Chlorates are the salts from chloric acid and are effective herbicides and disinfectants (biocides). They are strong oxidizers and are used, e.g. in the bleaching of paper, tanning of leather, surface treatment of metals and in pyrotechnics. Due to their disinfecting properties, they can also be used in cosmetics and, for oral hygiene purposes, in mouthwash and toothpaste.
Chlorates are also effective as herbicides and disinfectants (biocides). The herbicidal effect is based on the oxidative destruction of the plant tissue via the release of oxygen. Chlorates don’t work selectively, but rather as total herbicides. Since 2010, however, there has been an EU-wide ban on the use of herbicides containing chlorate.
Sodium chlorate is also no longer permitted for use in biocide products.
Chlorates used in plant protection products are covered under Regulation EU 396/2005. Since the substance is no longer authorized and, thus far, no specific MRL for chlorate residues in food has been established, the MRL of 0.01 mg/kg provided in regulations valid for all such cases in the EU, is applicable. Therefore, produce whose chlorate content has been verified as exceeding this generally applicable MRL may not be marketed or traded with.
In a recently published report, authorities in Germany have undertaken a special monitoring programme and analyzed fruit, vegetable and cereal samples for the presence of chlorate and perchlorate.
Over 1,000 samples analyzed and approximately 25% have been found to contain chlorate residues between of 0.01 to 2.7 mg/kg. The highest levels of chlorate measured were in :
- beans (0.84 mg/kg) – Cambodia
- broccoli (0.97 mg/kg) – Cambodia
- basil (1.4 and 1.9 mg/kg) – Cambodia
- coriander (2.7 mg/kg) – Cambodia
- chilli peppers (0.84 and 0.92 mg/kg) from Uganda
Amongst the samples (approx 200) from organic food production, 25% contained chlorate levels of 0.01 to 0.19 mg/kg.
Both chlorate and perchlorate was found only in 8% of the samples tested. Presence of high levels of chlorate does not necessarily correlate with high levels of perchlorate.
Source and Cause of Chlorates
The cause of chlorate residues has not yet been determined. In the EU it cannot be precluded that unauthorized applications maybe leading to the accumulation/formation of chlorate residues.
The source of the chlorate residues detected in the analyzed samples is not yet known. In general, various points of entry are conceivable:
- Residues from the use of chlorinated washing water, the use of chlorine dioxide to disinfect washing water, or an illegal, direct chlorination of food by means of a procedure from which chlorine is formed “in situ”, e.g. chlorine electrolysis;
- Environment, e.g. atmospheric deposits, contaminated sprinklers or irrigation water, etc.;
- Unauthorized application of chlorate as an herbicide;
- Absorption of chlorate via plants from soil contaminated either from the environment or due to an earlier application of chlorate as an herbicide or from contaminated fertilizer.
Chlorate reversibly inhibits the absorption of iodide in the thyroid and, at high doses, especially in sensitive groups such as children, pregnant women or people with thyroid dysfunction or iodine deficiency can cause health hazards. In addition to affecting the thyroid function, chlorate can also cause damage to red blood cells such as the formation of methaemoglobin and hemolysis.
There is currently no acute reference dose (ARfD) for chlorate available. As an initial estimation, the Federal Institute for Risk Assessment (BfR), recommends applying the acceptable daily intake (ADI) of 0.01 mg/kg body-weight, as derived by the World Health Organisation, as the basis for calculating both chronic and acute risk.
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