Jen-How Huang

Impacts of Shewanella putrefaciens strain CN-32 cells and extracellular polymeric substances on the sorption of As(V) and As(III) on Fe(III)-(hydr)oxides.

We investigated the effects of Shewanella putrefaciens cells and extracellular polymeric substances on the sorption of As(III) and As(V) to goethite, ferrihydrite, and hematite at pH 7.0. Adsorption of As(III) and As(V) at solution concentrations between 0.001 and 20 μM decreased by 10 to 45% in the presence of 0.3 g L(-1) EPS, with As(III) being affected more strongly than As(V). Also, inactivated Shewanella cells induced desorption of As(V) from the Fe(III)-(hydr)oxide mineral surfaces. ATR-FTIR studies of ternary As(V)-Shewanella-hematite systems indicated As(V) desorption concurrent with attachment of bacterial cells at the hematite surface, and showed evidence of inner-sphere coordination of bacterial phosphate and carboxylate groups at hematite surface sites. Competition between As(V) and bacterial phosphate and carboxylate groups for Fe(III)-(oxyhydr)oxide surface sites is proposed as an important factor leading to increased solubility of As(V). The results from this study have implications for the solubility of As(V) in the soil rhizosphere and in geochemical systems undergoing microbially mediated reduction and indicate that the presence of sorbed oxyanions may affect Fe-reduction and biofilm development at mineral surfaces.

Impact of Microorganisms on Arsenic Biogeochemistry: A Review

Microorganisms are abundant in many surface and near-surface geochemical environments. They interact with arsenic through a variety of mechanisms, including sorption, mobilisation, precipitation and redox and methylation transformation; sometimes, this is to their benefit, while other times it is to their detriment, substantially affecting the fate and transport of arsenic in the environment. Here, an attempt was made to review the current state of knowledge concerning microbial influences on arsenic transformation and retention processes at the water–solid interface with the goal to elucidate the ability of microorganisms to react with arsenic, and to quantify the role of microorganisms in the biogeochemical arsenic cycle. Such knowledge is indispensable for comprehensive understanding arsenic behaviour in the environment and support accurate assessment of the threat of arsenic contamination to human and environmental health, as well as for the development of novel technologies for arsenic bioremediation.

Influence of arsenate adsorption to ferrihydrite, goethite, and boehmite on the kinetics of arsenate reduction by Shewanella putrefaciens strain CN-32.

The kinetics of As(V) reduction by Shewanella putrefaciens strain CN-32 was investigated in suspensions of 0.2, 2, or 20 g L(-1) ferrihydrite, goethite, or boehmite at low As (10 μM) and lactate (25 μM) concentrations. Experimental data were compared with model predictions based on independently determined sorption isotherms and rates of As(V) desorption, As(III) adsorption, and microbial reduction of dissolved As(V), respectively. The low lactate concentration was chosen to prevent significant Fe(III) reduction, but still allowing complete As(V) reduction. Reduction of dissolved As(V) followed first-order kinetics with a 3 h half-life of As(V). Addition of mineral sorbents resulted in pronounced decreases in reduction rates (32-1540 h As(V) half-life). The magnitude of this effect increased with increasing sorbent concentration and sorption capacity (goethite < boehmite < ferrihydrite). The model consistently underestimated the concentrations of dissolved As(V) and the rates of microbial As(V) reduction after addition of S. putrefaciens (∼5 × 10(9) cells mL(-1)), suggesting that attachment of S. putrefaciens cells to oxide mineral surfaces promoted As(V) desorption and thereby facilitated As(V) reduction. The interplay between As(V) sorption to mineral surfaces and bacterially induced desorption may thus be critical in controlling the kinetics of As reduction and release in reducing soils and sediments.

Leaching characteristics of vanadium in mine tailings and soils near a vanadium titanomagnetite mining site

A series of column leaching experiments were performed to understand the leaching behaviour and the potential environmental risk of vanadium in a Panzhihua soil and vanadium titanomagnetite mine tailings. Results from sequential extraction experiments indicated that the mobility of vanadium in both the soil and the mine tailings was low, with <1% of the total vanadium readily mobilised. Column experiments revealed that only <0.1% of vanadium in the soil and mine tailing was leachable. The vanadium concentrations in the soil leachates did not vary considerably, but decreased with the leachate volume in the mine tailing leachates. This suggests that there was a smaller pool of leachable vanadium in the mine tailings compared to that in the soil. Drought and rewetting increased the vanadium concentrations in the soil and mine tailing leachates from 20μgL(-1) to 50-90μgL(-1), indicating the potential for high vanadium release following periods of drought. Experiments with soil columns overlain with 4, 8 and 20% volume mine tailings/volume soil exhibited very similar vanadium leaching behaviour. These results suggest that the transport of vanadium to the subsurface is controlled primarily by the leaching processes occurring in soils.

Speciation of vanadium in Chinese cabbage (Brassica rapa L.) and soils in response to different levels of vanadium in soils and cabbage growth.

