Maryland ? The Food and Drug Administration says the industrial chemical melamine and a byproduct cyanuric acid have now been detected in four of 89 containers of infant formula made in the United States, doubling previously reported positive results. The contamination is extremely minute, at levels federal regulators say are safe for babies.

In November, The Associated Press reported previously undisclosed FDA tests, obtained under the Freedom of Information Act, showing that out of 77 containers of domestic infant formula tested, a can of milk-based liquid Nestle Good Start Supreme Infant Formula with Iron contained traces of melamine while Mead Johnson’s Enfamil LIPIL with Iron had traces of cyanuric acid.

The FDA has now updated its response to the AP’s FOIA request by posting results of 89 tests on its Web site. Those results show that two additional containers of Enfamil LIPIL with Iron had traces of cyanuric acid.