Table 4 Discussion of the 3-stepped approach of the BPR “Guidance on Disinfection By-Products” (ECHA, 2017 [2])
Concepts | Step 1 “Worst-case”-calculation (PEC/PNEC) | Step 2 Group parameter approach (AOX, TOC) | Step 3 Whole effluent testing (WET) |
|---|---|---|---|
Approach | 100% conversion of a.s. into known "marker" DBPs | Formation of DBPs correlates with the increase of group parameters (TOC, AOX) | Whole effluent testing to cover known and unknown DBPs |
Pros | • No complicated choice of relevant DBPs • Relatively simple calculation • Consideration of the "worst-case scenario" for known DBPs | • Not expensive & elaborate as no single substance analysis is necessary | • Consideration of unknown DBPs • Consideration of mixture toxicity • Existing established procedures for aqueous matrices ([172, 173]) |
Cons | • Suitable only for known DBPs, unknown DBPs not considered • "Marker" DBPs maybe represent only a small fraction • Limited monitoring data (bias) lead to bias of DBPs considered as marker DBPs • High number of DBPs (PEC/PNEC) compared to a group parameter such as AOX • Own risk assessment (effect data, exposure assessment) for each DBP may be necessary • Overestimation of exposure due to 100% conversion to one DBP (“which is not reasonable for most/some cases) | • Unclear if group parameters correlate with DBP formation (identity, number) quantitatively • Trigger threshold unclear (depending on PTs, matrices, etc.) • Group parameters not directly correlated with environmental risk, unclear how to incorporate in ERA | • No specific determination of ecotoxicity of single DBPs • Correlation of ecotoxicity with single DBPs difficult • DBPs responsible for ecotoxicity remain unidentified • Representativeness of the samples is questionable, high number of measurements necessary • Only established for aqueous samples • Selection of harmonized bioassays necessary • Not established for continuous processes • Unclear how it relates to exposure assessment |
Conclusions | • High workload for risk assessments for all marker DBPs and PTs and application types, considering the key parameters • Limited explanatory power • Applicability of the guidance and experimental suggestions for implementation in non-aqueous PT (PTs 1, 2, 3, 4) is missing (requires further guidance) • Focus of the guidance is only on halogenated DBPs, with no consideration of non-halogenated DBPs • No detailed recommendations and guidance in the case of conflicting data on the different steps • No guidance on how to perform a risk assessment for chemicals, which are a.s. and DBPs simultaneously | ||