Acid Volatile Sulfide Research Articles

An evaluation on the bioavailability of heavy metals in the sediments from a restored mangrove forest in the Jinjiang Estuary, Fujian, China

The bioavailability of heavy metals in restored mangrove wetland sediments at the Jinjiang Estuary was assessed through acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM). The results indicated that the SEM distributions were more even than the AVS in the restored regions, and the AVS acted as an important carrier for SEM. SEM-Zn was a major part (61.4–70.6%) of ∑SEM, whereas the most toxic metal, Cd, accounted for approximately 0.2%. The possible adverse effects increased in the surface and subsurface sediments (0–20 cm), with no potential bioavailability in deeper layers. This was probably due to the higher AVSs binding to heavy metal ions in the restored regions compared to the mudflat (control group). The conclusions were also similar when taking TOC concentrations into account. Mangrove wetland restoration has significant effects on the bioavailability of heavy metals in sediments. According to the thresholds for metal toxicity on benthic organisms in sediments, Pb, Cu and Ni had potential adverse effects on benthic organisms in this restored wetland.

Microbial sulfate reduction decreases arsenic mobilization in flooded paddy soils with high potential for microbial Fe reduction

Arsenic (As) tends to mobilize in flooded paddy soil due to the reductive dissolution of the iron (oxyhydr)oxides to which As sorbs, resulting in elevated As accumulation in rice that poses a potential risk to the food safety and human health. Microbial sulfate reduction is an important biogeochemical process in paddy soils, but its impact on As mobilization remains poorly understood. In this study, we incubated eight As-contaminated paddy soils under flooded conditions to investigate the effect of sulfate addition on As mobility. Porewater Fe and As concentrations and As species were determined. Among the eight soils, an addition of 50 mg S kg−1 as sodium sulfate decreased porewater arsenite only in two soils, which also showed a high mobilization of Fe2+. Further experiments showed that the addition of sulfate to these two soils stimulated microbial sulfate reduction but decreased porewater concentrations of both arsenite and Fe2+. Additionally, the supply of sulfate increased the fractions of As associated with acid volatile sulfides in the solid phase and decreased As uptake by rice in pot experiments under similar conditions. The effect of sulfate addition on porewater As was diminished by the addition of molybdate, an inhibitor of sulfate reducing bacteria. These results suggest the formation of secondary FeS minerals which co-precipitate or sorb arsenite as a likely mechanism of As immobilization, which was also supported by thermodynamic modeling of the pore water. Thus, sulfate additions can immobilize As and reduce its availability to rice plants in paddy soils containing a high potential for microbial Fe reduction, providing an efficient way to mitigate the As transfer to the food chain.

Spatial distribution and pollution assessment of metals in intertidal sediments, Korea.

We measured the concentrations of acid volatile sulfide (AVS), chemical oxygen demand (COD), and metals (As, Cd, Cu, Hg, Pb, and Zn) in surface sediments of 74 intertidal sectors along the western and southern coasts of Korea to determine their spatial distribution and pollution status. The concentrations of AVS, COD, and metals were relatively higher in northwestern and southeastern coasts due to human and industrial activities around metropolitan, industrial complexes, and large-scale farms. The results of the sediment quality guidelines and geoaccumulation index for organic matter and metal revealed that almost all intertidal sediments were unpolluted with regard to AVS, COD, Cd, Cu, Hg, Pb, and Zn and some intertidal sediments in northwestern and southeastern coasts were moderately polluted with regard to As. However, the results of pollution load index and ecological risk index for metal showed that intertidal sediments in the southeastern coast are significantly polluted and could have an adverse effect on benthic organisms. Thus, the appropriate management policy and restoration plan for intertidal sectors with high metal pollution level in Korea is necessary to improve the quality of intertidal sediment.

Optimization of pretreatment procedure for MeHg determination in sediments and its applications.

Methylmercury (MeHg) in sediment is difficult to be determined due to its low concentration and binding compounds like sulfide and organic matter. Moreover, wet sediment samples have been suggested to behave differently from certified reference materials in MeHg analysis. Optimal pretreatment procedure for MeHg determination in sediments has not been ascertained and whether the procedure could apply to sediment samples with complex matrix merits further research. This work firstly compared recovery results of five pretreatment procedures for MeHg determination using ERM-CC580. Using the optimal pretreatment procedure, recovery results were analyzed in different sediment samples after manipulation of moisture content, organic matter, and acid volatile sulfide. The procedure using CuSO4/HNO3 as leaching solutions and mechanical shaking as extraction method was proved to produce the most satisfactory recovery results (100.67 ± 6.75%, mean ± standard deviation). And when moisture content varied from 20 to 80%, average recovery results in sediment samples ranged from 100 to 125%. Furthermore, before and after the manipulation of organic matter or acid volatile sulfide, spiking recovery results varied little and were all within acceptable limit (85~105%). Therefore, the procedure of CuSO4/HNO3-mechanical is proposed as a universal pretreatment method for MeHg determination in sediment samples with various characteristics.

