Refrigerated autosampling for the assessment of bacteriological water quality

Abstract

This study compared manual and automatic sampling techniques at two urban creeks of varying faecal impact in Sydney, Australia. Changes in refrigerated (3°C) automatic sampler samples were followed for up to 18 h for total coliforms, faecal coliforms, total heterotrophs, pH, conductivity and turbidity. Significant differences ( P = 0.000) in faecal coliform densities between manual and automatic samples 0.101 log 10cfu/100 ml were detected at the less impacted site. Also, total coliform levels decreased and then increased during refrigerated storage at the less impacted site. Total heterotrophs grown at 20 or 35°C were not significantly ( P > 0.05) affected by either the method of sampling or storage time. At both sites, the pH of manual samples was consistently lower than that of automatic samples and could not be accounted for by bottle type. In contrast, the higher conductivity of manually collected samples could largely be accounted for by the use of glass rather than plastic bottles. Conductivity at both sites decreased with storage time in plastic bottles. These results signify an inherent difference between samples collected manually and those collected automatically, but indicate that these differences are minimal in practical terms, particularly when water samples are polluted. Sampling technique and storage time appeared to be more critical when the level of contamination to be detected was low.