Detection and prioritization of unknown compounds in water extracts from drinking water production.

The goal of this study is to enhance the identification of unknown compounds in
LC chromatograms of untreated raw water used for drinking water production by
(1) preconcentration of samples and (2) prioritization of the unknown peaks based
on their bioactivity. Preconcentration was done by solid phase extraction (SPE) of
3L large volume (LV) groundwater samples or by 6-week passive sampler (PS)
deployment in the groundwater, using divinylbenzene as active phase. Bioactivity
of the samples was tested as a decrease in bioluminescence in the Allivibrio
fischeri bioassay, which was chosen as a broad-scale bioanalytical tool responding
to many different types of pollutants. Samples were collected at three different
drinking water production stations with low or high degree of anthropogenic
influence. At two stations, different groundwater inlets were sampled. At one
station, samples were taken at different stages in the drinking water production
process. SPE and PS extracts were used for target analysis and non-target
screening, and for testing in the bioassay before and after high-resolution
fractionation. More target compounds were detected in the concentrated LV and
PS extracts than in a 1 mL direct injection of the water. As expected least
compounds and lowest bioassay responses were detected in the raw water from
the station with least anthropogenic influence. PS extracts gave much higher
bioassay responses than the LV extracts. Both chemical and bioassay analysis of
samples collected during subsequent steps in the drinking water production
process confirmed the efficient removal of (bioactive) contaminants. In addition to
the 4 peaks detected in the bioassay chromatogram of the reference station, the
more anthropogenically influenced stations showed additional peaks indicative for
the presence of anthropogenic substances. Identification of suspect compounds
responsible for these additional peaks will proceed according to a three-step
procedure, i.e. based on (1) exact mass and isotopic pattern of compounds
available in different suspect lists, (2) fragment ions assigned to a precursor
available in spectral libraries, and (3) estimated elemental composition. Reference
standards will be obtained for the suspect compounds to confirm their retention
time and bioactivity. Results from the identification process are available by the
end of May 2020, and will be presented at the SETAC Europe conference.