Fluxes of PAHs from coal tar-impacted river sediment under variable seepage rates.

The flux of several polycyclic aromatic hydrocarbons (PAHs) from coal tar-impacted river sediment was measured under various seepage rates in a laboratory scale. The batch PAH equilibrium data between aqueous phase (C(eq)) and sediment phase was well-explained using a Raoult's law approach. In the flux measurement from column study, the steady-state PAH concentrations (C(infinity)) in the effluent solution were affected by a time-dependent nonequilibrium process; the seepage velocity was inversely proportional to the C(infinity) of PAH in the effluents. With a high seepage velocity of 4.06 cm d(-1), a large initial concentration was observed, possibly due to the greater disparity between C(infinity) and C(eq). This initial-flush export leveled off after a few pore volumes had been displaced. The chemical flux pattern of PAH was conceptually depicted by superimposing two analytical solutions, such as a slug lease followed by rate-limited solute lease. Under quiescent conditions, the sediment pore-water reached dissolution equilibrium with the solid phase. However, under dynamic groundwater seepage conditions, the seepage water flowing through sediment pores did not reach dissolution equilibrium, which was evidence of nonequilibrium dissolution. In conclusion, the mass flux of PAHs from coal tar-impacted sediment is determined by concurrent effect of the groundwater seepage rate and rate-limited PAH concentration in seepage water.

Reductive debromination of polybrominated diphenyl ethers in anaerobic sediment and a biomimetic system.

Because of the bioaccumulation of penta- and tetrapolybrominated diphenyl ether (PBDE) flame retardants in biota,the environmental biotransformation of decabromodiphenyl ether (BDE-209) is of interest. BDE-209 accounts for more than 80% by mass of PBDE production and is the dominant PBDE in sediments. Most sediments are anaerobic and reports of microbial reductive dehalogenation of hydrophobic persistent organohalogen pollutants are numerous. Reductive debromination of BDE-209 in the environment could provide a significant source of lesser-brominated PBDEs to biota. Moreover, a recent study showed that BDE-209 debrominates in sewage sludge, and another demonstrated that some halorespiring bacteria will debrominate BDE-209. To determine whether reductive debromination of BDE-209 occurs in sediments, parallel experiments were conducted using anaerobic sediment microcosms and a cosolvent-enhanced biomimetic system. In the biomimetic system, reductive debromination occurred at rates corresponding to bromine substitution levels with a BDE-209 half-life of only 18 s compared with a halflife of almost 60 days for 2,2',4,4'-tetrabromodiphenyl ether. In sediment, the measured debromination half-life of BDE-209 was well over a decade and was in good agreement with the predicted value obtained from the biomimetic experiment. Product congeners were predominantly double para-substituted. BDE-209 debrominated in sediment with a corresponding increase in nona-, octa-, hepta-, and hexa-PBDEs. Nine new PBDE congeners appeared in sediment from reductive debromination. Given the very large BDE-209 burden already in sediments globally, it is important to determine whether this transformation is a significant source of lesser-brominated PBDEs to the environment.

Implication of hydraulic properties of bioremediated diesel-contaminated soil.

The hydraulic properties, such as hydraulic conductivity and water retention, of aged diesel-contaminated and bioremediated soils were examined and implications of the hydraulic properties for assessing bioremediation performance of soils were proposed. Bioremediation of diesel-contaminated soil was performed over 80 d using three treatments; (I) no nutrient added, column-packed soil, (II) nutrient added, column-packed soil, and (III) nutrient added, loosen soil. Diesel reduction in treatment I soil (control soil) was negligible while treatment III showed the greatest extent of diesel biodegradation. All treatments showed greatest rates of diesel biodegradation during the first 20 d, followed by a much retarded biodegradation rate in the remaining incubation period. Reduction of the degradation rate due to entrained diesel within inaccessible soil pores was hypothesized and tested by measuring the hydraulic properties of two column-packed soils (treatments I and II). The hydraulic conductivity of treatment II soil (nutrient added) was consistently above that of treatment I soil (no nutrient added) at pressure heads between 0 and 15 cm. In addition, the water retention of treatment II soil was greater at pressure heads <100 cm (equivalent to pore size of >30 microm), suggesting that biodegradative removal of hydrocarbons results in enhanced wettability of larger soil pores. However, water retention was not significantly different for control and biodegraded soils at pressure heads >100 cm, where smaller size soil pores were responsible for the water retention, indicating that diesel remained in smaller soil pores (e.g., <30 microm). Both incubation kinetics and hydraulic measurements suggest that hydrocarbons located in small pores with limited microbe accessibility may be recalcitrant to bioremediation.

Influence of a soil enzyme on iron-cyanide complex speciation and mineral adsorption.

