Sludge Watch ==> Human Pathogens - Infiltration, Survival, Growth within Fruits and Veggies

[Maureen Reilly]

Sludgewatch Admin:

This is a paraphrase of an argument made by some collegues:

Does it really make sense to use reclaimed sewer water for growing crops 
eaten raw---especially the organic foods?   That is the practice in the 
'Salad Bowl' of Salinas Valley California.  We know that the standards and 
tests of California's reclaimed water "Title 22" fail to detect all the 
pathogens that may be present in the water.  The indicator bacteria will not 
reflect or detect newly emerging infectious diseases. They can't see viable 
but non-culturable pathogens with Title 22 lab tests. There is no 
opportunity to test for pathogen regrowth in the delivery system.

They don't test for ameobae, nor do they test the water once it leaves the 
plant, and it is not tested at point of use in the field. Thus the 
regulators can NOT know the quality of the water used on the crop, whether 
it has been contaminated (there is some serious question about the pipes 
having leaks), and the issue of shedding pathogens from loaded biofilms 
within the piping system.

Thus the quality of the water coming out of the end of the pipe may be quite 
different from what went in. Further,what went in imay be also full of 
pathogens. Thus tertiary treated water is not the safe water that some 
people claim it to be. The problem is that people running sewer plants have 
no training or background in these areas, they don't know that they don't 
know.

That is dangerous.

..............................................................................................................

U. S. Food and Drug Administration
Center for Food Safety and Applied Nutrition
November 1999

Potential for Infiltration, Survival and Growth Of Human Pathogens within 
Fruits and Vegetables
Waterborne Contamination


Several studies have indicated that processing procedures may contribute to 
the microbial contamination of fruits and vegetables. A study on 
high-pressure washing of citrus has suggested that spray washing does not 
generally cause visible damage to sound fruit but will rupture fruit that 
has been previously physically damaged (Petracek et al., 1998).

Although spray washing does not appear to compromise sound fruit, there is 
suggestive evidence that microorganisms can be internalized into intact 
fruit in a dump tank. A team of FDA scientists performed a study to assess 
the potential for intact oranges and grapefruit to internalize bacteria from 
contaminated water, using dye to represent bacteria (Merker et al., 1999). 
This potential internalization of pathogens from contaminated water can 
occur if fruit is placed in a hydrocooler or a dump tank, and also may occur 
on the tree during a heavy rain.

The study demonstrated that infiltration of water into what appears to be 
intact fruit can occur. All fruit used in this study was stringently culled 
prior to use so that it was representative of fruit used for juicing in 
operations with rigorous pre-sorting systems. Uptake occurred most often 
when warm fruit was placed into cold water, so that the resulting pressure 
differential favored uptake. However, there was evidence of low levels of 
dye uptake in grapefruit even when there was no temperature differential. 
Grapefruit were generally more susceptible to infiltration than oranges. In 
most cases, dye was taken up through natural structures, e.g., the stem scar 
on fruit, but occasionally an older puncture wound that appeared to be 
"healed" served as the route of entry.

Buchanan and coworkers (1999) also studied the susceptibility of apples to 
waterborne contamination. They found that when warm apples were submerged in 
colder water contaminated with E. coli O157:H7, as might occur in processing 
operations where flume water or dump tanks are not hygienically maintained, 
the pathogen was occasionally internalized. These results were confirmed 
with dye studies in which 6 percent of warm apples immersed in cold dye 
solution internalized dye through open channels leading from the blossom end 
into the core region.

Zhuang and coworkers (1995) found that tomatoes took up higher numbers of 
cells of Salmonella spp. from an aqueous environment when placed in water 
that was 15°C cooler than the tomatoes. Showalter (1979) and Bartz and 
Showalter (1981) found that when tomatoes were dipped into water that was 
colder than the fruit, creating a negative temperature differential, 
tomatoes took up 1 to 4 percent of the fruit weight in water from the 
environment; most of the water uptake appeared to be in the vascular area 
beneath the stem scar.

In addition to the temperature differential, Bartz (1982) has shown that, 
with tomatoes, the amount of water uptake from the environment is partially 
dependent upon the depth of submersion of the fruit. The author found that 
infiltration of tomatoes was influenced by both the temperature differential 
phenomenon and hydrostatic pressure; there was a positive correlation 
between water uptake and depth of submersion.