Fj. Cervantes et al., Anaerobic mineralization of toluene by enriched sediments with quinones and humus as terminal electron acceptors, APPL ENVIR, 67(10), 2001, pp. 4471-4478
The anaerobic microbial oxidation of toluene to CO2 coupled to humus respir
ation was demonstrated by use of enriched anaerobic sediments from the Amst
erdam petroleum harbor (APH) and the Rhine River. Both highly purified soil
humic acids (HPSHA) and the humic quinone moiety model compound anthraquin
one-2,6-disulfonate (AQDS) were utilized as terminal electron acceptors. Af
ter 2 weeks of incubation, 50 and 85% of added uniformly labeled [C-13] tol
uene were recovered as (CO2)-C-13 in HPSHA- and AQDS-supplemented APH sedim
ent enrichment cultures, respectively; negligible recovery occurred in unsu
pplemented cultures. The conversion of [C-13] toluene agreed with the high
level of recovery of electrons as reduced humus or as anthrahydroquinone-2,
6-disulfonate. APH sediment was also able to use nitrate and amorphous mang
anese dioxide as terminal electron acceptors to support the anaerobic biode
gradation of toluene. The addition of substoichiometric amounts of humic ac
ids to bioassay reaction mixtures containing amorphous ferric oxyhydroxide
as a terminal electron acceptor led to more than 65% conversion of toluene
(1 mM) after 11 weeks of incubation, a result which paralleled the partial
recovery of electron equivalents as acid-extractable Fe(II). Negligible con
version of toluene and reduction of Fe(III) occurred in these bioassay reac
tion mixtures when humic acids were omitted. The present study provides cle
ar quantitative evidence for the mineralization of an aromatic hydrocarbon
by humus-respiring microorganisms. The results indicate that humic substanc
es may significantly contribute to the intrinsic bioremediation of anaerobi
c sites contaminated with priority pollutants by serving as terminal electr
on acceptors.