Formation of polychlorinated dibenzo- p-dioxins/dibenzofurans (PCDD/Fs) from a refinery process for zinc oxide used in feed additives: A source of dioxin contamination in Chilean pork

► Remarkably high concentrations of dioxins were found in Chilean pork. ► From penta- to hexa-PCDFs were the dominant congeners in the contaminated pork. ► Zinc oxide in feed was the major source of dioxin contamination in pork. ► The dioxins were formed from a metal refinery process to collect zinc oxide. The Republic of Korea found dioxin at concentrations exceeding the Korean maximum residue limit (MRL) in pork (2 pg TEQ g −1 fat) imported from Chile in June 2008. Korea and Chile collaborated and investigated to find out the sources of contamination. An isotope dilution method and high resolution gas chromatography/mass spectrometry (HR–GC/MS) were used for the analysis of PCDD/Fs. PCDD/Fs were found from 2.17 to 36.7 pg TEQ g −1 fat from Chilean pork. 2,3,4,7,8-PeCDF, 1,2,3,4,7,8-HxCDF, 1,2,3,6,7,8-HxCDF, and 2,3,4,6,7,8-HxCDF were found as the major congeners in pork samples. 2,3,4,7,8-PeCDF showed the highest concentration and contributed about 30% among the congeners in most of the samples. 2,3,7,8-TCDD, 1,2,3,7,8,9-HxCDD, OCDD, 2,3,7,8-TCDF, 1,2,3,7,8-PeCDF, 1,2,3,7,8,9-HxCDF, and OCDF were not detected or exist at background levels in the less contaminated samples. Remarkably high concentrations of PCDD/Fs were found in samples of zinc oxide (17 147 pg TEQ g −1), zinc oxide based premix (6673 pg TEQ g −1), and the residue crust (800 pg TEQ g −1) in a mixing chamber in the feed mill. From the results of various investigations, this case concluded that zinc oxide in the feed was the major source of the dioxin contamination in pork. The dioxins were formed from a metal refinery process to collect zinc oxide.