Diane Purchase

The treatment of metals in urban runoff by constructed wetlands

Abstract The use of constructed wetlands for the treatment of domestic wastewater is now well established in the UK and their ability to treat a range of industrial wastewaters is now being investigated. However, their ability to treat urban runoff is relatively untested despite the fact that this application could have important environmental and operational benefits, in both industrial and developing countries. In response to this, the Environment Agency have developed constructed wetland treatment systems at two selected sites in south-east England, both of which receive large volumes of urban runoff. The sites are located at Brentwood and Dagenham and were completed in April 1995. Water and sediment samples have been collected at bi-monthly intervals at each site since October 1995 and analysed for a range of parameters including the total concentrations of six trace metals — cadmium, copper, nickel, chromium, lead and zinc. Similar analysis has been carried out on plants collected from both sites in the spring of 1997. Results show a wide variation in pollutant levels, reflecting the highly variable quality characteristics of urban runoff. Mean removal efficiencies of metals in the water vary between sites in dry weather conditions, with maximum removal efficiencies being recorded at the Dagenham wetland during a storm event. Analysis of plant tissues indicates that the reeds bioaccumulate trace metals and that metal uptake is greatest in the roots. Sediment metal concentrations are typical of a site receiving urban runoff. At both sites the highest sediment concentrations are consistently recorded in samples collected from the settlement tanks.

Consideration of the bioavailability of metal/metalloid species in freshwaters: experiences regarding the implementation of biotic ligand model-based approaches in risk assessment frameworks

After the scientific development of biotic ligand models (BLMs) in recent decades, these models are now considered suitable for implementation in regulatory risk assessment of metals in freshwater bodies. The BLM approach has been described in many peer-reviewed publications, and the original complex BLMs have been applied in prospective risk assessment reports for metals and metal compounds. BLMs are now also recommended as suitable concepts for the site-specific evaluation of monitoring data in the context of the European Water Framework Directive. However, the use is hampered by the data requirements for the original BLMs (about 10 water parameters). Recently, several user-friendly BLM-based bioavailability software tools for assessing the aquatic toxicity of relevant metals (mainly copper, nickel, and zinc) became available. These tools only need a basic set of commonly determined water parameters as input (i.e., pH, hardness, dissolved organic matter, and dissolved metal concentration). Such tools seem appropriate to foster the implementation of routine site-specific water quality assessments. This work aims to review the existing bioavailability-based regulatory approaches and the application of available BLM-based bioavailability tools for this purpose. Advantages and possible drawbacks of these tools (e.g., feasibility, boundaries of validity) are discussed, and recommendations for further implementation are given.

Effects of temperature on metal tolerance and the accumulation of Zn and Pb by metal-tolerant fungi isolated from urban runoff treatment wetlands

Aims:  To investigate the ability of two fungi to accumulate Zn and Pb, the effect of temperature on their metal tolerance and possible mechanisms involved in metal accumulation.

Survival and nodulating ability of indigenous and inoculated Rhizobium leguminosarum biovar trifolii in sterilized and unsterilized soil treated with sewage sludge.

Rhizobium leguminosarum biovar trifolii was detected in soil from 41 of 47 plots, within nine sewage sludge-treated sites with different soil characteristics and heavy metal contents. However, although population size varied widely, there was no consistent correlation with soil heavy metal concentration. Indigenous populations in 20 plots within four selected sites retained their ability to induce effective nodule formation after incubation of soil in the dark for 165 days. In sterilized (γ-irradiated) soil, Rhizobium survival varied from 0.01% to 95% depending on the soil sample and strain used. Metal-resistant strains with non-mucoid colonies survived less well than mucoid metal-sensitive strains.

