Michael V. Ruby

In situ formation of lead phosphates in soils as a method to immobilize lead.

Considerable evidence, both theoretical and experimental, support the assertion that lead phosphates are the most stable environmental soil lead form and that they may form rapidly when adequate phosphate is present. This study demonstrated that the weathering of galena to insoluble lead phosphates in soils at a port facility historically used for shipment of ore concentrates is due to the presence of adequate soil phosphate. Geochemical modeling indicated that the addition of a phosphate amendment to Pb-bearing soil would result in lead phosphate formation with an estimated aqueous lead solubility of 0.1 μg/L in soil

Bioavailability of arsenic in soil and house dust impacted by smelter activities following oral administration in cynomolgus monkeys

This study was conducted to determine the extent of arsenic (As) absorption from soil and house dust impacted by smelter activities near Anaconda, Montana. Female cynomolgus monkeys were given a single oral administration via gelatin capsules of soil (0.62 mg As/kg body wt) or house dust (0.26 mg As/kg body wt), or soluble sodium arsenate by the gavage or intravenous route of administration (0.62 mg As/kg body wt) in a crossover design with a minimum washout period of 14 days. Urine, feces, and cage rinse were collected at 24-hr intervals for 168 hr. Blood was collected at specified time points and area under the curves (AUCs) was determined. Arsenic concentrations for the first 120 hr, representing elimination of greater than 94% of the total administered dose for the three oral treatment groups, were < 0.021 to 4.68 micrograms/ml for the urine and < 0.24 to 31.1 micrograms/g for the feces. In general, peak concentrations of As in the urine and feces were obtained during the collection intervals of 0-24 and 24-72 hr, respectively. The main pathway for excretion of As for the intravenous and gavage groups was in the urine, whereas for the soil and dust groups, it was in the feces. Mean absolute percentage bioavailability values based on urinary excretion data were 68, 19, and 14% for the gavage, house dust, and soil treatments, respectively, after normalization of the intravenous As recovery data to 100%. Corresponding absolute bioavailability values based on blood were 91, 10, and 11%. The bioavailability of soil and house dust As relative to soluble As (by gavage) was between 10 and 30%, depending upon whether urinary or blood values were used. These findings suggest that risks associated with the ingestion of As in soil or dust will be reduced compared to ingestion of comparable quantities of As in drinking water.

Relative bioavailability of lead from mining waste soil in rats

The purposes of this study were to determine the extent of absorption of lead (Pb) in mining waste soil from Butte, Montana, and to investigate the effect of mining waste soil dose (g soil/day) on tissue lead concentrations. Young, 7- to 8-week-old male and female Sprague-Dawley rats (5/sex/group) were given mining waste soil that contained 810 or 3908 ppm lead mixed in a purified diet (AIN-76) at four different dose levels (0.2, 0.5, 2, and 5% dietary soil) for 30 consecutive days. Standard groups included untreated controls and dosed feed soluble lead acetate groups (1, 10, 25, 100, and 250 micrograms Pb/g feed). The test soil dose levels bracketed a pica childs soil exposure level and the lead acetate concentrations bracketed the test soil dose levels of lead. Liver, blood, and femur were analyzed for total lead concentration using graphite furnace atomic absorption spectroscopy. Clinical signs, body weight, food consumption, and liver weights for test soil and standard groups were similar to control. Tissue lead concentrations from test soil animals were significantly lower than the tissue concentrations for the lead acetate group. Relative percentage bioavailability values, based on lead acetate as the standard, were independent of the two different test soils, dose levels, and sex and were only slightly dependent on the tissue (blood > bone, liver). Mean relative percentage bioavailability values of lead in the Butte mining waste soil were 20% based on the blood data, 9% based on the bone data, and 8% based on the liver data. The results of this study will provide the information needed to determine the significance of lead exposure from Butte soils in assessing human health risks as part of the Superfund Remedial Investigation/Feasibility Study process.

