Agriculture Reference
In-Depth Information
Vereen and others (2007) studied the occurrence of camplyobacters in six streams
in Georgia in watersheds representing different agricultural uses. The isolation of
campylobacters ranged from 17 to 100% depending upon the watershed. Mean con-
centrations ranged from 2 to 158 per 100 ml (highest value 595/100 ml). The mean
campylobacter numbers and overall prevalence were greatest downstream from a
wastewater treatment plant that handled both human and poultry slaughterhouse
waste. A multivariate model showed that the levels were signifi cantly infl uenced by
increasing precipitation, which peaked during the summer months. In the United
Kingdom campylobacters were detected in 50% of the lake water samples and 20%
of brook water samples (Sails and others 2002).
Because of their greater resistance to chlorine disinfection, enteric virus and pro-
tozoa can be detected in any surface waters receiving sewage discharges. Chlorine
disinfection will reduce the level of enteric viruses, but will have little effect on pro-
tozoa (Gennaccaro and others 2003 ). Because
Giardia
and
Cryptosporidium
also have
animal reservoirs they can be expected to be present at any time in surface waters. In
a nationwide study in the United States
Cryptosporidium
was detected in 55% of the
sites with an average concentration of 43 oocysts per 1,00 l, and
Giardia
cysts were
detected in 16% of the samples with an average concentration of 3 per 1,00 l (Rose
and others 1991). In another study in the United States and Canada either
Giardia
and
Cryptosporidium
or both were detected in 97% of the surface waters at drinking water
treatment plant intakes sampled over a period of several months (LeChevallier and
others 1991 ).
Cryptosporidium
in surface waters usually originates from cattle and is
usually found in greater concentrations in surface water than
Giardia
. However,
Giardia
is a common infection in man, and sewage discharges usually have greater
concentrations than
Cryptosporidium
(Smith and Grimason 2003). Thus, surface
waters more impacted by sewage discharges or combined sewer overfl ows may have
more
Giardia
than
Cryptosporidium
.
Humans are believed to be the only signifi cant source of enteric viruses that cause
illness in man, although hepatitis E virus is excreted in the feces of pigs and perhaps
other animals (Mushahwar 2008). Although the occurrence of enteroviruses has been
the most studied, adenoviruses may be the most common in sewage discharges and
surface waters (Mena and Gerba 2008). Studies conducted in Europe have reported
enteric virus concentrations in surface waters of between 1 and 56 per liter, as deter-
mined by conventional cell culture methods (Bosch and others 2006). Jiang and Chu
(2004) reported that half of the river water they sampled in southern California heavily
impacted by treated sewage discharges contained adenoviruses. In half of the samples
collected at surface water inlets to drinking water treatment plants Chapron and others
(2000) detected enteroviruses and adenoviruses in cell culture using the polymerase
chain reaction.
Enteric pathogens are more likely to be detected in sediments than surface waters.
In the case of bacteria and viruses this is probably because of their attachment to
suspended particles and their settling. The protozoan parasites are large enough that
they will eventually settle out on their own. Once in the sediment they appear to be
capable of longer-term survival or growth (Hendricks 1971a; Smith and others 1978).
Hendricks (1971b) isolated salmonellae from 0.6% (1 of 195) of water samples and
from 4.6% (9 of 195) of bottom sediments in a length of river below a sewage outfall.
Van Donsel and Geldreich (1971) collected simultaneous sediment and water samples
