Metal bioavailability in marine sediments measured by chemical extraction and enzymatic mobilization

Geospeciation, toxicological evaluation, and hazard assessment of trace elements in superficial and deep sediments

To evaluate the hazard assessment of dredging and disposal of sediments, an in-depth chemical and toxicological characterization of sediments was carried out in Venice Lagoon. The bioaccessible and mobile concentration of trace elements in superficial and deep sediments (in the Holocene-Pleistocene limit) can deeply affect the quality of the aquatic ecosystem. Geospeciation and total concentration of trace elements in sediment cores were assessed and several toxicological tests were carried out. The indices of contamination (e.g., geochemical accumulation index, I_geo, pollution load index, PLI) and of speciation (individual contamination factor, ICF and global contamination factor, GCF) were evaluated. Factor Analysis (FA) was performed to explore possible significant correlations between toxicity data and sediment chemistry. Results underlined that the total concentration of trace elements cannot adequately assess the hazard, while bioavailability, mobility, and toxicity of trace elements allow a thorough evaluation of the environmental threats. The integration of results from chemical characterization ex ante and toxicity assays will provide for a better sustainable handling and management of sediments.

Bioavailability and toxicity of trace metals (Cd, Cr, Cu, Ni, and Zn) in sediment cores from the Shima River, South China

Five sediment cores (S1-S5) were collected from the Shima River to determine the bioavailability of trace metals (Cd, Cr, Cu, Ni, and Zn) using the modified European Community Bureau of Reference (BCR) procedure. The toxic effects of polluted sediment were assessed using the LUMISTox^® bioassay with Vibrio fischeri and chemical models such as the toxicity unit (TU) of each metal, sum of all TUs (∑TU), and toxic risk index (TRI). The results showed that Cd, Ni, and Zn were present mainly in the acid-soluble and residual fractions, and the residual fraction of Cr accounted for the majority of the metal content (44%), while Cu was present mainly in the reducible and residual fractions. Cd had a mean enrichment factor (EF) of 15.1 and was considered to be severely enriched, while there was a minor enrichment of Cr and moderately severe enrichment of Zn, Cu, and Ni. From the LUMISTox^® bioassay, an acute TU (TUa) value exceeding 0.4 was found at the upper and middle reach sites and was considered to represent slightly acute toxicity, whereas little acute toxicity was found at the lower reach site. The acid-soluble fraction of trace metals was the geochemical fraction mainly responsible for the acute toxicity of the sediment, and acid-soluble Zn and Ni were identified as important contributors to sediment toxicity.

Ability of 3 extraction methods (BCR, Tessier and protease K) to estimate bioavailable metals in sediments from Huelva estuary (Southwestern Spain)

The bioavailable fraction of metals (Zn, Cu, Cd, Mn, Pb, Ni, Fe, and Cr) in sediments of the Huelva estuary and its littoral of influence has been estimated carrying out the most popular methods of sequential extraction (BCR and Tessier) and a biomimetic approach (protease K extraction). Results were compared to enrichment factors found in Arenicola marina. The linear correlation coefficients (R(2)) obtained between the fraction mobilized by the first step of the BCR sequential extraction, by the sum of the first and second steps of the Tessier sequential extraction, and by protease K, and enrichment factors in A. marina, are at their highest for protease K extraction (0.709), followed by BCR first step (0.507) and the sum of the first and second steps of Tessier (0.465). This observation suggests that protease K represents the bioavailable fraction more reliably than traditional methods (BCR and Tessier), which have a similar ability.

Application of a new integrated sediment quality assessment method to Huelva estuary and its littoral of influence (Southwestern Spain)

A new integrated sediment quality assessment method composed of several assays (particle size profile, total metal content, protease K extraction, total organic carbon, toxicity bioassay with Photobacterium phosphoreum and macrobenthic community alteration) that provides a single result, the environmental degradation index (EDI), has been developed. The new method was tested on the Huelva estuary (southwest of Spain), a highly polluted area where metals dissolved in the water of the Tinto and Odiel rivers precipitate after flowing through the Iberian Pyrite Belt, one of the largest metallogenic areas of massive sulphide deposits in the world. The proposed method satisfactorily was able to reflect different degrees of pollution on the environmental degradation index. Thus, EDI categorized littoral samples as slightly degraded and all the Tinto and some of the Odiel as very highly degraded, emphasizing the lower zone of the Tinto estuary as the most deeply degraded of the entire study area.

Bioavailability of trace elements in surface sediments from Kongsfjorden, Svalbard

The bioavailability of trace elements in marine sediments from Kongsfjorden (Svalbard Islands, Norwegian Arctic) was assessed and discussed. Total concentrations of several elements were determined in two granulometric fractions and their bioavailability evaluated by both applying a sequential-selective extraction procedure and using a biomimetic approach based on proteolytic enzymes. Total concentration values and solid speciation patterns indicated overall that the anthropogenic impact of trace elements in the investigated area is negligible, although a minor enrichment with respect to crustal values was found for As, Cd, Cr, Ni, and V. Enrichment of trace elements in the <63-μm fraction compared to the coarser one was evident for As, Cd, Cr, and Ni. The evaluation of the bioavailable fractions showed that a large part of the total content of trace elements cannot enter the aquatic food chain and emphasised the risk of overestimating the environmental impact of heavy metals if the assessment is only based on total concentrations.