Is black carbon a better predictor of polycyclic aromatic hydrocarbon distribution in soils than total organic carbon?

Black carbon (BC) and total organic carbon (TOC) were quantified in the surface soils of Switzerland (N = 105) and Delhi (N = 36), India, to examine their relationships with contents of polycyclic aromatic hydrocarbons (PAH). BC content in Swiss (background) soils (N = 104) varied from 0.41 to 4.75 mg/g (median: 1.13 mg/g) and constituted 1-9% (median: 3%) of TOC. Indian (urban) soils had similar BC concentrations (0.37-2.05 mg/g, median: 1.19 mg/g), with relatively higher BC/TOC (6-23%, median: 13%). Similar to TOC, BC showed significant positive correlation with lighter PAH, but no correlation with heavier PAH in Swiss soils. In contrast, heavier PAH were significantly correlated only with BC in Delhi soils. It seems that TOC governs the distribution of PAH in organic matter rich background soils, while the proximity to emission sources is reflected by BC-PAH association in urban soils.     

Black carbon (BC) in urban and surrounding rural soils of Beijing, China: spatial distribution and relationship with polycyclic aromatic hydrocarbons (PAHs)

The concentrations of black carbon (BC), total organic carbon (TOC) and polycyclic aromatic hydrocarbons (PAHs) have been determined in soils from urban and rural areas of Beijing. The rural area can be divided into plain and mountainous areas which are close to and relatively far from the urban area, respectively. Concentration of BC (5.83 ± 3.05 mg g⁻¹) and BC/TOC concentration ratio (0.37 ± 0.15) in Beijing’s urban soil are high compared with that in world background soils and rural soils of Beijing, suggesting the urban environment to be an essential source and sink of BC. Concentration of BC in the urban area decreases from the inner city to exterior areas, which correlates with the urbanization history of Beijing and infers accumulation of BC in old urban soils. Black carbon in Beijing soils mainly comes from fossil fuel combustion, especially traffic emission. Median PAH concentration in the urban area (502 ng g⁻¹) is one order of magnitude higher than that in the rural plain (148 ng g⁻¹) and mountainous area (146 ng g⁻¹) where PAHs are supposed to mainly come from atmospheric deposition from the urban area. Concentrations of BC correlate significantly with those of PAHs (p < 0.01, except naphthalene) in the urban area and with those of heavier 4-, 5- and 6- ring PAHs (p < 0.01) in the adjacent rural plain area, while there is no significant correlation with any PAH in the farther rural mountainous area.     

Occurrence of polycyclic aromatic hydrocarbons in surface sediments of a highly urbanized river system with special reference to energy consumption patterns

Sediment samples collected from downstream of the Dongjiang River, a highly urbanized river network within the Pearl River Delta of South China, were analyzed for 28 polycyclic aromatic hydrocarbons (PAHs). Total concentrations of 28 PAHs, 16 priority PAHs designated by the United States Environmental Protection Agency (USEPA) and the seven carcinogenic PAHs classified by the USEPA ranged from 480 to 4600, 100 to 3400 and 10 to 1700 ng/g dry weight, respectively. Principal component analysis-based stepwise multivariate linear regression showed that sediment PAHs were predominantly derived from coal combustion, refined fossil fuel combustion and oil spills, accounting for 37%, 32% and 23%, respectively, of the total loading. The levels of sediment PAHs remained steady from 2002 to 2008, during which fossil fuel consumption had doubled, probably reflecting efforts to control PAH emissions from fossil fuel combustion. Finally, use of natural gas and liquefied petroleum gas in automobiles should be encouraged to improve environmental quality.     