Effects of nitrate dosing on the migration of reduced sulfur in black odorous river sediment and the influencing factors

At present, nitrates were widely used to remediate sulfur-rich sediment in black odorous rivers. However, the optimal nitrate dosage and influencing factors during remediation have not been fully investigated. In this study, various nitrate dosages and possible influencing factors were investigated for their efficiency in treating sulfur-rich sediment. The results indicated that acceptable remedial efficiency (the percentage of acid volatile sulfide (AVS) oxidation and the residual ammonium production) can be achieved when 1.6 times the theoretical nitrate dosage is used. Large amounts of AVS cannot be oxidized if too little nitrate is used and will regenerate after several days of remediation. Conversely, high concentrations of ammonium will form if too much nitrate is used. The results of this study indicated that a rapid AVS oxidation rate will be achieved in higher temperatures; no significant treatment efficiency was found when temperatures were in the range of 15–35 °C. Organic matter slowed the rate of nitrate reduction but did not affect its remedial efficiency for AVS oxidation in sediment. A high concentration of ferrous iron primarily influenced nitrate treatment efficiency in the oxidation of AVS in sediment, simultaneously causing the production of a high ammonium concentration. This study once again proved that microbial mediation of the autotrophic sulfide-driven denitrification dominates AVS oxidation in sediment. This study indicated that a universal nitrate dosage calculation equation should be established, and that factors such as ferrous iron concentration should be considered in future remediation of black odorous rivers.

Remediation of Caldas site by natural attenuation

Acid mine drainage (AMD) is one of the main environmental issue caused by chemical and bacterial oxidation of pyrite (FeS2) and other sulfite minerals when exposed to atmospheric conditions during mining. In Brazil, AMD occurs in a former uranium mine and contains radionuclides and other elements, which are precipitated from acidic water by liming. Due to the inefficiency of the treatment, contaminants overflow to the water reservoir of Indústrias Nucleares do Brasil – INB in Caldas. The multiplicity of interactions that can occur between the contaminants and the sediments of the reservoir requires a broader approach in order to understand the fixation and/or transport of these elements. In this work the natural remediation approach is reviewed and an initial chemical and radiochemical characterization of the reservoir sediments is presented. Uranium was determined by spectrophotometry, Ra-226, Ra-228 and Pb-210 by gamma spectrometry and zinc by ICP-OES. Twenty-six sediment samples were collected in the reservoir and a bathymetry survey by sonar was performed to determine the thickness of the sediment layer. All the data were processed using the ArcGIS program. To assess the potential mobility and bioavailability of contaminants and to study the role of bacterial sulfate reduction in the immobilization of these contaminants, Acid-volatile sulfide (AVS) analyzes will be performed as a further step.

Iron-sulfur distribution and its environmental significance in three typical areas of western Lake Taihu

