South Korea's food safety authorities called on beverage makers last week to withdraw vitamin C-enriched drinks that had been found to contain the carcinogen benzene.
The Korea Food and Drug Administration (KFDA) announced on Thursday that it had detected the chemical substance in 27 out of 30 vitamin-enriched drinks on sale in the country.
It said the detected amount of benzene - ranging from 5.7 to 87.8 parts per billion - was not harmful to humans but advised manufacturers of beverages containing more than 10 ppb of the substance to voluntarily recall the products.
The KFDA also called on the companies to improve their manufacturing methods to cut out the chemical.
Benzene is a known carcinogen, thought to form in the presence of two common beverage ingredients, sodium benzoate and ascorbic acid (or vitamin C). Heat and light exposure has also been shown to increase benzene formation.
While the chemical was first found in widely consumed drinks several years ago, concern over its presence has been renewed in recent months, following the admission of a US FDA scientist that recent tests had again found some soft drinks with benzene above the US water limit.
Since then food safety authorities around the world have re-examined levels of the chemical in the beverage sector.
The Korean agency said it plans to continue monitoring content of the chemical in drinks and conduct further research on preventing benzene's formation.
South Korea currently limits benzene content to 10 ppb in drinking water, the level recommended by the World Health Organisation. The United States and Canada restrict levels of the chemical to 5 ppb however, while the European Union imposes a stricter 1 ppb.
The three vitamin C drinks tested by the KFDA that had no benzene included Kwang Dong Pharm's Vita 500, Lotte Pharm's Vita Power and Sangil Pharm's Mega Vita.
According to the KFDA, the three companies avoided the chemical by using alternative manufacturing formulas.