Effects of arsenate (As5+) on growth and production of glutathione (GSH) and phytochelatins (PCs) in Chlorella vulgaris

The effect of arsenate (As5+) on growth and chlorophyll a production in Chlorella vulgaris, its removal by C. vulgaris and the role of glutathione (GSH) and phytochelatins (PCs) were investigated.C. vulgaris was tolerant to As5+ at up to 200 mg/L and was capable of consistently removing around 70% of the As5+ present in growth media over a wide range of exposure concentrations. Spectral analysis revealed that PCs and their arsenic-combined complexes were absent, indicating that the high bioaccumulation and tolerance to arsenic observed was not due to intracellular chelation. In contrast, GSH was found in all samples ranging from 0.8 mg/L in the control to 6.5mg/L in media containing 200 mg/L As5+ suggesting that GSH plays a more prominent role in the detoxification of As5+ in C. vulgaris than PC. At concentrations below 100 mg/L cell surface binding and other mechanisms may play the primary role in As5+ detoxification, whereas above this concentration As5+ begins to accumulate inside the algal cells and activates a number of intracellular cell defense mechanisms, such as increased production of GSH.The overall findings complement field studies which suggest C. vulgaris as an increasingly promising low cost As phytoremediation method for developing countries.

Enzymatic Formulation Capable of Degrading Scrapie Prion under Mild Digestion Conditions

The prion agent is notoriously resistant to common proteases and conventional sterilisation procedures. The current methods known to destroy prion infectivity such as incineration, alkaline and thermal hydrolysis are harsh, destructive, environmentally polluting and potentially hazardous, thus limit their applications for decontamination of delicate medical and laboratory devices, remediation of prion contaminated environment and for processing animal by-products including specified risk materials and carcases. Therefore, an environmentally friendly, non-destructive enzymatic degradation approach is highly desirable. A feather-degrading Bacillus licheniformis N22 keratinase has been isolated which degraded scrapie prion to undetectable level of PrPSc signals as determined by Western Blot analysis. Prion infectivity was verified by ex vivo cell-based assay. An enzymatic formulation combining N22 keratinase and biosurfactant derived from Pseudomonas aeruginosa degraded PrPSc at 65°C in 10 min to undetectable level -. A time-course degradation analysis carried out at 50°C over 2 h revealed the progressive attenuation of PrPSc intensity. Test of residual infectivity by standard cell culture assay confirmed that the enzymatic formulation reduced PrPSc infectivity to undetectable levels as compared to cells challenged with untreated standard scrapie sheep prion (SSBP/1) (p-value = 0.008 at 95% confidence interval). This novel enzymatic formulation has significant potential application for prion decontamination in various environmentally friendly systems under mild treatment conditions.

Enhanced determination of As–phytochelatin complexes in Chlorella vulgaris using focused sonication for extraction of water-soluble species

The most challenging areas in the analysis of As–GS/PC complexes are their extraction from small amounts of biological material and the maintenance of their stability during HPLC separation. Focused sonication was used to extract these complexes from Chlorella vulgaris and the integrity of such complexes was determined by HPLC online with simultaneous HR-ICP-MS and ES-MS/MS detection. Water soluble arsenic species were extracted with an improved 71.1% (SE 0.78) efficiency and much reduced extraction times (30 s) allowing the determination of unstable arsenic phytochelatin (PC) and glutathione (GS) species in small biomass making the method particularly well-suited for cell cultures. Here, it was found that C. vulgaris produces the following intact phytochelatins and homo-phytochelatins (with Ala and desGly instead of Gly) complexes when cells are exposed to As(III): As(III)–PC2, GS–As(III)–PC2, As(III)–(PC2)2, MMA(III)–PC2, As(III)–PC3, As(III)–PC4, As(III)–γ-(Glu–Cys)3–Ala, GS–As(III)–γ-(Glu–Cys)2–Ala, As(III)–γ-((Glu–Cys)2)2–Ala, MMA(III)–γ-(Glu–Cys)2–Ala, As(III)–γ-(Glu–Cys)2, GS–As(III)–γ-(Glu–Cys)2. When the alga was exposed to DMA, only DMASV–GS was found. In contrast, cells did not produce any complex when exposed to As(V). It is the first time that, as a result of the newly developed extraction method using sonication, such complexes have been identified in Chlorella vulgaris exposed to arsenic and their intact arsenic homo-phytochelatins have been reported in any organism.

