technical guidance documents - Institute for Health and Consumer ...

ENVIRONMENTAL EXPOSURE ASSESSMENT
which concentrations were averaged should be given too.
12) The time, day, month and year may all be important depending upon the release pattern of the chemicals. Time of sampling may be
essential for certain discharge/emission patterns and locations. For some modelling and trends analysis, the year of sampling will be
the minimum requirements.
13) Compartment characteristics such as lipid content, content of organic carbon and particle size should be specified.
14) For the local aqueous environment, detailed information on the distance of other sources in addition to quantitative information on flow
and dilution are needed.
15) It is necessary to consider whether there is a constant and continuous discharge, or whether the chemical under study is released as a
discontinuous emission showing variations in both volume and concentration with time.
When a substance is used in materials (e.g. polymers) it may be released to the environment
enclosed within the matrix of small particles of the material formed e.g. by weathering or
abrasion (see 2.3.3.5). In such cases it would be useful to know if the analytical method used is
able to detect also the fraction of substance that is associated with these particles. The
availability for analysis can be expected to be reduced for resistant materials and/or large
particles. Depending on use pattern, particles may end up in STP sludge/agricultural soil,
sediments affected by storm water outflows, industrial/urban soil and indoor dust.
Selection of representative data for the environmental compartment of concern
There are two distinct aspects to consider:
The level of confidence in the result, i.e. the number of samples, how far apart and how
frequently they were taken. The sampling frequency and pattern should be sufficient to
adequately represent the concentration at the selected site.
Whether the sampling site(s) represent a local or regional scenario. Samples taken at sites
directly influenced by an emission should be used to describe the local scenario, while samples
taken at larger distances may represent the regional concentrations.
It has to be ascertained if the data are results of sporadic examinations or if the substance was
detected at the same site over a certain period of time. Measured concentrations caused by an
accidental spillage or malfunction should not be considered in the exposure assessment.
Where outliers have been identified their inclusion/exclusion should be discussed and justified.
The data should be critically examined to establish whether high values reflect an increased or
new release, a recent change in emission pattern or a newly discovered occurrence in a specific
environmental compartment. The data should also be examined to check that the analytical
methodology was appropriate.
If many data are available, the following statistical approach for defining outliers may be used:
log( X i
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) > log( p ) + K(log(
p ) − log( p ))
(1)
Where Xi is the concentration, above which a measured value may be considered an outlier, pi is
the value of the i th percentile of the statistic and K is a scaling factor. This filtering of data with a
scaling K = 1.5 is used in most statistical packages, but this factor can be subject dependent.
Data from a prolonged monitoring programme, where seasonal fluctuations are already included,
are of special interest. If available, the distribution of the measured data could be considered for
each monitored site, to allow all the information in the distribution function to be used. For
regional PEC assessment, a further distribution function covering several sites could be
constructed from single site statistics (for example, median, or 90 th percentile if the distribution
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