I. D. Pulford

Phytoremediation of heavy metal-contaminated land by trees—a review

This paper reviews the potential for using trees for the phytoremediation of heavy metal-contaminated land. It considers the following aspects: metal tolerance in trees, heavy metal uptake by trees grown on contaminated substrates, heavy metal compartmentalisation within trees, phytoremediation using trees and the phytoremediation potential of willow (Salix spp.).

Heavy metal uptake by willow clones from sewage sludge-treated soil: the potential for phytoremediation.

ABSTRACT Willow (Salix spp.) has shown potential for use in the phytoremediation of soil contaminated with heavy metals. In particular, it can be grown in short rotation coppice systems to produce biomass that can be used for energy production. Twenty different species or varieties of willow, grown over 2 years (1995 to 1997) on a soil that was highly contaminated with heavy metals due to long-term sewage sludge disposal, showed considerable variation in survival, biomass production and metal uptake. The willows could be divided into two groups after the first harvest. One group had relatively low Ni and Cu in the bark and high Cd and Zn in the wood, with a good survival rate and biomass production. This group partitioned Cu, Cd, and Zn into the wood tissue from the bark, whereas Ni was excluded. The second group had relatively high Ni and Cu in the bark and low Cd and Zn in the wood and performed poorly in terms of survival and biomass production. Of the 20 types of willow used, 11 showed potential for use in phytoremediation, combining good survival and biomass production with high metal uptake. Of the others, 2 failed to survive until the second harvest and the other 7 had very poor survival rates.

Waste materials – catalytic opportunities: an overview of the application of large scale waste materials as resources for catalytic applications

In this overview, we present examples of the use of high volume waste materials in catalysis or for catalyst synthesis. Waste materials derived from both industrial and biological sources have attracted interest and this is briefly summarized. The materials described include red mud, aluminium dross, fly ash, blast furnace slag, rice husk and various kinds of shell.

Distributions, inventories and isotopic composition of lead in 210Pb-dated peat cores from contrasting biogeochemical environments: Implications for lead mobility

Abstract The use of concentration profiles of lead and other contaminant metals in 210 Pb-dated ombrotrophic peat cores for reconstruction of historical trends in atmospheric deposition has become relatively well established. However, uncertainty remains over the validity of the assumption of post-depositional immobility of lead in peats. In particular, a number of studies have suggested that in saturated peat systems, lead is subject to diagenetic remobilisation and redistribution, with the result that 210 Pb and lead profiles do not provide a historical record of deposition. Results are presented here for lead concentrations, inventories and stable isotope ratios and for 210 Pb activities in two peat cores from locations close to the Glasgow industrial area in west-central Scotland. Contrasting biogeochemical conditions prevailed at the two sampling sites, with one being unsaturated and ombrotrophic while the other was saturated and minerotrophic. The results for the ombrotrophic peat core were compatible with information from other peat and lake sediment core studies, data for archived herbage samples and with known historical trends both in industrial activity and in the use of lead as an additive to petrol, giving a high degree of confidence in the 210 Pb chronology and implied record of deposition. This provides strong support for the suggestion that lead is immobile in such systems. In contrast, the lead concentration profile and stable isotope data for the minerotrophic peat provided apparent temporal variations that were inconsistent with other studies and known historical trends, confirming that the saturated peat core did not provide a record of atmospheric deposition. This observation is consistent with the suggestion that lead is subject to diagenetic remobilisation and redistribution in saturated peats.

Influence of waterlogging and lime or organic matter additions on the distribution of trace metals in an acid soil

SummaryA study has been made of the influence of waterlogging on the distribution of trace metals between the various reservoirs in which they are held in a soil. Selective extractants have been used to remove metals held in 4 ways: soil solution and exchangeable; specifically adsorbed by inorganic sites; adsorbed or chelated by organic sites; adsorbed onto oxide surfaces.Waterlogging over a period of 16 weeks resulted in the release of both manganese and iron from the organic — and oxide — bound reservoirs to the soluble, exchangeable and inorganic reservoirs. Addition of both 1% dried grass (as an actively decomposing organic material) and 1% CaCO3 to the soil resulted in an acceleration of the metal redistribution.For manganese, selective extraction methods accounted for the distribution of all the metal in the reservoirs studied. In the case of iron however, there appeared to be some release from a reservoir not being extracted.

Investigation of contaminant metal dispersal from a disused mine site at Tyndrum, Scotland, using concentration gradients and stable Pb isotope ratios

