Humic Acid Toxicity in Biologically Treated Soil Contaminated with Polycyclic Aromatic Hydrocarbons and Pentachlorophenol

Abstract

Contaminated soil from a land treatment unit at the Libby Groundwater Superfund Site in Libby, MT, was amended with 14C pyrene and incubated for 396 days to promote biodegradation and the formation of soil-associated bound residues. Humic and fulvic acids were extracted from the treated soil microcosms and analyzed for the presence of pyrene residues. Biologic activity promoted 14C association with the fulvic acid fraction, but humic acid-associated 14C did not increase with biologic activity. The Aboatox flash toxicity assay was used to assess the toxicity of humic and fulvic acid fractions. The fulvic acid gave no toxic response, but the humic acid showed significant toxicity. The observed toxicity was likely associated with pentachlorophenol, a known contaminant of the soil that was removed by solvent extraction of the humic acid and that correlated well with toxicity reduction.

The impact on the soil microbial community and enzyme activity of two earthworm species during the bioremediation of pentachlorophenol-contaminated soils

“…The measurement of soil pH (combined glass electrode with soil/water=1/2.5), maximum water holding capacity (cutting ring method) and organic matter (potassium dichromate oxidation-volumetric method) followed previously described methods [14,22]. The fractionation of humic substances followed Nieman et al [26] and Scelza et al [27].…”

“…The tubes were sealed, placed on an orbital shaker at 180 rpm for 1 h, and then centrifuged at 3,000 g for 15 min. The supernatants were passed through a 0.45 μm filter and the precipitate was separated as humic acid, fulvic acid and humin fractions using 0.5 mol L -1 NaOH and HCl, respectively [26]. The earthworm-accumulated PCP was extracted according to Parrish et al [29], and the bound PCP residues were extracted from the three fractions as described by Nieman et al [26] and Scelza et al [27].…”

“…Urease and catalase activity were determined by the phenol-sodium hypochlorite colourimetric method and titration, respectively [26]. Invertase and cellulase activity were determined by the 3,5-dinitrosalicylate [25] and 3,5-dinitrosalicylate colourimetric methods [26].…”

Enhancing pentachlorophenol degradation by vermicomposting associated bioremediation

“…Soil samples were freeze-dried, and the samples (2 g, dry weight) were transferred into polycarbonate centrifuge tubes and added with 40 mL water:ethanol (50:50, v/v). The tubes were sealed, shaked at filter and the precipitate was separated to humic acid, fulvic acid, and humin fractions using 0.5 mol L -1 NaOH or HCl (Nieman et al, 2005). The earthworm-accumulated PCP was extracted according to Parrish (Parrish et al, 2006).…”

Effects of inoculation with Phanerochaete chrysosporium on remediation of pentachlorophenol-contaminated soil waste by composting

“…Ten grams samples (fresh wt) were solvent extracted by shaking at 200 rpm with 20 ml acetone and n-hexane (1:1, v/v) for 2 h. The solvent was decanted after centrifugation at 10,000 × g for 10 min. Isolated samples were allowed to dry at 30 • C for 24 h and subsequently extracted with 10 ml acetone and n-hexane (1:1, v/v) for 10 min followed by 10 min of centrifugation at 10,000 × g [27]. Solvent extracts were dried under a stream of nitrogen and redissolved in acetonitrile for HPLC analysis.…”