Waterworks-specific composition of drinking water disinfection by-products.

Reactions between chemical disinfectants and natural organic matter (NOM) upon drinking water treatment result in formation of potentially harmful disinfection by-products (DBPs). The diversity of DBPs formed is high and a large portion remains unknown. Previous studies have shown that non-volatile DBPs are important, as much of the total toxicity from DBPs has been related to this fraction. To further understand the composition and variation of DBPs associated with this fraction, non-target analysis with ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was employed to detect DBPs at four Swedish waterworks using different types of raw water and treatments. Samples were collected five times covering a full year. A common group of DBPs formed at all four waterworks was detected, suggesting a similar pool of DBP precursors in all raw waters that might be related to phenolic moieties. However, the largest proportion (64-92%) of the assigned chlorinated and brominated molecular formulae were unique, i.e. were solely found in one of the four waterworks. In contrast, the compositional variations of NOM in the raw waters and samples collected prior to chemical disinfection were rather limited. This indicated that waterworks-specific DBPs presumably originated from matrix effects at the point of disinfection, primarily explained by differences in bromide levels, disinfectants (chlorine versus chloramine) and different relative abundances of isomers among the NOM compositions studied. The large variation of observed DBPs in the toxicologically relevant non-volatile fraction indicates that non-targeted monitoring strategies might be valuable to ensure relevant DBP monitoring in the future

Mechanisms of Ultrashort Laser-Induced Fragmentation of Metal Nanoparticles in Liquids: Numerical Insights.

International audienceFemtosecond laser-induced fragmentation of gold nanoparticles in water is examined. Numerical calculations are performed to elucidate the roles of thermal and electrostatic effects due to electron emission in the corresponding decomposition mechanisms. The obtained results demonstrate that particles smaller than a well-defined size R* melt at smaller fluences than the ones required for electrostatic decomposition. The limiting size depends on the absorption coefficient calculated as a function of particle radius, which depends on laser wavelength and on the optical properties of the particle and the background environment. To decompose particles with radii larger than R*, a considerable increase in laser fluence is required. In this case, thermomechanical effects become prevailing. Both the calculated range of particle sizes to be decomposed by the considered laser pulses and the corresponding fluences agree with several experimental measurements