Current status and trends for hydrocarbons

Drilling equipment. Photo: subseaworldnews.com

Pollution 2013
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Oil contamination might be measured as the total hydrocarbon content (THC) which includes both aliphatic and aromatic hydrocarbons (PAHs). PAHs play a significant role in the Barents Sea where hydrocarbon resources are naturally present. PAHs also originate from incomplete combustion processes of organic material, they travel long distances in the atmosphere, and are toxic to animals and humans. Hence, PAH-emission is still ongoing. Atmospheric transport has been demonstrated to be the main route for PAHs to reach pristine areas such as the Arctic.

PAH in air, riverine input and in biota

Although levels of PAH in the atmosphere still are lower in the Barents Sea area (i.e. Andenes and Ny-Ålesund) compared to the southern parts of Norway (i.e. Birkenes), the PAH-levels measured in 2013 were the highest measured since 2007 and are up to three orders of magnitude higher than levels of legacy POPs (e.g. PCBs) (Nizzetto et al., 2014). Higher levels and more local PAH-emission in the northern regions are believed due to increased industrial activity (e.g. petroleum industry), tourism, and shipping as temperatures increase.

Passive sampling of PAH concentrations in rivers that drain into the Barents Sea were found to be below 1ng/l. Concentrations of light weight PAHs were significantly lower in river Pasvik compared to rivers in southeastern parts of Norway. Smaller differences were observed for the higher molecular weight PAHs (Kaste et al. 2014).

PAH-levels in lower trophic levels have increased 10 to 30 fold the last 25 years (De Laender et al., 2011). PAH-levels were low in blue mussels (Mytilus edulis) sampled close to Svolvær (Nordland, Norway) and Varangerfjorden (Finnmark, Norway) in 2011. Levels found were also lower than levels measured at Greenland, Island and the Faroe Islands (Jorundsdottir et al., 2014). Dominant compounds in the Norwegian samples were phenanthrene, chrysene, and benzo(a)pyrene in samples from Svolvær and phenanthrene, fluoranthene, and pyrene in samples from Varangerfjorden. PAHs were detected in eggs of common eider, European shag, and herring gull sampled in 2012 at Røst (Nordland, Norway) (Huber et al., 2014). PAHs included in the screening were: naphtalene, acenaphtalene, acenaphtene, fluprene, phenantrhrene, antracene, fluoranthene, pyrene, benz(a)anthracene, chrysene, benzo(b)fluoranthrene, benzo(k)fluoranthrene, benzo(a)pyrene, indeno(1,2,3-cd)pyrene, dibenz(ac/ah)anthracene, and benzo(ghi)perylene.  Levels of naftalene, antracene, fluoranten, pyrene, and chrysene were above the detection limit in herring gull eggs. Only pyrene was detected in common eider, while no PAHs were detectable in the European shag. PAH-levels were highest in herring gull eggs.

The levels of PAHs in fish are routinely monitored in Norway to control the possible effects of the petroleum industry on the marine environment. The levels of PAHs measured in the muscle of cod and haddock from the Barents Sea in 2006 were very low (background), below 6 µg/kg wet weight for total PAH in cod muscle and below 4 µg/kg wet weight in haddock, indicating no contamination (Grøsvik et al., 2007). In 2008 the fish monitoring was extended to include PAH and NPD measured in muscle and liver, as well as PAH metabolites measured in bile. This change resulted from measurements performed on fish after a Norwegian oil spill elsewhere where NPDs suddenly were high (Grøsvik et al, 2008). None of the measured parameters were high in the Barents Sea, but NPD concentrations were three times higher than the sum of 16 PAHs in haddock liver. The compound group contributing most to this difference was the trimethylnaphthalenes (Grøsvik et al, 2009).
This is consistent with Russian showing that the concentration of chlorinated hydrocarbons in fish muscle and liver tissue was well below allowable levels. The concentration of PAH was in most cases higher in the fish liver than in the muscles. This is natural as the liver is an accumulating organ. Among individual PAHs, phenanthrene was found at highest concentrations in fish muscle, naphthalene and benzo(g,h,i)perylene in liver. The concentrations of benz[a]pyrene in muscles of fish was below the detection limit of the applied method of analysis.

Hydrocarbons in Russian waters of the Barents Sea

G.V. Iljin (PINRO), A.E. Rybalko ( SEVMORGEO)

In recent years, total petroleum hydrocarbon concentrations have varied in different areas of the Russian zone of the Barents Sea within the range from 0 to 2 MPC [maximum permissible concentration] (Figure 4.4.17). The annual mean concentration of such hydrocarbons is about 0.01 mg/L [G. V. Iljin, 2015]. Elevated concentrations of petroleum products, exceeding the MPC (0.05 mg/L), are generally observed in coastal areas and in bays.

