hydrocarbon components reach the atmosphere. Through rainfall, they can enter the
ocean. Marine vegetation also produces hydrocarbons, and hydrocarbons are found in
all kinds of marine animals. The hydrocarbon concentration in marine organisms is
above 50 mg/kg dry weight, probably with an average of 400 mg/kg. If marine plant
production is 32% of the world plant production (Table 6) or about 24 X 109 t of
organic carbon per year, equivalent to 60 X 10 9 t of organic matter, then a minimum
of 3 million t of hydrocarbons are produced every year by the marine vegetation,
about as much as man introduces in form of petroleum into the world oceans
(Table 14). Such calculations, however, are rather speculative and there are many
question marks. It seems that recent marine organisms can synthesize only hydrocarbon compounds other than straight alkanes with up to 22 carbon atoms, but seawater contains many more compounds with higher numbers of carbon atoms than
could have been introduced with petroleum. Either they are rather persistent and
have a long life time in the sea, or there are unknown sources of such compounds in
the sea (Koons and Monaghan 1977).
Hydrocarbons formed by vegetation stand out by the predominance of even-numbered
carbon atoms in a series of compounds with different carbon atom counts. In petroleum hydrocarbons, there is no difference in even and uneven numbers. However,
some recent bacteria are also producing hydrocarbons without showing a preference
for even numbers of carbon atoms. One compound produced by vegetation is pristane,
while phytane is practically absent. In petroleum hydrocarbons 1.5 to 2.5 times more
phytane is present than pristane. Finally, it is characteristic in hydrocarbons produced by recent organisms that few components predOminate while petroleum
hydrocarbons distinguish themselves by a complex mixture of aromatic compounds
and cycloalkanes. It is clear that this mixture has not come into being recently
(Morris et al. 1976).
Among the polycyclic aromatic hydrocarbons found in the marine environment are
carcinogenic compounds like benzo(a)pyrene. It seems that even in the cleanest
oceanic seawater concentrations of benzo{a)pyrene are about 0.01 J.l.g/I, in nearshore
coastal waters up to 0.05 J.l.g/l. About 0.02 mg/kg are found in organisms, referring to
wet weight, and figures for sediments are 0.05 mg/kg, referring to the organic substance
in sediments. Fortunately, it seems that edible fish do not accumulate benzo(a)pyrene.
Concentrations are very low. However, this can be misleading because there is evidence that benzo(a)pyrene in fish is metabolized to other compounds which are cancerogenic, too. Levels in most shellfish samples were less than 0.1 mg/kg wet weight,
which is about the level in charcoal-grilled meat (Dunn and Fee 1979).
There are some signs to suggest that natural production by ocean bacteria and vegetation is more important in benzo(a)pyrene and other polycyclic aromatic compounds
than petroleum which contains around 100 mg/kg of polycyclic aromatic hydrocarbons (Andelman and Snodgrass 1974). Locally in dock constructions on the other
hand, wood treated with tar-derived impregnations and coatings is of significant
relevance to benzo{s)pyrene concentrations. While freshly caught lobsters (Homarus
vulgaris) in Canada had less than 1 J.l.g/kg in their meat, after they were kept in tidal
ponds constructed of creosoted timber, they contained up to 281 J.l.g/kg of carcinogenic hydrocarbons, more than in any other foodstuff known. Elevated concentrations
may also result from sewage effluents (Fig. 43), and in the polluted Severn Estuary
79
ocean. Marine vegetation also produces hydrocarbons, and hydrocarbons are found in
all kinds of marine animals. The hydrocarbon concentration in marine organisms is
above 50 mg/kg dry weight, probably with an average of 400 mg/kg. If marine plant
production is 32% of the world plant production (Table 6) or about 24 X 109 t of
organic carbon per year, equivalent to 60 X 10 9 t of organic matter, then a minimum
of 3 million t of hydrocarbons are produced every year by the marine vegetation,
about as much as man introduces in form of petroleum into the world oceans
(Table 14). Such calculations, however, are rather speculative and there are many
question marks. It seems that recent marine organisms can synthesize only hydrocarbon compounds other than straight alkanes with up to 22 carbon atoms, but seawater contains many more compounds with higher numbers of carbon atoms than
could have been introduced with petroleum. Either they are rather persistent and
have a long life time in the sea, or there are unknown sources of such compounds in
the sea (Koons and Monaghan 1977).
Hydrocarbons formed by vegetation stand out by the predominance of even-numbered
carbon atoms in a series of compounds with different carbon atom counts. In petroleum hydrocarbons, there is no difference in even and uneven numbers. However,
some recent bacteria are also producing hydrocarbons without showing a preference
for even numbers of carbon atoms. One compound produced by vegetation is pristane,
while phytane is practically absent. In petroleum hydrocarbons 1.5 to 2.5 times more
phytane is present than pristane. Finally, it is characteristic in hydrocarbons produced by recent organisms that few components predOminate while petroleum
hydrocarbons distinguish themselves by a complex mixture of aromatic compounds
and cycloalkanes. It is clear that this mixture has not come into being recently
(Morris et al. 1976).
Among the polycyclic aromatic hydrocarbons found in the marine environment are
carcinogenic compounds like benzo(a)pyrene. It seems that even in the cleanest
oceanic seawater concentrations of benzo{a)pyrene are about 0.01 J.l.g/I, in nearshore
coastal waters up to 0.05 J.l.g/l. About 0.02 mg/kg are found in organisms, referring to
wet weight, and figures for sediments are 0.05 mg/kg, referring to the organic substance
in sediments. Fortunately, it seems that edible fish do not accumulate benzo(a)pyrene.
Concentrations are very low. However, this can be misleading because there is evidence that benzo(a)pyrene in fish is metabolized to other compounds which are cancerogenic, too. Levels in most shellfish samples were less than 0.1 mg/kg wet weight,
which is about the level in charcoal-grilled meat (Dunn and Fee 1979).
There are some signs to suggest that natural production by ocean bacteria and vegetation is more important in benzo(a)pyrene and other polycyclic aromatic compounds
than petroleum which contains around 100 mg/kg of polycyclic aromatic hydrocarbons (Andelman and Snodgrass 1974). Locally in dock constructions on the other
hand, wood treated with tar-derived impregnations and coatings is of significant
relevance to benzo{s)pyrene concentrations. While freshly caught lobsters (Homarus
vulgaris) in Canada had less than 1 J.l.g/kg in their meat, after they were kept in tidal
ponds constructed of creosoted timber, they contained up to 281 J.l.g/kg of carcinogenic hydrocarbons, more than in any other foodstuff known. Elevated concentrations
may also result from sewage effluents (Fig. 43), and in the polluted Severn Estuary
79