ABUSE OF CHEMICALS IN THE COATING CLAY FOR CENTURY EGGS LEADING TO CONTAMINATION OF THE COMMERCIAL PRODUCTS

Abstract

The analysis of a significant number of commercial preserved or century duck eggs (abbreviated as
century eggs) showed that hydrated salts PbCO3.2H2O, CuSO4.5H2O, ZnSO4.7H2O were added to clay
for coating eggs with the purpose to shorten the incubation time. By ICP-MS determination, Pb was 69
- 4000 ppb in egg yolk, 135 – 6500 ppb in egg white; Cu 2700 - 6500 ppb in egg yolk, 5200 - 8800 in
egg white; Zn 18000 - 37000 ppb in egg yolk, 2800 - 10500 ppb in egg white. It appeared that these
residues exceeded those in fresh eggs: Cu (100% in whole egg yolk and white); Pb (100% in egg white,
80% in egg yolk); Zn (100% in egg white). Investigation also showed that dithiocarbamates were
formed and indirectly analyzed by hydrolysis to CS2: 0.2 - 0.5 ppm (MRL: 0.05 ppm according to MOH
Circular 50/2016/TT-BYT). These contaminants may threaten century egg safety.