Differential Cytotoxicity of Haloaromatic Disinfection Byproducts and Lead Co-exposures against Human Intestinal and Neuronal Cells

Abstract

Disinfecting drinking water with chlorine inadvertently generates disinfection byproducts (DBPs) which can cause potential adverse health effects to humans. Haloaromatic DBPs are a group of emerging DBPs recently identified, suspected to be substantially more toxic than haloaliphatic DBPs but have not been extensively studied. Simultaneously, service pipelines made of lead materials are widely used in water distribution systems and become a source of dissolved lead (Pb) in tap water. In this study, we investigated the cytotoxicity of nine haloaromatic DBPs and lead ion (Pb 2+ ), both separately as well as in combination, to human epithelial colorectal adenocarcinoma (Caco-2) and neuroblastoma (SH-SY5Y) cells. Results show that the cytotoxicity of the DBPs against Caco-2 cells followed the descending rank order of 2,4,6-triiodophenol ≅ 2,5-dibromohydroquinone > 2,4,6-tribromophenol > 3,5-dibromo-4-hydroxybenzaldehyde ≅ 2,4,6-trichlorophenol > 4-chlorophenol ≅ 3,5-dibromo-4-hydroxybenzoic acid > 2,6-dichlorophenol >5-chlorosalicylic acid, and the cytotoxicity of the DBPs against SH-SY5Y cells followed a similar rank order, 2,4,6-triiodophenol ≅ 2,5-dibromohydroquinone > 2,4,6-tribromophenol > 3,5-dibromo-4hydroxybenzaldehyde ≅ 2,4,6-trichlorophenol > 4-chlorophenol > 3,5-dibromo-4-hydroxybenzoic acid > 2,6-dichlorophenol ≅ 5chlorosalicylic acid. Lead in water did not change the toxicity of 3,5-dibromo-4-hydroxybenzoic acid (to either cell-type) or the toxicity of 4-chlorophenol (to the neuronal cell-type); but Pb 2+ exhibited different degrees of synergistic effects with other tested DBPs. The synergism resulted in different rank orders of cytotoxicity against both intestinal and neuronal cells. These data indicate that future prioritization and regulation of emerging haloaromatic DBPs in drinking water should be considered in terms of their own toxicity and combinatorial effects with lead in water.

Occurrence of Iodophenols in Aquatic Environments and the Deiodination of Organic Iodine with Ferrate(VI)

“…12 Iodophenols are toxic and carcinogenic. 9,13 In addition, to directly impact human health and the aquatic environment, odorous organic iodine would deteriorate aesthetic properties of drinking water, and they are precursors for the formation of I-DBPs. 6,14 I-DBPs are more cytotoxic and genotoxic than their chlorinated and brominated analogs.…”

“…2,6-Diiodo-4-nitrophenol (up to 3.9 ng/L) and 2,4,6-triiodophenol (up to 0.43 ng/L) were detected in tap water in Yangtze River Delta of China . Iodophenols are toxic and carcinogenic. , In addition, to directly impact human health and the aquatic environment, odorous organic iodine would deteriorate aesthetic properties of drinking water, and they are precursors for the formation of I-DBPs. , I-DBPs are more cytotoxic and genotoxic than their chlorinated and brominated analogs. , Although investigations showed that organic iodine existed in natural waters and iodinated phenolic compounds would form in the disinfection of iodine-containing waters as DBPs, the possible existence of iodinated phenolic compounds in natural waters was ambiguous.…”