China's food regulator has asked three milk producers in Shaanxi province to recall their infant formula products after excessive nitrate and selenium levels were found in tested samples.
The China Food and Drug Administration said on its website that excessive nitrate was found in five batches of milk powder products made by Shaanxi Guanshan Dairy and tested earlier in 2015.
Higher-than-permitted levels of selenium were found in another two batches of milk powder produced by Xi'an Guanshan Dairy and Shengtang Industry.
Though harmless, nitrate could become toxic if it encountered particular kinds of bacteria, according to the watchdog. The use of selenium as a nutrient in infant milk formula is yet to be approved by regulators.
The food safety watchdog also asked the province to severely punish milk product makers, if they have been found to have broken the law.
In a 19 June statement, Shaanxi Guanshan Dairy said it would recall the tainted products.
The Chinese people have largely been relying on foreign milk products after the deadly tainted milk scandal in 2008, when at least six children died and some 300,000 fell ill after consuming milk products contaminated by melamine.