The ducks from the market are mainly supplied to restaurants and supermarkets near Changsha, the provincial capital, according to the report.

After roughly removing the feathers, workers at the Yangjiashan poultry wholesale market dipped the birds in a large caldron filled with black, boiling industrial rosin and dirty foam. Afterwards, they rinsed the birds in bowls of water to make their skin white and remove any remaining feathers and hair, according to the report.

However, the use of industrial rosin is unsafe as it is not edible and contains heavy metals such as lead and other poisonous compounds. These substances penetrate the birds' skin under high temperature and can harm human livers and kidneys when consumed.

Workers at the market said they could depilate roughly 200 ducks a day with industrial rosin, which costs only half as much as edible rosin. They also said they did not remove the feathers by machine, because it was inefficient and could not totally remove all the feathers and hair from the birds, according to the report.