Relation between PAH and black carbon contents in size fractions of Norwegian harbor sediments

Distributions of total organic carbon (TOC), black carbon (BC), and polycyclic aromatic hydrocarbons (PAH) were investigated in different particle size fractions for four Norwegian harbor sediments. The total PAH (16-EPA) concentrations ranged from 2 to 113 mg/kg dry weight with the greatest fraction of PAH mass in the sand fraction for three of the four sediments. TOC contents ranged from 0.84% to 14.2% and BC contents from 0.085% to 1.7%. This corresponds to organic carbon (OC = TOC - BC) contents in the range of 0.81-14% and BC:TOC ratios of 1.3-18.1%. PAH isomer ratios suggested that the PAH in all four sediments were of pyrogenic origin. Furthermore, stronger correlations between PAH versus BC (r2 = 0.85) than versus OC (r2 = 0.15) were found. For all size fractions and bulk sediments, the PAH-to-BC ratios for the total PAHs were on average 6+/-3 mg PAH/g BC. These results suggest that PAH distributions were dominated by the presence of BC, rather than OC. As sorption to BC is much stronger than sorption to OC, this may result in significantly lower dissolved concentrations of PAH than expected on the basis of organic carbon partitioning alone.     

Persistence,variance and toxic levels of organochlorine pesticides in fluvial sediments and the role of black carbon in their retention

The present study assesses the persistence and variation of organochlorine pesticides (OCPs) and their regulation by total organic carbon (TOC) and black carbon (BC) in freshwater sediment. Sediment samples from the Yamuna River, a major tributary of the Ganges (one of the most populated and intensively used rivers in Asia), had high levels of Σ₂₀OCPs (21.41 to 139.95 ng g^?1). β-Hexachlorocyclohexane (β-HCH) was the most predominant component. ΣHCH and Σdichloro-diphenyl-trichloroethane (DDT) constituted ~86 % of Σ₂₀OCPs. Isomer ratios indicated fresh usage of lindane, DDT and technical-grade HCH. Toxicological comparison with freshwater sediment quality guidelines showed γ-HCH and DDT at high levels of concern. β-HCH, α-HCH, endrin, heptachlor epoxide, dichloro-diphenyl-dichloroethane (DDD), dichloro-diphenyl-dichloroethylene and chlordane were above some of the guideline levels. TOC and BC had mean concentrations of 1.37?±?0.51 % and 0.46?±?0.23 mg g^?1, respectively. BC constituted 1.25 to 10.56 % of TOC. We observed low to moderate correlations of BC with isomers of HCH, p,p′-DDT and methoxychlor while of TOC with Σ₂₀OCPs, γ-HCH, endosulfan sulfate and methoxychlor. Principal component analysis enabled correlating and clustering of various OCPs, BC and TOC. OCP distribution was related with pH, electrical conductivity, soil moisture and finer fractions of sediment. OCPs with similarity in properties that determine their interactions with carbonaceous components of sediment clustered together. A number of factors may, thus, be involved in the regulation of interactive forces between BC and OCPs. BC in this study may be more important than TOC in the retention of some OCPs into fluvial sediments, thereby reducing their bioavailability. The finding is probably the first of its kind to report and emphasises the role of BC in the persistence of OCPs in fluvial sediments.     

Historical record of black carbon in urban soils and its environmental implications

Energy use in urbanization has fundamentally changed the pattern and fluxes of carbon cycling, which has global and local environmental impacts. Here we have investigated organic carbon (OC) and black carbon (BC) in six soil profiles from two contrast zones in an ancient city (Nanjing) in China. BC in soils was widely variable, from 0.22 to 32.19 g kg⁻¹. Its average concentration in an ancient residential area (Zone 1) was, 0.91 g kg⁻¹, whereas in Zone 2, an industrial and commercial area, the figure was 8.62 g kg⁻¹. The ratio of BC/OC ranged from 0.06 to 1.29 in soil profiles, with an average of 0.29. The vertical distribution of BC in soil is suggested to reflect the history of BC formation from burning of biomass and/or fossil fuel. BC in the surface layer of soils was mainly from traffic emission (especially from diesel vehicles). In contrast, in cultural layers BC was formed from historical coal use. The contents of BC and the ratio of BC/OC may reflect different human activities and pollution sources in the contrasting urban zones. In addition, the significant correlation of heavy metals (Cu, Pb, and Zn) with BC contents in some culture layers suggests the sorption of the metals by BC or their coexistence resulted from the coal-involved smelting.     

