Assessing the bioavailability of complex petroleum hydrocarbon mixtures in sediments

Several experimental methods have been developed to assess the bioavailability of individual organic compounds. So far none of them has however been applied to complex mixtures, such as oil (petroleum hydrocarbons), which is an ubiquitous pollutant. In the present study, we tested the potential of five of these experimental methods and that of a model approach to predict bioaccumulation of oil in the aquatic worm Lumbriculus variegatus exposed to 14 field-contaminated sediments. Actual and predicted bioaccumulation were compared in terms of both total bioaccumulative petroleum hydrocarbon concentrations and the relative distribution pattern of separate boiling point fractions (hydrocarbon blocks). None of the experimental methods was able to directly assess bioaccumulation in L. variegatus and correction factors were needed to match predicted and actual concentrations. These factors appeared concentration-dependent for solid phase micro extraction (SPME) and extractions with Tenax and cyclodextrin, most probably due to artifacts. Moreover, the hydrocarbon block pattern produced by these methods considerably differed from the pattern observed for worms; an additional reason for disqualification also applying to headspace-SPME. In contrast, the pattern produced by polyoxymethylene solid phase extraction (POM-SPE) closely mimicked the worm pattern and a sediment, hydrocarbon block, and concentration-independent correction factor (17) could be derived, based on which actual bioaccumulation could be predicted within a factor of 3. Finally, the model predicted bioaccumulation directly within a factor of 2. The accompanying hydrocarbon block pattern however deviated significantly more from the worm pattern than the POM-SPE pattern did. We therefore conclude that POM-SPE may be the overall best approach for predicting bioaccumulation of complex hydrocarbon mixtures in aquatic worms, all the more since an experimental approach will implicitly capture all factors determining bioavailability, which may prove difficult through a modeling approach.     

Addition of carbon sorbents to reduce PCB and PAH bioavailability in marine sediments: physicochemical tests

The addition of activated carbon as particulate sorbent to the biologically active layer of contaminated sediment is proposed as an in-situ treatment method to reduce the chemical and biological availability of hydrophobic organic contaminants (HOCs) such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). We report results from physicochemical experiments that assess this concept. PCB- and PAH-contaminated sediment from Hunters Point Naval Shipyard, San Francisco Bay, CA, was contacted with coke and activated carbon for periods of 1 and 6 months. Sediment treated with 3.4 wt % activated carbon showed 92% and 84% reductions in aqueous equilibrium PCB and PAH concentrations, 77% and 83% reductions in PCB and PAH uptake by semipermeable membrane devices (SPMD), respectively, and reductions in PCB flux to overlying water in quiescent systems up to 89%. Adding coke to contaminated sediment did not significantly decrease aqueous equilibrium PCB concentrations nor PCB or PAH availability in SPMD measurements. Coke decreased PAH aqueous equilibrium concentrations by 38-64% depending on coke dose and particle size. The greater effectiveness of activated carbon as compared to coke is attributed to its much greater specific surface area and a pore structure favorable for binding contaminants. The results from the physicochemical tests suggest that adding activated carbon to contaminated field sediment reduces HOC availability to the aqueous phase. The benefit is manifested relatively quickly under optimum contact conditions and improves in effectiveness with contact time from 1 to 6 months. Activated carbon application is a potentially attractive method for in-situ, nonremoval treatment of marine sediment contaminated with HOCs.     

Metal-solid interactions controlling the bioavailability of mercury from sediments to clams and sipunculans

The bioavailability of sedimentary Hg(II) and methylmercury (MeHg) was quantified by measuring the assimilation efficiency (AE) in the clam Ruditapes philippinarum and the extraction of the gut juices from the sipunculan Sipunculus nudus. Three factors (Hg concentration in sediment, Hg sediment contact time, and organic content of sediments) were modified to examine metal-solid interactions in controlling Hg bioavailability. The Hg AEs in the clams were strongly correlated with the extraction from the sipunculan gut juices for both Hg species. The bioavailability of both Hg(II) and MeHg generally increased with increased sediment Hg concentration but decreased with sedimentmetal contact time and increasing organic content (except that MeHg was not influenced by organic content). Hg(II) speciation in sediments, quantified by sequential chemical extraction (SCE), was dependent on geochemical conditions and greatly controlled the mobility and bioavailability of Hg(II) in sediments. Most bioavailable Hg(II) originated from the strongly complexed phase (e.g., Hg bound up in Fe/Mn oxide, amorphous organosulfur, or mineral lattice), whereas Hg bound with the organocomplexed phase (Hg humic and Hg2Cl2) was not bioavailable. Hg bound with the other geochemical phases (water soluble, HgO, HgSO4, and HgS) contributed very little to the bioavailable Hg due to their low partitionings. Further, the amount of bioavailable Hg was inversely related to the particle reactivity of Hg with the sediments. Detailed analyses of metal-solid interactions provide a better understanding of how Hg in sediments can predict Hg concentration and therefore bioavailability in benthic invertebrates.     

