Karen J. Mizon

Sources of lead in soil and dust and the use of dust fallout as a sampling medium

Abstract Pilot investigations using stable lead isotope and scanning electron microscopic analyses have been undertaken in different environments ranging from mining and smelting to urban in order to better understand the source of, and relationships between, soil and house dust. House dust is characterised by vacuum cleaner dust and/or surface wipes and compared with long-term dust (dust fall) accumulations over a > 3-month interval or with airborne particulates. Finer grain sizes of soils have lead concentrations from 2 to 9 times those measured in the bulk fractions. In Broken Hill isotopic ratios show that the major source of lead in soils is from the orebody, with rare examples containing lead from paint sources. In inner Sydney, soil lead values vary from 37 to 2660 ppm Pb in bulk samples and up to 3130 ppm in the finer fractions. The lead may be from diverse sources such as gasoline or paint. Finer fractions of vacuum cleaner dust from both Broken Hill and Sydney may contain up to three times the amount of lead measured in the bulk samples. In Broken Hill, the percentages by weight of total lead in the −250-μm fraction range from 11 to 51%. Bulk vacuum cleaner dusts from Broken Hill contain up to 4490 ppm Pb. Bulk vacuum cleaner dusts from inner Sydney contain up to 2950 ppm Pb. Isotopic variations in fractions of vacuum cleaner dust containing > 1000 ppm Pb from inner Sydney indicate that the lead in dust has come from different sources and such differences lessen the usefulness of analyses of bulk vacuum cleaner dust. Our results reinforce the importance of analysing the finer fraction of soil and house dust, especially those in the −150-μm (or even −100-μm) fraction for soils and the −100-μm fraction for vacuum cleaner dust. Dust-fall accumulations have many advantages over more conventional methods for estimating lead in house dust, such as vacuum cleaner dust or surface wipes. These advantages include: low cost; no power source required; can be set up by a technician; minimal inconvenience to householder (i.e., no power required, no noise, out of the way, a few minutes to set up and collect); integrates lead flux over a specific period; usually unbiased (in contrast to vacuuming or wipes where the householder may clean prior to a sampling visit); easy to ‘control’ by placement of other dishes in the same house. For Broken Hill, a strong correlation ( r = 0.95) was obtained between the isotopic composition of lead in blood and dust-fall accumulation.

Use of lead isotopes in soils to identify the source of lead contamination near Adelaide, South Australia.

Soil profiles from an urban-rural transect near Adelaide, South Australia, have been analyzed by using lead isotopes as a discriminant for the source of soil lead. Analyses of the top 10 cm of soil profiles taken from sites up to 50 km from Adelaide show that this surface horizon mainly contains Precambrian lead, such as that found in the Broken Hill or Mount Isa deposits. There is also a small amount of younger lead present, similar to that derived from Missouri and young Canadian deposits. Both types of lead are used in the manufacture of tetraethyllead for Adelaide gasoline. Natural soil lead, derived from parent rock, occurs throughout the profiles; however, it is only a relatively minor component in the surface horizons but is the major component a t depths greater than 30-40 cm. Assessment of the data suggests that orchard sprays, power stations, and smelters are not the main source of lead in the surface horizons-rather, contamination derived from tetraethyllead from gasoline is indicated.

Blood Lead Changes during Pregnancy and Postpartum with Calcium Supplementation

Pregnancy and lactation are times of physiologic stress during which bone turnover is accelerated. Previous studies have demonstrated that there is increased mobilization of lead from the maternal skeleton at this time and that calcium supplementation may have a protective effect. Ten immigrants to Australia were provided with either calcium carbonate or a complex calcium supplement (~ 1 g/day) during pregnancy and for 6 months postpartum. Two immigrant subjects who did not conceive acted as controls. Sampling involved monthly venous blood samples throughout pregnancy and every 2 months postpartum, and quarterly environmental samples and 6-day duplicate diets. The geometric mean blood lead at the time of first sampling was 2.4 μg/dL (range, 1.4–6.5). Increases in blood lead during the third trimester, corrected for hematocrit, compared with the minimum value observed, varied from 10 to 50%, with a geometric mean of 25%. The increases generally occurred at 6–8 months gestation, in contrast with that found for a previous cohort, characterized by very low calcium intakes, where the increases occurred at 3–6 months. Large increases in blood lead concentration were found during the postpartum period compared with those during pregnancy; blood lead concentrations increased by between 30 and 95% (geometric mean 65%; n = 8) from the minimum value observed during late pregnancy. From late pregnancy through postpartum, there were significant increases in the lead isotopic ratios from the minimum value observed during late pregnancy for 3 of 8 subjects (p < 0.01). The observed changes are considered to reflect increases in mobilization of lead from the skeleton despite calcium supplementation. The identical isotopic ratios in maternal and cord blood provide further confirmation of placental transfer of lead. The extra flux released from bone during late pregnancy and postpartum varies from 50 to 380 μg lead (geometric mean, 145 μg lead) compared with 330 μg lead in the previous cohort. For subjects replete in calcium, the delay in increase in blood lead and halving of the extra flux released from bone during late pregnancy and postpartum may provide less lead exposure to the developing fetus and newly born infant. Nevertheless, as shown in several other studies on calcium relationships with bone turnover, calcium supplementation appears to provide limited benefit for lead toxicity during lactation.

