title: Use of isotope dilution method to predict bioavailability of organic pollutants in historically contaminated sediments.
abstract: Many cases of severe environmental contamination arise from historical episodes, where recalcitrant contaminants have resided in the environment for a prolonged time, leading to potentially decreased bioavailability. Use of bioavailable concentrations over bulk chemical levels improves risk assessment and may play a critical role in determining the need for remediation or assessing the effectiveness of risk mitigation operations. In this study, we applied the principle of isotope dilution to quantify bioaccessibility of legacy contaminants DDT and PCBs in marine sediments from a Superfund site. After addition of 13C or deuterated analogues to a sediment sample, the isotope dilution reached a steady state within 24 h of mixing. At the steady state, the accessible fraction (E) derived by the isotope dilution method (IDM) ranged from 0.28 to 0.89 and was substantially smaller than 1 for most compounds, indicating reduced availability of the extensively aged residues. A strong linear relationship (R2=0.86) was found between E and the sum of rapid (Fr) and slow (Fs) desorption fractions determined by sequential Tenax desorption. The IDM-derived accessible concentration (Ce) was further shown to correlate closely with tissue residue in the marine benthic polychaete Neanthes arenaceodentata exposed in the same sediments. As shown in this study, the IDM approach involves only a few simple steps and may be readily adopted in laboratories equipped with mass spectrometers. This novel method is expected to be especially useful for historically contaminated sediments or soils, for which contaminant bioavailability may have changed significantly due to aging and other sequestration processes.
authors.affiliation: Department of Environmental Sciences, University of California , Riverside, California 92521, United States.
authors.forename: Fang
authors.initials: F
authors.lastname: Jia
authors.forename: Lian-Jun
authors.initials: LJ
authors.lastname: Bao
authors.forename: Jordan
authors.initials: J
authors.lastname: Crago
authors.forename: Daniel
authors.initials: D
authors.lastname: Schlenk
authors.forename: Jay
authors.initials: J
authors.lastname: Gan
mesh_terms: D000818:Animals; D001682:Biological Availability; D002247:Carbon Isotopes; D019015:Geologic Sediments / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D007553:Isotope Labeling / Q000379:methods*; D007700:Kinetics; D009930:Organic Chemicals / Q000032:analysis*; D011077:Polychaeta / Q000378:metabolism; D011078:Polychlorinated Biphenyls / Q000032:analysis; D011108:Polymers; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D002247:Carbon Isotopes; D009930:Organic Chemicals; D011108:Polymers; D014874:Water Pollutants, Chemical; C010514:tenax; D011078:Polychlorinated Biphenyls