Application of Microalgae and Fungal-Microalgal Associations for Wastewater Treatment

Microalgal applications represent potential green and smart solutions for the treatment of different types of wastewaters. Fungal–microalgal associations are gaining increasing attention as a low cost and an efficient strategy for the concentration of microalgal cells and the additive contribution of their components to the production of value-added chemicals and biofuels. In spite of the obvious attractiveness of microalgal-based bioremediation, there are still some challenges that can affect their economic viability. The costs associated with removing microalgal cells from treated wastewaters and harvesting them for the production of value-added products can account for up to 50 % of the total cost. With both biological components known to be involved in absorption of key nutrients and microelements from growing environments, fungal–microalgal consortiums show cumulative and synergistic effects on wastewater treatment efficiencies. This review covers the potential of microalgal representatives and their association with filamentous fungi for the treatment of different types of wastewaters and conversion of generated biomass into value-added chemicals and biofuels.

The mechanisms of detoxification of As(III), dimethylarsinic acid (DMA) and As(V) in the microalga Chlorella vulgaris

The response of Chlorella vulgaris when challenged by As(III), As(V) and dimethylarsinic acid (DMA) was assessed through experiments on adsorption, efflux and speciation of arsenic (reduction, oxidation, methylation and chelation with glutathione/phytochelatin [GSH/PC]). Our study indicates that at high concentrations of phosphate (1.62mM of HPO4(2-)), upon exposure to As(V), cells are able to shift towards methylation of As(V) rather than PC formation. Treatment with As(V) caused a moderate decrease in intracellular pH and a strong increase in the concentration of free thiols (GSH). Passive surface adsorption was found to be negligible for living cells exposed to DMA and As(V). However, adsorption of As(III) was observed to be an active process in C. vulgaris, because it did not show saturation at any of the exposure periods. Chelation of As(III) with GS/PC and to a lesser extent hGS/hPC is a major detoxification mechanism employed by C. vulgaris cells when exposed to As(III). The increase of bound As-GS/PC complexes was found to be strongly related to an increase in concentration of As(III) in media. C. vulgaris cells did not produce any As-GS/PC complex when exposed to As(V). This may indicate that a reduction step is needed for As(V) complexation with GSH/PC. C. vulgaris cells formed DMAS(V)-GS upon exposure to DMA independent of the exposure period. As(III) triggers the formation of arsenic complexes with PC and homophytochelatins (hPC) and their compartmentalisation to vacuoles. A conceptual model was devised to explain the mechanisms involving ABCC1/2 transport. The potential of C. vulgaris to bio-remediate arsenic from water appeared to be highly selective and effective without the potential hazard of reducing As(V) to As(III), which is more toxic to humans.

Mycoremediation of Heavy Metal/Metalloid-Contaminated Soil: Current Understanding and Future Prospects

In natural environments, heavy metals and metalloids are widely dispersed as a consequence of anthropogenic (e.g. mining) and geological (e.g. volcanic eruption) activities. The toxicity of these metals/metalloids could adversely affect the ecosystem as well as causing major human health concerns. Mycoremediation (remediation by fungi) has received attention from many researchers as an alternative to conventional chemical and physical methods in removing toxic metals and metalloids. A number of regulatory mechanisms to control the concentrations and counteract the toxicity of these pollutants have been observed in fungi. These mechanisms include: (i) precipitation or binding to cell surface materials, (ii) intracellular chelation and precipitation, (iii) biotransformation and (iv) control of membrane transport systems. This chapter examines the use of fungi to bioremediate metals and metalloids and their detoxification mechanisms, with special focus on an extremophilic fungus, Acidomyces acidophilus, isolated from a disused tin mine in the UK, to illustrate some of the mechanisms involved. Future biotechnological and nanotechnological prospects of metal/metalloids bioremediation using fungi are also discussed.