Unregulated iodinated disinfection by-products in drinking water

: Occurrence, pathways and cycling of precursors in rivers in southern England considering a potential public health risk

Abstract

Contaminants of emerging concerns (CECs) from anthropogenic and industrial sources are ubiquitous in raw water, and some of these compounds are potential precursors to regulated and unregulated disinfection by-products (DBPs) formed during disinfection of drinking water. Iodinated DBPs (I-DBPs) and Brominated (Br-DBPs) are currently unregulated in most countries and are purported to be more toxic than the regulated chlorinated equivalents.

There is limited literature regarding these emerging I-DBPs and their precursors, namely, bromide, iodide and iodinated X-ray contrasting media (ICM), found in raw water, especially publications focusing on United Kingdom (UK) since 2016. The concentration of I-DBPs in drinking water, and their associated toxicological impacts are unknown. A four-year period sampling the environmentally protected chalk rivers Itchen and Test as well as a two-year sampling of the rivers Medway and Rother, demonstrated the presence of CECs, including I-DBP precursors. During low river (Q95) flow and Dry Weather Flow (DWF) discharge conditions (Q80) from the wastewater treatment works (WTWs), de facto reuse was circa 4.3%, 11.2%, 32.9 % and 6.7% in the rivers Itchen, Test, Medway and Rother, respectively.

The knowledge of the presence of de facto reuse in these afore-mentioned rivers, promoted the development of a sampling campaign to investigate the presence of CECs and correlating the findings with the extent of de facto reuse. This research identified the presence of I-DBP precursors and I-DBPs in both raw and drinking water which led to the question of toxicity of these compounds. The fast response N-acetyl-L cysteine (NAC) thiol reactivity assay was thus used to assess an oxidative stress (toxicity) response from these sources. At high concentration factors, both sources were toxic, relative to a negative control, however, drinking water was more toxic than raw water in all cases except for the River Medway and the associated Burham water supply works (WSW). While it was determined that the precursor compounds and I-DBPs were present in raw and drinking water sources, the next step in the research was to generate some I-DBPs under laboratory- controlled conditions, using a deionized water matrix and a pre-disinfected water sample from Burham WSW. The findings concluded the production of iodophenolic compounds purported to be more toxic even at low concentrations, however a greater concentration of these compounds was observed in drinking water sampled directly from Burham WSW. Analytical challenges and reported limits of detection (LoD) impacted a comparison of I- DBPs data with global literature.

Given it was a challenge to single out the exact regulated DBP or even I-DBP that caused a toxic response using the NAC assay, this research progressed to identifying the toxicity of seven I-DBP and ten regulated DBPs standards was determined using a battery of assays namely, the NAC assay, the SOS-ChromotestTM assay, a bacterial assay for determining genotoxicity, the MTT assay used to evaluate cytotoxicity responses and, the Nrf2 bioassay, a mammalian cell assay used to determine oxidative stress. These experiments were performed using available I-DBP standard solutions with a wide range of concentrations. One I-DBP, namely, 4-iodo-2-methylphenol, and 3 unregulated haloacetic acids (HAAs) namely monochloroacetic acid (MCAA), trichloroacetic acid (TCAA) and dribromoacetic acid (DBAA) generated an oxidative stress response at the concentrations tested using the NAC assay, while the results from the SOS ChromotestTM assay were inconclusive. Using the Nrf2 bioassay, an oxidative stress response was observed with two I-DBPs namely, 2,4,6 triiodophenol and iodoacetamide (IAM), and one HAA namely monobromoacetic acid (MBAA). Regulated trihalomethanes (THMs) in the UK have a total concentration of 100 g/l, however higher concentrations of individual compounds in the THM family, did not produce a toxic response at high concentrations using any of the assays in this research.

Date of Award	Nov 2024
Original language	English
Awarding Institution	University of Brighton
Supervisor	Ian Mayor-Smith (Supervisor) & Alison Lansley (Supervisor)