Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
processing
5667-6: 1985 Sampling - Part 6: Guidance on sampling of rivers and
streams
The design of a water monitoring programme would be incomplete
without consideration of the demographic and socioeconomic
characteristics, and also an understanding of the historical
development, of the potentially exposed community. The evolution of
materials used in distribution systems changes the profiles of
pollutants requiring measurement. Cultural and socio-economic factors
affect usage patterns, which in turn influence the extent of exposure
to contaminants in drinking-water.
In order to ensure the representativeness and validity of water
samples, sampling techniques must be carefully selected (WHO, 1992,
1993). The first step in the design of a sampling programme is to
develop concise objectives, accounting for
* the nature of the substance to be measured
* point of exposure
* the duration of time over which measurements will be taken.
The type and magnitude of spatial and temporal variations in the
concentration of water constituents will depend upon both their
sources and their behaviour in the distribution and service systems.
Substances can be classified into two main types:
* Type 1. Substances whose concentration is unlikely to vary during
distribution. The concentration of these substances in the
distribution system is largely governed by the concentration in the
water going into the supply, and the substances do not undergo any
reaction in the distribution system. Examples of such substances
are arsenic, chloride, fluoride, hardness, pesticides, sodium and
total dissolved solids.
* Type 2. Substances whose concentrations may vary during
distribution. These include
- substances whose concentration during distribution is dependent
mainly on the concentration in the water going into the supply,
but which may participate in reactions (which change the
concentration) within the distribution system. Examples are
aluminium, chloroform, iron, manganese and hydrogen ion (pH).
- substances for which the distribution system provides the main
source, such as benzo [a]pyrene, copper, lead and zinc.
This classification applies only to piped water supplies. In all
other types of supply, water constituents should be regarded as type 1
substances. The same substance may belong to different classes in
different distribution systems.
7.3.3 Sample collection
The location, frequency and time of sampling is strongly
http://www.inchem.org/documents/ehc/ehc/ehc214.htm
Page 130 of 284
6/1/2007