以太湖西岸聚藻区、清淤区和开阔水域3种典型区域为对象，对沉积物中硫铁的分布进行研究.结果显示，各区域沉积物中铁还原均比硫还原活跃，硫铁氧化还原菌的分布表明硫铁循环主要集中于0~15 cm表层沉积物.开阔水域未发现明显硫离子（dS^2-）释放与酸性可挥发性硫化物（AVS）沉积，硫还原较弱；二价铁离子（dFe²⁺）平均浓度为dS^2-的5.2倍，说明沉积物仍以铁还原为主导.清淤区硫酸盐还原菌（SRB）相对丰度与dS^2-含量均为所有区域中最低，且未见明显dFe²⁺释放，表明清淤抑制了硫铁还原的进行.聚藻区表层沉积物SRB相对丰度达到2.7%，且出现dS^2-和AVS的显著升高，说明沉积物中发生着强烈的微生物硫还原.在表层沉积物也出现了明显的dFe²⁺释放，反映出强烈的铁还原，但沉积物中铁还原菌（FeRB）的平均丰度仅为0.6%，这一数值与其他区域相似，显然无法解释聚藻区与其他区域巨大的dFe²⁺差异，因此微生物铁还原并不是铁还原的主要途径.考虑到硫铁化合物的沉积与Fe（Ⅲ）氧化物的消耗一致，沉积物中的铁还原是由ΣS^2-诱导的化学铁还原主导.dFe²⁺平均浓度为dS^2-的4.8倍，监测培养沉积物的dS^2-、dFe²⁺变化所得的铁还原速率是硫还原速率的7.4倍，说明铁还原仍比硫还原活跃.但由于AVS的沉积对ΣS^2-的消耗，真实硫还原速率应高于测量值.;Geochemical characteristic of sulfur and iron was investigated in three types of sediments including algae accumulated sediment, dredged sediment and sediment away from lake shore. It was found that iron reduction dominated in all sediments rather than sulfate reduction. Both reduction concentrated in 0-15 cm surface sediments according to the distribution of microorganisms of iron and sulfur species. Accumulation of dS^2- and acid volatile sulfide(AVS)was not observed in sediment away from lake shore, indicating that sulfate reduction is minor. Iron reduction was more active than sulfate reduction as the mean concentration of dFe²⁺ was 5.2 folds of dS^2-. Sulfate reducing bacteria (SRB) abundance and dS^2- content in dredged sediments were the lowest and dFe²⁺ release was not found, suggesting the depressed iron and sulfate reduction by dredging. SRB abundance in algae accumulated sediment reached to 2.7% and intensive dS^2- release and AVS deposition were found, indicating the strong sulfate reduction. Active iron reduction was also found with high dFe²⁺ concentration in algae accumulated sediment. However, the mean abundance of iron reducing bacteria (FeRB) was only 0.6%, which was similar to other sediments and was obviously not able to explain the huge difference of dFe²⁺ concentrations. Thus, microbial iron reduction was not the main pathway of iron reduction. Considering the corresponding dissolution of Fe(Ⅲ) oxides and deposition of iron sulfides, sulfide-mediated chemical iron reduction was the dominating pathway. The mean concentration of dFe²⁺ was 4.8 folds of dS^2-, and iron reduction rate was 7.4 folds of sulfate reduction rate by monitoring dS^2- and dFe²⁺ variations, suggesting iron reduction was more active than sulfate reduction. However, as AVS generation could consume dS^2-, the real rate of sulfate reduction was higher than the measured rate. Transition of iron and sulfur cycling would cause various negative effects and even extreme cases including dead zones in marine and black bloom in freshwater lakes. Although similar phenomenon was only observed in algae accumulated sediment, concern should still be raised.

Potential bioavailability assessment and distribution of heavy metal(oids) in cores from Portman Bay (SE, Spain)

A total of 120 sediments from 12 cores of Portman Bay (SE Spain) were studied to assess the degree of contamination and ecological risk related to potentially toxic elements (PTEs) by combining a geochemical and mineralogical characterization with the assessment of the bioavailable forms of trace metals (As, Cd, Cu, Fe, Pb, Zn). With this purpose, sediment contamination was assessed by total and water-soluble content, and potential bioavailability by the simultaneously extracted metals and acid-volatile sulphides (SEM-AVS) approach, and by an oral bioaccessibility extraction procedure. The sediments are essentially sandy (>80%). The most important minerals are: iron phases such as siderite, iron oxides and hydroxides and pyrite; clay minerals such as clinochlore, greenalite and biotite; and quartz. Occasionally, jarosite and carbonates (calcite and dolomite) appear. The total PTEs content is high whereas the sediments generally have a very low soluble PTE content. The SEM/AVS ratio is less than unity in most samples, indicating that there is enough sulphur so that if there was a release of metals, they could precipitate as sulphides. After the bioaccessibility extraction, the results showed that zinc and cadmium are more bioaccessible in the intestinal environment (alkaline) while the rest of the elements have greater availability in the stomach (acid). Supplementary material: values of pH (1:1 extract) and concentration of different metals and arsenic in the sediments studied is available at https://doi.org/10.6084/m9.figshare.c.4272176

The impact of declining oxygen conditions on pyrite accumulation in shelf sediments (Baltic Sea)

