Excessive levels of a cancer-causing toxin were found in milk produced in Sichuan in October by dairy giant Mengniu, the mainland's product quality watchdog said at the weekend. The General Administration of Quality Supervision, Inspection and Quarantine announced on Saturday that pure milk produced by a Mengniu subsidiary in Meishan on October 18 contained as much as 1.4 times the national standard for aflatoxin M1. Milk produced by another firm, Changfu in Fujian, also had excessive levels of the toxin in the same inspection round. Aflatoxin, classified as carcinogenic to humans by the World Health Organisation because of its ability to damage the liver, thrives in warm and wet environments and cannot be killed by pasteurisation, the process of partial sterilisation the dairy industry uses to make milk safe to drink. Industry experts said the toxin mostly likely came from mouldy feed and could be detected in milk within 24 hours of being consumed. Mengniu spokesman Lu Jianjun said the batch was caught at the factory before reaching the market and was destroyed. Lu said the company traced the problem to dairy farms that improperly stored feed in damp weather. He said all the products on the market were safe because of the company's strict quality inspection procedures. But he did not say how the problematic raw milk, which normally goes through similar tests before being processed, was not stopped by internal checks. Mengniu published two statements on Sunday to apologise to customers and assure them that its products were safe. 'Mengniu would like to express our sincere apologies to consumers,' it said. 'We will learn a big lesson from this incident and will work harder to meet all national and corporate standards on quality.' The mainland's dairy industry is still scrambling to regain consumers' confidence after a series of scandals, especially one three years ago when milk adulterated with the industrial chemical melamine killed at least six children and made 300,000 others ill with kidney problems. Dairy farmers used the melamine so poor-quality raw milk could pass tests for protein content. A dairy farmer and a milk salesman were executed and 19 other people jailed for their role in selling the tainted milk products. In April, at least 251 school students in Yulin fell ill after drinking milk made by the a Mengniu subsidiary in Baoji, Shaanxi.