Bioavailability of Arsenic in Soil Impacted by Smelter Activities Following Oral Administration in Rabbits

This study determined the extent of arsenic (As) absorption from soil from Anaconda, Montana. Prepubescent male and female SPF New Zealand White rabbits (5/sex/group) were given a single oral (capsule) administration of soil (3900 ppm As) at three different dose levels (0.2, 0.5, and 1.0 g of soil/kg, corresponding to 0.78, 1.95, and 3.9 mg As/kg, respectively). Standard groups included untreated controls, an intravenous sodium arsenate group (1.95 mg As/kg), and a gavage sodium arsenate group (1.95 mg As/kg). Urine, cage rinse, and feces were collected at 24-hr intervals for 5 days and were analyzed for total As concentration. Clinical signs, body weights, and food consumption for treated animals were similar to controls. Maximum As concentrations were obtained over the initial 24-hr collection interval. A dose-dependent delay in urinary As excretion, the major elimination pathway, was observed in the oral soil group compared to that in the gavage group. For the animals in the soil groups, approximately 80% of the administered As dose was eliminated in the feces compared to approximately 10 and 50% for the intravenous and oral gavage groups, respectively. The relative oral bioavailabilities (+/- SD) of As in the gavage and test soil groups based on comparison with excreta data from the intravenous group were approximately 50 +/- 5.7 and 24 +/- 3.2%, respectively (after normalization of intravenous groups As recovery data to 100%). These results indicated that As in the soil was probably in a less soluble and therefore a less absorbable form than sodium arsenate.

Bioavailability of Soil-Borne Chemicals: Abiotic Assessment Tools

ABSTRACT The abiotic tools that are available, or under development, for evaluating the oral and dermal bioavailability of contaminants from soils are described in this article. These tools generally rely on one of two approaches: (1) characterizing the form of the contaminant and the chemical binding of the contaminant to the soil matrix, and (2) chemical extractions intended to evaluate the fraction of the chemical that would be liberated in biological fluids (gastrointestinal fluid or sweat). For the purpose of human health risk assessment, abiotic methods to estimate the bioavailability of inorganic contaminants in soil are considered generally to be “screening” level tools at this time. Development work for physiologically based extraction tests (PBETs) is ongoing for many inorganic contaminants, and these methods hold great promise for eventual use in making quantitative bioavailability adjustments in risk assessment. The availability of abiotic tools to evaluate the bioavailability of organic contaminants from soils lags behind that for metals, due to the difficulty in conducting in vivo bioavailability studies with organic compounds and their complex interactions with soil. However, considerable research is being conducted in this field, and new assessment tools are being validated for use in human health risk assessment.

Selective Soil Particle Adherence to Hands: Implications for Understanding Oral Exposure to Soil Contaminants

Over the last 30 years, there has been extensive research designed to quantify the extent of oral bioavailability and bioaccessibility of organic and inorganic contaminants in soil. One aspect of this research is the soil particle size selected to represent environmental exposures, which may affect study results and comparability across studies. Different research groups have studied soil particle sizes ranging from <45 μm to <2000 μm. This article reviews the historical and technical considerations that pertain to the selection of an appropriate particle size fraction for evaluating the relative oral bioavailability of chemicals from soil, which include (1) how the resultant data will be used in human health risk assessment, (2) soil fractions historically used in oral bioavailability studies, (3) studies of soil adherence to human hands, (4) the distribution of contaminants in soils as a function of particle size, and (5) the effect of differential bioavailability as a function of soil particle size and geochemical matrix. These factors are first discussed from a general perspective, applicable to all contaminants in soil, and then more specifically for polycyclic aromatic hydrocarbons (PAHs) in soil. Based on this review, a specific soil particle size of <150 μm is recommended for future studies on the oral bioavailability and bioaccessibility of PAHs in soil.

Factors controlling lead bioavailability in the Butte mining district, Montana, USA.

