The existing ISO methods are now under revision. Table 8.7 shows the proposed modifications. The unification of temperature precision has been introduced by ISO as 36 ± 2 °C and 44 ± 0.5 °C.
8.6 Field analyses
Field analysis embraces all the tests that can be performed completely or partially at the site of sampling. Several field analysis techniques have been developed for drinking waters, where the principal requirement is the absence of indicator organisms (Manja et al., 1982; Bernard et al., 1987; Dange et al., 1988; Dutka and El-Shaarawi, 1990; Smoker, 1991; Ramteke, 1995; Grant and Ziel, 1996). Quantitative on-site analysis using the MF technique is also possible (Bartram and Ballance, 1996).
The microbiological quality of bathing waters is presently assessed by the techniques described previously for indicator organisms. Field analyses may be preferred when the time between the collection of the sample and its examination will be long. Field laboratory equipment with filtration and incubation devices are being marketed. The time taken to obtain presumptive results will be the same as at a standard laboratory.
On-site filtration with a delayed incubation is another possibility when conventional procedures are impractical, i.e. when it is not possible to maintain the desired temperature during transport, and when the time between sample collection and analysis will exceed the optimum time limit. With this procedure, filters are placed in water tight plastic Petri dishes with a transport medium, and in conditions that maintain viability but will not allow visible growth. The test is completed at the laboratory by transferring the membranes to appropriate selective media and incubating them for the period of time required. It has to be recognised that growth will start if high temperatures are encountered during transport. Delayed incubation has been found to produce results consistent with those from immediate standard tests (Chen and Hickey, 1983, 1986; APHA/AWWA/WPCF, 1995; Brodsky et al., 1995).
The continuous demands for more rapid techniques that can be performed on site and provide direct results have yet to be satisfied, despite the advances in analytical methods, particularly those based on DNA chips or arrays (Eggers et al., 1997). By contrast, a one-hour assay for thermotolerant coli-forms has been demonstrated for marine bathing beaches, based on MUG detection of β-glucuronidase activity with a portable fluorometer (Davies and Apte, 1996, 1999).
8.7 Data recording, interpretation and reporting
Analysis may be performed as part of a regulatory monitoring programme, as part of a survey of an area used for water recreation, or as part of an epidemiological study in which water quality is related to risks to health from infectious diseases. Each approach has its own requirements which are specified at the outset by the regulatory authority or the study director. One of the most important functions of the analyst is to provide reliable and accurate results in a form that can be recorded for statistical interpretation and reporting, as described in Chapter 3. The following guidance will help the microbiological analyst achieve this aim.