United States
Environmental Protection
Agency
Office of Health and
Environmental Assessment
Washington DC 20460
Research and Development
EPA/600/S6-88/010 Dec. 1988
&EPA Project Summary
Qualitative Pathogen Risk
Assessment for Ocean Disposal
of Municipal Sludge
This document focuses on
microbial contaminants of municipal
wastewater sludges that have been
actually or potentially implicated in
producing human illness; it
summarizes available data on the
occurrence, transport and fate of
these pathogens in the marine
environment; and describes the
possible hazards to human health
associated with the disposal of
sludges In open ocean waters.
Following the presentation of
background information, a dis-
cussion of risks associated with
ocean disposal of sludge are
presented. The scope of the risk
assessment Is restricted, therefore,
to pathogens present in municipal
sludge discharged at the open ocean
dump sites.
Because of a limited number of
studies on the pollution of marine
environments by sludge disposal, it
is difficult to assess these risks. It is
known that pathogens can persist in
sediments for an extended period of
time and that animals (for example,
rock crabs) dwelling at a dump site
can pick up these organisms and
move away from the site. It is also
known that sludge-impacted
sediments can drift long distances
from point of discharge. Whether
these sediments (and their
associated pathogens) can reach
coastal environments does not seem
likely under normal conditions, but in
the event of storms and quakes it is a
distinct possibility. It is logical to
assume that this pollution is less
likely to happen when a sludge is
disposed at the 106-mile site than at
the New York Bight or Philadelphia
dump sites, because of the distances
involved.
Predictions on viral and bacterial
decay following ocean disposal of
sludge will require information on the
vertical and horizontal movement of
discharged sludge as well as on the
survival of pathogens attached to
sludge particles. The latter
information is not currently available.
Studies on how far aerosols can
travel and how long pathogens can
survive in them are also incomplete.
Obviously, consumption of seafood
(from in and around a dump site) is
riskier to health than swimming
because of the bioconcentration of
pathogens by filter feeders.
This Project Summary was devel-
oped by EPA's Environmental Criteria
and Assessment Office, Cincinnati,
OH, to announce key findings of the
research project that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
Ocean disposal of domestic sewage
and sludge has been carried out off the
coast of the United States since the New
York Bight site opened in 1924.
Discharge of waste at sites such as the
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New York Bight (to be closed in 1988),
the Philadelphia dump site (closed in
1980), the Puerto Rico Trench dump site
(closed) and the 106-mile deep water
ocean waste disposal site in the mid-
Atlantic Bight (which opened in March
1986 on a five-year interim basis) has
generally been accomplished from
barges. The amount of sludge dumped
into the ocean by U.S. municipalities and
industries in the 1970s was estimated to
be 5x106 wet metric tons/year.
Human exposure to pathogenic
microorganisms from ocean-disposed
sludge may occur through primary
contact recreation such as bathing,
scuba and skin diving, water skiing, and
during occupational activities such as
commercial and military diving
operations. In addition, ingestion of raw
or partially cooked seafood that has
become contaminated may be harmful.
Bivalve mollusks such as oysters and
clams are of particular concern because
they feed by filtering particulate matter,
including microbes contained in large
volumes of seawater. Inhalation of
contaminated dust or aerosol droplets
containing pathogens from sewage is
also a potential exposure route.
Sludge Characteristics and
Disposal Methods
Ocean disposal of sludge is
accomplished by construction of offshore
sewage outfalls or by barging the waste
several miles offshore and discharging it
at a designated dump site. Because
offshore outfalls have been shown to
release high concentrations of bacteria
and viruses into marine waters, the
principal method of ocean disposal is to
dump sludge into a barge, tow the barge
to a disposal site, open disk valves fixed
in the bottom of specially constructed
holding tanks in the hull of the barge.and
allow the sludge to drift away. Sludge
may be dumped from a moving barge
(line dump, which results in the greatest
dispersal) or from a stationary barge
(spot dump).
The New York Bight dump site began
receiving municipal sludge in 1924 and
will cease operations in 1988. The site is
a coastal ocean area at the apex of New
Jersey and Long Island situated roughly
12 miles (19.2 km) equidistant from the
shores of New York and new Jersey at
the entrance to the Hudson Canyon. The
sludge dumping area occupies 100 km2
at latitude 40 25'04"N and longitude
73°44'53"W. Depth at the dump site is
~30 m, and bottom temperature ranges
from 9.8-12.3°C in the summer. During
1965-1970, the average annual input of
sludge to the New York Bight was
3.2x109 kg.
Fecal coliforms have been isolated
from New York Bight bottom sediments
in concentrations as high as 2.3x104/100
m€, and coliform bacteria have also been
found in crabs, lobsters and scallops that
inhabit the area. Acanthamoeba protozoa
and human enteroviruses such as
coxsackie B3 and B5 (<108/kg of
sediment) and echo 1 and 7 (<182/kg)
have been identified in surface water,
sediment and crabs collected from this
dump site. However, no evidence exists
that sewage sludge disposal at the New
York Bight dump site increases the risk
of swimming-associated disease at any
New Jersey, New York City or Long
Island beaches. Moreover, Clostridium
perfringens spore densities in the water
column or bottom sediments indicate that
dumped sludge does not reach the shore
in significant quantities anywhere along
the Bight.
