Chlorate in Drinking Water – An Update

Ein Bericht aus unserem Laboralltag

Dr. Carmen Breitling-Utzmann

 

Photo. In order to prevent bacterial contamination in drinking water, chlorine-containing agents are often used for water treatment. Unwanted disinfection by-products such as chlorate can also end up in the water, however. Last year the European Food Safety Authority (EFSA) conducted a toxicological evaluation of chlorate. Within this context, our findings of chlorate in drinking water from 2014 and 2015 will be reviewed.

 

In December 2014 we published a report on our investigations into chlorate in drinking water on our homepage [1]. At that time a legal evaluation of the chlorate amounts found in drinking water wasn’t possible due to the absence of a maximum level for chlorate in drinking water and a lack of data for toxicological evaluation.

 

What’s the current situation?

On 24 June 2015 EFSA published a statement regarding the toxicological evaluation of chlorate in food and drinking water [2]. Due to the possible inhibition of iodine absorption, a tolerable daily intake (TDI) of 3 micrograms chlorate per kg bodyweight per day (3 µg/kg BW/day) was established. A high intake of chlorate on a single day could also pose a toxicological risk because the blood’s ability to take in oxygen could be impaired, and it could also cause kidney failure. Therefore, EFSA also recommended a safe maximum daily intake of chlorate (the so-called „acute reference dose“ (ARfD)) of 36 µg/kg bodyweight per day.

 

According to EFSA, it is mainly drinking water that contributes to the chronic intake of chlorate.

 

How are the measured amounts in drinking water evaluated?

Using EFSAs levels of safe daily intake amounts, we calculated the amounts of chlorate in drinking water at which the TDI and ARfD would be exhausted. We assumed an average daily consumption of two liters of water for adults and one liter for young children (approx. 12 to 18 months old, weighing 10 kg).

 

Table 1: Calculated chlorate amounts, at which the normal intake of drinking water would exhaust the Tolerable Daily Intake (TDI) or the Acute Reference Dose (ARfD)
  Adults (60 kg, 2 l / day) Young Children (10 kg, 1 l / day)
TDI reached at: 0,09 mg/l 0,03 mg/l
ARfD reached at: 1,08 mg/l 0,36 mg/l

 

As shown here, the TDI is exceeded at a quantity as low as 0.03 mg chlorate per liter drinking water for young children and at 0.09 mg/l for adults. The acute reference dose is exceeded at 0.36 and 1.08 mg/l chlorate for young children and adults, respectively.

 

If we take into account the guidance level of 0.7mg/l chlorate in drinking water provided by the World Health Organization (WHO), the TDI for young children and adults would be considerably exceeded – for young children even the acute reference dose.  

 

In 2014 and 2015 a total of 141 drinking water samples from the region of Stuttgart were analyzed in terms of chlorate contamination.

 

Illustration 1: Chlorate amounts in 141 drinking water samples from the region of Stuttgart, from 2014 and 2015. The highest measured amounts were 0.39 mg/l and 1.15 mg/l.

Illustration 1: Chlorate amounts in 141 drinking water samples from the region of Stuttgart, from 2014 and 2015. The highest measured amounts were 0.39 mg/l and 1.15 mg/l.

 

Illustration 1 shows that the quantity of chlorate in most of the drinking water samples lay below the TDI of 0.03 mg/l for young children (80 % of 113 samples). Only a small number of samples contained amounts of chlorate exceeding 0.03 mg/l (13 % of 19 samples); or even the TDI for adults of 0.09 mg/l (6 % of 9 samples).

 

It must be taken into account that more than half of the samples were analyzed due to risk-oriented concerns; these included drinking water from private, municipal, or association water sources that had been treated with a chlorine-containing disinfectant [1].

 

The two samples with the highest measured chlorate values exceeded the ARfD for young children (0.39 mg/l and 1.15 mg/l).

 

What influences the amount of chlorate in drinking water?

Our investigations have shown that the chlorate content in drinking water is affected by disinfectants used in water treatment [1]. The use of chloric gas results in considerably lower amounts of chlorate, for example, than the use of chlorine dioxide or chlorine bleaching lye (solution of sodium hypochlorite).

 

Furthermore, very high amounts of chlorate can arise in chlorine bleaching lye during storage [3]. Illustration 2 shows, however, that the storage of sodium hypochlorite solution in cool, dark conditions significantly reduces the formation of chlorate.

 

It was possible to significantly lower the amount of chlorate in the drinking water with the highest measured amount of 1.15 mg/l (see above) with the application of fresh chlorine bleaching lye.

 

Illustration 2: Degradation of active chlorine and formation of chlorate in a sodium hypochlorite solution in various storage conditions [3].

Illustration 2: Degradation of active chlorine and formation of chlorate in a sodium hypochlorite solution in various storage conditions [3].

 

Future development

Currently, the Umweltbundesamt (Federal Environmental Agency) is working on the establishment of a maximum value for chlorate to be included in the list of treatment substances and disinfection procedures in compliance with § 11 of the German Drinking Water Ordinance of 2001.

 

Summary

Even though the quantity of chlorate in most of the drinking water samples was found to be below the tolerable daily intake (TDI) limit, there were also individual samples with levels considerably higher than the TDI. However, chlorate levels in drinking water could be minimized by taking appropriate measures such as proper storage and regular controls of the disinfectants.

 

Infokasten

What is chlorate?

Chlorates are the salts of chloric acid (HClO3). In the past sodium chlorate and potassium chlorate were used as herbicides. However, products containing chlorate are no longer authorized for use as plant protecting agents or biocides in the EU. However, chlorate can occur as a disinfection byproduct during the treatment of drinking water.

 

The intake of chlorate can damage red blood cells as well as inhibit the intake of iodine into the thyroid gland. In sensitive individuals an inhibited intake of iodine could potentially lead to changes in the thyroid hormone levels [2].

 

References

[1] Report from CVUA Stuttgart from 10 Dec., 2014

[2] Scientific Opinion, Risks for public health related to the presence of chlorate in food, EFSA Panel on Contaminants in the Food Chain (CONTAM), European Food Safety Authority (EFSA), Parma, Italy, EFSA Journal 2015;13(6):4135

[3] Chlorit und Chlorat ; 03/2012 166, Wasseraufbereitung Bädertechnik | AB Archiv des Badewesens

 

Artikel erstmals erschienen am 24.08.2016