Contaminant Metal Behaviour During Re-suspension of Sulphidic Estuarine Sediments

Abstract

Sediment re-suspension experiments have been conducted to predict contaminants release from sediments to the water column, during dredging operations. In this context, polluted, anoxic estuarine sediments from Rio de Janeiro, SE Brazil, were suspended in oxygenated estuarine water, in laboratory experiments intended to simulate their dispersion by flood flow or dredging operations, in order to measure any release into solution of heavy metals originally present as sulphides that might suffer oxidation. Oxidation of sulphides to sulphate acidified the waters but only after at least 5 h of suspension. Furthermore, the oxidation of acid volatile sulphide (AVS) to sulphate was more rapid and only proceded to completion within 5 days, when large quantities of sulphide forming metals other than Fe were not present. In sediment heavily polluted with zinc, oxidation of AVS was slower and incomplete, resulting in soluble release of a much smaller fraction of the Zn present in the sediment and a maximum dissolved zinc concentration that was much lower than that resulting from less contaminated sediment. The maximum percentages of sulphide-bound metals appearing in solution at any time during re-suspension were low, less than 46% in all cases and typically less than 10%. These maxima were manifested only after acidification by sulphate formation. Appreciable metal dissolution would not occur in an estuary if dilution and dispersion separated the sediment from acid generated or if dredged material settled before acidification occurred.

Relation of acid-volatile sulfides (AVS) with metals in sediments from eutrophicated estuaries: Is it limited by metal-to-AVS ratios?

“…This contrasts with the lower potential to retain metals in the form of AVS found in most samples from station MR, which presented significantly higher values of all AVSderived variables. The observed metal, AVS, and TOC data reflected anthropogenic influences in both stations, as previously indicated for the western area of the bay and other impacted areas in Rio de Janeiro coast (Carreira et al 2002;Maddock et al 2007;Pereira et al 2008). Contrasting concentration profiles between sites were found for all sediment constituents (Fig.…”

Mercury accumulation in sediments along an eutrophication gradient in Guanabara Bay, southeast Brazil

“…An FeS accumulation in the upper 20 cm of sediments from the Iguaçu River estuary was previously indicated by elevated levels of acid-volatile sulfides (110-245 µmol g -1 ). [30][31] Coarser sediments were observed in core E, while cores G and I presented intermediate contents of fine particles, and core M showed the greater contents of these particles (Table 2). These differences were reflected in the lower water content and greater density values of cores E and G (Table 2).…”

Metal bioleaching from anaerobic sediments from Reconquista River basin (Argentina) as a potential remediation strategy

“…3 Total percentages of Cu and Zn of the bioheaps leached out and reached pH values of the solutions for each system studied: no sulphur added; 1, 2 and 5 % of sulphur; and 5 % of superficial sulphur. S sulphur carbonates, sulphates, ferric hydroxides or clay minerals (Caille et al 2003;Maddock et al 2007). Therefore, the solid phases containing these metals and sulphates in the treated sediment would be more soluble in water after the process (Akinci and Guven 2011), which could suggest that the amount of washing water used in our process was underestimated.…”

“…These processes have been intensively studied through static assays (Kersten and Förstner 1991) and dynamic experiments of anaerobic sediment oxidation systems by re-suspension or desiccation (Maddock et al 2007;Di Nanno et al 2007Cappuyns and Swennen 2011;Ye et al 2013;Porzionato et al 2013Porzionato et al , 2014.…”