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.

The Challenge Posed to Children's Health by Mixtures of Toxic Waste: The Tar Creek Superfund Site as a Case-Study

“…Research on metal bioavailability in mine wastes has led to conflicting conclusions. In vitro assessments of bioavailability using sequential extractions and physiologically-based extraction tests and in vivo assessments in rats and rabbits have revealed that Pb salts such as Pb acetate, PbSO 4 and PbO generally are more bioavailable than PbS and Pb-containing mining ores (14,15,16). The relatively low bioavailability of metals in sulfides and mine ore have been cited as an explanation for the observation that children in mine-impacted areas have tended to have lower blood Pb than would be expected given the total Pb concentrations in their surroundings, especially compared to children in urban and smelter-impacted areas (17,18).…”

Bioaccessibility of trace elements in soils in Northern Ireland

“…This 'bioavailable' fraction of the pseudo-total PTE soil concentration is in turn dependent on the fraction, which is 'bioaccessible' along an identified exposure pathway (Ruby, 2004). With regard to oral intake as a significant PTE exposure pathway in environmental exposure scenarios, this bioaccessible fraction refers to the PTE fraction released in the gastro-intestinal (GI) tract by digestive juices, thus representing the maximum contaminant concentration available for intestinal absorption .…”

Pilot study of temporal variations in lead bioaccessibility and chemical fractionation in some Chinese soils

“…In the last few decades, the methodology for determining the bioavailability of soil heavy metals to humans has seen rapid development, although no standard method of estimating bioavailability has yet been approved by regulatory agencies. Physiologically based extraction (in vitro) tests, which have been well-validated through comparison with animal (in vivo) tests, have proven to be a fast, cost-effective and reliable approach for estimating the bioavailability of heavy metals in soils to humans [10][11][12][13]. In vitro methods have been used to estimate the bioaccessibility of heavy metals (e.g.…”

“…In vitro methods have been used to estimate the bioaccessibility of heavy metals (e.g. Pb, cadmium and chromium) in soils near ore smelters, mine tailings and other polluted sites [10][11][12][13][14][15][16][17], as well as to evaluate the effectiveness of soil remediation technologies [18][19][20][21].…”