Restriction of sulfate reduction on the bioavailability and toxicity of trace metals in Antarctic lake sediments

Effect of organic matter on the environmental behavior of sulfur and heavy metals in mariculture sediments during the aging process

Organic matter (OM) significantly impacts the environmental behavior of sulfur and heavy metals. In this study, the effects of OM on the migration and transformation of sulfur and heavy metals in mariculture sediments were investigated. The results indicated that baiting had a strong impact on the accumulation of acid volatile sulfur (AVS) (P < 0.05) and increased the environmental risk of sulfide in sediments. The addition of bait promoted the generation of chromium (II)-reducible sulfur (CRS); however, the resistance of AVS to CRS conversion increased with increasing bait addition. The addition of bait considerably influenced Cd accumulation. The acid-soluble fractions of Cr and Cu and the oxidizable fraction of Cd were primarily affected by the bait addition (coefficient of variation>15 %). An increase in the reducible fraction promoted the conversion of AVS to CRS, which reduced the degree of sediment aging. Higher OM levels reduced the diversity and abundance of the bacterial communities. The sulfate respiration functional microbiota was particularly affected by OM.

Equilibrium partitioning approach for metal toxicity assessment in tropical estuarine sediment of Bandon Bay, Thailand

An equilibrium partitioning approach (EqPA) was employed to evaluate the metal toxicity and define sediment quality guidelines (SQGs) for arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn), and mercury (Hg) in the cockle cultivated areas located in Bandon Bay, Thailand. An assessment of metal toxicity using the [∑SEM]-[AVS] and [∑SEM]-[AVS]/foc models indicated no adverse effect on benthic organisms. The normalized total metal concentrations in this area were below the established SQG values for As, Cd, Cu, Ni, Pb, Zn, and Hg, namely respectively 21.3, 0.8, 84.6, 36.0, 34.6, 440.9 mg/kg dry weight, and 49.3 μg/kg dry weight on sand and calcium carbonate free with 1 % total organic carbon basis, suggesting low metal toxicity. This study provides locality adapted SQG values for supporting sediment quality management specifically in Bandon Bay, potentially serving as a model for other coastal areas.

MeHg production in eutrophic lakes: Focusing on the roles of algal organic matter and iron-sulfur-phosphorus dynamics

The mechanisms by which eutrophication affects methylmercury (MeHg) production have not been comprehensively summarized, which hinders accurately predicting the MeHg risk in eutrophic lakes. In this review, we first discussed the effects of eutrophication on biogeochemical cycle of mercury (Hg). Special attentions were paid to the roles of algal organic matter (AOM) and iron (Fe)-sulfur (S)-phosphorus (P) dynamics in MeHg production. Finally, the suggestions for risk control of MeHg in eutrophic lakes were proposed. AOM can affect in situ Hg methylation by stimulating the abundance and activities of Hg methylating microorganisms and regulating Hg bioavailability, which are dependent on bacteria-strain and algae species, the molecular weight and composition of AOM as well as environmental conditions (e.g., light). Fe-S-P dynamics under eutrophication including sulfate reduction, FeS formation and P release could also play crucial but complicated roles in MeHg production, in which AOM may participate through influencing the dissolution and aggregation processes, structural order and surface properties of HgS nanoparticles (HgS_NP). Future studies should pay more attention to the dynamics of AOM in responses to the changing environmental conditions (e.g., light penetration and redox fluctuations) and how such variations will subsequently affect MeHg production. The effects of Fe-S-P dynamics on MeHg production under eutrophication also deserve further investigations, especially the interactions between AOM and HgS_NP. Remediation strategies with lower disturbance, greater stability and less cost like the technology of interfacial O₂ nanobubbles are urgent to be explored. This review will deepen our understanding of the mechanisms of MeHg production in eutrophic lakes and provide theoretical guidance for its risk control.

Developing ecological risk assessment of metals released from sediment based on sediment quality guidelines linking with the properties: A case study for Kaohsiung Harbor

This study aimed to introduce sediment properties (total organic carbon (TOC), acid-volatile sulfides (AVS), particle size distribution) into sediment quality guideline-based risk quotients to assess the potential toxicity of metals (Ni, Cu, Zn, Cr, Cd, and Pb) released from sediments. Sediment was collected at three times points in 20 sampling sites in Kaohsiung Harbor. The Microtox® toxicity test was used to assess the sediment toxicity and the relationship between sediment toxicity and risk quotient estimated based on the metal concentration was constructed. To improve the toxicity prediction and modify the risk quotient according to the sediment properties, stepwise multiple linear regression (MLR) models that have been tested over wide ranges of TOC, AVS, and particle size distribution to determine the key sediment properties. Common multimetal indices, including the pollution load index, modified degree of contamination index, Nemerow pollution index, potential ecological risk index, and total toxic risk index, were compared with sediment toxicity to evaluate the degrees of correlation. By modifying the relationship between metal toxicity and the risk quotient by including TOC and AVS, the prediction showed that sediments in Kaohsiung Harbor were generally of slight acute toxicity to acute toxicity to organisms, with sampling sites near an industrial zone showing a higher probability of high acute toxicity. In particular, the acute risk of adverse effects on aquatic organisms from sediments in the Salt River estuary was significantly higher than that at other sites, which was consistent with the results of assessment based on the multimetal indices. This study suggests that the MLR-based approach may facilitate the adoption of updated site-specific metals standards that more accurately account for the parameters affecting metal bioavailability than metal concentration standard alone.

