Accreditation of analytical laboratories and proficiency testing: experiences from Thailand on the issues of pesticide analysis.

Thailand, the economic growth of which largely depends on agriculture-based industry, recognizes the importance of international standards for harmonization of international food trade and for protection of human health from chemicals used as food additives or those present as contaminants. Pesticides which are widely used in Thailand are the anticholinesterase pesticides, pyrethroids, coumarin derivatives, bipyridinium salts, and to some extent organochlorine compounds such as DDT in malaria control. Proficiency testing and accreditation of laboratories are recognized as effective means to ensure quality and validity of data and to enable adequate risk assessment of pesticide residues in food, work environment and environment in general. The paper is a synthesis of relevant local reviews and in-depth interviews with experts in the area of pesticide laboratory accreditation and proficiency testing. The paper refers to other schemes for quality assurance such as ISO guide 25, ISO 9000, and ISO 14000, and addresses future prospects of ongoing activities such as accreditation of inspection bodies in the area of industrial chemicals and occupational safety and health.

Laboratory proficiency testing of aflatoxins in corn and peanuts--a cooperative project between Thailand and the United States.

The objective of this project was to conduct an aflatoxin proficiency test program in government, academia, and industry laboratories in Thailand. Aflatoxin-free corn and peanuts and corn and peanuts naturally contaminated with aflatoxins diluted to approximately 25 micrograms/kg were analyzed. Homogeneity of prepared, naturally contaminated test samples was checked on multiple replicates. The test was conducted according to the ISO/IUPAC/AOAC INTERNATIONAL Harmonized Protocol with z scores indicating laboratory performance. The participants used 3 methods: enzyme-linked immunosorbent assay, thin-layer chromatography, and the minicolumn. Of 19 laboratories that reported results for aflatoxins in naturally contaminated corn, 13 (68%) performed satisfactorily, on the basis of the mean obtained by an expert laboratory, a calculated target value for standard deviation, and the z score. Of 21 laboratories that reported results for aflatoxins in naturally contaminated peanuts, 10 (48%) performed satisfactorily. For aflatoxin-free corn, 6 laboratories reported finding aflatoxins at > or = 10 ng/g, chiefly by the minicolumn method; for aflatoxin-free peanuts, 1 laboratory reported finding aflatoxins at > 10 ng/g. Subsequently, a workshop of lectures and laboratory sessions was conducted to improve performance. A new and simple successive outlier removal procedure applied to the same data removed the same laboratories as did the use of z scores.