Nonsingular adsorption/desorption of chlorpyrifos in soils and sediments: experimental results and modeling

At environmentally relevant concentrations in soils and sediments, chlorpyrifos, a hydrophobic organic insecticide, showed strong adsorption that correlated significantly with organic matter content. Chlorpyrifos desorption followed a nonsingular falling desorption isotherm that was estimated using a memory-dependent mathematical model. Desorption of chlorpyrifos was biphasic in nature, with a labile and nonlabile component. The labile component comprised 18-28% of the original solid-phase concentration, and the residue was predicted to slowly partition to the aqueous phase, implying long-term desorption from contaminated soils or sediments. The newly proposed mechanism to explain sorption/desorption hysteresis and biphasic desorption is the unfavorable thermodynamic energy landscape arising from limitation of diffusivity of water molecules through the strongly hydrophobic domain of soils and sediments. Modeling results suggest that contaminated soils and sediments could be secondary long-term sources of pollution. Long-term desorption may explain the detection of chlorpyrifos and other hydrophobic organic compounds in aquatic systems far from application sites, an observation that contradicts conventional transport predictions.     

Actinomycete bacteria isolated from the sediments at coastal and offshore area of Nagasaki Prefecture, Japan: diversity and biological activity

About 800 strains of actinomycetes were isolated from marine environments around Nagasaki Prefecture, Japan. The isolates were compared with taxa and biological activities of their secondary metabolites. It is suggested that a variety of actinomycetes are isolated from different marine environments.     

Role of sediment resuspension in the remobilization of particulate-phase metals from coastal sediments

The release of particulate-phase trace metals due to sediment resuspension has been investigated by combining erosion chamber experiments that apply a range of shear stresses typically encountered in coastal environments with a shear stress record simulated by a hydrodynamic model. Two sites with contrasting sediment chemistry were investigated. Sediment particles enriched in silver, copper, and lead, 4-50 times greater than the bulk surface-sediment content, were the first particles to be eroded. As the shear-stress level was increased in the chamber, the total mass eroded increased, butthe enrichment of these trace metals fell, approaching the bulk-sediment content. From the temporal distribution of shear stress generated by the hydrodynamic model for a site in Boston Harbor, resuspension fluxes were estimated. The erosion threshold of this site is exceeded during spring tides, releasing the particles enriched in trace metals into the water column. Due to the higher trace metal content and the regularity of resuspension, low-energy resuspension events (up to a shear stress of 0.2 N/m(2)) contribute up to 60% of the resuspension metal flux in an average year. The estimated annual quantity of copper and lead resuspended into the water column is higher than estimates of the total riverine flux for these metals. These results indicate that sediment resuspension is a very important mechanism for releasing metals into the water column and provide new insight into the chemical and physical processes controlling the long-term fate of trace metals in contaminated sediments.     

Influences of amphiphiles on dechlorination of a trichlorobenzene by nanoscale Pd/Fe: adsorption, reaction kinetics, and interfacial Interactions

The influences of amphiphiles on the catalytic dechlorination of 1,2,4-trichlorobenzene (124TCB) bythe nanoscale Pd/Fe particles were comprehensively examined. The fresh and reacted Pd/ Fe particles were characterized with XRD, TEM, SEM, FTIR spectrometry, and goniometry. Adsorption of amphiphiles on the Pd/Fe particles, iron dissolution, and H2 evolution in the Pd/Fe-water system were quantified to expound the influences of the various amphiphiles on the dechlorination process. The Langmuir-Hinshelwood model is used to elucidate the dechlorination kinetics, and it provides insight into the influence of amphiphiles on 124TCB partitioning to the interfacial layer and the resulting dechlorination rates. The rate constants increased by a factor of 1.5--2.5 with the presence of cationic cetyltrimethylammonium bromide (CTAB). In the anionic sodium deodecyl sulfate(SDS) or nonionic nonylphenol ethoxylate (NPE) and octylphenolpoly (ethylene glycol ether)x (TX-100) surfactant solutions, the 124TCB dechlorination rates were slightly increased over those observed in ultrapure water. However, when concentrations of the surfactants were above their CMCs, the dechlorination rates decreased. The findings also showed that DPC (dodecylpyridinium chloride) and NOM (natural organic matter) might be the competitive H2 acceptors to 124TCB, and they significantly retarded its catalytic dechlorination by the Pd/Fe particles. CTAB at a concentration below the CMC appeared to be the most benign to the 124TCB dechlorination.     

