Analysis of Perchlorate in Food Samples of Plant Origin Applying the QuPPe-Method and LC-MS/MS
Ellen Scherbaum , Julia Hepperle, Anne Wolheim, Chemisches und Veterinäruntersuchungsamt (CVUA) Stuttgart
This study reports about how to integrate the environmental contaminant perchlorate into the QuPPe multiresidue method for the analysis of polar pesticides. Perchlorate, along with a number of polar pesticides, was extracted with acidified methanol. The extracts were filtered and subjected to liquid chromatography-triple quadrupole mass spectrometry (LC-MS/MS). 18O-labeled perchlorate was used as internal standard. The assay was validated for apple and barley matrix at 0.01 and 0.1 mg/kg, showing average recoveries between 93 % and 108 % and relative standard deviations (RSDs) between 2.2 % and 5.0 %. Up to now, we have analyzed 350 conventionally and 78 organically grown food samples (vegetables, fruits, cereals, legumes, mushrooms and processed foods) from the local market for perchlorate. Perchlorate could be detected in 66 (19 %) of the conventional samples and in two (2.6 %) of the organic samples; in six samples the provisional maximum tolerable daily intake (PMTDI) of 0.01 mg/kg bodyweight was exceeded.
In 2012, the environmental contaminant perchlorate was frequently detected in conventionally and organically grown fruit and vegetable samples from the local market. Perchlorates are salts of perchloric acid (HClO4) arising from natural as well as from anthropogenic sources. The perchlorate anion is a stable but strong oxidant as the chlorine atom possesses an oxidation state of +7. Most perchlorates are soluble in water and circulate within the hydrologic cycle. They naturally occur ubiquitous in atmospheric water and soil compartments in low concentrations. However, perchlorate contamination in food cannot result from natural sources as the appearing environmental concentrations are too low. Aside from natural occurrence, perchlorates are anthropogenically spread, since they are widely used in the metalworking industry, in paper upgrading and, as oxidants, for propellants in pyrotechnic materials like rockets, fireworks and explosives. In diagnostic radiology, perchlorates are medically applied in iodine contrast agents keeping the exposure to high iodine concentrations at a low level by blocking the thyroid. Another source of perchlorate contamination are fertilizers or sewage sludge which are both widely applied in agriculture. Perchlorates also come along with chlorate, a substance which has formerly been used as a herbicide in plant protection products. However, pesticides containing chlorate as an active substance have been banned within the EU since May 2010. Like chlorate, perchlorate can act as a herbicide, but is not approved as a pesticide within the European Union and there is no maximum residue level listed in Regulation (EC) 396/2005.