and Zn), as well as their distribution in operationally defined solid phases, mineralogy, particle size distribution, and total content of radionuclides and radiological dose calculations; and (3) its organic characterization. Results from this study showed that Santa Lucía peloid was non-contaminated and showed low metal mobility and acceptable radiological dose levels, being safe for therapeutic uses. Additionally, these results contribute to the understanding of the organic composition of peloides, provide strong evidences to scientifically explain the therapeutic action of peloids in the treatment of inflammatory diseases, and set a new frame to improve peloid guidelines in Cuba and other countries.

Metal transfer budgets in a Mediterranean marine environment subjected to natural and anthropogenic inputs: case of the Mejerda River Delta (Gulf of Tunis, northern Tunisia)

Deltaic sediments are important for biogeochemical metal cycling since they are hotspots for metal inputs. In addition, they are potential sites for diagenetic processes leading to either the burial of inorganic contaminants or their release. Diffusive fluxes of certain metals (Fe, Mn, Pb, Zn, Cu and Cd) in the sediments of the Mejerda River Delta (MRD) (Gulf of Tunis, Tunisia) were quantified by modeling the available concentration profiles in the pore water. The metals' burial and sedimentation fluxes were also calculated using both the asymptotic concentrations of available metal profiles and sediment trap results. These fluxes were assembled with the exchange fluxes at the sediment-water interface in order to develop complete metal transfer budgets. The results showed that budgets of Cu and Zn are almost neutral. The sediment appears to be a good trap for iron since its average burial flux at the three studied stations is about 332.6 g m^-2 year^-1. Organic matter degradation, carbonate dissolution, and oxyhydroxide reduction are the main mechanisms which accelerate the release of metals associated with the suspended particle matter once they reach the pore water in the seabed.

Assessing the potential ecological risk of Co, Cr, Cu, Fe and Zn in the sediments of Hooghly-Matla estuarine system, India

Hooghly-Matla estuarine system along with the Sundarbans mangroves forms one of the most diverse and vulnerable ecosystems in the world. We have investigated the distribution of Co, Cr, Cu, Fe and Zn along with sediment properties at six locations [Shamshernagar (S1), Kumirmari (S2 and S3), Petuaghat (S4), Tapoban (S5) and Chemaguri (S6)] in the Hooghly estuary and reclaimed islands of the Sundarbans for assessing the degree of contamination and potential ecological risks. Enrichment factor values (0.9-21.6) show enrichment of Co, Cu and Zn in the intertidal sediments considering all sampling locations and depth profiles. Geo-accumulation index values irrespective of sampling locations and depth revealed that Co and Cu are under class II and class III level indicating a moderate contamination of sediments. The pollution load index was higher than unity (1.6-2.1), and Co and Cu were the major contributors to the sediment pollution followed by Zn, Cr and Fe with the minimum values at S1 and the maximum values at S5. The sediments of the Hooghly-Matla estuarine region (S4, S5 and S6) showed considerable ecological risks, when compared with effect range low/effect range median and threshold effect level/probable effect level values. The variation in the distribution of the studied elements may be due to variation in discharge pattern and exposure to industrial effluent and domestic sewage, storm water and agricultural run-off and fluvial dynamics of the region. The study illuminates the necessity for the proper management of vulnerable coastal estuarine ecosystem by stringent pollution control measures along with regular monitoring and checking program.

How useful are geochemical and mineralogical indicators in assessing trace metal contamination and bioavailability in a post-restoration Mediterranean lagoon?

Tunis's Lake North (LNT), located on the Mediterranean Sea, and Tunisia's most important lagoon due to its economic value and its strategic position within the city, has recently undergone a vast sanitation project. To study the lagoon's level of metal pollution, three sediment cores were taken and the sediments were analyzed for trace and major elements, acid volatile sulfides (AVS), total organic carbon (TOC), and minerals. Results showed that TOC concentrations (0.2-3.1%) decreased following the lagoon's restoration. In addition, in comparison to historical data, concentrations of Cu (16-69.5 μg g^-1), Zn (60.6-191.4 μg g^-1), and Pb (13-100.9 μg g^-1) also decreased. Enrichment factor calculation with respect to the crust and local background showed that the sediment had long been contaminated by human pollution and especially by Pb, Zn, and Cu. The AVS to simultaneously extracted metal (SEM) ratio revealed values generally less than 1 indicating no sediment toxicity risks. Statistics revealed a detrital origin for certain metals and a diagenetic origin for FeS₂ and carbonate minerals.