Mixing of arsenic-rich groundwater and surface water in drinking water distribution systems: Implications for contaminants, disinfection byproducts and organic components

Heavy metal, organic matter, and disinfection byproduct release from drinking water pipe scales under stagnant conditions

“…1 In our previous study where we monitored how different compositions of surface water and groundwater in this WDS affected metal concentrations, we noted that changes in source water composition caused such transitional effects, inducing the release of Fe, Mn, Al and As. 14 However, these changes did not cause Pb release. Lead concentrations in source waters were very low (below 1 μg L −1 ) (Table S2 †).…”

“…Ca 2+ , Na + and HCO 3 − were the dominant ions in the sample reflecting a combination of Ca-HCO 3 -and Na-HCO 3 -type waters. 56 Importantly, WDS 1 was supplied with water containing elevated As concentrations (30 to 50 μg L −1 ) for many decades immediately prior to the installation of a new treatment plant in 2020, 14 shortly before pipe sections were collected. Basic physicochemical parameters, as well as DBP, OM, and metal concentrations were monitored under stagnation conditions across the 96 h experimental period (Table S4 †).…”

“…The concentrations of both classes of DBPs were lower than expected based on our previous research in which we examined this WDS in greater detail. 14 However, the tap water used for these current experiments was sampled during winter, when a lower concentration of DBPs was expected. 66 3.4.2.…”

“…[76][77][78] DCAA and TCAA were found to be the dominant HAAs (Table S1 †), in support of our previous research which showed a strong correlation between the tryptophan-like OM component and TCAA concentrations. 14 Li et al (2020) 40 have also found that tryptophan-like substances play a major role in producing DBPs derived from biofilms. The ∼10% higher HAAs concentrations measured during the experiment with pipe scale 2 (compared to HAAs levels in the tap water) were probably related to the release of OM from scale.…”

“…3,[10][11][12] However, irregular or periodic changes in supply-water quality (and velocity) can cause transitional effects, including the destabilization and mobilization of scale materials into the broader water supply system. 1,13,14 Chemical destabilization, for example, may occur when pH, oxidation-reduction potential and ion composition in the supply water changes or, alternatively, when disinfection processes change. 1 The release of certain metals can cause water discoloration 12,[15][16][17] and potentially pose a health risk to end users.…”