The Philadelphia sewage sludge
dump site is a 172-km2 area located
-70 km east of Ocean City, MD, at
roughly 23°23'N and 74°15'W. The site,
which lies over the continental shelf in
waters 40-60 m deep, received sludge
from Philadelphia, PA, and Camden, NJ,
from 1973 until its closing in 1980.
Between 1973 and 1977, 2.8x109 kg of
sludge was deposited there.
Changes in the benthic environment in
the vicinity of the Philadelphia site during
and after its operation have included
accumulation of metals and other toxics
in organisms and sediment, alterations in
community structure, changes in abun-
dance of various species, increased rates
of mortality of the ocean quahog (Mica
islandica) and the appearance of sludge
beds, sewage bacteria (total coliforms,
fecal coliforms and fecal streptococci),
pathogenic protozoa (Acanthamoeba),
human enteroviruses (coxsackie B3 and
B5, echo 1 and 9 and polio 2) and
diseases in crabs.
The 106-mile deep water site off the
New Jersey coast was used primarily for
disposal of >5x106 metric tons of
chemical wastes from 1961-1978. Only
~4x105 metric tons of sludge were
dumped at the 106-mile site before
1978, but in 1984 EPA designated the
area as a permissible sewage sludge
disposal site on a five-year interim
basis. Furthermore, as of March 1986
permittees using nearshore sites may
dispose of wastes at the 106-mile site.
It is expected that ~ 7x106 metric tons of
New York/New Jersey sewage currently
being dumped at the 12-mile
site will be discharged at the 106-mi
site.
The Puerto Rico Trench dump si
was used primarily for pharmaceutic
wastes and is now closed for dumping.
Pathogens of Concern
Processed sewage wastes mi
contain residual pathogens, such <
viruses, bacteria, cysts of protozoa ar
ova of helminths. However, mo
outbreaks of sewage-related disea:
have been attributed to the use of rs
sewage, raw sludge or night soil on fo(
crops consumed raw, and I
contamination of drinking water fro
septic tanks or by consumption of rz
shellfish from sewage-polluted water
The principal pathogens found in sewa<
can be divided into four groups: bacteri
protozoa, helminths and viruses. Sewat
treatment practices reduce the number
the four groups of pathogens, but there
evidence to indicate that effluents ar
sludges contain detectable amounts. Tl
amounts and variety of pathogei
present in sewage vary from communi
to community and are dependent up<
urbanization, season, population densil
ratio of children to adults and the sanita
habits of the community.
Exposure Pathways
Potential pathways of enteric pathog<
transport in the marine environment a
illustrated in Figure 1.
Field studies at the New York Big
and Philadelphia dump sites have shov
that fecal indicator bacteria and vii
pathogens occur in surface waters ai
accumulate in sediments. Crabs in tl
vicinity of these sludge disposal sit
have been shown to contain humi
enteroviruses. Such contamination m;
occur through intake of sediment mater
during feeding and by ingestion
infected fish and shellfish. Shellfish a
filter feeders and tend to accumula
bacteria and viruses at much high
concentrations than the surroundii
water. It is possible that pathogens m
be passed through several species in t
marine food chain.
Contact with pathogens may al
result from bathing or diving in pollut
marine waters. Although ocean dur
sites are located offshore, currents, wir
storms and dredging activity can result
resuspension and transport
contaminated sediments to nearshc
locations that may pose a potential risk
human health.
Aerosols generated during disposal)
sludge and by wave action or dredgi
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Sea water
Dredging
Aerosols
Ocean Disposed
Sludge
Sediments
Seawater
Crabs and Other
Crustacea^
1i
Polycheate Worms
1
Fish
Figure 1. Potential pathways of enteric pathogen transport in the marine environment.
activity may transport bacteria and
viruses as far as 160 km from the ocean
by winds.
Persistence of Pathogens in
the Marine Environment
The survival of fecal indicator bacteria
and viruses in marine waters has
received a great deal of attention.
Numerous studies have been conducted
on the factors controlling the survival of
specific bacteria pathogens, protozoa
and helminths.
Sunlight and temperature appear to
be the dominant factors controlling
survival of coliform bacteria in marine
waters,but salinity also plays a role.
Temperature is critical to viral survival,
and sunlight may be important but its
influence has not been studied exten-
sively. Persistence of these pathogens in
sediments and in mollusks appears to be
prolonged; however, no previous studies
have been conducted on survival of
sludge-associated microorganisms in
the marine environment. Field studies at
the Philadelphia dump site suggest that
sludge accumulated in sediments may
greatly prolong or cause the growth of
fecal indicator bacteria.
Bacterial and viral survival in water
follows an exponential curve, so that the
probability of a bacterium dying in a
given time interval is independent of its
age. Time for 90% inactivation of
coliform bacteria is considerably faster
for seawater (0.6-8 hours) than for
freshwater (20-115 hours). Inactivation
time decreases sharply with increasing
temperature. In warm climates with
sewage temperatures of 25-30"C,
>99% reduction in indicator bacteria
concentration may be expected in 10-
15 days.