Microprobe analyses of 38 soil and 5 mine-waste samples from Butte, Montana, demonstrated that the samples contain predominantly sulphide/sulphate and oxide/phosphates of lead (Pb)-bearing phases associated with mine waste. The sulphide/sulphate assemblage consists primarily of galena altering to anglesite and plumbojarosite, with secondary jarosite precipitating and rinding the Pb-bearing minerals. In addition, galena was encapsulated within pyrite or quartz grains. The oxide/phosphate assemblage consists of pH-neutral soils in which a plausible paragenetic sequence of PbO to Pb phosphates, PbMnO, or PbFeO is proposed, dependent on the activity of P, Mn, Fe, and Cl in the soil. In addition, Pb-bearing grains are occasionally armoured by the presence of a 1- to 3-(μm rind of authigenic silicate. The low solubility of the Pb-bearing minerals resulting from encapsulation in non-Pb-bearing reaction rinds may provide an explanation for the limited Pb bioavailability observed when Butte soils were fed to rats (Freemanet al., 1992). Further evidence of the lack of absorption of lead from these soils is provided by the results of a blood-Pb study indicating very low blood-Pb levels in Butte children. The lower bioavailability of Pb from mining sites, compared to smelting and urban environments, is also due to kinetic limitations that control dissolution rates of Pb-bearing solids relative to the residence time of soil in the gastrointestinal (Gl) tract. When the test soil was fed to New Zealand White rabbits, only 9% of the total Pb was solubilised in the stomach, and therefore available for absorption. Anin vitro assay, developed to estimate maximum available Pb from soil, demonstrates that ingestion of mine-waste-bearing soil results in limited Pb dissolution, and produces results similar to thein vivo testing.

Oral Bioavailability, Bioaccessibility, and Dermal Absorption of PAHs from Soil—State of the Science

This article reviews the state of the science regarding oral bioavailability, bioaccessibility, and dermal absorption of carcinogenic polycyclic aromatic hydrocarbons (cPAHs) in soil by humans, and discusses how chemical interactions may control the extent of absorption. Derived from natural and anthropomorphic origins, PAHs occur in a limited number of solid and fluid matrices (i.e., PAH sources) with defined physical characteristics and PAH compositions. Existing studies provide a strong basis for establishing that oral bioavailability of cPAHs from soil is less than from diet, and an assumption of 100% relative bioavailability likely overestimates exposure to cPAHs upon ingestion of PAH-contaminated soil. For both the oral bioavailability and dermal absorption studies, the aggregate data do not provide a broad understanding of how different PAH source materials, PAH concentrations, or soil chemistries influence the absorption of cPAHs from soil. This article summarizes the existing studies, identifies data gaps, and provides recommendations for the direction of future research to support new default or site-specific bioavailability adjustments for use in human health risk assessment.

Percutaneous absorption of arsenic from environmental media

Current knowledge of percutaneous absorption of arsenic is based on studies of rhesus monkeys using soluble arsenic in aqueous solution, and soluble arsenic mixed with soil (Wester et al., 1993). These studies produced mean dermal absorption rates in the range of 2.0-6.4% of the applied dose. Subsequently, questions arose as to whether these results represent arsenic absorption from environmental media. Factors such as chemical interactions, the presence of other metals, and the effects of weathering on environmental media all can affect the nature of arsenic and its potential for percutaneous absorption. Therefore, research specific to more relevant matrices is important. The focus of this effort is to outline study design considerations, including particle size, application rates, means of ensuring skin contact and appropriate statistical evaluation of the data. Appropriate reference groups are also important. The potential for background exposure to arsenic in the diet possibly obscuring a signal from a dermally applied dose of arsenic will also be addressed. We conclude that there are likely to be many site-or sample-specific factors that will control the absorption of arsenic, and matrix-specific analyses may be required to understand the degree of percutaneous absorption.

The Bioavailability of Lead in Mining Wastes: Physical/Chemical Considerations

AbstractIn this paper we review the physiological and geochemical factors affecting lead bioavailability, and particularly, the unique physical/chemical properties of lead derived from mining wastes based on both theory and empirical observations. The relationship between blood lead levels and soil lead concentrations derived from epidemiological studies indicates that lead in soil from mining sites appears to have less of an effect on blood lead levels in children than does lead at urban sites or sites with an active lead smelter. Differences in bioavailability of various lead species offers a plausible explanation for the relative differences in their impact on blood lead. In this paper, we evaluate from a physiological viewpoint aqueous solubility, absorption/desorption processes, and uptake mechanisms that may control lead bioavailability within the Gl tract. A number of these processes, including the role of passive diffusion, competition with calcium for a common transport mechanism, and the role of...