Identification of carbonaceous geosorbents for PAHs by organic petrography in river floodplain soils

Organic petrographic analysis was applied to provide direct information on carbonaceous geosorbents for PAHs in river floodplain soils. The anthropogenic OM group (primarily coal and coal-derived particles) displayed large volume amounts for all the soil samples. Distinct PAH concentrations with similar PAH distribution patterns were determined in grain size and density fractions for each sample. Two-ring PAHs had stronger correlation to organic carbon (OC) than black carbon (BC) contents, while heavier PAHs showed correlation to BC, rather than OC. In this study, we combined grain size and density separation, PAH determinations, TOC and BC measurements, and organic petrographic identification, and concluded that two-ring PAHs in soils were associated to coal particles. Other heavier PAHs could be more controlled by black carbon (BC), which were mostly coal-derived particles from former coal mining and coal industrial activity.     

Source apportionment of polycyclic aromatic hydrocarbons in surface soil in Tianjin, China

Principal component analysis and multiple linear regression were applied to apportion sources of polycyclic aromatic hydrocarbons (PAHs) in surface soils of Tianjin, China based on the measured PAH concentrations of 188 surface soil samples. Four principal components were identified representing coal combustion, petroleum, coke oven plus biomass burning, and chemical industry discharge, respectively. The contributions of major sources were quantified as 41% from coal, 20% from petroleum, and 39% from coking and biomass, which are compatible with PAH emissions estimated based on fuel consumption and emission factors. When the study area was divided into three zones with distinctive differences in soil PAH concentration and profile, different source features were unveiled. For the industrialized Tanggu-Hangu zone, the major contributors were cooking (43%), coal (37%) and vehicle exhaust (20%). In rural area, however, in addition to the three main sources, biomass burning was also important (13%). In urban-suburban zone, incineration accounted for one fourth of the total.     

Inventory of aerosol and sulphur dioxide emissions from India. Part II—biomass combustion

A spatially resolved biomass burning data set, and related emissions of sulphur dioxide and aerosol chemical constituents was constructed for India, for 1996–1997 and extrapolated to the INDOEX period (1998–1999). Sources include biofuels (wood, crop waste and dung-cake) and forest fires (accidental, shifting cultivation and controlled burning). Particulate matter (PM) emission factors were compiled from studies of Indian cooking stoves and from literature for open burning. Black carbon (BC) and organic matter (OM) emissions were estimated from these, accounting for combustion temperatures in cooking stoves. Sulphur dioxide emission factors were based on fuel sulphur content and reported literature measurements. Biofuels accounted 93% of total biomass consumption (577 MT yr⁻¹), with forest fires contributing only 7%. The national average biofuel mix was 56 : 21 : 23% of fuelwood, crop waste and dung-cake, respectively. Compared to fossil fuels, biomass combustion was a minor source of SO₂ (7% of total), with higher emissions from dung-cake because of its higher sulphur content. PM_2.5 emissions of 2.04 Tg yr⁻¹ with an “inorganic fraction” of 0.86 Tg yr⁻¹ were estimated. Biomass combustion was the major source of carbonaceous aerosols, accounting 0.25 Tg yr⁻¹ of BC (72% of total) and 0.94 Tg yr⁻¹ of OM (76% of total). Among biomass, fuelwood and crop waste were primary contributors to BC emissions, while dung-cake and forest fires were primary contributors to OM emissions. Northern and the east-coast India had high densities of biomass consumption and related emissions. Measurements of emission factors of SO₂, size resolved aerosols and their chemical constituents for Indian cooking stoves are needed to refine the present estimates.     