Enteric viruses have been reported to
survive from 2-130 days in seawater in
laboratory studies. Time for 90%
inactivation has been estimated to be
between 15 and 70 hours.
Survival of amoeba cysts in water is
primarily dependent upon temperature.
At 25QC, Entamoeba histolytica may
survive for 7-20 days; survival time at
5°C may be >1 month. Sewage
treatment may remove 52-93% of
Giardia cysts.
Laboratory experiments have
determined that 97% of Ascaris eggs are
killed after two days in seawater. Ascaris
eggs are considerably hardier than
Trichuris, hookworm or Entrobius eggs,
but somewhat less resistant than Taenia
eggs. Hookworm eggs can survive in
sludge at 27°C for <43 days, but in
seawater their survival is <5 hours
compared to >30 hours for Ascaris
eggs. Helminth eggs tend to settle in
seawater and accumulate in bottom
sediments.
In estuary water >80% of fecal
indicator bacteria are directly associated
with suspended sediments, and this
association appears to prolong their
survival in the aquatic environment.
Several recent field studies indicate that,
on a volume basis, greater numbers of
coliforms and bacterial pathogens occur
in bottom sediments than in overlying
water. Coliform bacteria have been
detected in areas of sludge disposal at
both the Philadelphia and New York Bight
dump sites; at the Philadelphia location,
the microbes survived s 4 years after the
last sludge was dumped. Fecal indicator
bacteria with multiple drug resistance
were found 30 months after cessation of
sludge dumping.
Field studies have documented the
occurrence of enteroviruses and
rotaviruses in marine sediments, and
laboratory studies have demonstrated
that virus adsorption to sediments
prolongs survival time in marine waters.
Enteroviruses were isolated from
sediments taken from the Philadelphia
sewage sludge dump site 17 months
after dumping stopped, but tests for
viruses were negative 24 and 36 months
after the site's closure.
Infective Dose for
Microorganisms
Estimation of minimum infectious
doses (MIDs) for various pathogens in
polluted marine water, food and
sediments is difficult because of
uncertainties in the immune status of
host, assay technique, sensitivity of host,
virulence of pathogen, use of upper 95%
confidence limit, route of exposure,
choice of dose-response model, syn-
ergism/antagonism, dietary consider-
ations and distribution of subjects among
doses and number used. In addition, it
should be realized that infection does not
necessarily mean disease.
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In many studies, small numbers of
viruses (as few as 1 or 2 tissue culture
plaque-forming units), primarily vaccine
strains, have produced infection in
human subjects. The infective dose of
protozoan cysts such as Giardia lamblia
and Entamoeba by the oral route
appears to be as low as between 1 and
10 cysts. Essentially one helminth egg
can be considered to be infectious,
although symptoms may be dose
related.
MIDs for bacteria are generally higher
than those for viruses and parasites. The
number of ingested bacteria required to
cause illness appears to range from
102-108, although recent studies
suggest that the infective dose for
Salmonella may be <10 organisms.
Virulence of the particular type and strain
of microorganism and host factors may
play roles in determining the actual
number of microbes required to cause
infection.
Qualitative Risk Assessment
Because of a limited number of
studies on the pollution of marine
environments by sludge disposal, it is
difficult to assess the risks. It is known
that pathogens can persist in sediments
for an extended period of time and that
animals (for example, rock crabs)
dwelling at a dump site can pick up
these organisms and move away from
the site. It is also known that sludge-
impacted sediments can drift long
distances from the point of discharge.
Whether these sediments and their
associated pathogens can reach coastal
environments does not seem likely under
normal conditions, but in the event of
storms and quakes it is a distinct
possibility. It is logical to assume that
this pollution is less likely to happen
when sludge is disposed at the 106-
mile site than at the New York Bight or
Philadelphia dump sites because of the
distances involved.
Predictions on viral and bacteria
decay following ocean disposal of sludgi
will require information on the vertica
and horizontal movement of discharge!
sludge as well as on the survival o
pathogens attached to sludge particles
The latter information is not currently
available. Studies on how far aerosol:
can travel and how long pathogens cai
survive in them are also incomplete
Consumption of seafood from in am
around a dump site is riskier to healtl
than swimming because of the
bioconcentration of pathogens by filte
feeders.
In summary, with what little
information is available, it is only possible
to speculate on the occurrence of humar
health risks from pathogens in municipa
sludge disposed in the ocean. More
research is needed in order to develop «
definitive risk assessment methodology.
This Project Summary was prepared by staff of the Environmental Criteria and
Assessment Office, Cincinnati, OH 45268.
Larry Fradkin is the EPA Project Officer (see below).
The Complete report entitled "Qualitative Pathogen Risk Assessment for Ocean
Disposal of Municipal Sludge," (Order No. PB 89-126 593/AS; Cost: $21.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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Official Business
Penalty for Private Use $300
EPA/600/S6-88/010
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