Insight into the Modulation of Dissolved Organic Matter on Microbial Remediation of PAH-Contaminated Soils

Abstract

Microorganisms play a key role in degradation of polycyclic aromatic hydrocarbons (PAHs) in environments. Dissolved organic matter (DOM) can enhance microbial degradation of PAHs in soils. However, it is not clear how will the soil microbial community respond to addition of DOM during bioremediation of PAH-contaminated soils. In this study, DOMs derived from various agricultural wastes were applied to remediate the aging PAH-contaminated soils in a 90-day microcosm experiment. Results showed that the addition of DOMs offered a more efficient and persistent elimination of soil PAHs compared to the control which had no DOM addition. PAH removal effects were different among treatments with various DOMs; the addition of DOMs with high proportion of hydrophobic fraction could remove PAHs more efficiently from the soil. Low-molecular-weight (LMW) PAHs were more easily eliminated than that with high-molecularweight (HMW). Addition of DOMs significantly increased abundance of 16S ribosomal RNA (rRNA), pdo1, nah, and C12O genes and obviously changed community compositions of nah and C12O genes in different ways in the PAHcontaminated soil. Phylogenetic analyses of clone libraries exhibited that all of nah sequences and most of C12O sequences were affiliated into Gammaproteobacteria and Betaproteobacteria. These results suggested that external stimuli produced by DOMs could enhance the microbial degradation of PAHs in soils through not only solubilizing PAHs but also altering abundance and composition of indigenous microbial degraders. Our results reinforce the understanding of role of DOMs in mediating degradation of PAHs by microorganims in soils.

Effect of alternating bioremediation and electrokinetics on the remediation of n-hexadecane-contaminated soil

“…Han et al . 13 found that the addition of DOM could enhance the microbial degradation of organic contaminants in soils; similar results were shown in increases in the solubility and biodegradation of contaminants due to the exogenous application of DOM 14 15 . However, a competitive effect can be induced if excessive concentrations of DOM are added, which is not conductive to biodegradation 16 17 18 .…”

Effects of dissolved organic matter derived from forest leaf litter on biodegradation of phenanthrene in aqueous phase

“…Han et al demonstrated that residual PAH concentrations in soil were lower after addition of DOM derived from mushroom cultivation substrate waste (MCSW) or DOM derived from cow manure (CM) than after addition of DOM derived from wheat stalks (WS) due to the higher proportion of the hydrophobic fraction in DOM-MCSW and DOM-CM than in DOM-WS [2].…”

“…Lu (2011) [10] reported that the addition of gaseous toluene as a co-substrate promoted the growth of degrading bacteria and improved degradation enzyme activity, thereby promoting phenanthrene degradation. Han (2015) [2] showed that DOM derived from agricultural wastes enhanced the mobility of PAHs and increased nutrient levels for indigenous soil microorganisms.…”

“…For example, HA (a form of DOM ) which has been described with a micellar microstructure similar to that of surfactants, can incorporate dissolved PAHs [12], and a fraction of micellar-phase PAHs is directly bioavailable to cells and does not need to be dissolved in the liquid phase [59]. DOM with many hydrophobic and nonpolar components may be more effective for biodegradation of PAHs because degrading bacteria can access to the incorporated DOM-PAHs directly, and the bioavailability of DOM-PAHs is higher than that of dissolved PAHs [2,22,32]. What is more, HA can transport phenanthrene towards the degrading bacteria as well, which enhances their ability to take up both dissolved and bound PAHs [60,61].…”

“…Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants with stable ring structures, poor water solubility, and high octanol-water partition coefficients. PAHs can persist in soils and sediments, where they pose a serious threat to the environment and human health [1,2]. The forest canopy can 4 against both PAHs and their degrading microorganisms [21][22][23].…”