Analysis of inorganic arsenic in feed and food

Arsenic occurs in many different forms in various sample types, as inorganic arsenic or organic arsenic compounds. Inorganic arsenic is more toxic than organic forms of arsenic [1]. Some food may contain elevated levels of inorganic arsenic, e.g. rice and rice products, and seaweed. Feed ingredients of marine origin are typically sources of inorganic arsenic in animal feed. Total arsenic and inorganic arsenic are included in the European Union (EU) feed and food legislation. There are maximum level (ML) for inorganic arsenic in rice and rice products [2], but not in feed or feed ingredients [3]. However, a footnote to ML for arsenic states, “Upon request of the competent authorities, the responsible operator must perform an analysis to demonstrate that the content of inorganic arsenic is lower than 2 ppm”. Hence, there is a need for robust and standardised methods for the analysis of inorganic arsenic in feed and food. The European Committee for Standardization (CEN) has validated methods for the analysis of inorganic arsenic in food [4] and feed [5]. The methods are based on the same principle; determination of inorganic arsenic (as sum of arsenite, As(III), and arsenate, As(V)) using HPLC-ICPMS following acidic extraction in a water bath. The European Union Reference laboratory for metals and nitrogenous compound in feed and food (EURL-MN) included arsenic and inorganic arsenic in their proficiency tests (PTs) in 2018 and 2019 in order to evaluate the capability of national Reference laboratories (NRLs) to analyse these analytes. The PTs materials were a mixed corn poultry feed, chili powder, and a seaweed meal, and part of the scope was to assess the performance of the NRLs in determining the mass fraction of arsenic and inorganic arsenic in feed and food. The PTs were conducted according to ISO 13528:2015. The assigned values were consensus values based on the results of the participants, and the performance of the NRLs were evaluated using z and ζ scores. Overall, the performance of the NRLs was very satisfactory. For arsenic and inorganic arsenic, the performance of participants was very good to excellent. Although for inorganic arsenic less than half of the members of the EURL-MN network participated.The results of the PTs will be discussed in detail, with focus on the methods used by the NRLs to determine arsenic and inorganic arsenic in food and feed.