Simultaneously Extracted Metals Acid-volatile Sulfide Research Articles

Trace metal partitioning and potential mobility in the naturally acidic sediment of Lake Caviahue, Neuquén, Argentina

Lake Caviahue, in Patagonia (Argentina), is a very acid water body (Patagonia, Argentina) due to the influx of volcanic fluids. Over the past 18 years, the lake has been progressively alkalinizing and pH is close to the ferric iron precipitation threshold (pH>3,0). Should iron precipitate, wáter and sediment composition will be altered. To set a baseline, trace metal partitioning (Cu, Cd, Cr, Pb, Zn and Mn) was studied for three sediment cores (0 to 16 cm depth) at three sampling stations using a sequential extraction procedure (SEP) and the acid volatile sulfide/simultaneously extracted metals (AVS/SEM) protocol. The total metals content of the sediments ranged between 0 to 408 μg g-1 of dry sediment, with Pb>Cr>Mn>Cu>Zn>Cd. No Cd was measured above the limit of detection. The sediment was richest in Mn and Cr, two non-toxic metals at the pH / Eh combination of the lake basin. Total Pb was at a moderate contamination level although it is associated with the most recalcitrant fraction and therefore has low mobility. The sediment fractions with higher metal content were the oxidizable and residual, the former commonly associated with labile organic matter and pyrite while the latter are related to recalcitrant organic matter and rock forming minerals. In addition, a high correlation was found between Cr, Pb and Mn,thus these metals may be subject to analogous precipitation processes and possibly to co-variation in the volcano effluents. Furthermore, no metals were detected in the exchangeable/carbonates fraction, which is the most labile of all the sediment fractions. The metal content in (SEM) was likewise below the toxicity thresholds of two international sediment quality guidelines and the ratio AVS/SEM was over one, indicative of non-toxicity. Both results indicate that metal mobility in the acidic sediments of lake Caviahue is very low.

Characterization of trace metal removal products in vertical flow bioreactor substrates at the Mayer Ranch Passive Treatment System in the Tar Creek Superfund Site

A passive treatment system (PTS), including two parallel vertical flow bioreactors (VFBR), was constructed in 2008 for the treatment of unabated net-alkaline ferruginous mine drainage in the Tar Creek Superfund Site in northeastern Oklahoma. Water quality data collected since the PTS began operation indicate significant removal of trace metals in the VFBR. Results of a sequential extraction procedure (SEP) performed on substrate samples showed that the majority of Cd, Co, Fe, Ni, Pb, and Zn were retained in the refractory organic/sulfide fraction. Subsequent acid volatile sulfide/simultaneously extracted metals (AVS/SEM) analyses confirmed the retention of Cd, Fe, Pb, and Zn as sulfides, but Co and Ni results were less certain. The majority of trace metals were retained as insoluble products in the VFBR, while up to 20% of most of the trace metals were retained in soluble, bioavailable fractions. Nearly 70% of Mn was retained in the soluble and bioavailable exchangeable, carbonate, and labile organic fractions.

Metal removal mechanisms in a short hydraulic residence time subsurface flow compost wetland for mine drainage treatment

The performance of an innovative pilot-scale subsurface flow compost wetland for the attenuation of zinc in mine drainage was investigated. The particular novelty of the system, which operated under ambient environmental conditions, was the short hydraulic residence time (HRT) of 7.5–14.5h. Short HRT is crucial because it reduces absolute wetland size and construction cost, which can be major impediments to use of wetlands. Over a 2year period mean treatment efficiency was 67.5% (total Zn) and 84.4% (0.45μm filtered Zn). Mean volume-adjusted removal rates for total and filtered Zn were 0.92g/m3/day and 1.05g/m3/day respectively. Both water and compost analyses showed bacterial sulfate reduction to be the most important Zn removal process within the subsurface flow wetland: water analyses showed consistent decreases in sulfate concentration through the system, whilst Acid Volatile Sulfide − Simultaneously Extracted Metals (AVS-SEM) analysis of the compost revealed concentrations of Zn up to 12,227mg/kg and AVS up to 9066mg/kg. Geochemical modelling using PHREEQC also showed that biogeochemical conditions within the wetland favored Zn attenuation as its sulfide: ZnS was the only solid Zn phase that was super-saturated in the wetland effluent water (mean Saturation Index of +9.52). Preliminary investigation of the use of liquid waste carbon sources to further enhance performance were ambiguous, but the results of the research nevertheless show the potential of short hydraulic residence time subsurface flow compost wetlands as a low cost treatment option for metal-polluted abandoned mine drainage.