Petrogenesis of Late Cenozoic volcanic rocks from the Taupo Volcanic Zone, New Zealand, in the light of new lead isotope data

Abstract Lead isotopes and U Pb concentrations have been measured for a wide range of volcanic rocks from the Taupo Volcanic Zone (TVZ), New Zealand. Combined geochemical and isotope plots suggest that the majority of mafie-intermediate volcanic rocks result from contamination (AFC) of primitive basalt by Mesozoic metasedimentary basement. Lead isotope data indicate that some previously published petrogenetic models require modification, notably in the choice of parental magma and in the composition and proportion of the crustal assimilant. Evidence is also presented to show that the voluminous ignimbrites and rhyolites of the TVZ could be derived by melting of early-formed andesites (with accompanying minor crustal contamination) and rule out previous models such as direct melting of Mesozoic basement rocks or contamination of mantle derived melts.

Lead Bioavailability in the Environment of Children: Blood Lead Levels in Children Can Be Elevated in a Mining Community

Lower blood lead averages in mining communities, compared with other child exposure settings, e.g., innercity areas of the United States and smelter communities, have been attributed to lower bioavailability of lead to children in the mining areas. Direct supporting evidence of the lower bioavailability has, however, generally been lacking. Elevated blood lead levels for approximately 85% of children with > 10 micrograms/dl have been reported from the Broken Hill mining community in Australia. Lead isotope, optical, and scanning electron microscope analyses on the lead species from soils and dusts show them to be derived mainly from weathered ore body material. Solubility tests using 0.1M HCl on the -53 + 38 microns fraction of soil and dust show the lead species to have a high degree of bioavailability. Ingestion of soil and dust, either directly or via mouthing activity, is the main source and pathway for elevated blood lead in children from this community.

Lead isotopes as a tool for gossan assessment in base metal exploration

Abstract Lead isotope measurements on gossans may be used as an exploration tool for Pb-Zn-Cu deposits of the “stratiform” type. The method is based on the homogeneous isotopic composition of stratiform orebodies and the close fit of their ratios to the so-called “growth curve”. These features also characterize oxidized outcrops. (gossans) of the primary sulphide ore. The retention of homogeneous Pb isotope ratios during oxidation was tested and proved for true gossans derived from known mineralization in which there was a variation in vertical depth from gossan to primary sulphide, different ages and different geological environments. The deposits included Pb-Zn-Cu (Woodlawn), Pb-Zn (Broken Hill), Zn-Pb (Dugald River), Zn-Cu-Pb (Currawang). The method has been extended to distinguish true gossans from false (pseudo) gossans where the base metals and associated trace elements have been scavenged from the surrounding rocks. It has also been applied to a company exploration program in which a number of ironstone cappings had been drilled and other geochemical information was available. Diamond drilling indicated that five prospects were barren, i.e. underlain by iron sulphides devoid of significant base metal mineralization. On the Pb isotope data, three of the prospects would be rejected; a fourth shows a particularly high potential and is worthy of further exploration, whilst the fifth initially showed high potential but a comparison of gossan and sulphide Pb isotope data after drilling suggests that the drill hole was sited on the fringes of economic mineralization. The Pb isotope method may be utilized further in exploration at the drilling stage. If sulphides are intersected, Pb isotopes may be used to distinguish barren sulphides from those with economic potential, even though they both may contain similar base metal concentrations.

Source of lead in humans from Broken Hill mining community.

