1. FAOSTAT database,http://faostat3.fao.org/faostat-gateway/go/to/download/Q/QC/E(accessed April 15, 2014) .
2. Codex Standard 193–1995. Codex general standard for contaminants and toxins in food and feed,http://www.codexalimentarius.net/download/standards/17/CXS_193e.pdf(accessed April 15, 2014) .