Levels and spatial distribution of chlorophenols - 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol in surface water of China

The chlorophenol pollutants (CPs) have been reported to occur at relatively high concentrations in some Chinese waters. To map the distribution of CPs in the surface water throughout China, samples were collected from over 600 sites in the seven major watersheds and three drainage areas. The samples were analyzed for the representative CPs including 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol. In general, it was observed that 2,4-dichlorophenol and 2,4,6-trichlorophenol were more frequently detected at higher concentrations in the rivers of North China compared with those of South China. High concentration sites of 2,4-dichlorophenol and 2,4,6-trichlorophenol mainly occurred in the Yellow River, Huaihe River, and Haihe River watersheds, while pentachlorophenol contamination mainly occurred in the Yangtze River watershed. The pentachlorophenol was the most ubiquitous CPs being detected in 85.4% of samples (median=50.0ngl(-1); range <1.1-594.0ngl(-1)), 2,4-dichlorophenol was detected in 51.3% (median=5.0ngl(-1); range <1.1-19960.0ngl(-1)) and the 2,4,6-trichlorophenol was detected in 54.4% of water samples (median=2.0ngl(-1), range <1.4-28650.0ngl(-1)). The results of this investigation indicated that 2,4-dichlorophenol and 2,4,6-trichlorophenol contaminations of Yellow River, Huaihe River, and Haihe River watersheds were of particular concern, while the pentachlorophenol contamination mainly occurred in the Yangtze River watershed. These results showed that CPs contamination in the surface water of China was similar to other places of the world.     

Distribution,source, and ecological risk assessment of PAHs among size and density fractions in contaminated sediments from the Yellow River of Henan section

This study investigated particle size and density distributions of polycyclic aromatic hydrocarbons (PAHs) in two surface sediments (JZ and KF), collected from the Yellow River of Henan section, China. The concentrations of Σ₁₅PAHs ranged from 35.6 to 45862?ng g^?1 dry wt, which were greatly elevated in coarse particles and low-density fractions. The Σ₁₅PAHs concentrations in low-density fractions were 533 (JZ) and 996 (KF) times higher than those in the corresponding high-density fractions. However, due to relatively less quantities of low-density fractions (0.27–2.33%), most of the PAHs were contributed by the high-density components. For both sediments, the influence factors of PAHs source in the environment were very complex, more so than the level of TOC and BC content. JZ sediment was dominated by 4-ring to 6-ring PAHs (61.5–75.1%), while, 2-ring to 3-ring PAHs were abundant in KF samples (39.8–72.6%). Ratios of specific PAHs reflected PAHs among the size- and density-fraction of each sediment may be contaminated by mixed of pyrolytic and petrogenic origin. Additionally, ecological risk assessment of PAHs suggested that total toxic equivalent values of PAHs in the low-density fractions were much higher than those of the corresponding high-density fractions in the studied area.     

Chemical characterization and source identification of polycyclic aromatic hydrocarbons in aerosols originating from different sources

To obtain the characteristic factors or signatures of particulate polycyclic aromatic hydrocarbons (PAHs) to help identify the sources of particulate PAHs in the atmosphere, different carbonaceous aerosols were generated by burning different fossil fuels and biomass under different conditions in the laboratory, and the chemical characteristics of 14 PAHs were studied in detail. The results showed that (1) carbonaceous aerosols derived from domestic burning of coal, diesel fuel, and gasoline have much higher concentrations of PAHs than those derived from domestic burning of biomass; (2) carbonaceous aerosols derived from domestic burning of diesel fuel/gasoline have similar PAH components as those derived from high-temperature combustion of diesel fuel/gasoline, although the former have much higher concentrations of PAHs than the latter, suggesting that the burning temperature obviously affects the emitting amount of particulate PAHs, but only slightly influences the PAHs components; and (3) the ratios of benzo[b]fluoranthene/acenaphthylene, benzo[b]fluoranthene/fluorene, dibenzo[a,h]anthracene/acenaphthylene, dibenzo[a,h]anthracene/fluorine, and benzo[b]fluoranthene/benzo[k]fluoranthene in carbonaceous aerosols are sensitively dependent on their sources, indicating that these ratios are suitable for use as characteristic factors or signatures of particulate PAHs in the atmosphere.     

