The Impact of Different Root Exudate Components on Phenanthrene Availability in Soil

Abstract

This study investigated the impact of different root exudate components (RECs) on the availability of phenanthrene as a representative of polycyclic aromatic hydrocarbons (PAHs) in soil (TypicPaleudalfs) using laboratory batch assays. Four typical RECs were compared including malic acid, alanine, serine, and fructose. An n‐butanol extraction procedure and a sorption–desorption experiment were used to predict the availability of phenanthrene in soil. We found that the n‐butanol extractable amounts of phenanthrene in soil increased with increasing REC concentrations. The extractability of phenanthrene in soil with various treatments decreased in the following order: malic acid > alanine > serine > fructose treatments. Organic acid (malic acid) resulted in the most significant increase in PAH extractability by soil. Phenanthrene sorption by soil could be described using a linear model regardless of the presence of RECs. The simulated distribution constants (Kd) and carbon‐normalized distribution constants (Koc) for phenanthrene sorption decreased significantly with the addition of all test RECs. Malic acid enhanced desorption of phenanthrene from soils. In contrast, lower concentrations of test amino acids promoted phenanthrene desorption, while higher concentrations inhibited desorption. Fructose had a minimal effect on PAH desorption. The mechanism of REC‐influenced availability of PAH in soil is discussed based on the observed metal dissolution, soil organic matter reduction, and dissolved organic matter release from soil solids.