Toxicity measurements in concentrated water samples - Rivm

For less than 4 test species, the single species approach can be used. This method is also used for the
assessment of whole effluents. The criteria indicate effects based on exceeding toxicity levels.
Figure 1-3. Microtox® test (left) and algae test (PAM, right) which can be applied to very small volumes.
If more toxicity data are available (four or more test species), a risk analysis can be used based on a
species sensitivity distribution (SSD) (Posthuma et al., 2002). The potential fraction affected is derived
from the sensitivity distribution at the original sample concentration (Figure 1-4).
Potentially Affected
Fraction species (%)
toxic
pressure
= 14%
100
90
80
70
60
50
40
30
20
10
0
0.01 0.1 1 10 100 1000
original
water sample (C F original
water sample (C = 1) F = 1)
NECF NECF 90% Confidence
Interval (C.I.)
(concentration factor no effect)
Figure 1-4. Example of a cumulative species sensitivity distribution curve for the end-points of five bioassay
tests, and its extrapolation for the ecological risk in the not concentrated sample (Struijs and De
Zwart, 2003).
Metals are not extracted from the water sample with XAD. However, for most relevant metals, large
toxicity datasets are available. These data can be used to calculate a potentially affected fraction (PAF)
for measured metals using SSD. Options for calculating toxic pressure for metals are presented in
Appendix III.
A detailed description of the interpretation methods is given in chapter 5.
20 RIVM Report 607013010