The pork balls were found to contain 0.4 parts per billion (ppb) of the livestock feed additive, officials said at a press conference held to announce the results of a recent inspection of food materials used by breakfast stores in the city, reports Focus Taiwan.

Liu Shu-yu, a city health official, said the meat used to make the pork balls was traced back to a shipment totalling 260kg from Yunlin County, according to Focus Taiwan.

The city health department has recalled 119kg of the pork, but the remaining 141kg has been made into pork balls and sold to 17 breakfast stores, Liu said.

The 17 stores are located in Taipei, New Taipei, Keelung, Taoyuan and include popular chain stores, Liu said, adding that the 0.4ppb level can be metabolised by the human body.

Yunlin County health authorities said that the pork balls came from a single food supplier in the county, which ordered the meat from a Taipei importer, according to the report.

The inspection in New Taipei also found pork burger meat that contained 9.3ppb of chloramphenicol, an antibiotic that is also banned in pork in Taiwan.

Consumption of chloramphenicol may affect growth of red blood cells and lead to heart failure, city health authorities said, adding the substance is banned in most countries.

As many countries ban the antibiotic, the 9.3ppb level can be considered high enough, Liu told Focus Taiwan.

All 72kg of pork found to be tainted with chloramphenicol has been sold, with most of it being purchased by breakfast stores in Taipei and New Taipei, officials said.

Suppliers of tainted pork violate the Act Governing Food Sanitation and face a fine of between NT$60,000 (US$2,046) and NT$6 million, officials said.

Taiwan's Legislature passed amendments to the food safety act in late July allowing ractopamine in beef imports, a move that was welcomed by the United States, which had long railed against Taiwan's ban on the drug in beef imports.

The Food and Drug Administration has set a maximum allowable residue level of the drug at 10ppb.

The government has stated that a total ban on the drug in imported pork will be maintained, reported Focus Taiwan.