Can root exudate components influence the availability of pyrene in soil?

Little information is currently available regarding the influence of different root exudate components (RECs) on the availability of persistent organic pollutants in the soil environment. In this study, we investigated the impacts of different RECs including organic acids, amino acids, and fructose on the availability of pyrene as a representative polycyclic aromatic hydrocarbon (PAH) in soils. Citric acid, oxalic acid, malic acid, serine, alanine, and fructose were used in the experiments as representative RECs. Pyrene-spiked soils (TypicPaleudalfs) with present RECs were incubated for 30 days, and the available fraction of pyrene was determined using n-butanol extraction procedure. The amount of n-butanol-extractable pyrene in soil increased with the addition of tested RECs and increased when REC concentrations are enhanced within the range of 0-21 g kg(-1). The extractability of pyrene in soil with REC treatments and the enhancement ratio (r, %) of the extractable pyrene in soil by the addition of RECs after a 30-day incubation decreased in the following order: organic acids (oxalic acid a parts per thousand yen citric acid > malic acid) > amino acid (alanine > serine) > fructose. This decrease was observed irrespective of soil sterilization, although the concentrations of extractable pyrene were lower in non-sterilized soils compared to sterilized soils. The concentrations of metal cations and dissolved organic matter (DOM) in solution increased when organic acids were added. The tested RECs at concentrations of 0-21 g kg(-1) clearly enhanced the availability of pyrene in soils, and larger amounts of RECs resulted in higher pyrene availabilities in the tested soils. Microbial biodegradation diminished the amount of available pyrene irrespective of the presence of RECs. The mechanism of REC-influenced availability of pyrene in soil may be related to the metal dissolution and release of DOM from soil solids. The results of this study will be useful in assessing PAH-related risks to human health and the environment and will be instructive in food safety and remediation strategies at contaminated sites.