very effective in removing viruses if pH, coagulant concentration, and mixing
are carefully controlled. Laboratory data show that a 99 percent virus re—
moval is possible in a good occulation system [56]. Unfortunately, in the
community water supply study discussed at the beginning of this chapter,
only 17 percent of the systems surveyed included clarication as part of their
water treatment, and half the systems neither claried nor disinfected the wa—
ter [57].
O. C. Liu of the EPA’S Northeastern Water Hygiene Laboratory, in a paper submitted to the “Safe Drinking Water” hearings, summarized the status
of knowledge about the efciency of present water treatment processes by
saying that, although some of the water treatment processes now in use are
relatively efcient in removing or destroying enteroviruses, only a small num—
ber of viruses have been studied and a general pattern for all types and
groups of the human enteroviruses is not yet clear [58]. Liu added that little is
known about the virus density of various surface waters and thus “it is impos—
sible to accurately assess what safety margin the present treatments may provide when polluted sources are used.” [59] In his opinion, there is always a
potential danger of waterborne hepatitis outbreaks, and they will recur if the
conditions of untreated water or the methods used to treat water favor the in—
crease of the virus population or if, a‘s may be the case, the transmission of
low virus concentrations by water is responsible for some portion of the pres—
ent incidence of infectious hepatitis [60].
Soil Bacteria.
Rising bacterial counts in some waterways may not be the
result of increased intestinal bacteria, but an indication of the presence of soil
bacteria. Soil microorganisms—fungi, bacteria, protozoa—may be pathogenic
(capable of producing disease in people). Although these soil microorganisms
may be washed out of the soil and into water frequently, they usually repre—
sent no hazard to people because, under natural conditions, they cannot live
and reproduce in water. Barry Commoner has described surface waters,
therefore, as a “very effective biological barrier to the movement of pathoge—
nic microorganisms from the soil to man because the water ordinarily con—
tains insufcient organic matter to support the growth of the pathogen.” [61]
But as eutrophication and organic pollution increase, the increased organic
content of water gives it, like soil, the ability to support heavy bacterial
growth. This, in turn, can lead to the growth of some types of highly toxic
amebas.
Medical journals have recently reported cases of amebic men—
ingoencephalitis, a disease caused by a free-living soil ameba. The infectious —
stage of this organism is stimulated by the presence
of bacteria often found in
abundance in ponds and lakes toward the end of summer as well as near sew—
age outfalls and wherever there is an adequate source of organic material that
will serve as food for bacteria. A recent report described three fatal cases of
amebic meningoencephalitis in Florida; the Victims had been swimming in
small, land—locked lakes, and the amebas recovered from their spinal uid
were also found in lake water samples [62].
Biological Hazards 167
are carefully controlled. Laboratory data show that a 99 percent virus re—
moval is possible in a good occulation system [56]. Unfortunately, in the
community water supply study discussed at the beginning of this chapter,
only 17 percent of the systems surveyed included clarication as part of their
water treatment, and half the systems neither claried nor disinfected the wa—
ter [57].
O. C. Liu of the EPA’S Northeastern Water Hygiene Laboratory, in a paper submitted to the “Safe Drinking Water” hearings, summarized the status
of knowledge about the efciency of present water treatment processes by
saying that, although some of the water treatment processes now in use are
relatively efcient in removing or destroying enteroviruses, only a small num—
ber of viruses have been studied and a general pattern for all types and
groups of the human enteroviruses is not yet clear [58]. Liu added that little is
known about the virus density of various surface waters and thus “it is impos—
sible to accurately assess what safety margin the present treatments may provide when polluted sources are used.” [59] In his opinion, there is always a
potential danger of waterborne hepatitis outbreaks, and they will recur if the
conditions of untreated water or the methods used to treat water favor the in—
crease of the virus population or if, a‘s may be the case, the transmission of
low virus concentrations by water is responsible for some portion of the pres—
ent incidence of infectious hepatitis [60].
Soil Bacteria.
Rising bacterial counts in some waterways may not be the
result of increased intestinal bacteria, but an indication of the presence of soil
bacteria. Soil microorganisms—fungi, bacteria, protozoa—may be pathogenic
(capable of producing disease in people). Although these soil microorganisms
may be washed out of the soil and into water frequently, they usually repre—
sent no hazard to people because, under natural conditions, they cannot live
and reproduce in water. Barry Commoner has described surface waters,
therefore, as a “very effective biological barrier to the movement of pathoge—
nic microorganisms from the soil to man because the water ordinarily con—
tains insufcient organic matter to support the growth of the pathogen.” [61]
But as eutrophication and organic pollution increase, the increased organic
content of water gives it, like soil, the ability to support heavy bacterial
growth. This, in turn, can lead to the growth of some types of highly toxic
amebas.
Medical journals have recently reported cases of amebic men—
ingoencephalitis, a disease caused by a free-living soil ameba. The infectious —
stage of this organism is stimulated by the presence
of bacteria often found in
abundance in ponds and lakes toward the end of summer as well as near sew—
age outfalls and wherever there is an adequate source of organic material that
will serve as food for bacteria. A recent report described three fatal cases of
amebic meningoencephalitis in Florida; the Victims had been swimming in
small, land—locked lakes, and the amebas recovered from their spinal uid
were also found in lake water samples [62].
Biological Hazards 167