Date: April 2016
Determining perchlorate and chlorate in foodstuffs using LC-MS/MS
Perchlorates are salts of the perchloric acids. They are highly water-soluble and very persistent in the environment. Perchlorate occurs naturally in mineral deposits. It is also used industrially, for example in the metalworking industry or in paper manufacture. In the past, sodium chloride and potassium chloride were used in weed control. In the EU, the use of pesticides containing chloride or biocide products is no longer permitted. However, chloride and perchloride can arise as by-products when chlorinated substances are used for cleaning or disinfection purposes or as fertilisers. The industrial use of perchlorates, as well as the use of chlorinated substances, present a possible cause of contaminations of foodstuffs with perchlorates and chlorates.
The intake of chlorate or perchlorate reversibly inhibits the intake of iodine in the thyroid. Over the long term, this can lead to changes in hormone levels in the thyroid, and therefore to wide-ranging impairments to health. In October 2014, the EFSA issued a statement on the health risks caused by the occurrence of perchlorate in foodstuffs, especially in fruit and vegetables. In this statement, the EFSA set a tolerable daily intake (TDI) of 0.3 µg/kg body weight. This represents a 30th of the provisional maximum tolerable daily intake (PMTDI value) derived from the JECFA in 2010, which was 0.01 mg/kg. The EFSA came to the conclusion that chronic exposure to perchlorate, especially among heavy eaters in younger age groups, gave rise to concerns of low to medium iodine shortage.
Since 2010, chlorate has been banned as a pesticide in the EU. As legacy active substances, chlorates fall under the regulatory umbrella of Directive (EC) 396/2005. As no specific maximum residue content has been specified for chlorate, article 18, paragraph 1, letter b of this directive applies, meaning that the general limit value is 0.01 mg/kg. In the EU, perchlorates are not currently permitted to be used as pesticides or biocidal substances. At the moment, there are no legal regulations specifying a maximum permitted perchlorate content. Perchlorate findings therefore fall under the provisions of the Contaminants Directive, which contains a general minimising obligation as a preventative precaution to protect consumers. For some culture groups, in a note the EU Commission has set out reference values for trade within the EU.
The methodological framework for the determination of perchlorate and chlorate in foodstuffs is the QuPPE method. Perchlorate and chlorate are extracted from the homogenised sample using a water/methanol/glacial acetic acid mixture. Depending on the matrix, the sample may also be subjected to solid-phase extraction via a polymer sorben. Quantification is by LC-MS/MS using the methods of our internal standards. Using the analysis methods established by the Institut Kirchhoff Berlin GmbH, chlorate and perchlorate can be detected from 2 µg/kg and quantified from a content of 6 µg/kg. The matrices that we investigate most often include tea, fruit and vegetables, fruit juices, milk products and baby and infant food, among other things.