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

Abstract

There is a lack of understanding about the potential for remobilisation of polycyclic aromatic hydrocarbons (PAHs) residues in soils, specifically after the removal of readily available fractions, and the likelihood to cause harm to human and environmental health. Sequential solvent extractions, using butanol (BuOH), dichloromethane/acetone, and methanolic saponification were used to investigate the time-dependent remobilisation of B[a]P residues in aged soils, after removal of readily available or total-extractable fractions. After 120 d of aging, BuOH-remobilised B[a]P were small or extremely small ranging from 2.3 ± 0.1 mg/kg to 4.5 ± 0.5 mg/kg and from 0.9 ± 0.0 mg/kg to 1.0 ± 0.1 mg/kg, after removal of readily available and total-extractable fractions, respectively. After removal of readily available fractions, the remobilisation rates of B[a]P residues were constant over 5 re-equilibration times, as shown by first-order kinetics. The amounts of B[a]P remobilised significantly (p < 0.05) decreased with aging, particularly in hard organic carbon-rich soils. After 4 years of aging, BuOH-and totalremobilised B[a]P were generally < 5% of the initially spiked 50 mg/kg. Based on the findings of this study, the potential or significant potential for B[a]P NERs in soils to cause significant harm to human and environmental health are minimal.

Efficiency of Penicillium canescens in Dissipating PAH in Industrial Aged Contaminated Soil Microcosms and Its Impact on Soil Organic Matter and Ecotoxicity

“…1-Butanol (BuOH) was selected as the extraction solvent for measuring PAH bioavailability in soil (adapted from Umeh et al [19,20]). After 8 months of incubation, 3 mL of BuOH was added to 1 g of PAH-polluted soil in a 22-mL glass centrifuge tube for each quadruplicate.…”

“…In order to investigate the toxicity decrease in BA4 compared to C, bioavailable PAH were assessed. We selected BuOH as a solvent for extracting bioavailable PAH, as recommended by Semple's research team [19,20] for risk-based PAH-polluted soils management. As Figure 3 shows, the bioavailable PAH level in BA4 was dramatically reduced, by 41% compared to C. After 8 months of incubation with P. canescens, the bioavailable PAH in BA4 only represented 29.8% of the initial total PAH, compared to 45% in C. This interesting result could partly explain the toxicity decrease versus the nematode, C. elegans, as the test organism, observed for BA4.…”

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

“…Previous investigations reported the time-dependent remobilisation of B[a]P in soils, and the associated effects of soil properties and B[a]P concentrations, after the complete removal of totalextractable and readily available fractions 9,10 . One of the key observations of these solventextractions based investigations was that the concentrations of B[a]P that were remobilised from B[a]P NERs in soils that had been aged up to 4 years, were extremely small 9,10 . The lingering question is whether PAH NERs in long-term contaminated soils can be bioaccumulated in sufficient quantities that they become lethal, or sublethal by genotoxicity, to bioindicator organisms, such as earthworms.…”