Distinguishing the relative contribution of fossil fuel and biomass combustion aerosols deposited at Summit,Greenland through isotopic and molecular characterization of insoluble carbon

Quantifying combustion aerosols transported to Summit, Greenland has typically involved the measurement of water-soluble inorganic and organic ions in air, snow, and ice. However, the ubiquitous nature of atmospheric soluble ions makes it difficult to separate the combustion component from the natural component. More specific combustion indicators are therefore needed to accurately quantify inputs from biomass and fossil-fuel burning. This work reports on radiocarbon (¹⁴C) analysis of elemental carbon (EC) and quantification of polycyclic aromatic hydrocarbons (PAHs) of water-insoluble particles from a snowpit excavated at Summit, Greenland in 1996. The ¹⁴C measurements allowed us to quantify the relative contribution of EC from biomass burning and fossil-fuel combustion transported to and deposited at Summit during periods of 1994 and 1995. Specific PAHs associated with conifer combustion helped to identify snowpit layers impacted by forest fires. Our results show that fossil EC was the major component during spring and fall 1994, while biomass EC and fossil EC were present in roughly equal amounts during summer 1994. PAH ratios in spring layers of the snowpit indicate substantial inputs from anthropogenic sources and the ΣPAH depth profile displays springtime maxima that coincided with non-sea-salt sulfate ion maximum concentrations. In other layers, ammonium ion concentrations were independent of the isotopic and molecular carbon measurements. This work demonstrates the utility of radiocarbon techniques to quantify the two different sources of combustion-generated particles at Summit; however, portions of the ¹⁴C results were indeterminate due to large uncertainties that were the result of chemical impurities introduced in the EC isolation technique. Additionally, PAH measurements were successfully performed on as little as 100 ml of snowmelt water, demonstrating the potential for future finer sample resolution.     

Polycyclic aromatic hydrocarbons in the surface sediments from Yellow River, China

Fourteen surface sediment samples were collected from Lanzhou Reach of Yellow River, China in July 2005. The concentrations of 16 priority polycyclic aromatic hydrocarbons (PAHs) were determined by gas chromatography equipped with a mass spectrometry detector (GC-MS). Total concentrations of the PAHs ranged from 464 to 2621 ng/g dry weight. Sediment samples with the highest PAH concentrations appeared at the downstream of Lanzhou City, where there was the biggest wastewater discharge pipeline from Lanzhou Oil Refinery Factory and Lanzhou Chemical Industry Company. Municipal sewage also contributed to the PAH contamination in the sediments. A correlation existed between the sediment organic carbon content (f(oc)) and the total PAH concentrations (r(2)=0.57), suggesting that sediment organic carbon content played an important role in controlling the PAHs levels in the sediments. According to the observed molecular indices, PAHs contamination in Lanzhou Reach of Yellow River originated both from the high-temperature pyrolytic processes and from the petrogenic source, showing a mixed PAH input pattern, which was also confirmed by the results of a principal component analysis (PCA). According to the numerical effect-based sediment quality guidelines (SQGs) of the United States, the levels of PAHs at most studied sites in Lanzhou Reach of Yellow River should not exert adverse biological effects. Although at some sites (such as S10, S12, etc.) one PAH may exceed the effects range low (ERL), individual PAH did not exceed the effects range median (ERM). The results indicated that sediments in all sites should have potential biological impact, but should have no impairment.     

