2014/15 – Noosa (Queensland) – Bromate, Chlorate

Noosa WTP (Queensland) – Bromate

“DWI-507-00090. Noosa WTP (Bromate 0.021 mg/L, 22/12/2014). Short duration spike in the bromate concentration due to elevated levels of bromide in the source water which is subsequently oxidized during water treatment by the ozonation process step. A review of results found that this was an isolated occurrence with low bromide/bromate levels (less than the LOR of 0.05 mg/L) in the preceding and following weeks. This incident occurred during the last reporting period, but was reported to WSR on 28/07/2015. The most significant issue in this incident was that the exceedance was not identified by the contracted laboratory or Seqwater’s Laboratory Information System (LIMS). This resulted in a delay in notifying the Water Supply Regulator as Seqwater only became aware of the exceedance during a review of its data for the 2014-15 reporting year. Both laboratories have reviewed their processes and LIMS systems to prevent recurrence.”


Bromate: Regulatory Standard = 0.02mg/L (Also see section of desalination). A suspected carcinogen. Bromate is formed when ozone used to disinfect drinking water reacts with naturally occurring bromide found in source water. Bromate formation in disinfected drinking water is influenced by factors such as bromide ion concentration, pH of the source water, the amount of ozone and the reaction time used to disinfect the water.

2015: Noosa (Queensland) – Chlorate

2015: Noosa (Queensland) – Chlorate 1.11mg/L (max)

Noosa WTP (Chlorate 0.98 mg/L, 13/04/2015; and 1.11 mg/L, 20/04/2015). Seqwater confirmed the exceedance by retesting (internal laboratory result 1.11 mg/L, 22/04/2015). The sodium hypochlorite which was held on site was pumped out and replaced with fresh supplies. Seqwater confirmed the effectiveness of replacing the sodium hypochlorite through testing of the chemical and follow up testing of the treated water.

SEQWater Annual Drinking Water Quality Plan 2014/15

Chlorite: ADWG Health 0.3mg/L.

Chlorite and chlorate are disinfection by-products of chlorine dioxide disinfection process.

“… industry are having serious problems meeting chlorite/chlorate limits that were proposed in the new Australian Drinking Water Guidelines, especially for disinfection in long distance pipelines that are dosed with sodium hyptochlorite” pers comm 18/5/11.

“Chlorite occurs in drinking water when chlorine dioxide is used for purification purposes. The
International Agency for Research on Cancer (IARC) has concluded that chlorite is not classifiable as carcinogenic to humans and is listed in the Group 3 category. Changes in red blood vessels due to oxidative stress are a major concern with excessive levels of Chlorite in drinking water. According to the US EPA, potential health problems for people drinking Chorite above safe drinking water guideline include: Anemia in infants and young children and nervous system effects.” https://water.epa.gov/drink/contaminants/index.cfm

“Chlorine dioxide (chlorite) is rarely used as a disinfectant in Australian reticulated supplies.
When used, the chlorite residual is generally maintained between 0.2mg/L and 0.4mg/L. It is
particularly effective inthe control of manganese-reducing bacteria. Few data are available on
chlorate levels in Australian water supplies….Chlorine dioxide, chlorite, and chlorate are all
absorbed rapidly by the gastrointestinal tract into blood plasma and distributed to the major
organs. All compounds appear to be rapidly metabolised. Chlorine dioxide has been shown to
impair neurobehavioural and neurological development in rats exposed before birth. Experimental studies with rats and monkeys exposed to chlorine dioxide in drinking water have shown some evidence of thyroid toxicity; however, because of the studies’ limitations, it is difficult to draw firm conclusions (WHO 2005) The primary concern with chlorite and chlorate is oxidative stress resulting in changes in red blood cells. This end point is seen in laboratory animals and, by analogy with chlorate, in humans exposed to high doses in poisoning incidents (WHO 2005).” Australian Drinking Water Guidelines – National Health and Medical Research Centre

“…Subchronic studies in animals (cats, mice, rats and monkeys) indicate that chlorite and chlorate cause haematological changes (osmotic fragility, oxidative stress, increase in mean corpuscular volume), stomach lesions and increased spleen and adrenal weights… Neurobehavioural effects (lowered auditory startle amplitude, decreased brain weight and decreased exploratory activity) are the most sensitive endpoints following oral exposure to chlorite…” https://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/chlorite-chlorate/indexeng.
php#sec10_1Guidelines for Canadian Drinking Water Quality.