China's quality watchdog Sunday announced they found protein powder imported from a U.S. company contained too much selenium.

The Shanxi Entry-Exit Inspection and Quarantine Bureau has discovered selenium in the protein powder imported from the U.S.-based Jarrow Formulas Inc. exceeded Chinese food safety standards, said sources with the General Administration of Quality Supervision, Inspection and Quarantine.

Selenium, which is essential to life, could be poisonous when taken too much. All the powder has been returned.

Details of the quantities of the powder seized or the names of the importers are unavailable.

The administration asked importers to specify food safety requirements when importing U.S. food products, in an effort to lower trade risks.