Fractionation of lead in soil by isotopic dilution and sequential extraction

‘Reactivity’ or ‘lability’ of lead is difficult to measure using traditional methods. We investigated the use of isotopic dilution with 204Pb to determine metal reactivity in four soils historically contaminated with contrasting sources of Pb, including (i) petrol-derived Pb, (ii) Pb/Zn minespoil, (iii) long-term sewage sludge application and (iv) 19th century urban waste disposal; total soil Pb concentrations ranged from 217 to 13 600 mg kg–1. A post-spike equilibration period of 3 days and suspension in 5.0 × 10–4 M ethylenediaminetetraacetic acid provided reasonably robust conditions for measuring isotopically exchangeable Pb. However, in acidic organic soils a dilute Ca(NO3)2 electrolyte may be preferable to avoid mobilisation of ‘non-labile’ Pb. Results showed that the reactive pool of soil Pb can be a large proportion of the total soil lead content 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 ‘carbonate’ and ‘oxide-bound’ Pb fractions included non-labile forms of Pb. The individual isotopic signatures of labile and non-labile Pb pools suggested that, despite prolonged contact with soil, differences between the lability of the original contaminant and the native soil Pb may remain

Using isotopic dilution to assess chemical extraction of labile Ni, Cu, Zn, Cd and Pb in soils

Chemical extractants used to measure labile soil metal must ideally select for and solubilise the labile fraction, with minimal solubilisation of non-labile metal. We assessed four extractants (0.43 M HNO3, 0.43 M CH3COOH, 0.05 M Na2H2EDTA and 1 M CaCl2) against these requirements. For soils contaminated by contrasting sources, we compared isotopically exchangeable Ni, Cu, Zn, Cd and Pb (EValue, mg kg-1), with the concentrations of metal solubilised by the chemical extractants (MExt, mg kg-1). Crucially, we also determined isotopically exchangeable metal in the soil–extractant systems (EExt, mg kg-1). Thus ‘EExt - EValue’ quantifies the concentration of mobilised non-labile metal, while ‘EExt - MExt’ represents adsorbed labile metal in the presence of the extractant. Extraction with CaCl2 consistently underestimated EValue for Ni, Cu, Zn and Pb, while providing a reasonable estimate of EValue for Cd. In contrast, extraction with HNO3 both consistently mobilised non-labile metal and overestimated the EValue. Extraction with CH3COOH appeared to provide a good estimate of EValue for Cd; however, this was the net outcome of incomplete solubilisation of labile metal, and concurrent mobilisation of non-labile metal by the extractant (MExt EValue). The Na2H2EDTA extractant mobilised some non-labile metal in three of the four soils, but consistently solubilised the entire labile fraction for all soil-metal combinations (MExt ≈ EExt). Comparison of EValue, MExt and EExt provides a rigorous means of assessing the underlying action of soil chemical extraction methods and could be used to refine long-standing soil extraction methodologies

EFFICACY TESTS OF DIFFERENT RODENTICIDES ON SOME SPECIES OF RATS IN THAILAND

Two acute rodenticides, zinc phosphide and Vacor, at different concentrations were tested on the rice field rats (Rattus argentiventer) and the bandicoot rats (Bandicota indica) with a choice-feeding procedure. It was found that zinc phosphide at 0.5%, 0.8%, 1.6% caused 30%, 30%, and 60% mortality, respectively, to R. argentiventer, and at 1.6% caused death only 30% to B. indica, whereas Vacor at 0.5%, 0.8%, 1.6% caused 70%, 60% and 80% mortality, respectively to R. argentiventer and this compound at 1.6% killed 60% of B. indica. Five anticoagulants Actosin-P, warfarin, Racumin, brodifacoum, and chlorophacinone also were tested on R. argentiventer and only brodifacoum was tested on B. indica at an appropriate concentration with a non-choice feeding procedure. It was found that with one day consumption of the poisoned bait brodifacoum 0.005% is the only anticoagulant that caused 100% mortality to R. argentiventer and B. indica. whereas, Actosin-P, warfarin, Racumin, and chlorophacinone killed 20%, 20%, 30%, and none of R. argentiventer, respectively

Efficacy tests of different rodenticides on some species of rats in Thailand

Two acute rodenticides, zinc phosphide and Vacor, at different concentrations were tested on the rice field rats (Rattus argentiventer) and the bandicoot rats (Bandicota indica) with a choice-feeding procedure. It was found that zinc phosphide at 0.5%, 0.8%, 1.6% caused 30%, 30%, and 60% mortality, respectively, to R. argentiventer, and at 1.6% caused death only 30% to B. indica, whereas Vacor at 0.5%, 0.8%, 1.6% caused 70%, 60% and 80% mortality, respectively to R. argentiventer and this compound at 1.6% killed 60% of B. indica. Five anticoagulants, Actosin-P, warfarin, Racumin, brodifacoum, and chlorophacinone also were tested on R. argentiventer and only brodifacoum was tested on B. indica at an appropriate concentration with a non-choice feeding procedure. It was found that with-one day consumption of the poisoned bait brodifacoum 0.005% is the only anticoagulant that caused 100% mortality to R. argentiventer and B. indica, whereas, Actosin-P, warfarin, Racumin, and chlorophacinone killed 20%, 20%, 30%, and none of R. argentiventer, respectively

Measuring reactive pools of Cd, Pb and Zn in coal fly ash from the UK using isotopic dilution assays

Large volumes of coal fly ash are continually being produced and stockpiled around the world and can be a source of environmentally sensitive trace elements. Whilst leaching tests are used for regulatory purposes, these provide little information about the true geochemical behaviour and ‘reactivity’ of trace elements in coal ash because they are poorly selective. Isotope dilution (ID) assays are frequently used in soil geochemistry as a means of measuring the reactive pools of trace metals that are in equilibrium with soil pore waters. This paper examines the applicability of multi-element ID assays in measuring the labile or reactive pool of Cd, Pb and Zn in a range of fresh and weathered fly ash, where pH is generally much more alkaline than in soils. The method generally worked well using 0.0005 M EDTA as a background electrolyte as it provided robust analytical ICP-MS measurements as well as fulfilling the important principle of ID that non-labile metal should not be solubilised. Reactive pools were equivalent to 0.5–3% of the total Pb pool and 4–13% of the total Cd pool. For Zn, where samples had pH 11.5 were tested, the method failed as the spiked isotope appeared to be sorbed or precipitated. Ash weathering was found to exert little impact on the lability of Cd, Pb and Zn. Isotope dilution results were compared with 0.43 M HNO3 and 0.05 M EDTA extractions, these commonly being used as analogues of the ID assay, and concluded that these can be used as fast, cost-effective and simple proxies for the ID assays. Results suggest that ID methods can be used to enhance knowledge of trace element behaviour in fresh and weathered fly ash