Toxic Pollution 147
lead water pipes and plated their brass cooking and eating utensils with
lead in order to avoid copper’s unpleasant taste and toxicity. Nowadays lead
utensils and lead pipes are not in general use, but industry and cars emit
quantities of lead into the environment. The tetraethyl lead added to gasoline to improve its octane rating is significantly more toxic than metallic
lead. It is estimated that in the 1970s 400,000 tons of tetra ethyl lead were
emitted into the air annually, a big part of which wound up in the oceans.
The rate at which lead is mined is around 10 times higher than the rate
of natural decay of the rocks containing it, whereas emissions of lead into
the air are almost exclusively due to anthropogenic sources. Lead is the
only heavy metal whose concentration in the open ocean has increased substantially because of human activities. It has also been found that between
the years 1750 and 1960 the deposition of lead on polar glaciers increased
20-fold; however, after 1970 a big decrease was observed. In recent years
the more widespread use of unleaded gasoline in cars has significantly
reduced lead emissions, resulting in lower concentrations of lead in the air
of cities as well as in the atmosphere as a whole.
Plants do not easily take up metallic lead from the soil. However, they
take up tetraethyl lead much more easily from the soil and possibly directly
from the air as well.
7.4.2 Mercury
Mercury (Hg) is used in the production of chlorine and caustic soda, in
the electrical equipment industry, in the manufacture of paints and dental
amalgams, in the paper industry, in the manufacture of thermometers, in
the production of agricultural fungicides, etc. It is likely that half of the
mercury produced annually is released into the biosphere. Another source
of mercury pollution is the burning of coal and oil, which contain traces of
mercury. However, there are no indications of wide-scale pollution of the
biosphere, as has been the case with lead. The presence of mercury in the
air is not caused by anthropogenic emissions only but is also due to natural
causes, since mercury and its compounds are very volatile. Through the
implementation of recycling methods and the restriction of emissions for
environmental reasons, the production of mercury fell from 9600 tons in
1971 to 5400 tons in 1989. There is now a trend towards banning the use
of mercury thermometers.
Inorganic mercury occurs in the environment either in metallic form,
mostly as steam, or in a variety of inorganic compounds. It is toxic but
not to a great degree and does not accumulate in tissues. Its principal toxic
action is exercised on the kidneys and the liver. The maximum permissible
concentration in atmospheric air is 0.05 mg/m 3 .
lead water pipes and plated their brass cooking and eating utensils with
lead in order to avoid copper’s unpleasant taste and toxicity. Nowadays lead
utensils and lead pipes are not in general use, but industry and cars emit
quantities of lead into the environment. The tetraethyl lead added to gasoline to improve its octane rating is significantly more toxic than metallic
lead. It is estimated that in the 1970s 400,000 tons of tetra ethyl lead were
emitted into the air annually, a big part of which wound up in the oceans.
The rate at which lead is mined is around 10 times higher than the rate
of natural decay of the rocks containing it, whereas emissions of lead into
the air are almost exclusively due to anthropogenic sources. Lead is the
only heavy metal whose concentration in the open ocean has increased substantially because of human activities. It has also been found that between
the years 1750 and 1960 the deposition of lead on polar glaciers increased
20-fold; however, after 1970 a big decrease was observed. In recent years
the more widespread use of unleaded gasoline in cars has significantly
reduced lead emissions, resulting in lower concentrations of lead in the air
of cities as well as in the atmosphere as a whole.
Plants do not easily take up metallic lead from the soil. However, they
take up tetraethyl lead much more easily from the soil and possibly directly
from the air as well.
7.4.2 Mercury
Mercury (Hg) is used in the production of chlorine and caustic soda, in
the electrical equipment industry, in the manufacture of paints and dental
amalgams, in the paper industry, in the manufacture of thermometers, in
the production of agricultural fungicides, etc. It is likely that half of the
mercury produced annually is released into the biosphere. Another source
of mercury pollution is the burning of coal and oil, which contain traces of
mercury. However, there are no indications of wide-scale pollution of the
biosphere, as has been the case with lead. The presence of mercury in the
air is not caused by anthropogenic emissions only but is also due to natural
causes, since mercury and its compounds are very volatile. Through the
implementation of recycling methods and the restriction of emissions for
environmental reasons, the production of mercury fell from 9600 tons in
1971 to 5400 tons in 1989. There is now a trend towards banning the use
of mercury thermometers.
Inorganic mercury occurs in the environment either in metallic form,
mostly as steam, or in a variety of inorganic compounds. It is toxic but
not to a great degree and does not accumulate in tissues. Its principal toxic
action is exercised on the kidneys and the liver. The maximum permissible
concentration in atmospheric air is 0.05 mg/m 3 .