The chemical reactivity of lead in soil is difficult to assess and depends on both soil conditions and the origins of the lead. This paper tests the combined application of lead isotopic techniques and chemical extraction to our understanding of lead fractionation in soils. Possibly against expectation, it appears that the 'reactivity' of lead can be high and yet there is tentative evidence that the original source of the metal affects its fractionation in soil, even after long contact times. Abstract 'Reactivity' or 'lability' of lead is difficult to measure using traditional methods. We investigated the use of isotopic dilution with 204 Pb to determine metal reactivity in four soils historically contaminated with contrasting sources of Pb, including (i) petrol-derived Pb, (ii) Pb/Zn mine-spoil, (iii) long-term sewage sludge application and (iv) C19 th urban waste disposal; total soil Pb concentrations ranged from 217 -13600 mg kg -1 . A post-spike equilibration period of three days and 5.0 x 10 -4 M EDTA electrolyte provided reasonably robust conditions for measuring isotopically-exchangeable Pb although in acidic organic soils a dilute Ca(NO 3 ) 2 electrolyte may be better to avoid mobilisation of 'non-labile' Pb. Results showed that the reactive pool of soil Pb is often larger than may be intuitively expected but varies with the original Pb source. A comparison of isotopic exchangeability with the results of a sequential extraction procedure showed that (isotopically) 'non-labile' Pb may be broadly equated with 'residual' Pb in organic soils. However, in mineral soils the 'calcareous' and 'oxide-bound' Pb fractions included non-labile forms of Pb. De-coupling the isotopic signature of labile and nonlabile Pb pools suggested that, despite prolonged contact with soil, differences between the lability of the original contaminant and the native soil Pb may remain.
Urban waste disposal occurred on fenland to the west of Manchester, England, between 1900 and 1964. The reclaimed fenland, Chat Moss, is now used for mixed arable farming. A total of 1.92 Mt of waste including privy midden, street sweepings, clinkers and slaughterhouse refuse was incorporated into the moss resulting in a modified topsoil with raised pH and reduced organic matter content compared with the subsoil. Elevated levels of potentially toxic elements (PTEs) are observed in the topsoil beyond the typical depth of atmospheric contamination; Cd and As concentrations exceed soil guideline values (SGVs) at 1.8 and 43 mg/kg, respectively. Sequential extraction indicates that waste‐derived Pb, Zn and Ni remain predominantly in the residual fraction, whereas Cu was mainly organically bound. Arsenic was predominately found in oxide and organic matter fractions with Cd in carbonate, oxide, organic matter and residual fractions. Pot trials indicated limited uptake of PTEs by vegetables grown on the waste‐amended soil, with the exception of Cd uptake by lettuce (0.22 mg/kg FW) and Pb uptake by radish (0.16 mg/kg FW), which exceeded current EU limits of 0.2 and 0.1 mg/kg FW, respectively. Hazard quotients (HQs) identified no risks to adults from consumption of vegetables grown in these soils with the exception of lettuce consumption with a HQ of 1.4. Risks to children were slightly greater with HQs >1 for Cd in lettuce, spinach, carrots and onion, As in lettuce, parsley and onion and for Zn in spinach.
As Asian countries enter the twenty-first century, they face a litany of environmental problems which are particularly reflected in the poor quality of urban settlements and diminishing natural resources. Many commentators look to the failure of regulation to explain these problems. In response, efforts are currently being made to strengthen existing regulatory structures in a number of countries throughout Asia. In the meantime, there is a growing consensus in the West that traditional "command and control" mechanisms are not necessarily the most effective means of resolving environmental problems. Alternative instruments such as enviromental assessment, environmental audits and management systems may be used more strategically to prevent pollution at source and to ensure that the polluter pays. This article considers the brief history of the use of these instruments in Asia to date and then considers what lessons might be drawn from the experience of other countries in respect to both the "command and control" and the more "strategic" forms of regulation as a basis for more fundamental reform. In conclusion, the paper considers the implications of education and training in Asia.
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