The shockwaves caused by the problematic cooking oil recycled from kitchen waste in Taiwan have yet to create ripples on the mainland although it has been revealed that some food made with such oil may have crossed the Straits. Yet, there is no reason for consumers on the mainland to be optimistic about the food safety situation and neither is there any reason for watchdogs to relax their vigilance against substandard or unsafe food products.

The impact this scandal has caused is unprecedented. That thousands of food manufacturers on the island and in the Hong Kong and Macao special administrative regions are involved is beyond our imagination because mainlanders usually believe supervision over food safety is tighter in these regions.

This scandal again verifies the fact that self-discipline based on conscience is not reliable. The temptation of greater profits can always lead people astray.

Earlier this month, a workshop was discovered in suburban Beijing where pigs' feet were soaked in a hydrogen peroxide solution and caustic soda. This increased their weight and made them look nicer, but made them unsafe to eat.

From problematic baby formula to poisonous duck eggs to chemicals used to feed pigs to make the meat leaner and to problematic cooking oil recycled from kitchen waste and grease from animal skin, as well as the recent scandal of expired meat products used by fast food restaurants, there seems to be no end to the revelations of the lengths unscrupulous producers, dealers and retailers will go to in search of greater profits.

There is no telling what new ways will be conceived to adulterate the food we eat by heartless people who are willing to risk the health and lives at others in their pursuit of personal gain. But it is certain they will find some as long as they think there is more money to make.

This sensational cooking oil scandal in Taiwan should serve as a reminder to the food safety watchdogs that part of their job is to narrow the space that illegal dealers can use to push unsafe or even poisonous foods into the market. It is also a reminder to quarantine officers in customs that quarantine and testing of imported food should never be slackened to allow unsafe food into the domestic market.

There must be unceasing vigilance as it is a battlefield where each piece of ground that is won is of the greatest importance.