Deterioration of oxygen conditions in water below the halocline has been observed in the Baltic Sea. Deoxygenation is linked to the reduced frequency and volume of inflows of highly saline surface water from the North Sea (major Baltic inflows—MBIs) in the second half of the twentieth century and the increased organic matter respiration due to eutrophication. In the present study, the impact of worsening oxygen conditions on pyrite content in the Gdańsk Deep (max. depth of 118 m, southern Baltic Sea) sediments was determined. Geochemical parameters (acid volatile sulfides, pyrite sulfur, reactive iron, organic carbon, sedimentation rate and sediment age) were analyzed in relation to the variation in bottom water oxygen concentration and the occurrence of MBI. The obtained results demonstrate that pyrite content in the study area decreased after 1960. The declining pyrite content coincided with the deterioration of oxygen conditions (concentration < 2 ml l−1) in bottom water. In the same period, reactive iron concentration decreased and organic carbon increased in sediment. In the period 1616–1960, average pyrite accumulation rate was 322 µmol m−2 day−1. In the subsequent years, its average accumulation rate decreased to 210 µmol m−2 day−1. Fluctuations of oxygenation of bottom water in the study area were manifested by highly variable degree of pyritization (36 ± 11%) and particulate organic carbon to pyrite sulfur ratio (2.8–37).

A new paper sensor method for field analysis of acid volatile sulfides in soils.

Monitoring of biogenic sulfide is important because acid volatile sulfides (AVS) represent a reactive pool responsible for immobilization of toxic metals. We propose a new sulfide paper sensor method for semiquantitative determination of AVS in which developed color is compared to a reference chart. The method was validated against the ion-selective microelectrode and the purge-and-trap methods. For fieldwork, readings should fall within 1 to 10 μmoles S2- . Considering that the volume of soil used ranged between 1 and 16 cm3 , the corresponding soil sulfides concentration range spans from 0.06 to 10 mmoles S2- cm-3 . The sulfide paper sensor method is highly suitable for field screening and has sensitivity levels comparable to laboratory methods. Environ Toxicol Chem 2018;37:3025-3031. © 2018 SETAC.

Effect of Sulfate Load on Sulfur Removal in Model Constructed Wetlands

Four model constructed wetlands (CWs) were designed to investigate the effects of sulfate load on sulfate and sulfide removal. The results showed that as the sulfate load increased from 1.42 to 7.01 g S m–3 d–1, the sulfate removal rate increased from 1.42 to 3.16 g S m–3 d–1, and the sulfide discharge rate increased from 0.08 to 1.46 g S m–3 d–1. The total sulfur removal rate ranged between 1.29 and 1.74 g S m–3 d–1. The sulfide in the effluent only accounted for 5.55%–46.9% of the removed sulfate. This indicated that CWs can effectively reduce sulfide discharge while removing sulfate. The conversion of dissolved sulfide into deposited sulfur by CW matrix was a main way for sulfide removal. Elemental sulfur, acid volatile sulfide (AVS), and pyrite-sulfur were the main forms of sulfur deposition in this study. The accumulations of these three sulfur compounds were 16.6–36.2, 22.3–36.0, and 49.7–63.6 mg S kg–1 gravel, respectively. Sulfur balance analysis showed that 42.9%–71.1% of the removed sulfate was deposited in the matrix, and only 0.84%–2.34% was absorbed by the plant.

Stability of silver nanoparticle sulfidation products

The adoption of silver nanoparticles in consumer goods has raised concerns about the potential environmental harm of their widespread use. We studied chemical transformations that Ag NPs may undergo as they pass through sulfide-rich conditions common in waste water treatment plants (WWTPs), which may limit the release of Ag+ from Ag NPs due to the formation of low-solubility silver sulfide (Ag2S). However, it is uncertain whether sulfidation is complete and if sulfidized Ag NPs continue to release Ag+. To address these uncertainties, we monitored the reaction of Ag NPs with various levels of sulfide with an ion selective electrode and UV/visible spectrophotometry over the course of two months. We characterized the products of the sulfidation reactions with a purge-and-trap acid volatile sulfide (AVS) analysis, which served as a measure of the stability of the sulfidized products because sulfide would be readily lost to oxidation unless it is stabilized as Ag2S. The Ag NP surface plasmon resonance (SPR) absorbance peak was initially diminished and then returned over the course of several days after reaction with limited amounts of sulfide, suggesting a dynamic system that may retain some characteristics of the pristine Ag NPs. However, ICP-MS analysis of sulfidized Ag NP suspensions over a two-month period demonstrates that sulfidation limits the release of Ag+ ions from nanosilver that pass through a WWTP, even when sulfide concentrations are limited relative to silver.

