The effect of turbidity on ultraviolet inactivation characteristics of Cryptosporidium parvum
oocysts and Giardia muris cysts suspended in samples of untreated lake water was determined.
Prepared suspensions of parasites were exposed to controlled doses of UV radiation from a
medium pressure UV lamp in collimated beam exposure experiments. The level of turbidity in
the exposed suspensions was varied from 0.25 to 20.0 NTU by addition of aliquots of suspended
solids concentrated from the lake water. Average germicidal UV dose was maintained at
constant targets of 5 and 40 mJ/cm2 by increasing the exposure times to account for the effect of
the turbidity on UV transmittance of unfiltered water samples. Inactivation of the parasites was
determined using established mouse infectivity procedures. Analysis of variance conducted on
the outcomes of factorial designed experiments revealed that turbidity had a modest, but
statistically significant effect on the UV inactivation characteristics of C. parvum oocysts at the
99% level. An effect was also observed for G. muris, but was significant only at the 94%
confidence level. On average, increasing turbidity from 0.25 to 20.0 NTU resulted in a 0.8 log-
unit and 0.5 log-unit decreases in inactivation of C. parvum and G. muris, respectively, at
average germicidal UV doses of 5 and 40 mJ/cm2. The turbidity effect was independent of UV
dose in this UV dose range. The mechanism that accounted for the reduction of inactivation
with increased turbidity was not determined, but should be investigated further.
Includes 14 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 310 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 11 |
| Published : | 11/01/2002 |