Figure 4.4.17. Distribution of hydrocarbons in the water along projected Shtocman pipeline.Figure 4.4.17. Distribution of hydrocarbons in the water along projected Shtocman pipeline.

Paraffins make up the majority of hydrocarbons dissolved in waters of the Barents Sea. The profile of normal paraffins is represented by C10 to C30 compounds. Their total concentration varies in the range from 1.1 to 20.0µg/L. Concentrations up to 90µg/L [G. V. Iljin, 2015] are observed in localized areas. Hydrocarbons of plant and bacterial origin (C20-C25 alkanes) account for up to 30%-33%, and predominate in central parts of the Sea. In coastal areas, especially Motovsky- and Kola Bays, short-chain C12-C22 alkanes predominate in the paraffin structural series. Elevated pristane/phytane isoprenoid ratios and low CPIs (carbon preference indices) are also observed in the structure of the alkanes. These parameters indicate a relatively elevated petrogenic hydrocarbon background level in areas experiencing high anthropogenic impact.

Studies investigating paraffin composition in upper layers of the water column near Franz Josef Land and the Shilling Strait [show that] the aliphatic hydrocarbon profile is limited to normal C15–C24 paraffins.  C18 (28%) and C23 (19%) alkanes dominate. Hypothetically, the observed aliphatic hydrocarbon background in waters surrounding the archipelago is not associated with petroleum contamination, but rather is created by metabolites of organisms of the marine biota. The total concentration of normal paraffins is not more than 1.5µg/L — two orders of magnitude lower than in commercially developed southern areas of the Sea (Iljin, 2009; Iljin et al., 2011).

The total concentration of polyaromatic hydrocarbons (PAHs) in the Barents Sea is low, and PAH constituent composition is depleted. In the southern part of the Sea, PAH concentration varies from 12 to 80ng/L (Figure 4.4.18). Concentrations of perylene, pyrene, phenanthrene, fluorene, fluoranthene, and benz[b,k]fluoranthene have been reliably determined. Concentrations of carcinogenic polyaromatic compounds, including benz[a]pyrene, are below the detection threshold. Arenes, perylene, and benz[b,k]fluoranthene dominate PAH composition; these are indicators of anthropogenic emissions associated with pyrolysis of organic fuel. But the major role in transport of PAHs in the open sea is probably played by atmospheric deposition [Shevchenko, 2009].
 
An increase in PAH concentration, associated with anthropogenic impact, occurs in coastal areas. Concentrations up to 80-90ng/L have been observed in the western margin of the Sea. In the southeastern part (Pechora Sea), PAH concentration is reduced to 15-67ng/L [G. V. Iljin, 2015].

In offshore areas, PAH concentration appreciably increases in bottom layers of the water column near oil and gas fields. In deep-water areas of Central Trough, where the Shtokman gas condensate field is located, PAH concentration can be 260-330ng/L [G. V. Iljin, 2015]. In shallow waters of the Pechora Sea near Prirazlomnoye field, total PAH concentration in the bottom layer increases up to 120ng/L.

 Figure 4.4.18.  Distribution of PAH in waters of the Barents Sea. Figure 4.4.18.  Distribution of PAH in waters of the Barents Sea.

Hydrocarbons in bottom sediments

by S. Boitsov (IMR)

PAHs play a significant role in the Barents Sea where hydrocarbon resources are naturally present. PAHs found in marine sediments may be due to natural processes such as erosion of coal-bearing bedrock at Svalbard or seepages of oil and gas from the seabed. Anthropogenic sources of hydrocarbons play a lesser role in the Barents Sea.

In most areas, the background levels of PAHs in sediments are low, and have been at 400-500
μg/kg dry weight on average for a sum of 48 PAHs throughout the western Barents Sea. The levels are highest closer to Svalbard, whereas the sediments from the shelf areas of southern Barents Sea mapped under the MAREANO program had very low levels of PAH, mostly < 300 μg/kg dry weight for the same group of compounds. The latest results from the previously disputed area along the Norwegian-Russian border in central Barents Sea, obtained in 2013, indicate similarly low PAH levels.

Accumulation of petroleum products in bottom sediments in open areas of the Barents Sea is quite patchy, and concentrations may vary from trace amounts up to 80µg/g dry weight. Highest concentrations are observed in coastal sediments and in sediments of the Central Trough, where accumulation of the finely dispersed fraction of residues occurs. The range of hydrocarbon concentration in different morphological zones of the sea is shown in Table 4.4.7. In Murman coastal sediments, especially close to Kola- and Motovsky Bay, the concentration of petroleum products increases. Areas of petroleum product accumulation ranging from 120 to 700µg/g dry weight have been observed during different years in this area of the coast.

The structural composition of the paraffinic hydrocarbons in bottom sediments is broader than in aquatic environments (Table 4.4.7). Dominant paraffins are C12–C17 and C18–C24 aliphatic compounds.

