Oil contamination may be measured as total hydrocarbon content (THC) which includes both aliphatic and aromatic hydrocarbons. THC levels in sediments vary from below detection limit to below 20 µg/g dry weight throughout south-western and central parts of the Barents Sea, but are in the range of 50 to 70 µg/g dry weight in the areas closer to Svalbard (ibid.) in the North-Western Barents Sea.
In 2004, THC was measured in the offshore waters of the Norwegian part of the Barents Sea. The results were in the low μg/L range, reaching background levels at almost all the locations (ibid.) Near the offshore fields the levels of hydrocarbons are on or close to the background level. The exception in 2007 was a higher level of THC at three stations on the Snøhvit field.
Concentrations of aliphatic hydrocarbons (n-alkanes) found in the upper layer of the bottom sediments from Svalbard area varyed from 1 to 240 µg/g dry weight in 2005. Aliphatic hydrocarbons of biogenic origin (paraffins) dominated. The levels of n-alkanes (C10-C32) in upper layers of bottom sediments varied from 0,13 to 0,5 g/g dw in western and central regions, and from 0,3 to 3,3 g/g dw in the south-eastern region of the Barents Sea in 2006. The relation between the isoprenoides prystane (iC19) and phytane (iC20) can be used as a fractional conversion marker for the nature and condition of hydrocarbons in bottom sediments. The fact that hydrocarbons of biogenic origin dominate in aliphatic compounds is demonstrated by their ratio: prystane/phytane 2. There are no specific guidelines regarding n-alkanes concentrations in bottom sediments. Total aliphatic hydrocarbons levels in bottom sediments from the studied fishing areas in the Barents Sea were below the 340 g/g dw background level, indicating anthropogenic influence. This level is representative for upper layers of bottom sediments on the western Arctic Shelf.
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 20 PAHs throughout the Western Barents Sea, see Figure. 4.4.10 (Boitsov et al., 2007). The levels of PAH measured in sediments in the southern Barents Sea in 2006 and 2007 were very low, mostly < 300 µg/kg dry weight.
Sediments in areas close to Svalbard have PAH levels at above 3000 µg/kg dry weight (ibid.), at least an order of magnitude greater than the levels measured elsewhere in the Barents Sea. Russian data from 2005 (Figure 4.4.11) reveal the same pattern. Maximum levels of polyaromatic hydrocarbons (PAH) (sum 16 compounds, EPA protocols 8310) were found in the bottom sediments in the fishery areas of the Western Spitsbergen and Spitsbergen bank.
Sum of carcinogenic PAH [benz(a)anhtracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benz(a)pyrene, indeno(1,2,3–cd)pyrene and dibenz(a,h)anthracene] varied from 29,3 ng/g to 340 ng/g dry weight, and constituted from 10 % to 40 % of the total PAH concentrations in the samples. Sum toxicity given as benz(a)pyrene equivalents for the investigated samples of bottom sediments varied from 7,50 ng/g to 76,8 ng/g dry weight. The results demonstrate the higher concentrations of PAH in bottom sediments from the coastal areas of Spitsbergen in comparison with other parts of the Barents Sea. The concentrations of PAH and benz(a)pyrene in bottom sediments in the investigated areas adjacent to Spitsbergen archipelago correspond to levels of “moderate contamination” (SFT 1997), although the levels are caused by natural processes.
A ratio of the sum of low molecular weight PAH concentrations to the sum of higher molecular weight PAH concentrations was used as criterion for PAH origin in Barents Sea bottom sediments. For the majority of stations, the ratio was below 1. This indicated that PAHs had formed as a result of fossil fuel burning. Quantitative measures indicated low concentrations of PAHs in bottom sediments within areas studied; this was particularly true for central and southwestern areas of the Barents Sea. In Russia, there were no specific classification guidelines for concentrations of contaminants in marine bottom sediments. According to Norwegian guidelines (SFT 1997), PAH and benzo(a)pyrene concentrations in bottom sediments at most stations within the areas studied, did not exceed background levels: 300 ng/g dw and 10 ng/g dw. PAHs in the upper layers of the bottom sediments were mainly of pyrogenic origin.
Despite an intensive technological burden, upper horizons of the geological environment (bottom sediment and quaternary holocene deposits) in the Russian part of the area are not disturbed. Contamination is absent over most of the area. The most contaminated areas are the Kola bay and some smaller bays where ships are stationed. There, the bottom sediments contain high amount of hydrocarbons. An example is the Kola bay where oil spills have lead to the formation of sea bottom deposits with a gross content of hydrocarbons, up to 5-10 mg/kg.
Although data on hydrochemistry of the bottom water suggests that the implemented clean-up measures have been effective, there is still a large reserve of hydrocarbons and other toxins in the bottom sediments. These toxins present a potential threat as a source for secondary contamination of the water column.
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).
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.