Total arsenic and inorganic arsenic content in Norwegian fish feed products

Samples of complete feedingstuffs for fish, and fishmeals from the Norwegian Fish Feed Monitoring Programme in 2003 were analysed for their total arsenic and inorganic arsenic contents. Microwave assisted wet digestion with nitric acid and hydrogen peroxide was used for the sample preparation for total arsenic analysis by ICPMS. Microwave assisted alkaline-alcoholic dissolution of the sample was used for liberation of inorganic arsenic prior to analysis by anion-exchange chromatography High Performance Liquid Chromatography Inductively Coupled Plasma Mass Spectrometry (HPLC-ICPMS). Concentrations in the ranges of 3.4-8.3 and 0.010-0.061 mg kg-1 for complete feedingstuffs were found for total arsenic and inorganic arsenic, respectively. The results are in accordance with typical arsenic levels for fish reported in the literature and indicate that no transformation of chemical arsenic species occurs during the processing of complete feedingstuffs. Several of the complete feedingstuff samples had total arsenic concentrations above the EU maximum content of 6 mg kg-1 in complete feedingstuffs for fish and complete feedingstuffs for fur animals. However, the species of toxicological relevance, i.e. inorganic arsenic, constitutes less than 1.2% of the total arsenic concentration in these samples. The data illustrate that fish feed with high levels of arsenic, but low levels of inorganic arsenic are at risk of being unnecessarily rejected from the fish feed market. Additionally, the results suggest that the maximum level for total arsenic in fish feed should be re-evaluated and future maximum levels should be based on the chemical species of toxicological relevance, namely inorganic arsenic, rather than on total arsenic.