Short-chain C10–C14 compounds are observed practically over the entire Barents Sea. But, these light compounds are more typical in bottom sediments of the Central Trough, which may be due to elimination of light hydrocarbons from the sedimentary cover.

Bottom sediments near Franz Josef Land have low petroleum hydrocarbon concentrations: 40-160mg/kg dry weight. This is 1-2 orders of magnitude lower than in southern areas. To evaluate the indicated quantities, and set standards for the approximate permissible concentration of total petroleum products in uncontaminated marine sediments, we can use the standards of the Norwegian Pollution Control Authority (SFT): 50 mg/g dry weight (Molvaer et al., 1997).

In most samples of bottom sediment taken during 2014 in Teriberka Bay (SMG), the concentration of petroleum products was low and did not exceed the background level for contamination by petroleum products according to the Norwegian scale, except for a station located in upper Dolgaya Bay (Figure 4.4.19).

Figure 4.4.19. Distribution of total hydrocarbon content (THC) in Teriberka Bay sediments (2014)Figure 4.4.19. Distribution of total hydrocarbon content (THC) in Teriberka Bay sediments (2014)  

Although PAH distribution in bottom sediments is not uniform over the entire southern part of the Barents Sea (from 20 to 400ng/g dry weight), maximum PAH accumulation occurs in sediments of the Central Trough and bays along the Murman Coast (Table 4.4.7).
 

Table 4.4.7. Concentration of petroleum products, PAHs, and indices of paraffin composition in bottom sediments in the southern Barents Sea.


Pyrogenic compounds predominate in sediments: pyrene, benzanthracenes and dibenzanthracenes, fluoranthene, etc., which have carcinogenic properties. The benz[a]pyrene concentration varies from 0 to 14ng/g dry weight. Sediments of the Central Trough typically have the maximum level of carcinogen accumulation.

In open areas of the Sea, accumulation of PAHs of petrogenic origin is typical: chrysene and phenanthrene. These arenes result from the metamorphis of organic matter, and enter the environment as bottom sediments erode.
 
On the coast of the Pechora Sea in the east, total PAH concentration is significantly lower than in central and western parts of the Sea, and varies from 5 to 80ng/g dry weight. It is slightly elevated in oil and gas field areas within the Pechora Sea basin; major arenes found among the PAHs are naphthalene (5-40ng/g dry weight) and fluoranthene (0.2-0.4ng/g dry weight), which are compounds of petrogenic and anthropogenic genesis. The concentration of benz[a]pyrene is very low: from 0.0 to 5.2ng/g dry weight.

In western coastal areas, the PAH profile is significantly broader. Near the mouth of Kola Bay, in Motovsky Bay, and in Varanger Fjord, major aromatic compounds in the sediments become compounds of petrogenic genesis: naphthalene and fluoranthene, indicating long-term anthropogenic impacts. Total PAH concentration here is generally low: from 7 to 147ng/g dry weight, many times lower than the "contamination" threshold according to the SFT classification. A trend of increasing concentrations from Varanger Fjord to Kola Bay has been observed. Sediments in Pechenga Bay and Ura Bay — the southern and central parts ("bends") of Kola Bay — are significantly more heavily contaminated than open areas of Varanger Fjord and Kola Bay.

The PAH concentration in sediments of Franz-Victoria Trough is low and typical for central parts of the Barents Sea. However, variability in the concentration level is considerable: ranging from 200 to 600ng/g dry weight. Analysis of the PAH composition shows relatively high concentration of phenanthrene, naphthalene, and its methylated homologs. Potential sources of these compounds include: erosion and abrasion of rocks on surrounding archipelagos containing coal; airborne transport of dusty material; and  invasion of light PAHs (naphthalenes) from sedimentary cover (Figure 4.4.20). 

Figure 4.4.20. Distribution of PAH in the sediments of the Barents Sea.Figure 4.4.20. Distribution of PAH in the sediments of the Barents Sea.

PAHs found in marine sediments may be due to natural processes such as erosion of coal-bearing bedrock at Svalbard or seepage of oil and gas from the seabed. Offshore environmental monitoring indicates that differences in physical characteristics of sediments correlate to natural background levels of chemical substances. The highest concentrations of THC and heavy metals are found at some regional monitoring stations where sediments have high content of pelite and total organic matter (TOM).

Gas production at Snøhvit began in 2007; this was the only producing field in 2011 in the Norwegian part of the Barents Sea. Drilling has not occurred between 2007 and 2010, and emissions are insignificant. Levels of THC in sediments close to Fish, Salina, Ververis, and Caurus vary between 4 – 10mg/kg. Highest levels of THC were found at Snøhvit and Norvarg, with maximum concentrations between 13.4mg/kg and 13.9mg/kg (Mannvik et al. 2011).

 

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