Chlorate level - a new challenge for the food industry?

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Chlorate as a contaminant in foodstuffs.

In 2015 the European Food Safety Authority (EFSA) published a scientific opinion on risks for public health related to the presence of chlorate in the food assessed by the EFSA Panel on Contaminants in the Food Chain (CONTAM Panel). The hypothetical Maximum Residue Limit (MRL) of 0.7 mg/kg in all foodstuffs and drinking water was assessed for its reduction of acute/chronic exposures and related risks. The review of current situation you can analyse on page Risks for public health related to the presence of chlorate in food.

Source of chlorate in the food.

Hypochlorite, chlorate and perchlorate are used in the food industry in small amounts as a disinfectant in the washing water for fruits & vegetables or during cleaning any food processing lines and equipment. During chlorination of water chlorate is formed from hypochlorite by disproportionation: 3 NaOCl -> NaClO3 + 2 NaCl. Also perchlorate can be formed in reaction: 4 NaClO3 -> 3 NaClO4 + NaCl. These reactions are also present in disinfectant solutions, and chlorate level is build up, especially if solutions with hypochlorite are stored longer time. Reactions are additionally catalysed by transition metals (like Cu, Ni), so its reduction in high-quality disinfectants will reduce chlorate formation. These reactions are catalysed by temperature and light and these two factors have to be considered to decrease risk with chlorate contamination, as well.

Chlorination is common practice in drinking water production and is also used in southern Europe for the disinfection of rainwater or surface water used for irrigation. Besides, we know about the presence of chlorate in water, usage of chlorate, perchlorate or hypochlorite containing disinfectant was not well regulated.

Sources for chlorate other than water disinfection are pesticide formulations. We can also observe a natural contamination in mineral fertilisers like Chile saltpetre. Today, these sources of chlorate are minimised or not significant in the EU. Since 2010, there has been an EU-wide ban on the application of plant protection products containing chlorate.

Risk of the food contamination

Due to multiple uses of water in food production and processing, chlorate from water might play an important role in the overall exposure to chlorate and uptake level from the food. Up to date the maximum amount of chlorate in the food was not well defined. This gap in legislation makes the use of chlorinated consumables in the food processing difficult.

Risk to human health

Following a request from the European Commission, the risks to human health related to the presence of chlorate in food were assessed by the EFSA Panel on Contaminants in the Food Chain (CONTAM Panel). Research shows, that the critical effect for chronic exposure to chlorate in humans is an inhibition of iodine uptake. Formation of methaemoglobin was identified as a direct effect of chlorate, especially in infants, toddlers and children. Chronic exposures are of concern in particular in younger age groups with mild or moderate iodine deficiency.

A Tolerable Daily Intake (TDI) of 3 µg chlorate/kg body weight was set by read-across from a TDI of 0.3 µg/kg body weight derived for this effect for perchlorate, multiplied by a factor of 10 to account for the lower potency of chlorate.

Discussion about limits for chlorate.

Based on the current practices in the food industry, application of a hypothetical MRL of 0.7 mg/kg for all foodstuffs and drinking water would only minimally reduce acute/chronic exposures and related risks, so it has to be reduced. Assuming chlorate concentrations of 0.7 mg/kg for all foods and drinking water consumed in a day, acute exposures would increase by up to about 5-fold and the acute reference dose are exceeded at mean estimates in all infants and toddlers and at 95% in children and adults. This situation is risky because as shows one survey in Stuttgart, Germany, 600 samples of plant origin were analysed in which 19.8% were found to have residues above the current MRL level. In some cases chlorate residues in fruit and vegetable were found level as high as 5 mg/kg. Even more worryingly, in addition to residue levels found on fruit and vegetables, high chlorate levels are being found in baby milk powder and yoghurts.

The report published by EFSA has at least started to bring some clarity to the situation. The report recommends two new safety levels. In terms of daily or chronic exposure to chlorates, it has set the TDI of 3 mcg/kg of body weight per day for long-term exposure to chlorate in food, which is higher than the current safety level being used.

EFSA also recognised that a high intake of chlorates in a single day could also pose a health risk. It has therefore proposed a Maximum Daily Intake (MDI), or an acute exposure level, of 36 mcg/kg of body weight in a single day.

For clarification is good to mention, that in the past chlorate has been treated as a pesticide residue rather than a food contaminant, because of its used as an herbicide. So, for chlorate has been set a default MRL of 0.01 mg/kg, which usually applies to all plant protection products where no other maximum level has been set. In accordance with EU regulations, the standard MRL of 0.01 mg/kg is valid also for chlorate residues in any foodstuff, especially a baby food. This level is problematic and due to a fundamental disagreement that exists across Europe as a result of different agricultural practices, the European Commission has agreed that member states don’t actually have to take any action when these levels are exceeded.

The European Commission has so far not set safety levels for chlorates in drinking water. The World Health Organisation has however set a guidance level of 0.7 mg/kg of water. EFSA is also calling for new research to investigate chlorate levels in meat.

The EFSA report did not look at the consequences of recommending these new safety levels on food hygiene practices.

Future action for standardisation.

At the moment, EFSA is calling for more research to explain high levels of chlorate in milk products. Now it is down to the European Commission to consider the new EFSA findings and see whether it can move towards an EU-wide safety standard. Up to the date, European food safety bodies wait for further guidance from the European Commission.

Analysis of the food to comply with future regulations.

The determination of chlorate and perchlorate is usually carried out using a single residue method with LC-MS/MS detection with a limit of quantification below of 0.01 mg/kg (10ppb).

    Special water treatment to reduce risk of the food contamination with chlorate

    In order to reduce a level of chlorate in a water there are considered different strategies:

    • working with water suppliers to reduce chlorate concentrations in source materials or to minimise the time from manufacture to delivery and use of water,
    • diluting water stock concentrations with water without chlorate,
    • filtering water for reduction chlorate level through carbon filters or anion-exchange resins,
    • store disinfectants in cool areas and out of direct sunlight,
    • converting to use of chlorine gas instead of hypochlorite,
    • setting rigorous quality specifications for the purchase of NaOCl.


    If you have any further questions do not hesitate to contact me.