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Use of isotope dilution method to predict bioavailability of organic pollutants in historically contaminated sediments.

Jia F, Bao LJ, Crago J, Schlenk D, Gan J - Environ. Sci. Technol. (2014)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Sciences, University of California , Riverside, California 92521, United States.

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.

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Fractions of isotopetracers (*HOC) in the sediment (solid triangle)and liquid phase (open triangle) in the PV8C sediment slurry as afunction of mixing time: (A) 13C-PCB 52; (B) p,p′-DDE-d4.
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fig1: Fractions of isotopetracers (*HOC) in the sediment (solid triangle)and liquid phase (open triangle) in the PV8C sediment slurry as afunction of mixing time: (A) 13C-PCB 52; (B) p,p′-DDE-d4.

Mentions: The time necessary for the externally added *HOCsto reach phase distribution equilibrium was subsequently determined.Upon introduction to the sediment slurry, *HOCs rapidly partitionedto the sediment phase and an apparent phase distribution equilibriumwas reached after a short period of mixing. Figure 1 shows the changes of aqueous (*Cw/*C0) or sediment phase fraction (*Cs/*C0) of 13C-PCB 52 and p,p′-DDE-d4 as afunction of mixing time. The kinetics of other *HOCs may be foundin the SI (Figure S3). The strong sorptionof *PCBs and *DDXs to the sediment resulted in rapid dilution of theadded isotope tracers in the aqueous phase, as reflected from therapid decreases in *Cw/*C0 (Figure 1). For example, after2 h of mixing, 90.2% and 89.1% of the initially added 13C-PCB 52 and p,p′-DDE-d4 werefound in the sediment phase for the PV8C sediment or the originalconcentration in the solution phase was diluted by 10.2 and 9.1 times,respectively. High percentages of dilution were also found for theother isotope-labeled HOCs (7.9–28.9 fold) in the PV8C sedimentat 2 h (Figure S3, SI). Fast partitioningof *HOCs was further observed for the PV6C sediment (Figure S4, SI). Dilution beyond the 2 h interval was muchmore gradual. From 24 to 192 h, the fractions of *HOCs in both sedimentand aqueous phases were essentially constant, suggesting that phasedistribution of the isotope-labeled tracers reached an apparent equilibrium.One-way ANOVA analysis showed no significant change in the fractionof *HOCs in the sediment or solution phases (p =0.276–0.890 for *PCBs, p = 0.536–0.624for *DDEs, and p = 0.388–0.769 for *DDDs)for the PV8C sediment between 24 and 192 h (Figures 1 and S3, SI). Similar results (p = 0.109–0.878) were also observed for the PV6Csediment (Figure S4, SI). At the steadystate, less than 2% of the introduced *HOCs remained in the aqueousphase for either PV8C or PV6C sediment.


Use of isotope dilution method to predict bioavailability of organic pollutants in historically contaminated sediments.

Jia F, Bao LJ, Crago J, Schlenk D, Gan J - Environ. Sci. Technol. (2014)

Fractions of isotopetracers (*HOC) in the sediment (solid triangle)and liquid phase (open triangle) in the PV8C sediment slurry as afunction of mixing time: (A) 13C-PCB 52; (B) p,p′-DDE-d4.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4215882&req=5

fig1: Fractions of isotopetracers (*HOC) in the sediment (solid triangle)and liquid phase (open triangle) in the PV8C sediment slurry as afunction of mixing time: (A) 13C-PCB 52; (B) p,p′-DDE-d4.
Mentions: The time necessary for the externally added *HOCsto reach phase distribution equilibrium was subsequently determined.Upon introduction to the sediment slurry, *HOCs rapidly partitionedto the sediment phase and an apparent phase distribution equilibriumwas reached after a short period of mixing. Figure 1 shows the changes of aqueous (*Cw/*C0) or sediment phase fraction (*Cs/*C0) of 13C-PCB 52 and p,p′-DDE-d4 as afunction of mixing time. The kinetics of other *HOCs may be foundin the SI (Figure S3). The strong sorptionof *PCBs and *DDXs to the sediment resulted in rapid dilution of theadded isotope tracers in the aqueous phase, as reflected from therapid decreases in *Cw/*C0 (Figure 1). For example, after2 h of mixing, 90.2% and 89.1% of the initially added 13C-PCB 52 and p,p′-DDE-d4 werefound in the sediment phase for the PV8C sediment or the originalconcentration in the solution phase was diluted by 10.2 and 9.1 times,respectively. High percentages of dilution were also found for theother isotope-labeled HOCs (7.9–28.9 fold) in the PV8C sedimentat 2 h (Figure S3, SI). Fast partitioningof *HOCs was further observed for the PV6C sediment (Figure S4, SI). Dilution beyond the 2 h interval was muchmore gradual. From 24 to 192 h, the fractions of *HOCs in both sedimentand aqueous phases were essentially constant, suggesting that phasedistribution of the isotope-labeled tracers reached an apparent equilibrium.One-way ANOVA analysis showed no significant change in the fractionof *HOCs in the sediment or solution phases (p =0.276–0.890 for *PCBs, p = 0.536–0.624for *DDEs, and p = 0.388–0.769 for *DDDs)for the PV8C sediment between 24 and 192 h (Figures 1 and S3, SI). Similar results (p = 0.109–0.878) were also observed for the PV6Csediment (Figure S4, SI). At the steadystate, less than 2% of the introduced *HOCs remained in the aqueousphase for either PV8C or PV6C sediment.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Sciences, University of California , Riverside, California 92521, United States.

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.

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