ever. Methyl mercury, an organic form, is by far the most toxic, and inorganic
mercury can be transformed into methyl mercury in nature.
Mercury toxicity depends on both the quantity absorbed by an organism
and the site of accumulation. Inorganic mercury accumulates in the human
body mainly in the kidney, but also in the brain, the liver, and the intestine.
Elemental mercury is relatively nontoxic when ingested. However, the inhalation of mercury vapor is extremely hazardous, and, since the vaporization
of mercury occurs quite readily, it has been the most serious industrial mer—
cury hazard.
Methyl mercury is much more readily absorbed by the body when it is in—
gested than is inorganic mercury: 90 to 95 percent of methyl mercury may be
absorbed by the intestine, in contrast to only two percent of inorganic mer—
cury. Methyl mercury diffuses through biological membranes much more
readily, is more evenly distributed throughout the body, and is excreted much
more slowly than other mercury compounds. Brain damage is more likely to
be caused by methyl mercury than by inorganic mercury poisoning [50].
The Minamata disaster in ]apan brought widespread attention to mer—
cury’s potential as an environmental polluter. Here 110 people became the
victims of mercury poisoning between 1953 and 1960 as a result of eating sh
taken from Minamata Bay where a vinyl chloride plant released methyl mer—
cury as one of its waste products [51]. Since that time, it has been learned that
-
methyl mercury is the most common form of mercury
found in the aquatic
environment. Fish excrete it very slowly; accumulations of mercury as high as
5000 times the amount found in water have been reported in sh. A study of
Lake St. Clair showed that mercury levels in sh had increased approximately
a hundredfold from 1935 to 1970. Methyl mercury makes up 95 to 100 per—
cent of the mercury found in sh [52].
Many U.S. industries have discharged inorganic mercury into the water;
the danger in this practice was overlooked even after the Minamata disaster
because organic methyl mercury had caused the poisonings in ]apan. It has
now been known for a number of years, however, that inorganic mercury can
be transformed in nature into methyl mercury which can then be accumu—
lated by sh and passed on to man in this highly toxic form. Mercury can be
methylated by the microorganisms (the bacteria and molds) found in lake or
river sediments. This reaction can be carried out by any microorganism that
can synthesize vitamin B12, that has a large supply of organic substances as a
source of food, and that, of course, has a supply of inorganic mercury. Methyl
mercury is not bound by the organic material in sediment, but is easily re—
leased into the water where it is soluble and available for consumption [53].
Thus, while many industrial rms have halted or reduced mercury dis—
charges, the great accumulation of inorganic mercury
in the sediments of the
aquatic environment provides a continuing source of methyl mercury and insures continuing contamination of the food chain.
It has also been suggested that bacteria living on the gills of sh can con—
vert inorganic mercury
into organic mercury. In addition, experiments with
birds have shown that when they are fed nonmethy1ated mercury compounds
Synergism and Antagonism
61
mercury can be transformed into methyl mercury in nature.
Mercury toxicity depends on both the quantity absorbed by an organism
and the site of accumulation. Inorganic mercury accumulates in the human
body mainly in the kidney, but also in the brain, the liver, and the intestine.
Elemental mercury is relatively nontoxic when ingested. However, the inhalation of mercury vapor is extremely hazardous, and, since the vaporization
of mercury occurs quite readily, it has been the most serious industrial mer—
cury hazard.
Methyl mercury is much more readily absorbed by the body when it is in—
gested than is inorganic mercury: 90 to 95 percent of methyl mercury may be
absorbed by the intestine, in contrast to only two percent of inorganic mer—
cury. Methyl mercury diffuses through biological membranes much more
readily, is more evenly distributed throughout the body, and is excreted much
more slowly than other mercury compounds. Brain damage is more likely to
be caused by methyl mercury than by inorganic mercury poisoning [50].
The Minamata disaster in ]apan brought widespread attention to mer—
cury’s potential as an environmental polluter. Here 110 people became the
victims of mercury poisoning between 1953 and 1960 as a result of eating sh
taken from Minamata Bay where a vinyl chloride plant released methyl mer—
cury as one of its waste products [51]. Since that time, it has been learned that
-
methyl mercury is the most common form of mercury
found in the aquatic
environment. Fish excrete it very slowly; accumulations of mercury as high as
5000 times the amount found in water have been reported in sh. A study of
Lake St. Clair showed that mercury levels in sh had increased approximately
a hundredfold from 1935 to 1970. Methyl mercury makes up 95 to 100 per—
cent of the mercury found in sh [52].
Many U.S. industries have discharged inorganic mercury into the water;
the danger in this practice was overlooked even after the Minamata disaster
because organic methyl mercury had caused the poisonings in ]apan. It has
now been known for a number of years, however, that inorganic mercury can
be transformed in nature into methyl mercury which can then be accumu—
lated by sh and passed on to man in this highly toxic form. Mercury can be
methylated by the microorganisms (the bacteria and molds) found in lake or
river sediments. This reaction can be carried out by any microorganism that
can synthesize vitamin B12, that has a large supply of organic substances as a
source of food, and that, of course, has a supply of inorganic mercury. Methyl
mercury is not bound by the organic material in sediment, but is easily re—
leased into the water where it is soluble and available for consumption [53].
Thus, while many industrial rms have halted or reduced mercury dis—
charges, the great accumulation of inorganic mercury
in the sediments of the
aquatic environment provides a continuing source of methyl mercury and insures continuing contamination of the food chain.
It has also been suggested that bacteria living on the gills of sh can con—
vert inorganic mercury
into organic mercury. In addition, experiments with
birds have shown that when they are fed nonmethy1ated mercury compounds
Synergism and Antagonism
61