Sample Processing - Waterborne Pathogens: Detection Methods and Applications - page 66

4.2. SAMPLING
Sampling is a critical step in the monitoring procedure because it
could represent the main contribution to error in the whole analytical
process. 15 As a consequence, appropriate sampling tools and methods are
required, which are easy to use and reliable, taking into account flow varia-
tions and allowing an adequate number of samples to be taken. A review
of this topic by Roig and colleagues in 2011 provides an excellent further
introduction to the topic. 15
When sampling procedures for microorganisms in drinking, irrigation,
and food processing water are considered, the questions which arise are: (1)
will a specific volume of water be representative, and (2) will the water
quality influence the sampling procedure? Pathogen presence in water often
displays a high degree of spatiotemporal variability. For example, heavy
rainfall and associated floods, if occurring, can flush microorganisms into
waterways and aquifers. Greater water flow contributes to increasing the
pathogen load and the penetration speed of pathogens into resource waters
and the drinking-water supply. 15
Furthermore, the techniques able to process relatively clean finished,
drinking water differ from those techniques that are suitable for potentially
“dirty” source waters, which might contain high amounts of particulate
and other matter. There is also a high degree of variability between different
source waters and techniques which work well in one catchment, or even
section of a catchment, might perform less well in other locations.
Selection of an appropriate sampling protocol depends primarily on
the clear identification of monitoring objectives ( Fig. 4.1 ). This will influ-
ence what to monitor, where, when, and how often. Additionally, the
monitoring aims will determine the type of detection technology which
is appropriate, thus having knock-on effects upon sample size and process-
ing techniques. The rest of the Chapter will describe sample processing
methodologies, whereas this section will focus on the sample collection
aspect. An overview of the types of field-based sampling/monitoring is
given in Box 4.2 below.
Water samples can be obtained through grab, or spot, sampling of a
certain volume at a particular time or through collection of a sample over
a time period, sometimes described as passive or automatic sampling. The
first approach rapidly obtains a sample which can be analyzed, whereas the
second has the advantage of providing a degree of evening out of temporal