Backyard Aquaponics
A place to discuss aquaponics

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.

FOOD POISONING AND WINE

Date: Sat 15 Nov 2003

Wine’s reputation for positive health attributes was initially confirmed in a study recently in the British Medical Journal. A team of esearchers led by Martin Weisse, M.D., of West Virginia University reported that both red and white wine efficiently wipe out bacteria responsible for food-related stomach ailments, such as food poisoning, dysentery and diarrhea, performing even better than bismuth salicylate (Pepto-Bismol).

Red and white wine proved superior to all other solutions in fighting the effects of the three bacteria tested: salmonella, shigella and E coli. "Whatever the active anti-microbial agent in wine," the investigators wrote, "we found that wine is a better antibacterial agent than bismuth salicylate against the most common genera of bacteria that cause traveler's diarrhea." .........