BIOAVAILABILITY OF FRESHLY ADDED AND AGED NAPHTHALENE IN SOILS UNDER GASTRIC pH CONDITIONS

Abstract

Abstract-The bioavailability of hydrophobic organic chemicals decreases with aging in soil because of sequestration. However, assessments of the risk of exposure to contaminated soils are usually dependent on either chemical concentrations, which are measured using vigorous extraction methods, or models that assume an equilibrium without considering the actual conditions. The objective of this research was to determine the availability and desorption kinetics of freshly added and aged naphthalene from a peat and a mineral soil; naphthalene was desorbed into solutions with pH levels that approximate those found in different gastric regions. Soil and peat samples were spiked with radiolabeled and unlabeled naphthalene at 2 and 20 g/g and were aged from 0 to 135 d. Desorption kinetics were determined using a simulated stomach solution (0.1 M NaCl, 0.1 M HCl, 0.01 M NH 4 Ac, pH ϭ 1.0) and a neutral solution (0.2 M NaCl, pH ϭ 6.7) that represented the pH of intestinal conditions and most soils. Peat sorbed much more naphthalene than did soil, and it allowed little desorption. Though both acidic and neutral extracting solutions could desorb naphthalene, little apparent effect of aging was observed in peat, whereas desorption from soil declined markedly with aging. In addition, the percentage of naphthalene that desorbed from soil was greater for the higher incubation concentration. The desorption of naphthalene from the peat and soil was higher into the neutral solution than into the gastric solution. These results suggest that aging, exposure conditions, concentration effect, and organic matter content should be taken into account in predictive models and risk assessments.

Assessment of the bioaccessibility of polycyclic aromatic hydrocarbons in soils from Beijing using an in vitro test

“…For the assessment of environmental risks associated with PAH-contaminated soil, it is important to evaluate the oral bioavailability of PAHs of ingested soils for humans, especially children. It has been reported that soil contaminants are less 100% available (Pignatello and Xing, 1996;Tang et al, 1998;Jin et al, 1999). Recently, much attention has been directed to the development of in vitro extraction test to mimic human digestion process for estimating bioavailability (Reeves et al, 2001;Jin et al, 1999).…”

Concentrations and bioaccessibility of polycyclic aromatic hydrocarbons in wastewater-irrigated soil using in vitro gastrointestinal test

“…For the assessment of environmental risks associated with PAHcontaminated soil, it is important to evaluate the oral bioaccessibility of PAHs of ingested soils for humans, especially for children. It has been reported that soil contaminants are less than 100% available (Tang et al 1998;Jin et al 1999). Moreover, given the discrepancies between the physiology of humans and other organisms, as well as the cost and time constraints associated with such studies, a more efficient alternative is desirable (Ruby et al 1999).…”

Peer Reviewed: Nonextractable Pesticide Residues in Soil

“…Two avenues of investigation would be useful in quantifying pesticide bioavailability: the development of standardized biological tools to measure or quantify bioavailability-perhaps at different trophic levels-and the development of nonsolvent-associated chemical methodologies that mimic bioavailability in key soil biota. Other interesting approaches include procedures to mimic the release of residues during passage through the gastrointestinal tract (42,43). In addition, it would be instructive to further exploit advanced analytical methodologies (44), which aim to characterize the form and fate of recalcitrant residues, to confirm their stability and negligible bioavailability or long-term biological significance.…”