Evaluation of Bioassays and Wastewater Quality ... - Oekotoxzentrum

Classification of risk quotients for the evaluation of water quality regarding priority
substances
In the pilot study at the WWTP Vidy Lausanne the risk quotients were classified according to a
classification system proposed by Götz et al. (2010) (Table 6).
Table 6: Proposed classification system for risk assessment to assess the water quality regarding
selected chemical substances (adapted from Götz et al., 2010; Kase et al., 2011). EC environmental
concentration, AA-EQS Annual Average EQS, RQ risk quotient.
Evaluation Condition/description
very good
good
moderate
insufficient
poor
The environmental concentration (EC) is
100 times smaller than the quality
criterion (AA-EQS)
The environmental concentration (EC) is
10 times smaller than the quality criterion
(AA-EQS)
The environmental concentration (EC) is
smaller than the quality criterion (AA-
EQS)
The environmental concentration (EC) is
smaller than the double quality criterion
(AA-EQS)
The environmental concentration (EC) is
smaller than the tenfold quality criterion
(AA-EQS)
The environmental concentration (EC) is
the same or greater than the tenfold
quality criterion (AA-EQS)
RQ < 0.01
0.01 ≤ RQ < 0.1
0.1 ≤ RQ < 1
1 ≤ RQ < 2
2 ≤ RQ < 10
RQ > 10
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Compliance
with quality
criterion
AA-EQS
passed
AA-EQS
exceeded
The evaluation of the water quality regarding micropollutants originating from municipal
wastewater was adapted according to the module ‘Physicochemical Water Quality’ (Liechti,
2010) of the modular stepwise procedure for Switzerland (www.modul-stufen-konzept.ch). This
classification system reflects the water quality and not the ecological quality. However, in the
European Union (EU) a connection between the ecological status and the chemical status is
made in the context of the Water Framework Directive (WFD): an exceedance of the AA-EQS for
one substance leads to the surpass of a good ecological status in the context of the EU-WFD
(EU, 2010), as very sensitive species are possibly impacted.
During the evaluation of micropollutants according to the classification based on single
substances described above, it was noticed that the detection and quantification limit for the
respective substances could influence the outcome. When the analytical limit of quantification for
a substance is above a category limit (see Table 6), the classification results as a minimum
category. For example if a substance is not detectable and if the limit of quantification is between
the AA-EQS/10 and the AA-EQS, then the minimum category can be designated “good+” since
the actual exposure concentration can be classified as “good” or “very good”.
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