Results are presented for a study of Pb and Zn concentrations and stable Pb isotope ratios for mining wastes, river sediments and 210Pb-dated peat cores from the vicinity of a derelict Pb/Zn mine at Tyndrum in central Scotland. Mining was carried out at Tyndrum between 1741 and 1862 and the original waste dumps were reworked between 1916 and 1925. Little remains of the original buildings and workings and the contemporary distribution and dispersion pathways of the residual waste are poorly defined. The mine and ore processing waste dumps were readily identified as highly polluted, barren areas, with concentrations of up to 21 and 3.4% Pb and Zn, respectively. The Pb in the waste was characterised by a 206Pb/207Pb atom ratio of 1.146±0.004 and a 208Pb/207Pb ratio of 2.432±0.007. Significant quantities of waste were also found along riverbanks and in river channel sediments in the vicinity of the mine, with concentrations of up to 5.22% Pb and 2.35% Zn. Concentrations of Pb and Zn in river channel sediments decreased markedly with increasing distance downriver from the mining area. However, the decrease in Pb concentrations in the <53 μm fraction was less pronounced, with a relatively high concentration of 0.076% being observed at a distance of 6.5 km from the mine, suggesting significant fluvial transport of this size fraction of waste. The stable Pb isotopic characteristics of the river sediments were consistent with the mine waste being the dominant source, along with minor inputs from local bedrock and vehicle exhaust emissions. The peat core data revealed high levels of Pb deposition throughout the period of the mining operation and very high levels of input in the early 20th century, almost certainly as a result of the reworking of the former waste dumps. As with the river sediments, the isotopic characteristics of the Pb in the peat cores were consistent with a dominant input from the mine waste and minor contributions from bedrock and vehicle exhaust emissions. The results suggest that waste from the mining operation has been a significant source of contaminant heavy metals for several hundred years and continues to be so. The apparent fluvial transport of Pb from the mine site is consistent with previous work suggesting that Tyndrum mine waste is the probable origin of anomalously high levels of Pb deposited in the sediments of Loch Tay, some 25 km to the east. The study highlights the utility of stable Pb isotope analyses in the investigation of sources and environmental dispersion of contaminant Pb.

Screening of willow species for resistance to heavy metals: Comparison of performance in a hydroponics system and field trials

Abstract The aim of this study was to ascertain whether metal resistance in willow (Salix) clones grown in a hydroponics screening test correlated with data from the same clones grown independently in a field trial. If so, results from a short‐term, glasshouse‐based system could be extrapolated to the field, allowing rapid identification of willows suitable for planting in metal‐contaminated substrates without necessitating long‐term field trials. Principal Components Analysis was used to show groups of clones and to assess the relative importance of the parameters measured in both the hydroponics system and the field; including plant response factors such as increase in stem height, as well as metal concentrations in plant tissues. The clones tested fell into two distinct groups. Salix viminalis clones and the basket willow Black Maul (S. triandra) were less resistant to elevated concentrations of heavy metals than a group of hardier clones, including S. burjatica ’Germany,’ S.x dasyclados, S. Candida and S. spaethii. The more resistant clones produced more biomass in the glasshouse and field, and had higher metal concentrations in the wood. The less resistant clones had greater concentrations of Cu and Ni in the bark, and produced less biomass in the glasshouse and field. Significant relationships were found between the response of the same clones grown the in short‐term glasshouse hydroponics system and in the field.

A historical record of atmospheric depositional fluxes of contaminants in west-central Scotland derived from an ombrotrophic peat core

An ombrotrophic peat core from west-central Scotland was subjected to multi-element analysis and 210Pb dating in order to estimate historical trends in atmospheric deposition of contaminants. The inferred depositional flux of ash (total inorganic material) exhibited small, transient increases from as early as the mid 18th century, followed by a larger increase from the mid 19th century to a pronounced maximum approx. 1960. A significant decrease was observed from the peak ash deposition of 29.2 g m−2 year−1 to the contemporary level of 11 g m−2 year−1, although this is still an order of magnitude greater than the pre-industrial value of 1 g m−2 year−1. Depositional fluxes of a wide range of elements (scandium, copper, arsenic, antimony, samarium, cobalt, bromine, lanthanum and lead) also exhibited major increases from the mid 19th century and peak values in the mid 20th century (approx. 1940–1950). Aluminium, cerium and bromine also showed evidence of transiently increased deposition as early as the mid 18th century. Normalisation of the concentrations of individual elements to that of aluminium confirmed that the peak depositional fluxes in the mid 20th century were not due to increased re-deposition of soil minerals from the atmosphere, but were attributable to other sources of contamination including heavy industry, coal burning and vehicle exhaust emission. Nevertheless, re-deposited soil minerals were estimated to constitute an important fraction of the ash, with peak input at the start of the 20th century and subsequent deposition at a relatively constant level, about half that of the maximum flux. Excellent agreement was observed between the inferred trends in contaminant deposition and the known history of industrial development of the area.

Hydrogen production from methane in the presence of red mud –making mud magnetic

Red mud, a waste product of the aluminium industry, has been shown to possess significant activity for the decomposition of methane, a by-product of oil refining and landfill, generating hydrogen and a carbon containing magnetic material. It is envisaged that the latter material could be of interest in terms of downstream purification processes and that its magnetic properties may facilitate separation/handling. In this way, two valuable end products can be generated from two waste products.

Chitosan as a potential amendment to remediate metal contaminated soil — A characterisation study

The potential of chitosan, a fishery waste-based material, as a soil amendment to clean-up metal contaminated soil was investigated. Chitosan was treated using glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) as cross-linking reagents to enhance its chemical stability in acidic media and to improve its physical properties. Cross-linking treatment had significant effects on chitosan surface area, pore diameter, surface morphology and crystallinity. Interaction with Ag(I), Pb(II) and Cu(II) decreased the crystallinity of the materials and changed their surface morphology significantly. FTIR analysis confirmed that N and O atoms served as binding sites for the metal ions. Chitosan and treated chitosans were able to bind metal ions, even in the presence of K(+), Cl(-) and NO(3)(-), which are dominant ions in soil. Therefore, remediation of metal contaminated soil using chitosan and cross-linked treated chitosans as soil amendments is feasible.