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2.2 MEASURED DATA
ENVIRONMENTAL EXPOSURE ASSESSMENT
For a number of existing substances measured data are available for air, fresh or saline water,
sediment, biota and/or soil. These data have to be carefully evaluated for their adequacy and
representativeness according to the criteria below. They are used together with calculated
environmental concentrations in the interpretation of exposure data.
The evaluation should follow a stepwise procedure:
• reliable and representative data should be selected by evaluation of the sampling and
analytical methods employed and the geographic and time scales of the measurement
campaigns (Section 2.2.1);
• the data should be assigned to local or regional scenarios by taking into account the sources
of exposure and the environmental fate of the substance (Section 2.2.2);
• the measured data should be compared to the corresponding calculated PEC. For naturally
occurring substances background concentrations have to be taken into account. For risk
characterisation, a representative PEC should be decided upon based on measured data and a
calculated PEC (Section 2.5).
2.2.1 Selection of adequate measured data
The available measured environmental concentrations have to be assessed first. The following
aspects could be considered in order to decide if the data are adequate for use in the exposure
assessment and how much importance should be attached to them:
Quality of the applied measuring techniques
The applied techniques of sampling, sample shipping and storage, sample preparation for
analysis and analysis must consider the physico-chemical properties of the substance. Measured
concentrations that are not representative as indicated by an adequate sampling programme or
are of insufficient quality should not be used in the exposure assessment.
The limit of quantitation (LOQ) of the analytical method, which is normally defined by the
analytical technique being used, should be suitable for the risk assessment and the comparability
of the measured data should be carefully evaluated. For example, the concentrations in water
may either reflect total concentrations or dissolved concentrations according to the sampling and
preparation procedures used. The concentrations in sediment may significantly depend on the
content of organic carbon and particle size of the sampled sediment. The soil and sediment
concentrations should preferably be based on concentrations normalised for the particle size (i.e.
coarsest particles taken out by sieving). All measurements below the LOQ constitute a special
problem and should be considered on a case-by-case basis. One approach that could be
considered would be to use a value corresponding to LOQ/2 before estimating a mean or
standard deviation (EC, 1999). As this method could heavily influence the mean and standard
deviation, other methods may also be considered (e.g. assuming same distribution of data below
and above the LOQ).
The aim is to obtain as much useful information on exposure from a data set as possible, but
there is inherent danger for inappropriate use of the data for risk assessment purposes. To
address this problem, two quality levels for existing data are given in Table 4 (taken from
OECD, 2000k). In recommending this table the OECD stressed “…these criteria should be
applied in a flexible manner. For example, data should not always be discounted because they do
not meet the criteria. Risk assessors should make a decision to use the data or not, on a case-by-
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