An alternative approach to bioaccumulation assessment of methyl-Hg, total-Hg, Cd, Pb, Zn in bivalve Anomalocardia brasiliana from Rio de Janeiro bays

We present an alternative approach for establishing in situ bioaccumulation assessment of methyl-Hg (MeHg), total-Hg, Cd, Pb and Zn in bivalve Anomalocardia brasiliana from four bays of Rio de Janeiro presenting varying degrees of eutrophication, acid volatile sulfides (2–55 μmol g−1), simultaneously extracted metals (SEM) and total metals (TM) in sediments. Using metal concentrations of composite samples from three size classes of bivalve and their incorporation rates (IR = metal concentration / total length), which depend on exposure time, we calculated asymptotic IR and respective consequent metal concentrations. Both IR and the metal concentration presented inverse relationships with total length (excepting MeHg) and bay contamination. Lead and zinc concentrations were above Brazilian legal criteria in the most anoxic and contaminated bay, suggesting significant metal bioavailability (SEM/TM between 8% and 63%).

Spatial distribution of hydrogen sulfide and sulfur species in coastal marine sediments Hiroshima Bay, Japan

This study aims to reveal spatial distribution of hydrogen sulfide and sulfur species in marine sediments in Hiroshima Bay, Japan, by direct analyses using a combination of detection tubes and X-ray absorption fine structure spectroscopy. In summer and autumn, the hydrogen sulfide concentration ranged from <0.1 to 4 mg-S L−1. In this study, only hydrogen sulfide was observed in autumn and at two stations in summer. In contrast, some earlier studies reported in all seasons in Hiroshima Bay the presence of acid volatile sulfide, which is used as a proxy of sulfide content. The sulfur species in sediments were mainly identified as sulfate, thiosulfate, elemental sulfur, and pyrite. Thiosulfate was a minor component compared to the other sulfur species. The formation of pyrite and sulfur derived from hydrogen sulfide oxidation played an important role in the scavenging of hydrogen sulfide.

Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments

Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] - [AVS])/foc, and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

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 (16-69.5μgg-1), Zn (60.6-191.4μgg-1), and Pb (13-100.9μgg-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.

From source to sink: Rare-earth elements trace the legacy of sulfuric dredge spoils on estuarine sediments

Land disposal of dredged sulfide-rich coastal sediments generates secondary coastal acid sulfate soils (CASS), as previously reduced sulfide minerals oxidise to produce acidic drainage rich in Fe, SO42− and rare-earth elements (REEs). Few studies investigate both the source and the sink of REEs in the context of interpreting their mobilisation and potential use in tracing anthropogenic activity. Here we investigate REE signatures in estuarine sediments (and overlying surface waters) that have received acute, long-term (>15 years) acidic drainage from legacy sulfuric dredge spoils. It was found that the dredge spoil continues to act as a source of acidity (pH 3.5–5.5), Fe and REEs during development of CASS, and contains negligible acid volatile sulfide (AVS, a proxy for FeS) and relatively low concentrations of ΣREE (mean 44.5 mg/kg, range 4.1–362 mg/kg). In the receiving sediments, high AVS concentrations (mean 92.2 μmol/g, range 0.38–278 μmol/g) reflect elevated FeS content, likely due to high inputs of Fe and SO42− from the acidic drainage, and correspond with a high concentration of total S (mean 852 μmol/g, range 105–2209 μmol/g) and an accumulation of ΣREE (mean 670 mg/kg, range 19.9–1819 mg/kg). Importantly, where drain sediments that were previously enriched in highly reactive sulfidic minerals and trace elements and have become exposed to the atmosphere (e.g. Site 3) and partially oxidised, they provide a further source of acidification, remobilising the REEs to the downstream sediments. Interestingly, we also found a clear positive correlation between phosphorous and REEs both in the dredge spoil and sediment, suggesting phosphate minerals may act as a sink for REEs in CASS influenced drain sediments. This is further supported by strong positive gadolinium anomalies (1.1–1.6) and high calculated anthropogenic Gd values (12–38%), which may reflect the influence of phosphate fertiliser on this eutrophic system.

Spatio-temporal Changes of Sediment Environment in the Taehwa River Estuary, Ulsan of Korea.

