Interface Change and Toxicity Risks of Loose Deposits Induced by Boiling in Water with Discoloration

Abstract

Boiling is commonly used as a point-of-use household water treatment. This study evaluated the effect of boiling on the water quality, with particles originating from loose deposits in drinking water distribution systems. Results showed that during the boiling process, turbidity did not have an obvious change before 60 °C, but it abruptly increased after 90 °C, and it finally reached about 220 NTU (initial 194 NTU) after boiling (100 °C) under a particle concentration of 100 mg/L with a slight initial discoloration. The particles had smaller size, more particle counts, and lower agglomeration after boiling. Boiling induced an increase of dissolved organic matter (DOM) in water, and the particles contributed to the DOM significantly. In addition, the particles had an increased specific surface area (from 106.8 to 123.4 cm2/g) and roughness after boiling. More importantly, the particles exhibited higher cytotoxicity after boiling for human gastric mucosal cells, and a good negative linear relationship was found between turbidity and cell viability. Interestingly, the increase of intracellular reactive oxygen species was observed in the water samples with particles added. Furthermore, particles promoted the formation of disinfection byproducts with a more aromatic structure, which had higher toxicity. This study states that removing particles before boiling is necessary.