ENVIRONMENTAL HEALTH 341
divalent mercury, phenylmercury, and alkoxialkylmercury
into methylmercury. The methylmercury thus formed, and
perhaps other types, in addition to that discharged in wastewa-
ters, are assimilated and accumulated by aquatic and marine
life such as plankton, small fi sh, and large fi sh. Alkaline
waters tend to favor production of the more volatile dimeth-
ylmercury, but acid waters are believed to favor retention of
the dimethyl form in the bottom deposits. Under anaerobic
conditions, the inorganic mercury ions are precipitated to
insoluble mercury sulfi de in the presence of hydrogen sul-
fi de. The process of methylation will continue as long as
organisms are present and they have access to mercury. The
form of mercury in fi sh has been found to be practically
all methylmercury and there is indication that a signifi cant
part of the mercury found in eggs and meat is in the form of
methylmercury.
The amount of mercury in canned tuna fi sh has averaged
0.32 ppm, in fresh swordfi sh 0.93 ppm, in freshwater fi sh
0.42 ppm (up to 1.4 and 2.0 ppm in a few large fi sh such
as Walleyed Pike), and as high as 8 to 23 ppm in fi sh taken
from heavily contaminated waters. The mercury in urban air
has been in the range of 0.02 to 0.2 m g per cu m, in drinking
water less than 0.001 ppm, and in rain water about 0.2 to 0.5
ppb ( m g/1). Reports from Sweden and Denmark (1967–69)
indicate a mercury concentration of 3 to 8 ppb (ng/gm) in
pork chops, 9 to 21 ppb in pig’s liver, 2 to 5 ppb in beef fi llet,
9 to 14 ppb in hen’s eggs, and 0.40 to 8.4 ppm in pike.
In view of the potential hazards involved, steps have been
taken to provide standards or guidelines for mercury. The
maximum allowable concentration for 8 hour occupational
exposure has been set at 0.1 mg metallic vapor and inorganic
compounds of mercury per cubic meter of air. For organic mer-
cury the threshold limit is 0.01 mg per cu m of air. A maximum
allowable steady intake (ADI) of 0.03 mg for a 70 kg man is
proposed, which would provide a safety factor of ten. If fi sh
containing 0.5 ppm mercury (the actionable level) were eaten
daily, the limit of 0.03 mg would be reached by the daily con-
sumption of 60 gm (about 2 ounces) of fi sh.^13 The proposed
standard for drinking water is 0.002 ppm. A standard for food
has not yet been established; 0.05 ppm has been mentioned.
There is no evidence to show that the mercury in the cur-
rent daily dietary intake has caused any harm, although appar-
ent health does not indicate possible non-detectable effects on
brain cells or other tissues. Nevertheless, from a conservative
health standpoint, it has been recommended that pregnant
women not eat any canned tuna or swordfi sh. Also implied
is caution against the steady eating of large fresh water fi sh
or other large saltwater fi sh. The general population should
probably not eat more than one fi sh meal per week.
The identifi cation of mercury as coming from manmade
and natural sources requires that every effort be made to
eliminate mercury discharges to the environment. At the
same time the air, drinking water, food, fi sh, and other wild-
life, aquatic plants and animals, surface runoff and leach-
ates, precipitation, surface waters, and man himself should
be monitored. This should be done not only for mercury,
but also for other potentially toxic and deleterious chemi-
cals. Further research and studies are needed to determinethe subtle and actual effects of mercury and other metals, as
normally found, on man and his environment.WATER SUPPLYA primary requisite for good health is an adequate supply of
water that is of satisfactory sanitary quality. It is also important
that the water be attractive and palatable to induce its use; for
otherwise, water of doubtful quality from some nearby unpro-
tected stream, well or spring may be used. Where a municipal
water supply as available, it should be used as such supplies
are usually under competent supervision, ample in quantity
and also provide fi re protection. However, this is not always
the case. Because of the excellent water service generally
available in the United States, the people and public offi cials
have tended to become complacent and take for granted their
water supply. As a result, in some instances, funds have been
diverted to other more popular causes rather than to mainte-
nance, opeation, and upgrading of the water supply system.Status of Water SupplyA survey^15 made by the Public Health Service in 1962 is of
interest in pointing out the number and type of public water
supplies in the United States and populations served. It was
reported that there were 19,236 public water supplies serving
approximately 150,000,000 people; 75% were ground water
supplies, 18% were surface water supplies, and 7% were a
combination. Of signifi cance is the fi nding that 75,000,000
people in communities under 100,000 population were served
by 18,873 public water supplies, and 77,000,000 people in
communities over 100,000 were served by 399 public water
supplies. Also, of the 19,236 supplies, 85% served communi-
ties of 5,000 or less. The information emphasizes the need for
giving at least equal attention to small public water supplies
as is given to large supplies. In addition, millions of people
on vacation in relatively uncontrolled rural environments
depend on small water supplies which often are not under
close surveillance.
The Public Health Service completed a study in 1970
covering 969 small to large public surface and ground water
supply systems serving 18,200,000 persons (12% of the total
United States population served by public water supplies)
and 84 special systems serving trailer and mobile home
parks, institutions, and tourist accommodations.^16 Although
the drinking water supplies in the United States rank among
the best in the world, the study showed the need for improve-
ments. Based on the 1962 USPHS Drinking Water Standards
it was found that in 16% of the 1969 communities surveyed
the water quality exceeded one or more of the mandatory
limits established for coliform organisms (120), fl uoride
(24), lead (14). It is of interest to note that of the 120 sys-
tems that exceeded the coliform standard, 108 served popu-
lations of 5,000 or less and that 63 of these were located in a
state where disinfection was not frequently practiced or was
inadequate. An additional 25% of the systems exceeded the
recommended limits for iron (96), total dissolved solids (95),C005_009_r03.indd 341C005_009_r03.indd 341 11/18/2005 10:24:46 AM11/18/2005 10:24:46 AM