To determine whether the water at your beach is contaminated, scientists use indicator bacteria . An indicator bacterium may not actually make you sick, but its presence in the water indicates that you could get sick. Indicator bacteria must be easy to detect and found only in polluted waters. Enterococcus is the indicator bacterium used by the US Environmental Protection Agency. The state of California also measures the total number of Coliform bacteria, and the number of Fecal Coliform bacteria. As the name implies, fecal coliform bacteria are found in the feces of warm-blooded animals such as humans, seals and birds.
A California beach must be closed if bacterial concentrations exceed the tabulated values.
|Kind of Bacteria|| Number Allowed
per 100 ml water
|Chance of Sickness|
|Total Coliform|| 10,000 if fecal/total ratio < 0.1
1,000 if fecal/total ratio > 0.1
| 1 in 60 (skin rash)
|Fecal Coliform||400|| example: E. Coli contaminations in food
have caused many deaths
about 1 bacterium / ml
|1 in 80 (stomach flu)|
Heal The Bay issues a beach report card based on these standards (www.healthebay.org). Note that for Enterococcus, the standard is about 1 bacterium per milliliter of water. Keep that in mind for future exercises.
What do you think of these standards? Are they strict enough? Too strict?
If you went to the beach on a day when it was almost, but not quite contaminated
enough to close, you would have about one chance in 100 of getting sick. So if
you went with 100 friends, one would probably get sick. Is that good enough?
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