Nicholas D. Kim

Trace elements in street and house dusts: sources and speciation

The sources and speciation of trace elements in street and house dusts are reviewed. Soil is a major component of both dusts, but a number of elements are enriched in both materials. These include Pb, Zn, Cu, Cd, As, Sb, Cr, Ca, Na, Au, Cl and Br. They arise from a number of contributing and polluting sources. In the case of house dust, some elements, such as Cu, Co, As, Sb, Zn, Cd, Au, Cl, C and Pb, are produced in the house. There are a number of problems associated with the determination of the speciation of trace elements in dusts. These include the low concentrations of many of the elements, and the interpretation of the results from selective sequential extractions. The mobility and potential availability of the trace elements from dust lies in the order Cd greater than Zn, Pb greater than Mn, Cu greater Fe.

EFFECTIVENESS OF A COMMONLY USED SEQUENTIAL EXTRACTION TECHNIQUE IN DETERMINING THE SPECIATION OF CADMIUM IN SOILS

Abstract Various cadmium-sorbed and cadmium-coprecipitated “soil phases” were prepared and sequentially extracted using the five-step method of Tessier et al. Reagent selectivity was assessed by performing sequential extractions of individual cadmium-spiked phases, and the extent of cadmium redistribution between phases during the course of the extractions was gauged by sequentially extracting a range of “synthetic” soils and and a real soil into which cadmium-spiked phases had been mixed. Reagent selectivity was in some cases very good. The main shortcoming in reagent selectivity was that a portion of the cadmium sorbed on humic acid and clay remained associated with those substrates until step 3 of the sequential extractions. Release during this step would lead to the incorrect classification of the formerly sorbed cadmium as “bound to easily reducible manganese oxides and/or amorphous iron oxides”. Redistribution of the cadmium liberated from each contaminated phase of the synthetic soil and real soil samples during the course of each sequential extraction was minimal. However, in some cases the pH of the material being extracted markedly influenced the relative proportions of cadmium liberated during steps 1 and 2 of the extractions.

Assessment of the extent of lead redistribution during sequential extraction by two different methods

Synthetic model soils were used to evaluate redistribution of lead (Pb) in both the three-stage sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR, now Standards, Measurements and Testing Programme) and the commonly applied procedure of Tessier et al. (1979). Redistribution of Pb in both schemes was found to be substantial, sufficient to render meaningless any attempts to quantify the original phase associations of Pb in cases where these are not known. In the model systems, the manganese oxide and humic acid phases were found to be responsible for most of this redistribution in both schemes. Despite the fact that both schemes allow severe Pb redistribution to occur, differences are apparent in the manner in which this occurs. Whereas Tessier et al.s procedure in all cases yielded the highest recovery of Pb at the reducing step, the three-stage BCR procedure released the most Pb at the oxidizing step, both irrespective of where it originated. These differences are attributable to a combination of high temperature (96 °C) and the presence of acetic acid (25%, vv) in Tessier et al.s reducing step. These conditions were found to reduce the sorptive capacity of humic acid by more than 50%, in addition to retaining more of the Pb in solution by acetate ions. Extensive redistribution in the three-stage BCR procedure was also observed in systems where natural soils were mixed with Pb-spiked synthetic phases. In keeping with the results related to synthetic soil models, the organic matter and Fe/Mn oxide fractions of the natural soils appear to dominate the redistribution of Pb during the extraction.

Evidence for a seasonal fluctuation of arsenic in New Zealand's longest river and the effect of treatment on concentrations in drinking water

A year-long survey, with samples collected weekly, was conducted to estimate long-term average concentrations of arsenic in treated and untreated drinking water for the city of Hamilton, New Zealand. The average concentration of arsenic in Waikato River water at Hamilton before processing was found to be (32.1 +/- 3.7) microg litre(-1), about three times above the new WHO limit of 10 microg litre(-1). However, full conventional water treatment effects a five-fold reduction in arsenic concentrations in drinking water to a level which meets the new standards of (6.2 +/- 0.8) microg litre(-1). The results of both this study and retrospective analysis of archived data suggest that total arsenic concentrations in the Waikato River are likely to follow a regular seasonal variation, being about 10-25 microg litre(-1) higher in the summer months. Changes in river flow rates have an almost negligible effect on the summer peak and winter trough; it is proposed that most of the variation in total arsenic concentrations may be due to the seasonal conversion of arsenic in the river sediments to more soluble forms.

The determination of major and minor elements in milk and infant formula by slurry nebulisation and inductively coupled plasma - optical emission spectrometry (ICP-OES)

A method for the analysis of Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn in infant formulas, milkpowders and liquid milk was developed using ICP-OES. Samples were prepared as slurries and determined against aqueous standards following Lu internal standard compensation for potential matrix effects. The instrument used was radially configured and incorporated a charge-transfer device detector allowing simultaneous acquisition of multi-element and multi-line measurements. Instrument and method performance parameters were estimated for precision, linearity, background equivalent concentrations, detection limits and accuracy. The method was found to be suitable for routine quality control monitoring of infant formulas and milkpowders, thereby improving sample throughput and analytical confidence.

