Sunlight inactivation rates of somatic coliphages, F-specific RNA bacteriophages (F-RNA phages), and fecal coliforms were compared in seven summer and three winter survival experiments. Experiments were conducted outdoors, using 300-liter 2% (vol/vol) sewage-seawater mixtures held in open-top chambers. Dark inactivation rates (kD s), measured from exponential survival curves in enclosed (control) chambers, were higher in summer (temperature range: 14 to 20°C) than in winter (temperature range: 8 to 10°C). Winter kD s were highest for fecal coliforms and lowest for F-RNA phages but were the same or similar for all three indicators in summer. Sunlight inactivation rates (kS ), as a function of cumulative global solar radiation (insolation), were all higher than thekD s with a consistentkS ranking (from greatest to least) as follows: fecal coliforms, F-RNA phages, and somatic coliphages. Phage inactivation was exponential, but bacterial curves typically exhibited a shoulder. Phages from raw sewage exhibitedkS s similar to those from waste stabilization pond effluent, but raw sewage fecal coliforms were inactivated faster than pond effluent fecal coliforms. In an experiment which included F-DNA phages and Bacteroides fragilis phages, thekS ranking (from greatest to least) was as follows: fecal coliforms, F-RNA phages, B. fragilis phages, F-DNA phages, and somatic coliphages. In a 2-day experiment which included enterococci, the initial concentration ranking (from greatest to least: fecal coliforms, enterococci, F-RNA phages, and somatic coliphages) was reversed during sunlight exposure, with only the phages remaining detectable by the end of day 2. Inactivation rates under different optical filters decreased with the increase in spectral cutoff wavelength (50% light transmission) and indicated that F-RNA phages and fecal coliforms are more susceptible than somatic coliphages to longer solar wavelengths, which predominate in seawater. The consistently superior survival of somatic coliphages in our experiments suggests that they warrant further consideration as fecal, and possibly viral, indicators in marine waters.

Management of faecal contamination of water would be improved if sources could be accurately identified through water analysis. Human faeces are generally perceived as constituting a greater human health risk than animal faeces, but reliable epidemiological evidence is lacking. United States waterborne disease data suggest that humanspecific enteric viruses account for over half the documented outbreaks. However, in New Zealand, where there is a high grazing animal:human ratio (increasing the relative importance of watertransmissible zoonoses), it seems prudent to assume that human and animal faecal pollution both constitute a risk to human health. Irrespective of the relative risks, the ability to identify sources would assist in overall management of microbial water quality. Faecal streptococci do not appear to provide reliable faecal source identification. Human and animal sources, respectively, maybe distinguishable by two tests on Bifidobacterium spp.-growth at 45°C in trypticase phytone yeast broth and sorbitol fermentation. Different species of Bacteroides tend to be present in humans and animals, but poor survival in water is a problem. Phages of the M97014

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The relative attenuation of rhodamine WT dye, two strains of Escherichia coli, Bacillus subtilis endospores, and the F-RNA bacteriophage MS2 in an alluvial gravel aquifer was investigated in two tracing experiments at Burnham, near Christchurch, New Zealand. A simulated concentration curve was fitted to the observed breakthrough curves using the contaminant transport model AT123D, by optimising hydraulic conductivity (K), longitudinal dispersivity (α x ), and a removal constant (λ) (which includes die-off and physical removal processes) with the Parameter Estimation (PEST) optimisation routine. When comparing the parameters, the hydraulic conductivity was converted to velocity (V). The V ranking was E. coli 2690 > B. subtilis endospores > rhodamine WT in Experiment 1 and E. coli J6-2 > phage MS2 > rhodamine WT in Experiment 2. These rankings are consistent with the concept of pore size exclusion, whereby larger particles are preferentially transported in the larger interconnected pores where water velocities are higher. The longitudinal dispersivity (α x ) rankings were consistent with pore size exclusion in Experiment 1, and broadly consistent in Experiment 2. Of the two parameters, V is considered to provide the more reliable result, because it is easier to determine peak position in time than peak height. Little useful information could be derived from the λ values in our study, because of high levels of uncertainty associated with determining peak heights, particularly in Experiment 1. Overall, the curve fits were better in Experiment 2, because of a greater number of bores and observations. Although this complicated between-experiment comparisons, an overall retardation (R) ranking of rhodamine WT > phage MS2; B. subtilis endospores > E. coli J6-2 > E. coli 2690 is broadly consistent with pore size exclusion. Overall, our study showed that the application of the AT123D model to the observed velocities of the tracer curves demonstrated an effect consistent with pore size exclusion.