Sim B.-R.; Kim H.C.; Kim C.-S.; Hwang D.-W.; Park J.-H.; Cho Y.-S.; Hong S., and Lee W.-C., 2018. Spatio-temporal changes of sediment environment in the Taehwa river estuary, Ulsan of Korea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 41–45. Coconut Creek (Florida), ISSN 0749-0208.The Taehwa River is a successful case for restoration of ecological system in Korea through the restoration project conducted during 1995–2005. To sustain this restored ecosystem, seasonal surveys for surface sediment quality were conducted in the entire area of the river estuary during the year 2012. It is noteworthy that the areas with pollutant source inflow exhibited higher organic carbon and acid volatile sulphide concentrations than the pollutant standard indices (20 mg C·g−1 and 0.2 mg S·g−1) in the spring and summer. Trace metal concentrations (As: 13.2; Cu: 64.2; Zn: 185.7; and Pb: 48.3; mg·kg−1) also showed a considerable increment from their respective Effect Range Low standards. The observed sediment oxygen demand (avg. 41.13 mmol O2m−2·d−1) in the prime habitat of Ruditapes philippinarum was substantially higher in this study than the average value (16 ± 6 mmol O2m−2·d−1) in Southern coastal area of Korea. The results from materials flux study suggest that high phosphate release from sediment into water column in summer and low sedimentation rate of nitrogenous nutrients during fall season could influence prolonging algal blooms in the Taehwa estuary. A further study is needed for a long-term of sediment monitoring on environment quality changes to maintain the restored ecological system and a safe consume of seafood.

Predicting trace metal bioavailability to chironomids in sediments by diffusive gradients in thin films

The technique of diffusive gradients in thin films (DGT) has been developed as a promising tool to assess metal bioavailability in sediment. However, it has yet to be determined whether the DGT-labile metal in sediment is representative of bioavailable fraction for benthic organisms. In this study, the performance of DGT for predicting metal bioavailability was evaluated by exposing DGT and chironomids Chironomus tentans to a series of metal-contaminated natural sediments in the laboratory. Conventional methods, including acid-volatile sulfides and simultaneously extracted metals method, and total recoverable and dilute-acid extractable metal concentrations were also used to assess the availability of Zn, Cu and Pb to chironomids. The bioassay results showed that >70% of the larvae (73 ± 1.7%–98 ± 0.5%) survived in all sediment samples, however, an enhanced uptake of Zn, Cu and Pb by C. tentans in contaminated sediments was observed compared to control sediments. The correlation analyses indicated that the total recoverable metal concentrations and DGT-metal fluxes in the surficial sediment (−1 cm) were all significantly associated with metal bioaccumulation in C. tentans (p < 0.01). Given the advantages of DGT devices for in situ and time-averaged measurement of the potentially bioavailable fraction, DGT-metal fluxes were proved to be a better surrogate to predict C. tentans response to metal contamination. The results further supported the applicability of the DGT technique as an alternative method to assess the bioavailability of metals in sediment to benthic invertebrates.

Sediment quality assessment in a coastal lagoon (Ravenna, NE Italy) based on SEM-AVS and sequential extraction procedure

Sediments from the Pialassa Piomboni coastal lagoon (NE Italy) were studied to assess the degree of contamination and ecological risk related to trace metals by combining a geochemical characterization of bulk sediments with the assessment of the bioavailable forms of trace metals. With this purpose, sediment contamination (Cd, Cu, Hg, Ni, Pb, and Zn) was assessed by Enrichment Factors (EFs), and potential bioavailability by the Simultaneously Extracted Metals and Acid Volatile Sulfides (SEM-AVS) approach (Cd, Cu, Ni, Pb, and Zn), and by Sequential Extraction Procedure (Co, Cr, Cu, Ni, Pb, and Zn). On average, Cr and Ni exhibited no contamination (EF ≤1.5), and a predominance in the residual fraction of the sediment, indicating natural origin for these metals. Cu, Pb and Zn displayed a local contamination, which resulted in a higher proportion of Cu bound to the reducible and oxidizable fractions (~30% and ~40% as median, respectively), and Pb mostly associated with the reducible phase (~60% as median). Hence, Cu and Pb could be mobilized when environmental conditions become reducing or oxidizing. Zn resulted mainly partitioned into the reducible and residual fractions (~50% as median, in both fractions). The Risk Assessment Code (RAC) indicated that approximately 30% of samples had >10% of total Zn weakly bound to the sediment, suggesting a medium risk of exposure for aquatic organisms. RAC results were consistent with the ∑SEM-AVS findings, pointing to possible adverse effects for aquatic biota in ~30% of samples, with Zn mostly accounting for the total metal bioavailability. Hg showed a moderate to very severe enrichment, indicating that a substantial amount of this metal derives from anthropogenic sources and may pose adverse effects on the aquatic biota of the Pialassa Piomboni lagoon.