Ecological risks assessment of sulfur and heavy metals in sediments in a historic mariculture environment, North Yellow Sea

The environment behaviors of sulfur and heavy metals in sediments are closely related to sediment aging in mariculture area. In this study, the distributions and ecological risks of reduced inorganic sulfur (RIS) and heavy metals were investigated, along with the relationships between different occurrences of RIS and heavy metals. The results indicated that the adequate organic matter in mariculture sediments significantly enhanced the accumulation of acid volatile sulfur (AVS) compared to the control area. In shellfish farming area, biological sedimentation contributed to accumulation of AVS. The chromium (II)-reducible sulfur (CRS) was the main component of RIS in mariculture area. The environmental risks of heavy metals in mariculture area presented low levels. Principal component analysis (PCA) showed that distribution of Cu closely related to mariculture activities compared to other heavy metals. For ecological risks of heavy metals, the ratio of ∑(acid-soluble fraction (F1) + reducible fraction (F2) + oxidizable fraction (F3))/AVS was the appropriate index rather than conventional simultaneous extraction of heavy metals (SEM)/AVS, because SEM/AVS would overestimate the toxicity of heavy metals. AVS/RIS ratios significantly positively correlated with Pb (F2/(F1 + F2 + F3 + residual fraction (F4)), F2/∑F), Pb (F3/∑F), and Zn (F3/∑F), while significantly negatively correlated with Pb (F4/∑F) and Cu (F1/∑F). These results indicated that the accumulation of AVS during the mariculture process was conducive to the formation of F2 and F3 of Pb, and F3 of Zn, conversely to the formation for F4 of Pb and F1 of Cu, because it was opposite to the accumulation of CRS.

Reconstructing Long-Term Changes in Avian Populations Using Lake Sediments: Opening a Window Onto the Past

The lack of long-term monitoring data for many wildlife populations is a limiting factor in establishing meaningful and achievable conservation goals. Even for well-monitored species, time series are often very short relative to the timescales required to understand a population’s baseline conditions before the contemporary period of increased human impacts. To fill in this critical information gap, techniques have been developed to use sedimentary archives to provide insights into long-term population dynamics over timescales of decades to millennia. Lake and pond sediments receiving animal inputs (e.g., feces, feathers) typically preserve a record of ecological and environmental information that reflects past changes in population size and dynamics. With a focus on bird-related studies, we review the development and use of several paleolimnological proxies to reconstruct past colony sizes, including trace metals, isotopes, lipid biomolecules, diatoms, pollen and non-pollen palynomorphs, invertebrate sub-fossils, pigments, and others. We summarize how animal-influenced sediments, cored from around the world, have been successfully used in addressing some of the most challenging questions in conservation biology, namely: How dynamic are populations on long-term timescales? How may populations respond to climate change? How have populations responded to human intrusion? Finally, we conclude with an assessment of the current state of the field, challenges to overcome, and future potential for research.

Sediment quality of the Bohai Sea and the northern Yellow Sea indicated by the results of acid-volatile sulfide and simultaneously extracted metals determinations

The surface sediments from the Bohai Sea (BS) and the northern Yellow Sea (NYS) were analyzed for acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) to assess the sediment quality. The results indicated that >60% of the samples were found to have possible adverse effects on aquatic life in the BS based on the difference between the concentrations of AVS ([AVS]) and SEM ([SEM]), and the corresponding percentage in the NYS was <25%. Nevertheless, there was no indication of adverse effects for all the BS and the NYS samples when the total organic carbon (TOC) concentration was introduced in the sediment quality evaluation with [AVS] and [SEM]. The grain size composition, TOC, water content and pH all had significant influence on the distribution of [SEM] and the [SEM]/[AVS] ratios; while, in contrast, the distribution of [AVS] could be mainly determined by the redox condition of sediment.

Advances in heavy metal removal by sulfate-reducing bacteria

Industrial development has led to generation of large volumes of wastewater containing heavy metals, which need to be removed before the wastewater is released into the environment. Chemical and electrochemical methods are traditionally applied to treat this type of wastewater. These conventional methods have several shortcomings, such as secondary pollution and cost. Bioprocesses are gradually gaining popularity because of their high selectivities, low costs, and reduced environmental pollution. Removal of heavy metals by sulfate-reducing bacteria (SRB) is an economical and effective alternative to conventional methods. The limitations of and advances in SRB activity have not been comprehensively reviewed. In this paper, recent advances from laboratory studies in heavy metal removal by SRB were reported. Firstly, the mechanism of heavy metal removal by SRB is introduced. Then, the factors affecting microbial activity and metal removal efficiency are elucidated and discussed in detail. In addition, recent advances in selection of an electron donor, enhancement of SRB activity, and improvement of SRB tolerance to heavy metals are reviewed. Furthermore, key points for future studies of the SRB process are proposed.