Effects of chemical structure and exposure on the microbial degradation of polycyclic aromatic hydrocarbons in freshwater and estuarine ecosystems

Abstract

The microbial mineralization of six polycyclic aromatic hydrocarbons (PAHs), containing two to five fused benzene rings, and hexadecane were investigated in sediment: water microcosms which modeled degradation in two freshwater and one estuarine ecosystem. A ranking of the PAHs by order of mineralization rates along with calculated half‐lives (range in weeks) are as follows: naphthalene (2.4‐4.4) ≥ hexadecane (2.2‐4.2) > phenanthrene (4‐18) > 2‐methylnaphthalene (14‐20) > pyrene (34‐>90) ≥ 3‐methylcholanthrene (87‐>200) ≥ benzo[a]pyrene (200‐>300). PAH residues persisted from two to over four times longer in a pristine ecosystem than in an ecosystem chronically exposed to low levels of petroleum hydrocarbons. The mineralization of higher‐molecular‐weight PAHs (> four rings) totaled 0.2 to 6.5% after 8 wk. Relative differences in PAH mineralization among the ecosystems were related to hexadecane mineralization rates, the occurrence and concentration of aromatic hydrocarbon residues in sediments, and elevated populations of hydrocarbon‐degrading microorganisms. Total heterotrophic microbial populations were not good indicators of PAH mineralization rates. Chemical analyses of residues in the microcosms detected the presence of extractable polar metabolites in water and sediments which accounted for 0.1 to 6% of the original PAHs.

Persistence of Polycyclic Aromatic Compounds of Different Molecular Size and Water Solubility in Surficial Sediment of an Intertidal Sandflat

“…The processes most likely to influence PAH persistence, discounting sediment transport (erosion losses, dilution with uncontaminated sediment), bioaccumulation, and bioturbation, are biological degradation by complex natural communities of bac- teria and fungi [7] and physicochemical phenomena (notably photochemical oxidation and dissolution). Microbial degradation rates for PAHs are generally higher in polluted sediments, where microbial adaption may be evident, than in pristine environments such as the Wiroa Island site of this study.…”

“…Microbial degradation rates for PAHs are generally higher in polluted sediments, where microbial adaption may be evident, than in pristine environments such as the Wiroa Island site of this study. Microcosm studies of microbial degradation of PAHs in aquatic ecosystems [7,13] showed that compounds with fewer than four rings degraded readily (e.g., the half-life, t 1/2 , for mineralization of PHE ϭ 4 weeks), whereas higher-molecular-weight compounds persisted much longer (e.g., BaP t 1/2 Ͼ 200 weeks), even in environments chronically exposed to petrogenic hydrocarbons. Biodegradation transformation times for naphthalene, PHE, and BaP, measured in oxidized surficial sediments of a polluted sediment (Boston Harbor, MA, USA) were 13.2 to 20, 7.9 to 19.8, and 53.7 to 82.3 d, respectively [36].…”

“…They exhibit a wide range of properties and environmental hazards. For example, 1-and 2-methylnaphthalene are some of the most acutely toxic, water soluble components of crude oils, whereas many PAHs with four to five rings have low acute toxicities but are genotoxic and carcinogenic to many organisms [6,7]. Polycyclic aromatic hydrocarbons may enter the environment in spills and seepages of crude oil and refinery products, be produced in situ through diagenic transformations of plant materials, or may be the result of (natural and anthropogenic) pyrolytic processes [8,9].…”

Polynuclear aromatic hydrocarbon metabolism in soils: Relationship to soil characteristics and preexposure

“…These products together usually accounted for less than 10% of the added [ 14 C]PAHs (data not shown). Metabolites have usually not been found to accumulate in soils and sediments, perhaps because the initial oxidation of PAHs may be the rate-limiting step in their metabolism [26][27][28] or because other members of the microbial community metabolize the intermediates via cometabolic reactions [29][30][31]. Limited metabolite accumulation may be beneficial to the environment, as early pathway metabolites are more water soluble and often more toxic than the parent PAH [8].…”

“…Carmichael and F.K. Pfaender contaminated [27,32,33] and uncontaminated soils/sediments [14]. This is one of the first reports, however, of extensive mineralization of chrysene.…”