Concentrations and sources of cadmium, copper, lead and zinc in house dust in Christchurch, New Zealand

The amounts (microgram m-2) and concentrations (microgram g-1) of cadmium, copper, lead and zinc have been measured in house dust in Christchurch, New Zealand. For 120 houses surveyed the geometric mean concentrations of the four metals are 4.24 micrograms g-1, 165 micrograms g-1, 573 micrograms g-1 and 10,400 micrograms g-1, respectively. In addition eleven variables, such as house age, carpet wear and traffic density, were recorded for each property and the results analysed with respect to their effects on the amounts and concentrations of the four elements. The amounts of all the metals were highly correlated with the overall dustiness of the houses, which was found to be predominantly determined by the degree of carpet wear. No one dominant source of cadmium was identified, although several minor sources including carpet wear, galvanized iron roofs and red/orange/yellow coloured carpets were implicated. Petrol lead and lead-based paints were identified as significant sources of lead in house dust. Rubber carpet underlays or backings were identified as a significant source of zinc, with some contribution from galvanized iron roofs. Road traffic and probably the existence of a fire place appear to contribute to the copper levels.

Seasonal variations in the concentrations of cadmium, copper, lead and zinc in leaves of the horse chesnut (Aesculus hippocastanum L.).

The concentrations of cadmium, copper, lead and zinc have been measured in the leaves of a deciduous tree the horse chestnut (Aesculus hippocastanum L.) over the period of their lifetime (7 months). The average concentrations for the total sample based on ash weight are: (microg g(-1)) cadmium, 0.197; copper, 129; lead, 294; and zinc, 299. The temporal trends in the concentrations of the metals can be related to their dominant source. Copper and zinc concentrations are highest in the new leaves and decrease with time, suggesting the main source of the elements are uptake from the soil. The decrease occurs partly because of dilution by leaf material as it increases over the growing period. In the case of zinc, however, aerial deposits appear to be also a significant source. Lead concentrations, on the other hand, show an increase with time, which can be related to increasing deposits from aerosol lead arising from the combustion of petrol lead. The increase is enough to offset the dilution effect. For cadmium there is no significant trend, but the tendency is a decrease with time. It is not possible, however, to distinguish between soil uptake and aerial deposit as both are small compared with increase in leaf material.

The concentrations, distribution and sources of cadmium, copper, lead and zinc in the atmosphere of an urban environment

The four metals Cd, Cu, Pb and Zn have been measured in residential city air in a relatively small urban environment. The atmospheric concentrations are Cd, 0.516, 0.305; Cu, 12.5, 8.22; Pb, 155, 70.2; and Zn 47.4, 22.4 ng m-3 at two different sites. Except for lead the concentrations are low and more typical of rural areas in more industrialised centres. The concentrations were found to be higher in the colder and more stable air conditions existing during the winter season. Also concentrations on the flat were higher than those on a hillside probably reflecting the influence of thermal inversions. Wind direction influences the concentrations, they being greater when the wind flow comes across the industrial areas of the city. Some of the major sources of the elements are coal, soil, tyre wear and automobile emissions.

Inhibition of Pb redistribution by two complexing agents (cryptand and NTA) during a sequential extraction of soil models

Abstract We previously reported a severe redistribution of Pb in both model soils and spiked real soil systems during two different sequential extraction schemes, and concluded that a manganese oxide and humic acid were the two main solid phases responsible for scavenging Pb liberated at the first extraction step. As an extension to that study, we have been examining a range of modifications to the first extraction step (0.11 M acetic acid, 16 h) of the three-stage sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR, now Standards, Measurements and Testing Programme) for a possible means of counteracting the Pb redistribution problem. In this study, the potential usefulness of two structurally-distinct soluble complexing ligands was investigated; cryptand 2.2.2 (a macrocyclic crown-like ligand) and nitrilotriacetic acid (NTA). The addition of each ligand to the first extraction solution of the BCR procedure generally improved the percentages of Pb recovered from our multi-phase model soils, with Pb originally spiked on calcite. However, the effectiveness of the cryptand and NTA at inhibiting redistribution (at concentrations of 9 × 10 −3 and 1 × 10 −4 M, respectively) was dependent on the percentages by weight of hausmannite and humic acid in each model system. In the presence of no more than 2% hausmannite, both cryptand and NTA, at the concentration used, could satisfactorily recover about 60% of the Pb, provided that the percentages of humic acid in the systems were not higher than 10% and 5%, respectively. The important preliminary criteria for selecting a potential useful soluble complexing agent suggested by the results of this study are that the ligand possess 1. (a) a high stability-constant for the ion involved, and 2. (b) a semi-encapsulated metal binding site (which appears to inhibit direct surface extraction from occurring). For Pb, we also found it desirable to decrease the extraction time of the first step in the BCR scheme as an aid to minimising opportunity for redistribution.

Spatial variation of refractive index in a pane of float glass

In the statistical interpretation of forensic glass evidence it is standard practice to make the assumption of homogeneity of the refractive index (RI) of the source glass, or of localized homogeneity. However, the work of Locke and Hayes showed that, for toughened windscreen glass, this assumption might not be true. This work is well cited, but there appears to have been little follow-on published research. Furthermore, the toughening process is something known to affect the refractive index, and is a process that float glass does not undergo. Float glass is a major component of casework in New Zealand and for that reason it would be interesting to know whether the findings of Locke and Hayes apply when dealing with float glass. In this paper we describe an experiment similar to that of Locke and Hayes, systematically examining the variation of RI in a pane of float window glass. It was found that, although there were no systematic differences in refractive index, there were observable differences across the pane.