THE PROBLEM O F OIL POLLUTION OF THE SEA
257
either damaging or stimulating. Flowering of several species was inhibited by oiling, probably because it kills the leaves and thus interferes with photoinduction. Subsequent growth stimulation probably
results from this inhibition, more nutrients being available for vegetative growth. Chronic pollution, for example by large volumes of
effluent containing a low proportion of oil, can eliminate all salt-marsh
plants, as would a single catastrophic oiling. Such damage denies their
normal feeding-grounds t o birds and other animals (see Harrison and
Buck, 1967) and may also seriously accelerate coastal erosion or alter
the pattern of silt deposition in an estuary.
The maritime vegetation of the cliffs and strand-line, often containing salt-marsh species or their relatives, is equally sensitive t o heavy
oil pollution, which it receives most often as droplets carried on windblown spray (see p. 236 above; Ranwell, 1968b). Most lichens are
known to be sensitive indicators of air pollution and only a few species
can survive in large towns (see, e.g., Fenton, 1964). The phytotoxic
action of hydrocarbons has, however, been studied in most detail using
terrestrial plants. I n agriculture, they have been used both as weedkillers and as carriers for insecticides. Currier and Peoples (1954) and
van Overbeek and Blondeau (1954) review previous work before reporting their own experiments on phytotoxic oils. Minshall and Helson
(1949) also discuss earlier studies. Spraying a series of pure hydrocarbons on plants showed that their toxicity increases in the order:
straight-chain paraffins, olefins, cycloparaffins, aromatics. Within each
series, smaller molecules are more toxic than the larger ones ; octane
and decane were toxic when tested by van Overbeek and Blondeau,
whereas dodecane and higher paraffins had scarcely any effect. However, C,, olefins showed marked effects and C,, aromatics were quite
toxic. According to Currier and Peoples, benzene is narcotic. in low
concentrations, depressing some cellular functions ; in high concentrations, low-boiling hydrocarbons in general are cytolytic and cause an
irreversible increase in permeability. As the concentration rises, the
cell contents leak out, the plant wilts and finally dies. van Overbeek
and Blondeau found that low-viscosity oils can penetrate stomata
(which aqueous solutions cannot do) and readily spread through the
intercellular spaces. They suggested that hydrocarbons become
incorporated in the lipoid portion of the plasma membrane, disrupting
its structure and thus rendering it permeable. Similar disturbance of
the fine structure of chloroplasts would account for the recorded
disturbances in photosynthesis following oil pollution and perhaps also
for the discharge of pigments which has often been observed. The
selective action of herbicidal oils may be due to differences of mem-
257
either damaging or stimulating. Flowering of several species was inhibited by oiling, probably because it kills the leaves and thus interferes with photoinduction. Subsequent growth stimulation probably
results from this inhibition, more nutrients being available for vegetative growth. Chronic pollution, for example by large volumes of
effluent containing a low proportion of oil, can eliminate all salt-marsh
plants, as would a single catastrophic oiling. Such damage denies their
normal feeding-grounds t o birds and other animals (see Harrison and
Buck, 1967) and may also seriously accelerate coastal erosion or alter
the pattern of silt deposition in an estuary.
The maritime vegetation of the cliffs and strand-line, often containing salt-marsh species or their relatives, is equally sensitive t o heavy
oil pollution, which it receives most often as droplets carried on windblown spray (see p. 236 above; Ranwell, 1968b). Most lichens are
known to be sensitive indicators of air pollution and only a few species
can survive in large towns (see, e.g., Fenton, 1964). The phytotoxic
action of hydrocarbons has, however, been studied in most detail using
terrestrial plants. I n agriculture, they have been used both as weedkillers and as carriers for insecticides. Currier and Peoples (1954) and
van Overbeek and Blondeau (1954) review previous work before reporting their own experiments on phytotoxic oils. Minshall and Helson
(1949) also discuss earlier studies. Spraying a series of pure hydrocarbons on plants showed that their toxicity increases in the order:
straight-chain paraffins, olefins, cycloparaffins, aromatics. Within each
series, smaller molecules are more toxic than the larger ones ; octane
and decane were toxic when tested by van Overbeek and Blondeau,
whereas dodecane and higher paraffins had scarcely any effect. However, C,, olefins showed marked effects and C,, aromatics were quite
toxic. According to Currier and Peoples, benzene is narcotic. in low
concentrations, depressing some cellular functions ; in high concentrations, low-boiling hydrocarbons in general are cytolytic and cause an
irreversible increase in permeability. As the concentration rises, the
cell contents leak out, the plant wilts and finally dies. van Overbeek
and Blondeau found that low-viscosity oils can penetrate stomata
(which aqueous solutions cannot do) and readily spread through the
intercellular spaces. They suggested that hydrocarbons become
incorporated in the lipoid portion of the plasma membrane, disrupting
its structure and thus rendering it permeable. Similar disturbance of
the fine structure of chloroplasts would account for the recorded
disturbances in photosynthesis following oil pollution and perhaps also
for the discharge of pigments which has often been observed. The
selective action of herbicidal oils may be due to differences of mem-