Concentration and distribution of platinum group elements (Pt, Pd, Rh) in airborne particulate matter in Frankfurt am Main, Germany

The concentrations and distribution of platinum group elements (Pt, Pd, Rh) in airborne particulate matter were studied in a period of one year from August 2001 to July 2002 in urban and in nonurban areas. Airborne dust samples were collected as a total amount (particles with an aerodynamic diameter <22 microm) and classified using an eight-stage Andersen impactor (<10 microm) at three locations with different traffic density roads in the Frankfurt am Main and nonurban areas. Sampling at the three locations was performed simultaneously for total airborne dust and fractionated airborne dust. Pd was determined by total reflection X-ray fluorescence after Hg coprecipitation. Pt and Rh were analyzed by adsorptive striping voltammetry after HPA digestion. The results show that the PGE concentrations in airborne samples depend on the traffic density. The highest PGE concentrations in air were found in the vicinity of major roads with heavy traffic, and the lowest ones were found in the nonurban area. The presence of PGE at the sampling station relatively free of traffic in a nonurban area hints to a transport of some of the emitted PGE from the city to this station by wind. At all three sampling locations, a heterogeneous distribution of the Pd, Pt, and Rh concentrations during the sampling year can be observed. The sum of PGE concentrations in total airborne dust is comparable with the sum of impactor samples. However, the concentration of Pt and Rh in total airborne dust (<22 microm) is on average higher than in impactor samples (<10 microm). On the contrary, Pd concentration is higher in impactor samples in most cases. The airborne PGE distribution is dominated by Pt, followed by Pd and Rh. The impactor samples are dominated by Pd, followed by Pt and Rh. This fact indicates that palladium occurs mainly in relatively fine airborne particles. The main fraction of PGE is found on average in particle sizes between 1.1 and 4.7 microm. Knowledge of the size distribution of particles containing PGE is important with respect to risk assessment of human inhalation.     

Direct evidence of sequestration in sediments affecting the bioavailability of hydrophobic organic chemicals to benthic deposit-feeders

In contrast to equilibrium partitioning model (EqP) calculations, biota to sediment accumulation factors (BSAF) of hydrophobic organic compounds for deposit-feeders are highly variable. Recent literature suggests that this variability can be attributed to differences in sequestration or the presence of slowly desorbing fractions in the sediment. In the present study, we investigated whether the observed relationship between bioavailability and sequestration is causal. We determined BSAF values and sequestration status, measured as the distribution over rapidly and slowly desorbing fractions, of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in a manipulated sediment as well as in the original, unmanipulated sediment The manipulation, 48 h suspending with Tenax, resulted in reduction of the rapidly desorbing fraction, while other factors such as contact time and sediment properties remained constant. Contrary to expectations based on EqP, BSAF values did not remain constant but were reduced by a factor of 2-27, proportional to the reduction in rapidly desorbing fractions. The results provide direct evidence of a causal relationship between sequestration and bioavailability to deposit-feeders. Furthermore, the present study demonstrates the need to modify traditional use of the equilibrium partitioning model to account for variation in the sequestration status of HOC in sediments.     

Level and degradation of Deepwater Horizon spilled oil in coastal marsh sediments and pore-water

This research investigates the level and degradation of oil at ten selected Gulf saltmarsh sites months after the 2010 BP Macondo-1 well oil spill. Very high levels (10-28%) of organic carbon within the heavily oiled sediments are clearly distinguished from those in pristine sediments (<3%). Dissolved organic carbon in contaminated pore-waters, ranging up to hundreds of mg/kg, are 1 to 2 orders of magnitude higher than those at pristine sites. Heavily oiled sediments are characterized by very high sulfide concentrations (up to 80 mg/kg) and abundance of sulfate reducing bacteria. Geochemical biomarkers and stable carbon isotope analyses fingerprint the presence of oils in sediments. Ratios of selected parameters calculated from the gas chromatograph spectra are in a remarkable narrow range among spilled oils and initial BP crude. At oiled sites dominated by C(4) plants, δ(13)C values of sediments (-20.8 ± 2.0‰) have been shifted significantly lower compared to marsh plants (-14.8 ± 0.6‰) due to the inflow of isotopically lighter oil (-27 ± 0.2‰). Our results show that (1) lighter compounds of oil are quickly degraded by microbes while the heavier fractions of oil still remain and (2) higher inputs of organic matter from the oil spill enhance the key microbial processes associated with sulfate reducing bacteria.     

