West Philippine Sea by Google Maps
MANILA — Scientists from the Philippines and Japan have detected unusually high levels of the radioactive isotope iodine‑129 in the West Philippine Sea (WPS), raising questions about how nuclear‑linked materials are traveling across regional waters despite the absence of nuclear facilities in the Philippines. The findings were published following a multi‑year study conducted by the Department of Science and Technology–Philippine Nuclear Research Institute (DOST‑PNRI), the University of the Philippines Marine Science Institute (UP MSI), and the University of Tokyo.
Researchers analyzed 119 seawater samples collected from multiple regions across the country. They found that iodine‑129 concentrations in the WPS were 1.5 to 1.7 times higher than levels detected in other Philippine waters, including the Philippine Rise and the Sulu Sea. A separate report noted that levels in the WPS were 50–70 percent higher than those in the Pacific side of the archipelago.
A Nuclear Tracer With Global Origins
Iodine‑129 is a long‑lived radioactive isotope with a half‑life of 15.7 million years, commonly used by scientists as a tracer for nuclear activities such as weapons testing, nuclear fuel reprocessing, and nuclear accidents. While naturally occurring in extremely small amounts, elevated concentrations typically indicate human‑related nuclear events.
Dr. Angel Bautista VII of DOST‑PNRI said the team initially expected higher readings on the Pacific side due to historical U.S. nuclear testing. Instead, the WPS showed significantly elevated levels. “From the 1970s onwards, mas mataas iyong levels ng iodine‑129 doon sa West Philippine Sea side kumpara sa Pacific Ocean side,” Bautista said.
Likely Source: Nuclear Contamination From Northern Waters
Despite public concern, scientists emphasized that the detected levels do not pose an immediate threat to public health or marine life. Instead, the findings highlight how nuclear contaminants can travel long distances through ocean currents.
UP MSI researchers concluded that the isotope likely originated from the Yellow Sea and Bohai Sea, regions previously documented to contain iodine‑129 from Cold War‑era nuclear weapons testing and nuclear fuel reprocessing in Europe and China. These materials settled into soil, washed into rivers, and eventually entered coastal seas before being carried southward by major current systems.
A Call for Regional Monitoring
Experts say the discovery underscores the need for stronger regional cooperation in marine environmental monitoring, especially given that nuclear‑linked materials can cross borders undetected. The study also demonstrates the value of iodine‑129 as a tool for understanding ocean circulation in the South China Sea.
“Unusually high doesn’t mean dangerous,” Bautista stressed. “But it tells us something important is moving through our waters”.
