Environmental Engineering Reference
In-Depth Information
such as paralytic shellfish neurotoxins, pose the threat of severe illness or, in rare
occasions, death when consumed along with shellfish meats by humans, especially
children and the immunocompromised, and by other animals. As already noted,
the toxic substance (e.g., saxitoxin) present in some poisonous shellfish flesh
results from the filtration of toxigenic marine dinoflagellates, Gonyaulax spp.,
and appears to be heat stable. Inorganic chemical elements of greatest concern as
a seafood hazard appear to be cadmium, lead, and mercury. The long-term effects
are nephropathy, anemia and central nervous system disorders, and retardation;
the latter two effects associated with lead and mercury are especially dangerous
to the human fetus and neonatal stages.
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Organic contaminants of fish flesh of
particular concern are polychlorinated biphenyls, doxins, chlorinated insecticides,
and furans as pertains to their potential as carcinogens and teratogens.
Illnesses associated with the consumption of poisonous plants and animals,
chemical poisons, and poisonous fungi are not strictly communicable diseases
but more properly noninfectious or noncommunicable diseases.
Vehicle or Means by Which Waterborne Diseases Are Spread
The means by which waterborne disease agents are transmitted to individuals
include drinking, bathing in swimming pools and recreational waters, showering
(mists), natural aerosols, contaminated hand towels and wash cloths, contami-
nated water (fish and shellfish), produce irrigated or washed with contaminated
water, contact with water containing invasive parasites, and bites of insects that
spend at least a part of the life cycle in water. The lack of potable water for
bathing, household cleanliness, and food preparation also contributes to poor
personal hygiene and sanitation and to the spread of disease. In addition, conta-
gious diseases of individuals, originally produced by contact with contaminated
water, may then be passed to another person. The discussions that follow will
cover the role of water as a source of disease-producing organisms and poisonous
substances.
The reporting of waterborne illnesses has, with rare exceptions, been very
incomplete. Various estimates have been made in the past, indicating that the
number reported represented only 10 to 20 percent of the actual number.
Hauschild and Bryan,
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in an attempt to establish a better basis for estimating
the number of people affected, compared the number of cases initially reported
with either the number of cases identified by thorough epidemiologic investiga-
tions or the number estimated. They found that for 51 outbreaks of bacterial,
viral, and parasitic disease (excluding milk), the median ratio of estimated cases
to cases initially reported to the local health authority, or cases known at the
time an investigating team arrived on the scene, was 25 to 1. On this basis
and other data, the annual food- and waterborne disease cases for 1974 to 1975
were estimated to be 1,400,000 to 3,400,000 in the United States and 150,000 to
300,000 in Canada. The annual estimate for the United States for 1967 to 1976
was 1,100,000 to 2,600,000.
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The authors acknowledge that the method used
to arrive at the estimates is open to criticism. However, it is believed that the