The role of dietary fiber in the bioaccessibility and bioavailability of fruit and vegetable antioxidants

Antioxidants are abundant compounds primarily found in fresh fruits and vegetables, and evidence for their role in the prevention of degenerative diseases is continuously emerging. However, the bioaccessibility and bioavailability of each compound differs greatly, and the most abundant antioxidants in ingested fruit are not necessarily those leading to the highest concentrations of active metabolites in target tissues. Fruit antioxidants are commonly mixed with different macromolecules such as carbohydrates, lipids, and proteins to form a food matrix. In fruits and vegetables, carbohydrates are the major compounds found, mainly in free and conjugated forms. Dietary fiber, the indigestible cell wall component of plant material, is considered to play an important role in human diet and health. Most studies on antioxidant bioavailability are focused on foods and beverages from which antioxidants are easily released. There is evidence indicating that food microstructure affects the bioaccessibility and bioavailability of several nutrients, referring mostly to antioxidants. Nevertheless, the specific role of dietary fiber in the absorption of antioxidants has not been widely discussed. In this context, the purpose of the present review is to compile and analyze evidence relating to the association between dietary fiber and antioxidants, and the physical and chemical interactions that modulate their release from the chyme in the gastrointestinal tract.     

Two years after the Hebei Spirit oil spill: residual crude-derived hydrocarbons and potential AhR-mediated activities in coastal sediments

The Hebei Spirit oil spill occurred in December 2007 approximately 10 km off the coast of Taean, South Korea, on the Yellow Sea. However, the exposure and potential effects remain largely unknown. A total of 50 surface and subsurface sediment samples were collected from 22 sampling locations at the spill site in order to determine the concentration, distribution, composition of residual crudes, and to evaluate the potential ecological risk after two years of oil exposure. Samples were extracted and analyzed for 16 polycyclic aromatic hydrocarbons (PAHs), 20 alkyl-PAHs, 15 aliphatic hydrocarbons, and total petroleum hydrocarbons using GC-MSD. AhR-mediated activity associated with organic sediment extracts was screened using the H4IIE-luc cell bioassay. The response of the benthic invertebrate community was assessed by mapping the macrobenthic fauna. Elevated concentrations of residual crudes from the oil spill were primarily found in muddy bottoms, particularly in subsurface layers. In general, the bioassay results were consistent with the chemistry data in a dose-dependent manner, although the mass-balance was incomplete. More weathered samples containing greater fractions of alkylated PAHs exhibited greater AhR activity, due to the occurrence of recalcitrant AhR agonists present in residual oils. The macrobenthic population distribution exhibits signs of species-specific tolerances and/or recolonization of certain species such as Batillaria during weathering periods. Although the Hebei Spirit oil spill was a severe oil exposure, it appears the site is recovering two years later.     

Occurrence and specific congener profile of 40 polybrominated diphenyl ethers in river and coastal sediments from Portugal

Forty polybrominated diphenyl ethers (PBDEs), from mono- through hepta-brominated, were analyzed in river and coastal sediment samples of the eight main river basins of Portugal to investigate the occurrence, geographical distribution, and detailed congener profiles. Thirty-two sediment samples taken along the different rivers from inland to the open sea revealed an increase toward the river mouth with a total PBDE concentration of 20 ng/g-dw, and levels decreased to 0.5 ng/g-dw in coastal sediments. PBDEs were detected in all samples analyzed, indicating a diffuse source of pollution in the aquatic environments. Maximum levels were encountered in sediments collected close to urban and industrial areas. Of 40 congeners included in the analytical work, 17 congeners were detected in river sediments. BDE 47 was found in all samples analyzed whereas BDEs 100 and 99 were found in more than 26 out of 32 samples analyzed at concentrations from 0.03 to 10 ng/g-dw. This study is unique in showing the presence of previously nondescribed lower brominated PBDEs in riverine and marine sediments. BDEs 7, 11, 12+13, 15, 30, 32, 17, 25, 28+33, 49, 75, and 71 were identified in two to five samples with a median of 0.03-0.55 ng/g-dw. The analytical method developed consisted of the use of Soxhlet extraction with a novel cleanup method employing alumina cartridges and analysis by gas chromatography-mass spectrometry operated in negative chemical ionization mode.     

