By tonight, the only known source of contamination was the Daschle letter.
"This is a precaution until we know exactly the source of contamination," Royle said.
Yet another possible source of contamination is so-called "flowback" water.
The company's factory in Greenville, S.C., is suspected as a source of contamination.
In recent years, imports have been the source of contamination, prompting broader worries about food safety.
Although water quality is affected by natural conditions, the word pollution usually implies human activity as the source of contamination.
Sulfide at mine tailing ponds poses a source of contamination to the surrounding environment.
After a recent inspection, health officials said they were unsafe because they "are not protected from potential source of contamination".
He referred to commercials citing a health department report indicating that the fireworks factory was the source of contamination that closed nearby water wells.
Grinders that do their own spot checks typically wait to test the finished product after the trim is mixed, which prevents identifying the source of contamination.
When Bausch stopped shipping the product to American stores in early April, the company emphasized that neither it nor federal investigators had found a source of contamination.
