Problems in the identification of anthropogenic hydrocarbons against natural background levels in the Antarctic

Hydrocarbons in the environment occur as complex mixtures. The detection of low-level anthropogenic contamination can be difficult as many of the compounds can also be found in biogenic materials. Results obtained in the Antarctic show that accepted methods of distinguishing biogenic from contaminating hydrocarbons are inconsistent. The samples taken from South Georgia in the vicinity of derelict whaling stations had odd-to-even carbon number ratios in the range 0.8–1.0. An offshore site had the highest levels for phytane and the lowest for pristane. The pristane-to-phytane ratio varied between 0.4 and 1.4 and contradicted the interpretation of the odd-to-even ratio at several sites. A value of less than 1.0 for these ratios has been taken to indicate anthropogenic origin. A number of polycyclic aromatic hydrocarbons were detected at all the sites, but the concentration gradient did not correspond with that of the n-alkanes. It is therefore recommended that recognition of anthropogenic input is based on quantification of all compounds against a well-defined baseline. The source of the pollution can then be estimated from the distribution patters of the hydrocarbons.