Cd adsorption properties of components in different freshwater surface coatings: the important role of ferromanganese oxides

Surface coatings developed in different natural waters were used to study the role of the composition of surface coatings in controlling Cd adsorption in aquatic environments. To investigate the adsorption property of each component, the method of extraction techniques followed by Cd adsorption and statistical analysis were employed. Hydroxylamine hydrochloride was used to remove Mn oxides selectively, sodium dithionite was used to remove Mn and Fe oxides, and oxalic acid was used to remove most metal oxides and part of the organic material. Adsorption of Cd to surface coatings was measured before and after extraction under controlled laboratory conditions. The observed Cd adsorptions to unextracted and extracted surface coatings were analyzed using nonlinear least-squares fitting to estimate the adsorption property of each surface coating constituent. In different waters, the relative contribution to Cd adsorption of each component was different, but in all the waters studied, ferromanganese oxides contributed most with lesser roles indicated for organic phase and Al oxides. The Cd adsorption ability of manganese oxides was significantly higher than that of the other components.     

Characterization of zinc, lead, and cadmium in mine waste: implications for transport, exposure, and bioavailability

We characterized the lability and bioaccessibility of Zn, Pb, and Cd in size-fractionated mine waste at the Tar Creek Superfund Site (Oklahoma) to assess the potential for metal transport, exposure, and subsequent bioavailability. Bulk mine waste samples contained elevated Zn (9100 +/- 2500 ppm), Pb (650 +/- 360 ppm), and Cd (42 +/- 10 ppm), while particles with the greatest potential for windborne transport and inhalation (< 10 microm) contained substantially higher concentrations, up to 220 000 ppm Zn, 16 000 ppm Pb, and 530 ppm Cd in particles < 1 microm. Although the mined ore at Tar Creek primarily consisted of refractory metal sulfides with low bioavailability, sequential extractions and physiologically based extractions indicate that physical and chemical weathering have shifted metals into relatively labile and bioaccessible mineral phases. In < 37 microm mine waste particles, 50-65% of Zn, Pb, and Cd were present in the "exchangeable" and "carbonate" sequential extraction fractions, and 60-80% of Zn, Pb, and Cd were mobilized in synthetic gastric fluid, while ZnS and PbS exhibited minimal solubility in these solutions. Our results demonstrate the importance of site-specific characterization of size-fractionated contemporary mine waste when assessing the lability and bioavailability of metals at mine-waste impacted sites.     

On the bioavailability of flavanols and anthocyanins: flavanol-anthocyanin dimers

The bioavailability of flavanols, anthocyanins and anthocyanin-derived pigments like flavanol-anthocyanin dimers already reported to occur in food products is a major unsolved issue. The absorption of the flavanol-anthocyanin dimer (+)-catechin-(4,8)-malvidin-3-O-glucoside (Cat-Mv3glc) through Caco-2 cells was assessed by performing transepithelial transport assays. The ability of Cat-Mv3glc to cross Caco-2 cells was compared with that of malvidin-3-glucoside (Mv3glc), (+)-catechin (Cat) and procyanidin B3 (Cat-Cat), in order to evaluate the influence of some structural features on the transport efficiency. The flavanol-anthocyanin dimer was absorbed in this intestinal model although with a lower efficiency than the monomers Cat and Mv3glc. On the other hand, Cat-Mv3glc was found to cross the intestinal barrier model more significantly than Cat-Cat. This feature may be related to the presence of the glucose moiety in its structure. Overall, this study brings more insights into the bioavailability of anthocyanins and flavanols and represents the first report on the bioavailability of flavanol-anthocyanins.     

Polychlorinated biphenyls in nonaccumulating, century-old sediments: sources, signatures, and mechanism of introduction

This study documents the occurrence of highly chlorinated PCB congeners in stream sediment deposited over 100 years ago. Penta- to heptachlorinated congeners (> 80%) have been found at concentrations up to 78.8 ng/g (dw) in core samples of a small, rural tributary of Lake Ontario. Lower chlorinated congeners and other organochlorine compounds occur sporadically; 210Pb and 137Cs are lacking. The most plausible mechanism is accumulation of dissolved-phase PCBs in permeable sediments adjacent to the creek channel. The similarity between core and air samples collected in the drainage basin suggests derivation from a residual fraction of atmospherically derived PCB congeners.