Comparison of Single- and Sequential-Solvent Extractions of Total Extractable Benzo[a]pyrene Fractions in Contrasting Soils

Abstract

The fate and behavior of polycyclic aromatic hydrocarbons (PAHs) in soil are of interest in the risk assessment of contaminated land and are usually based on determinations of fractions extracted from soil. For decades, either single- or sequential-solvent extractions have been used to determine PAH extractability in soils; however, there is a lack of certainty as to which fractions are being extracted by these techniques. This study is the first report of differences and similarities in the extractability of benzo[ a]pyrene (B[ a]P) in four contrasting soils (sandy loam, loamy sand, clayey loam, and sandy) when determined using both single-solvent (dichloromethane/acetone (DCM/Ace) mixture) and sequential-solvent (butanol followed by DCM/Ace) extraction. Residues after extraction were subjected to methanolic saponification (MeKOH). Butanol (BuOH) extractability and total extractability of B[ a]P following sequential-solvent extraction decreased significantly ( p < 0.05) with time after addition of B[ a]P. The decrease in BuOH extractability was particularly marked in the organic-matter-rich clayey-loam soil, which also had the largest (>40%) amounts of nonextractable residues. The cumulative amounts of B[ a]P extracted in each soil by single- and sequential-solvent extractions were similar ( p > 0.05) at each aging period, which indicated access to similar B[ a]P fractions in soil by both solvent extractions. The similarities in the amounts of B[ a]P nonextractable residues recovered by MeKOH from pre-extracted soils, through either of the extraction methods, confirms that the total extractable B[ a]P fractions from both methods are similar.

Bioaccumulation of benzo[a]pyrene nonextractable residues in soil by Eisenia fetida and associated background-level sublethal genotoxicity (DNA single-strand breaks)

“…The soil was a sandy-clayloam (21% clay, 62% sand) according to the USDA textural classification 9 , and contained 7.5% total organic carbon as measured by LECO combustion after excess acid hydrolysis of soils. Two environmentally relevant B[a]P concentrations (to supply 10 and 50 mg/kg in soil) were prepared in acetone/toluene (2:1, v/v) and spiked into the soil, following a method described previously 18 . The solvent-spiked soils were aged for 350 d before being used for earthworm exposure.…”

Extremely small amounts of B[a]P residues remobilised in long-term contaminated soils: A strong case for greater focus on readily available and not total-extractable fractions in risk assessment

“…The Soils were extracted with 1-BuOH following a previously described procedure with some modifications 27 . In the modified procedure, the butanolic supernatant was not decanted following centrifugation.…”

“…Instead, a 2 mL aliquot of the supernatant was transferred into a clean glass vial, vacuum-concentrated, redissolved in ACN, and filtered through 0.45 µm PTFE syringe filters before transfer into 2 mL amber HPLC vials for analysis. After BuOH extraction, soils were extracted with 3 mL DCM/Ace (1: 27 .…”

“…The concentrations of B[a]P were determined with an Agilent 1100 Series HPLC equipped with a fluorescence detector (excitation wavelength = 230 nm and emission wavelength = 460 nm) as in described previously 27 .…”

“…For the removal of readily available B[a]P fractions (A in Fig. 1), subsamples of soils (n = 18) were subjected to a mild BuOH extraction following quality control and quality assurance procedures described previously 27 . The resulting soil residues were then divided into 6 batches (n = 3) according to the design in Fig.…”