This paper documents the first precise lead isotope measurements for men, women and children from the same family in an attempt to determine the source of lead in their blood. The subjects reside in one of the worlds largest lead mining cities, Broken Hill, NSW, Australia. Biological and environmental samples have been compared using isotopic compositions and lead contents. Adult males have isotopic profiles (or compositions) which appear to be related to their occupations. Adult females have low blood leads (<10 μg dL−1) and their main source of lead is not from the mine dumps around which the city is built but probably from a mixture of petrol, food and perhaps water. The blood lead contents in children from 1 to 14 years old vary and are partly dependent on age. There is a moderate correlation of blood lead and isotopic compositions (r = 0.73) indicating that a significant component of blood lead derives from the mine dumps in children with elevated blood leads. Some children with blood leads <20 μg dL−1, however, also have a dominant component of mine lead in their blood

Stable lead isotope profiles in smelter and general urban communities: a comparison of environmental and blood measures

High-precision lead isotope ratios and lead concentrations have been compared statistically and graphically in women of child-bearing age (n = 77) from two smelter communities and one general urban community to evaluate the relative contributions to blood lead of tissue lead stores and lead from the contemporaneous environment (soil, floor dust, indoor airborne dust, water, food). Blood lead (PbB) contents were generally low (e.g. <10 μg dL−1). Statistically significant isotopic differences in blood and environmental samples were observed between the three cities although isotopic differences in blood for individual subjects living in close proximity (∼200 m radius) was as large as the differences within a city. No single environmental measure dominated the biological isotope profile and in many cases the low levels of blood lead meant that their isotopic profiles could be easily perturbed by relatively small changes of environmental exposure. Apportioning of sources using lead isotopes is possibly not feasible, nor cost effective, when blood lead levels are <5 μg dL−1. Interpretations based on statistical analyses of city-wide data do not give the same conclusions as when the houses are considered individually. Aggregating data from multiple subjects in a study such as this obscures potentially useful information. Most of the measures employed in this study, and many other similar studies, are markers of only short-to-medium integration of lead exposure. Serial sampling of blood and longer sampling times, especially for household variables, should provide more meaningful information.

Effect of plumbing systems on lead content of drinking water and contribution to lead body burden.

Stable lead isotopes and lead contents in drinking water from a number of Australian cities have been measured to determine the contribution of drinking water to body burden. Lead contents are generally < 2 micrograms/l and thus contribute an insignificant amount to the lead budget in humans in Australia. First-flush and running water samples taken at intervals of up to 10 min show that equilibrium is reached within 1 min or approximately 10 l by volume. There is, however, large variability in both lead content and isotopic composition within the first minute which brings into question the reliability of the recommended sampling time of 30 s. Extremely large isotopic differences between individual dwellings within the one city and between dwellings and the storage tanks for the water supply are attributed to differences in lead residing in the plumbing within the dwellings, usually from lead solder in brass fittings. Isotopic analysis of solder and water from two dwellings confirm this relationship.

Lead isotope ratio measurements using the isomass 54e in fully automatic mode

Abstract Attempts have been made to optimize the determination of Pb isotope ratios in over 700 analyses of standards and natural samples on an Isomass 54E in fully automatic operation. Amounts of Pb analysed for the N.B.S. standards 981 (common Pb) and 983 (radiogenic Pb) were initially about 100 ng Pb, but these have been increased to about 300 ng to conform with the usual amounts for natural samples. Over a period of three years, the following results have been obtained for standards (quoted errors are given as 2 standard deviations). t001 . TABLE1 No. of analyses 208Pb/206Pb 207Pb/206Pb 206Pb/204Pb SRM 981 493 2.1630±20 0.9139±4 16.906±19 (±0.097%) (±0.050%) (±0.12%) SRM 983 8 0.01386±14 0.07122±7 2698±60 (±1.0%) (±0.098%) (±2.2%) Caltech (CIT)Pb 10 2.1793±21 0.9300±5 16.606±21 (±0.096%) (±0.054%) (±0.13%) Broken Hill Pb18 (galena) 45 2.2256±27 0.9610±6 15.991±25 (±0.12%) (±0.062%) (±0.16%) Pooling the results of 207 analyses of 89 samples of gossans, soils, sulfides, oxides and rocks, twice the coefficients of variation (i.e. twice the relative standard deviations) for 208Pb/206Pb, 207Pb/206Pb and 206PB/204Pb ratios are ±0.11%, ±0.05% and ±0.12%, respectively. We consider that this represents a realistic estimate of our precision as it is based on natural samples and it is also consistent with the standard data. A statistical analysis of 195 runs of SRM 981 was carried out in an attempt to evaluate the bias in the estimated ratios caused by fractionation and to quantify the contribution of fractionation to the variability of the estimated ratios. The major source of error in the measurement arises from mass fractionation rather than random fluctuations and is contingent on sample loading variability.