Cryptosporidium and Giardia (oo)cyst concentrations are frequently used for assessing drinking water safety. The widely used USEPA Method 1623 provides total counts of (oo)cysts, but may not be accurate for human health risk characterization, since it does not provide infectivity information. The total counts and infectious fraction of Cryptosporidium oocysts and the total counts of Giardia cysts were assessed in major fecal pollution sources. Fresh calf and cow feces, their manure, and the discharge point were sampled in a small rural sub-watershed (n ¼ 20, 21, 10, 10). Median concentrations for total (oo)cysts were higher in calves (333 oocysts g À1 ; 111 cysts g À1 ) than in cows (52 oocysts g À1 ; 7 cysts g À1 ). Infectious oocysts were found in 17 (7%) of the samples and none were found in manure or at the discharge point. Urban sources were sampled in the influent and effluent (n ¼ 19, 18) of two wastewater treatment plants. Peak concentrations were 533 oocysts L À1 and 9,010 cysts L À1 for influents and 89 oocysts L À1 and 472 cysts L À1 for effluents. Infectious oocyst fractions varied from below the detection limit to 7-22% in the effluent and influent respectively.These infectious fractions are significantly lower than those currently used for quantitative microbial risk assessment estimates.
Drinking water treatment plants throughout the world are increasingly facing the presence of toxic cyanobacteria in their source waters. During treatment, the oxidation of cyanobacteria changes cell morphology and can potentially lyse cells, releasing intracellular metabolites. In this study, a combination of techniques was applied to better understand the effect of oxidation with chlorine, ozone, potassium permanganate, and hydrogen peroxide on two cell cultures (Microcystis, Dolichospermum) in Lake Champlain water. The discrepancy observed between flow cytometry cell viability and cell count numbers was more pronounced for hydrogen peroxide and potassium permanganate than ozone and chlorine. Liquid chromatography with organic carbon and nitrogen detection was applied to monitor the changes in dissolved organic matter fractions following oxidation. Increases in the biopolymer fraction after oxidation with chlorine and ozone were attributed to the release of intracellular algal organic matter and/or fragmentation of the cell membrane. A novel technique, Enhanced Darkfield Microscopy with Hyperspectral Imaging, was applied to chlorinated and ozonated samples. Significant changes in the peak maxima and number of peaks were observed for the cell walls post-oxidation, but this effect was muted for the cell-bound material, which remained relatively unaltered.
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