A new index for assessing heavy metal contamination in sediments of the Beijing-Hangzhou Grand Canal (Zaozhuang Segment): A case study

Zaozhuang Segment of the Beijing-Hangzhou Grand Canal is an important water conveyance line on the eastern route of the South-North Water Transfer Project in China and its water environment condition can exert a significant influence on diversion water quality safety. This paper analyzed contents of five heavy metals such as Cd, Cu, Ni, Pb and Zn as well as their chemical forms in surface sediments in this region. Methods including Threshold Effects Level-Probable Effects Level (TEL-PEL), Risk Assessment Code (RAC) and Acid Volatile Sulfide- Simultaneously Extracted Metals (AVS-SEM) were also employed to evaluate the quality of sedimentary environment in this region. With the aim to assess the eco-environmental risk revealing the information of the concentration, the chemical fractionation, the toxicity of heavy metals, a new assessment index known as Multivariable Evaluation Index (MEI) was introduced into this paper. Results indicated that contents of such five heavy metals in surface sediments were generally low. Overall, ecological risk was in the medium-low grade in addition to several locations where the level of risk was high. However, certain differences still existed among various assessment results. Comparing with other single evaluation methods, MEI may be able to reflect contamination status and ecological risks of heavy metals in sediments of a specific region more comprehensively. MEI also seemed able to overcome the limitations of other prevalent aggregated indexes to assess potential sediment pollution risk in aquatic systems.

Seasonal Variation of Acid Volatile Sulfide and Simultaneously Extracted Metals in Sediment Cores from the Pearl River Estuary

The simultaneously extracted metals/acid volatile sulfide (SEM/AVS) method is widely used to estimate the toxicity of metals in sediment. In this study, SEM and AVS concentrations were obtained by the cold-acid purge-and-trap technique during spring (April) and winter (December) at six sites in the Pearl River estuary. Total organic carbon, grain size distribution, and total metals were also measured in winter samples. AVS concentrations in spring sediments were slightly higher than those in winter sediments, except at site 2. AVS concentrations showed more distinct locational and temporal variation compared with SEM concentrations. Generally, AVS contents increased downcore, whereas SEM concentrations decreased slightly with depth. Higher SEM concentrations were observed in the west shoal (sites 2, 6, and 7) and site 4 (1.24 ∼ 4.28 μmol•g−1) compared with those at sites 1 and 3 (0.73 ∼ 2.14 μmol•g−1) in the middle shoal. Most SEM metals have a significant linear positive correlation with the total metals, especially for Cd, Zn, and Pb, which were easily extracted by 1 M HCl compared with Cr and Ni. According to the toxicity threshold value of 1.7 μmol•g−1 for the difference of SEM-AVS, a toxic effect is expected at sites 1, 2, and 4 in spring and at sites 4, 6, and 7 in winter, which also indicates a relatively obvious seasonal variation in heavy metal bioavailability. However, comparisons between the total heavy metal concentrations in winter sediments with the sediment quality guidelines of ERLs/ERMs and TELs/PELs showed that adverse biological effects may occasionally occur at sites 2, 4, 6, and 7. Therefore, SEM/AVS prediction in conjunction with sediment quality guidelines can give a more reliable evaluation of the bioavailability of heavy metal in sediments.