Concentrations, sources and spatial distribution of polycyclic aromatic hydrocarbons in soils from Beijing, Tianjin and surrounding areas, North China

The concentrations, profiles, sources and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) were determined in 40 surface soil samples collected from Beijing, Tianjin and surrounding areas, North China in 2007, and all sampling sites were far from industrial areas, roadsides and other pollution sources, and across a range of soil types in remote, rural villages and urban areas. The total concentrations of 16 PAHs ranged from 31.6 to 1475.0 ng/g, with an arithmetic average of 336.4 ng/g. The highest PAH concentrations were measured in urban soils, followed by rural village soils and soils from remote locations. The remote-rural village-urban PAH concentration gradient was related to population density, gross domestic product (GDP), long-range atmospheric transport and different types of land use. In addition, the PAH concentration was well correlated with the total organic carbon (TOC) concentration of the soil. The PAH profile suggested that coal combustion and biomass burning were primary PAH sources.     

Black carbon in Slovenian alpine lacustrine sediments

Black carbon (BC) contents were measured in recent sediments in five high altitude remote alpine lakes, i.e. Lake Krisko Sup., Lake Ledvica, Lake Planina, Lake Krn and Lovrensko Lake, and the eutrophic subalpine Lake Bled in Slovenia to follow the history of atmospheric pollution of fossil fuel and local biomass burning in Alps. Organic carbon (OC), its 13C values, total nitrogen and sedimentation rates using 210Pb activity data were also measured. The highest BC contents, reaching 20 mg/gdw, were noted in remote alpine lakes while in the subalpine Lake Bled sediment the concentrations were lower reaching 5 mg/gdw. Lower BC/OC ratios, ranging between 4% and 8%, were typical for remote alpine lakes and increased to about 10% in subalpine Lake Bled. The latter clearly shows the marked importance of local direct pollution sources in comparison to remote atmospheric input which decreases in a W-E direction in parallel with decreasing amounts of precipitation. Based on 210Pb sedimentation data, the minimal BC accumulation rates in sediment cores were detected in the pre-industrialisation period. In the last decades of 20th century the BC contents decreased probably due to reduced emission of pollutants.     

Polycyclic aromatic hydrocarbons, black carbon, and molecular markers in soils of Switzerland

Polycyclic aromatic hydrocarbons (PAH) were analysed in 23 soil samples (0–10 cm layer) from the Swiss soil monitoring network (NABO) together with total organic carbon (TOC) and black carbon (BC) concentration, as well as some PAH source diagnostic ratios and molecular markers. The concentrations of the sum of 16 EPA priority PAHs ranged from 50 to 619 μg/kg dw. Concentrations increased from arable, permanent and pasture grassland, forest, to urban soils and were 21–89% lower than median numbers reported in the literature for similar Swiss and European soils. NABO soils contained BC in concentrations from 0.4 to 1.8 mg/g dw, except for two sites with markedly higher levels. These numbers corresponded to 1–6% of TOC and were comparable to the limited published BC data in soil and sediments obtained with comparable analytical methods. The various PAH ratios and molecular markers pointed to a domination of pyrogenically formed PAHs in Swiss soils. In concert, the gathered data suggest the following major findings: (1) gas phase PAHs (naphthalene to fluorene) were long-range transported, cold-condensated at higher altitudes, and approaching equilibrium with soil organic matter (OM); (2) (partially) particle-bound PAHs (phenanthrene to benzo[ghi]perylene) were mostly deposited regionally in urban areas, and not equilibrated with soil OM; (3) Diesel combustion appeared to be a major emission source of PAH and BC in urban areas; and (4) wood combustion might have contributed significantly to PAH burdens in some soils of remote/alpine (forest) sites.     

