Here is a response to this question by Dr. James Rakocy, the Director of the University of the Virgin Islands Agricultural Experiment Station and who has been doing research in aquaponics for over 20 years.
Quote: Question :
What steps are taken in aquaponics to ensure that bacteria associated with fish solid waste (E. coli, etc.) do not contaminate crops to be consumed by humans?
Cary Mitchell, Purdue University
West Lafayette, Indiana
Answer :
Pathogenic organisms that enter water through fecal contamination are very difficult to isolate and identify.
However, coliform bacteria, which are present in large quantities in the intestinal tracts of humans and warm-blooded animals are easily tested and commonly used to indicate fecal contamination.
Each person discharges from 100 to 400 billion coliform bacteria per day. They aid digestion through the breakdown of food. The presence of coliforms does not always mean contamination with human or animal waste as some species can grow in soil but Escherichia coli (E. coli) are entirely of fecal origin.
Drinking water is considered safe when less than 5% of water samples test positive for total coliform bacteria. However, those samples testing positive must be tested for fecal coliforms.
No fecal coliforms are allowed in drinking water but the standard for recreational water is 235 organisms/100 ml in a single sample.
There are hundreds of strains of E. coli that are harmless. However, one strain, identified as O157:H7 and associated with cattle feces, creates powerful toxins and has caused many illnesses and deaths.
Aquaponic systems could be exposed to fecal contamination from warm-blooded animals. In an outdoor system contamination could come from birds for example. In an indoor system contamination could come from rodents.
However, the dose would be quite small and it would not occur regularly. Any coliform bacteria that get into the system would be highly diluted. I doubt that there would be any contamination from cattle feces.
In the 20 years we have been growing plants aquaponically at the University of the Virgin Islands, no one has ever gotten ill.
In the past we raised mainly lettuce, which was washed but not cooked to kill bacteria. Normally the leaves do not contact with the culture water, but some water gets on the leaves from splashing or during packaging operations.
Look at the alternative, which is field production of lettuce. Manures are often used as a soil amendment, including cattle manure. During rainstorms, soil splashes on the leaves. A field is a more natural habitat for birds, mice, rats, rabbits, squirrels, etc.
The issue should be studied. In the meantime, I would not be overly concerned about microbial health risks in aquaponic systems.
However... please note... the above response relates to warm blooded land animals ...
Fish are cold blooded animals... so I don't belive that their excretions contain fecal coliforms such as E. coli ....
Fish digestion works in a completely different way to humans or farm animals.
Fish excretory products pose no danger whatsoever to humans because they do not contain E-coli or any of the other potentially pathogenic bacteria or viruses that are found in human or farm sewage.
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.... and is true..... so ready sources of information would be helpful. I am willing to re-educate my market if necessary. There seems to be a scare-factor out there not always driven by complete facts.