This study highlights the accumulation and speciation of vanadium in Chinese cabbage (Brassica rapa L.) in relation to the speciation of soil vanadium with pot experiments at 122-622mgVkg(-1) by spiking NH4VO3. Cabbage planting decreased the bioavailable and residual vanadium based on sequential extraction, leading to enrichment of oxalate-extractable vanadium in soils. The biomass production increased with increasing concentrations of soil vanadium from 122 to 372mgVkg(-1), probably due to the increasing nitrogen availability and low vanadium availability in our soils with a consequent low vanadium toxicity. Although the concentrations of root vanadium (14.4-24.9mgVkg(-1)) related positively with soil vanadium, the bio-dilution alleviated the increase of leaf vanadium (2.1-2.7mgVkg(-1)). The predominance of vanadium(IV) in leaves (∼60-80% of total vanadium) indicates bio-reduction of vanadium in Chinese cabbage, since the mobile vanadium in oxic soils was usually pentavalent. Approximately 15-20% of the leaf vanadium was associated with recalcitrant leaf tissues. The majority of leaf vanadium was water and ethanol extractable, which is considered mobile and may cause more toxic effects on Chinese cabbage.

Readily available phosphorous and nitrogen counteract for arsenic uptake and distribution in wheat ( Triticum aestivum L.)

Elevated arsenic content in food crops pose a serious human health risk. Apart from rice wheat being another main food crop is possibly cultivated on contaminated sites. But for wheat uptake mechanisms are not entirely understood especially with regard to nutrient fertilization and different moisture regimes taking into account heavy rainfall events due to climate change. Here we show that especially higher P-fertilization under changing redox conditions may enhance arsenic uptake. This counteracts with higher N-fertilization reducing arsenic transfer and translocation into aboveground plant parts for both higher P-fertilization and reducing soil conditions. Arsenic speciation did not change in grain but for leaves P-fertilization together with reducing conditions increased the As(V) content compared to other arsenic species. Our results indicate important dependencies of nutrient fertilization, moisture conditions and substrate type on As accumulation of wheat as one of the most important crop plants worldwide with implications for agricultural practices.

Impact of Fish Farming on Phosphorus in Reservoir Sediments

Fish farming has seriously influenced the aquatic environment in Sancha reservoir in SW China since 1985 and has been strongly restricted since 2005. Thus, phosphorus speciation in a sediment core dated between 1945 and 2010 at cm-resolution and in surface sediments from Sancha reservoir may allow us track how fish farming impacts phosphorus dynamics in lake sediments. Fish farming shifts the major binding forms of phosphorus in sediments from organic to residual phosphorus, which mostly originated from fish feed. Sorption to metal oxides and association with organic matters are important mechanisms for phosphorus immobilisation with low fish farming activities, whereas calcium-bound phosphorous had an essential contribution to sediment phosphorus increases under intensive fish framing. Notwithstanding the shifting, the aforementioned phosphorus fractions are usually inert in the lake environment, therefore changing phosphorus mobility little. The use of fish feed and water-purification reagents, the most important additives for fish farming, introduce not only phosphorus but also large amounts of sand-sized minerals such as quartz into the lake, to which phosphorus weakly sorbs. The sand-sized minerals as additional sorbents increase the pool of easily mobilisable phosphorus in sediments, which will slow down the recovery of reservoir water due to its rapid re-mobilisation.

Arsenic trophodynamics along the food chains/webs of different ecosystems: a review

ABSTRACT In drinking water, arsenic (As) food chain accumulation may pose a risk to human health. An attempt was made to synthesise the published information concerning As trophic transfer along the food chain/web of various marine, freshwater, and terrestrial ecosystems. Some investigations included As speciation. Further objectives were to outline the factors potentially influencing As trophodynamics and to understand the consequence of As trophic transfer in the environment.

Metal biogeochemistry in constructed wetlands based on fluviatile sand and zeolite- and clinopyroxene-dominated lava sand

For the first time, speciation of Fe, Mn, Zn, Ni, Cu and Pb was determined along the profiles of 8 constructed wetlands (CWs) consisting of fluviatile sand (Fluv), clinopyroxene-dominated lava sand (Cl-LS) and zeolite-dominated lava sand (Ze-LS), aiming at quantifying metal behaviour in CWs and the impact caused by different filter materials. With the exception of Mn, which underwent reductive dissolution, CWs were sinks for the studied metals. Metal accumulation rates differed in the following order: Ze-LS ≥ Cl-LS > Fluv CWs, reflecting the highest metal adsorption capacity and the lowest hydraulic conductivity of Ze-LS. Sequential extraction data indicated the highest metal mobility (readily mobilised and adsorbed fractions summing up to ~60%) in Fluv CWs, implying a higher risk of metal release into adjacent environments if Fluv from CWs will be improperly disposed after usage. Zinc and Ni were transported into the deeper CW layers to a larger extent than Cu and Pb, reflecting adsorption affinity to all filter materials in the order of Pb > Cu > Zn > Ni. Therefore, understanding metal speciation and mobility in such materials is crucial when they are considered for application as filters in CWs.