This three year study compared the decay of the commonly used faecal indicator
organisms Escherichia coli, enterococci and coliphage in coastal water and sediment
using laboratory based microcosms with that for the pathogens Salmonella typhimurium
and S. derby. Results from the laboratory study were validated with in-situ decay rates of
faecal coliforms observed at a recreational coastal site following a significant stormwater
event. Results demonstrated that for both indicators and pathogens, greater decay was
observed in the overlying water compared with the surface sediment layer. In general, the
decay rates of Salmonella spp. were greater than either enterococci or coliphage in
overlying water and sediment. Decay rates of E. coli were similar to Salmonella spp. in
overlying water, although greater in sediment. Increased temperature resulted in an
increased decay rate for all organisms in the overlying water (and to a lesser extent in the
surface sediment layer). Results from a 12 month investigation into faecal coliform
concentrations at recreational coastal sites also demonstrated higher concentrations of
faecal coliforms in sediment compared with overlying water. Sediments were therefore
illustrated to act as a reservoir for both faecal indicator and pathogenic microorganisms
and may represent an increased exposure risk if these organisms are resuspended back
into the water column during recreational activities. Using measured decay rates and
available dose-response data, a quantitative microbial risk assessment (QMRA) utilizing
Monte Carlo simulation was undertaken to estimate the risk of infection to Salmonella spp.
following exposure to recreational coastal water subject to a range of faecal contamination
levels. For exposure to recreational water of extremely poor quality (106 CFU 100 mL-1) the
maximum risk of infection (95% CI) on the day of the contamination event was above 2.0 x 10-1 and remained above 1 x 10-3 for three days following the initial high concentration.
Includes 25 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 230 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 11 |
| Published : | 06/16/2002 |
