The FDA initiated the first recall in an Aug. 19 notice, announcing certain raw frozen shrimp products processed by Indonesian company PT. Bahari Makmur Sejati (doing business as BMS Foods) had tested positive for Cesium-137, also known as Cs-137. A handful of manufacturers sold these products under different brand names to retailers nationwide.

The FDA published an expanded recall notice on its website on Dec. 19, one of 12 notices that have been issued in the growing recall.

Cs-137 is a radioisotope of cesium, meaning it is a chemical element that emits radiation as it breaks down. It is man-made and is produced by nuclear fission, according to the FDA. In the United States, it is used in medical devices and measurement gauges.

Because it is widespread around the globe, trace amounts can be found in the environment, including soil, food and air, the FDA said. Agencies, including the FDA and U.S. Customs & Border Protection, test for, monitor and regulate the presence of the substance due to the risks associated with long-term exposure.

The FDA said low-level radiation exposure over time can lead to serious health complications. Exposure to Cs-137 alone can cause burns, acute radiation sickness, cancer and death. Due to the risks, governing agencies restrict potential exposure to lessen the possibility of these long-term impacts.