Oxidation of ketone groups in transported biomass burning aerosol from the 2008 Northern California Lightning Series fires

Submicron particles were collected from June to September 2008 in La Jolla, California to investigate the composition and sources of atmospheric aerosol in an anthropogenically-influenced coastal site. Factor analysis of aerosol mass spectrometry (AMS) and Fourier transform infrared (FTIR) spectroscopy measurements revealed that the two largest sources of submicron organic mass (OM) at the sampling site were (1) fossil fuel combustion associated with ship and diesel truck emissions near the ports of Los Angeles and Long Beach and (2) aged smoke from large wildfires burning in central and northern California. During non-fire periods, fossil fuel combustion contributed up to 95% of FTIR OM, correlated to sulfur, and consisted mostly of alkane (86%) and carboxylic acid groups (9%). During fire periods, biomass burning contributed up to 74% of FTIR OM, consisted mostly of alkane (48%), ketone (25%), and carboxylic acid groups (17%), and correlated to AMS-derived factors resembling brush fire smoke, wood smoldering and flaming particles, and biogenic secondary organic aerosol. The two AMS-derived biomass burning factors were identified as oxygenated and hydrocarbon biomass burning aerosol on the basis of spectral similarities to smoldering and flaming smoke particles, respectively. In addition, the ratio of oxygenated to hydrocarbon biomass burning OM shows a clear diurnal trend with an afternoon peak, consistent with photochemical oxidation. Back trajectory analysis indicates that 2–4-day old forest fire emissions include substantial ketone groups, which have both lower O/C and lower m/z 44/OM fraction than carboxylic acid groups. Air masses with more than 4-day old emissions have higher carboxylic acid/ketone group ratios, showing that atmospheric processing of these ketone-containing organic aerosol particles results in increased m/z 44 and O/C. These observations may provide functionally-specific evidence for the type of chemical processing that is responsible for biomass burning particle composition in the atmosphere.     

Relationships between organic matter, black carbon and persistent organic pollutants in European background soils: Implications for sources and environmental fate

Black carbon (BC) and total organic carbon (TOC) contents of UK and Norwegian background soils were determined and their relationships with persistent organic pollutants (HCB, PAHs, PCBs, co-planar PCBs, PBDEs and PCDD/Fs) investigated by correlation and regression analyses, to assess their roles in influencing compound partitioning/retention in soils. The 52 soils used were high in TOC (range 54-460 mg/g (mean 256)), while BC only constituted 0.24-1.8% (0.88%) of the TOC. TOC was strongly correlated (p < 0.001) with HCB, PCBs, co-PCBs and PBDEs, but less so with PCDD/Fs (p < 0.05) and PAHs. TOC explained variability in soil content, as follows: HCB, 80%; PCBs, 44%; co-PCBs, 40%; PBDEs, 27%. BC also gave statistically significant correlations with PBDEs (p < 0.001), co-PCBs (p < 0.01) and PCBs, HCB, PCDD/F (p < 0.05); TOC and BC were correlated with each other (p < 0.01). Inferences are made about possible combustion-derived sources, atmospheric transport and air-surface exchange processes for these compounds.     

Total Organic Carbon,an Important Tool in an Holistic Approach to Hydrocarbon Source Fingerprinting

The identification and allocation of multiple hydrocarbon sources in marine sediments is best achieved using an holistic approach. Total organic carbon (TOC) is one important tool that can constrain the contributions of specific sources and rule out incorrect source allocations in cases where inputs are dominated by fossil organic carbon. In a study of the benthic sediments from Prince William Sound (PWS) and the Gulf of Alaska (GOA), we find excellent agreement between measured TOC and TOC calculated from hydrocarbon fingerprint matches of polycyclic aromatic hydrocarbons (PAH) and chemical biomarkers. Confirmation by two such independent source indicators (TOC and fingerprint matches) provides evidence that source allocations determined by the fingerprint matches are robust and that the major TOC sources have been correctly identified. Fingerprint matches quantify the hydrocarbon contributions of various sources to the benthic sediments and the degree of hydrocarbon winnowing by waves and currents. TOC contents are then calculated using source allocation results from fingerprint matches and the TOCs of contributing sources. Comparisons of the actual sediment TOC values and those calculated from source allocation support our earlier published findings (5) that the natural petrogenic hydrocarbon background in sediments in this area comes from eroding Tertiary shales and associated oil seeps along the northern GOA coast and exclude thermally mature area coals from being important contributors to the PWS background due to their high TOC content.