Investigation of anthropogenic trace metals in sediments of Lake Illawarra, New South Wales

Surficial (<2 cm) and subsurface (cores 20 – 50 cm deep) sediments from Lake Illawarra were analysed for trace metals (Cd, Cu, Pb, Zn) to determine the extent and nature of anthropogenic influence. Sediment samples were size-normalised (<62.5 μm) to determine total acid-extractable metals in the fine fraction, as well as in whole sediment. A four-step sequential extraction technique was used to determine major chemical phases, whereas 1 M HCl, 0.05 M ethylenediamine tetra-acetic acid (EDTA) treatments gave an estimate of the bioavailable portion of the metals. The acid-volatile sulfide simultaneously extracted metals (AVS-SEM) technique was used to provide information on sediment toxicity. Griffins Bay is the most contaminated part of Lake Illawarra and is a major sink for trace metals. The source of metals to this embayment is primarily input from creeks draining the urban and industrial areas of the Port Kembla industrial complex, as opposed to direct atmospheric deposition, as is commonly believed. Trace metals in sediments of Griffins Bay are probably not bioavailable under current physico-chemical conditions, although oxidation of the sediment by anthropogenic or natural processes may result in the conversion to more bioavailable chemical forms.

Predicting sediment metal toxicity using a sediment biotic ligand model: methodology and initial application

An extension of the simultaneously extracted metals/acid-volatile sulfide (SEM/AVS) procedure is presented that predicts the acute and chronic sediment metals effects concentrations. A biotic ligand model (BLM) and a pore water-sediment partitioning model are used to predict the sediment concentration that is in equilibrium with the biotic ligand effects concentration. This initial application considers only partitioning to sediment particulate organic carbon. This procedure bypasses the need to compute the details of the pore-water chemistry. Remarkably, the median lethal concentration on a sediment organic carbon (OC)-normalized basis, SEM*(x,OC), is essentially unchanged over a wide range of concentrations of pore-water hardness, salinity, dissolved organic carbon, and any other complexing or competing ligands. Only the pore-water pH is important. Both acute and chronic exposures in fresh- and saltwater sediments are compared to predictions for cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) based on the Daphnia magna BLM. The SEM*(x,OC) concentrations are similar for all the metals except cadmium. For pH = 8, the approximate values (micromol/gOC) are Cd-SEM*(xOC) approximately equal to 100, Cu-SEM*(x,OC) approximately equal to 900, Ni-SEMoc approximately equal to 1,100, Zn-SEM*(x,OC) approximately equal to 1,400, and Pb-SEM*(x,OC) approximately equal to 2,700. This similarity is the explanation for an empirically observed dose-response relationship between SEM and acute and chronic effects concentrations that had been observed previously. This initial application clearly demonstrates that BLMs can be used to predict toxic sediment concentrations without modeling the pore-water chemistry.

Bioavailability and chronic toxicity of cadmium in sediment to the estuarine amphipod Leptocheirus plumulosus

AbstractNumerous studies have demonstrated the efficacy of interstitial water metal concentrations and simultaneously extracted metals/acid‐volatile sulfide (SEM/AVS) ratios in explaining the acute toxicity of sediment‐associated metals to benthic organisms. However, no full life‐cycle chronic marine or estuarine tests have been conducted for this purpose. In this study, cohorts of newborn amphipods, Leptocheirus plumulosus, were exposed to cadmium‐spiked estuarine sediment for 28 d to determine effects on mortality, growth, and reproduction relative to interstitial water and SEM/AVS normalization. Seven treatments of cadmium were tested: 0 (control), 0.34, 0.74, 1.31, 1.55, 2.23, and 4.82 M SEMcd/AVS ratios (measured concentrations). Interstitial water cadmium (IWcd) and sediment concentrations of SEMcd and AVS were monitored periodically and by depth during the exposure. When sediment SEMcd/AVS ratios were ≤1.55, mean IWcd concentrations were less than the 96‐h water‐only cadmium LC50 for juvenile and subadult L. plumulosus, and mortality, growth, and reproduction were not affected. When SEMcd/AVS ratios were ≥2.23, IWcd concentrations were more than 100 times greater than the 96‐h water‐only cadmium LC50, and all amphipods died. These results are consistent with predictions of metal bioavailability from acute tests with metal‐spiked sediments, i.e., that sediments with SEMcd/AVS ratios &lt;1 are not toxic, while sediments with SEMcd/AVS ratios &gt;1 may be toxic.