Effect of soil acidification on n‐hexane extractable PAH fractions. (20th November 2015)

• Record Type: Journal Article
• Authors: Mahanty, B.; Kim, C.‐G.
• Is Part Of: European journal of soil science. Volume 67:Number 1(2016:Feb.)
• Page Start: 60
• Page End: 69
• Publication Date: 2015-11-20
• Subjects: Soil science -- Periodicals; 631.4
• DOI: 10.1111/ejss.12310
• Languages: English
• ISSNs: 1351-0754

Abstract

Summary: This study was designed to assess the effect of soil acidification on the extractability of polycyclic aromatic hydrocarbons (PAHs) distributed across various soil organic matter fractions. Phenanthrene, anthracene and pyrene (each at 3.2 mg kg −1 soil) were applied to a natural soil and to an artificially acidified soil, and the samples were incubated for 10 days. Several solvents were tested for the recovery of PAHs from soil, and n ‐hexane was the best for extraction efficiency. Soil was treated with hydroxypropyl‐β‐cyclodextrin (HPCD), pyrophosphate or pyrophosphate‐HPCD in sequence followed by the recovery of residual PAHs in n ‐hexane. Recovery of PAHs by a single‐step non‐exhaustive n ‐hexane extraction from acidified soil was significantly less than that from the original non‐acidified soil ( P = 0.023). Based on the sequential extraction, the pool of n ‐hexane extractable PAHs was classified operationally into four fractions: one portion that is shared with HPCD (HS), one shared with pyrophosphate (PS) and one with both HPCD and pyrophosphate (HPS), and one that is not shared (US). The sum of PAHs recovered from acidified soil was significantly less than that for non‐acidified soil when compared for PS fractions (5.37 and 14.42%, respectively, with P = 0.003) or US fractions (47.76 and 54.00%, respectively, P < 0.001). In contrast, soil acidification increased the sum of PAHs recovered in HS (from 4.29% (non‐acidic) to 5.39% (acidified), P = 0.014) and HPS fractions (from 23.8% (non‐acidic) to 30% (acidified), P < 0.001). The results suggest that soil acidification reduces the pool of PAHs that is accessible exclusively by organic solvents, but increases the fraction that can be extracted with HPCD or pyrophosphate or both. Spectroscopic analysis (Fourier transform infrared spectroscopy and ultraviolet–visible analysis) of isolated humic substances reveals their greater aromaticity when extracted from acidified soil, which might explain the larger proportion of surface‐adsorbed PAHs in soil organic matter that can be dissolved by an aqueous extractant.