Cyanide is commonly found as ferrocyanide [Fe(II)(CN)(6)](-4) and in the more mobile form, ferricyanide [Fe(III)(CN)(6)](-3) in contaminated soils and sediments. Although soil minerals may influence ferrocyanide speciation, and thus mobility, the possible influence of soil enzymes has not been examined. In a series of experiments conducted under a range of soil-like conditions, laccase, a phenoloxidase enzyme derived from the fungi Trametes versicolor, was found to exert a large influence on iron-cyanide speciation and mobility. In the presence of laccase, up to 93% of ferrocyanide (36-362ppm) was oxidized to ferricyanide within 4h. No significant effect of pH (3.6 and 6.2) or initial ferrocyanide concentration on the extent or rate of oxidation was found and ferrocyanide oxidation did not occur in the absence of laccase. Relative to iron-cyanide-mineral systems without laccase, ferrocyanide adsorption to aluminum hydroxide and montmorillonite decreased in the presence of laccase and was similar to or somewhat greater than that of ferricyanide without laccase. Laccase-catalyzed conversion of ferrocyanide to ferricyanide was extensive though up to 33% of the enzyme was mineral-bound. These results demonstrate that soil enzymes can play a major role in ferrocyanide speciation and mobility. Biotic soil components must be considered as highly effective oxidation catalysts that may alter the mobility of metals and metal complexes in soil. Immobilized enzymes should also be considered for use in soil metal remediation efforts.

Birnessite mediated debromination of decabromodiphenyl ether.

Decabromodiphenyl ether (BDE-209) is a major component of a commercial flame retardant formulation; however, there is limited information on the fate of BDE-209 in the environment, including metal oxide mediated degradation. Laboratory experiments were conducted to investigate the birnessite (delta-MnO(2))-promoted debromination of BDE-209 in tetrahydrofuran (THF)-water systems as well as catechol solutions. Up to 100% (0.1044 micromol initial charge) of BDE-209 disappeared upon reaction with birnessite in THF/H(2)O (4:6-9:1). The formation of aqueous Br(-) from BDE-209 reduction was determined and up to 16 mole% of initial bromine was released over the course of the reaction indicating approximately 1.7 Br-C bonds were reduced per BDE-209 molecule. The distribution of debrominated congeners, however, indicated a much greater extent of debromination for some products than what was inferred from an average bromine mass balance. The produced congeners varied from tetra- to nona-bromodiphenyl ether, including BDE-47 and -99, during the 24 h reaction. Experiments with deuterated water indicated that water was not the major hydrogen donor in the reduction but rather THF provided the reducing power. This conclusion was supported by the presence of succinic acid, which was produced from oxidation of THF. The reactions with aqueous catechol, rather than THF-water mixtures, were performed to assess the possible role that compounds found in natural environments, such a tannin-like phenols, might have on the chemistry. These experiments indicated that birnessite mediated debromination of BDE-209 might occur in natural settings.

Photodegradation of decabromodiphenyl ether adsorbed onto clay minerals, metal oxides, and sediment.

The photodebromination of decabromodiphenyl ether (BDE-209) adsorbed onto six different solid matrixes was investigated in sunlight and by irradiation with 350 +/- 50 nm lamps (four lamps at 24 W each). After 14 days of lamp irradiation, BDE-209 degraded with a half-life of 36 and 44 days, respectively, on montmorillonite or kaolinite, with much slower degradation occurring when sorbed on organic carbon-rich natural sediment (t1/2 = 150 days). In late summer and fall sunlight (40.5 degrees N, elevation 600 ft), the half-lives of BDE-209 sorbed on montmorillonite and kaolinite were 261 and 408 days, respectively. Under both irradiation schemes, no significant loss of BDE-209 occurred when sorbed to aluminum hydroxide, iron oxide (ferrihydrite), or manganese dioxide (birnessite). Upon exposure to both lamp and solar light and in the presence of montmorillonite and kaolinite, numerous lesser brominated congeners (tri- to nonabromodiphenyl ethers) were produced. Nearly identical product distribution was evident on montmorillonite and kaolinite. Dark control experiments for each mineral showed no disappearance of BDE-209 or appearance of degradation products. These results suggest that photodegradation of BDE-209 on mineral aerosols during long-range atmospheric transport may be an important fate process for BDE-209 in the environment.

Treatment of 2,4-dichlorophenol polluted soil with free and immobilized laccase.

Enzyme treatment is currently considered for remediation of terrestrial systems polluted with organic compounds. In this study, two soils from Pennsylvania with 2.8 or 7.4% organic matter contents (Soils 1 and 2, respectively) were amended with 14C-labeled 2,4-dichlorophenol (2,4-DCP) and incubated with a laccase from Trametes villosa (free or immobilized on montmorillonite). 2,4-DCP was either transformed to methanol-soluble polymeric products (11-32%) or covalently bound to soil organic matter (53-85%); unaltered 2,4-DCP could be recovered from soil by methanol extraction (0-38%) at the completion of a 14-d incubation period. In Soil 1, both free and immobilized laccase removed 100% of 2,4-DCP without regard for moisture conditions. In Soil 2, immobilized laccase removed more 2,4-DCP (about 95%, regardless of moisture conditions) than free enzyme (55, 75, and 90% at 30, 55, and 100% of maximum water-holding capacity, respectively). Binding of 2,4-DCP in the humin fraction was nearly the same for free and immobilized laccase. More 2,4-DCP, however, was bound to humic and fulvic acids in the presence of immobilized laccase than in the presence of free laccase. In general, immobilized laccase performed better than free laccase. However, for practical applications, the higher activity of immobilized laccase is offset by a 23% loss in enzyme activity during immobilization, which approximates the 30% increase in free laccase needed to achieve the same level of remediation. Furthermore, immobilized laccase is more costly than free T. villosa laccase.