MANILA : Scientists from the University of the Philippines Marine Science Institute (UP MSI) have detected unusually elevated levels of iodine-129, a radioactive isotope associated with nuclear activity, in seawater samples collected from the West Philippine Sea (WPS)—a finding that has drawn regional and international attention despite assurances that the levels pose no immediate risk to public health or the marine environment.
Elevated Readings in Strategic Waters
According to UP MSI, iodine-129 concentrations in the West Philippine Sea were measured at approximately 1.5 to 1.7 times higher than levels found in other Philippine marine regions. These include the Philippine Rise, the Sulu Sea, and multiple offshore sites across the archipelago.
The Philippines does not operate an active nuclear power plant and has no nuclear weapons program, making the presence of elevated nuclear tracers in its surrounding waters scientifically notable.
The findings are based on the analysis of 119 seawater samples, collected and examined as part of a collaborative research effort involving UP MSI’s Geological Oceanography Laboratory, the Department of Science and Technology - Philippine Nuclear Research Institute (DOST-PNRI), and researchers from the University of Tokyo.
What Is Iodine-129?
Iodine-129 is a long-lived radioactive isotope with a half-life of about 15.7 million years. Because it is released in measurable quantities during nuclear weapons testing and nuclear fuel reprocessing, scientists worldwide use it as a tracer to track the movement of nuclear contaminants through the atmosphere, rivers, and oceans.
Unlike more hazardous radioactive isotopes, iodine-129 is typically found at extremely low concentrations in seawater and, at present levels, is not considered biologically dangerous.
Tracing the Possible Source
After comparing isotopic signatures and regional circulation patterns, researchers concluded that the iodine-129 detected in the West Philippine Sea most likely originated far beyond Philippine waters, with the Yellow Sea identified as the probable source region.
UP MSI said its results align with earlier Chinese and international studies showing elevated iodine-129 in the Yellow Sea. Those studies traced the isotope back to European nuclear weapons testing and nuclear fuel reprocessing activities conducted decades ago, particularly during the Cold War. The isotope entered soils and river systems in northeastern China through atmospheric fallout and river discharge, eventually reaching coastal seas.
How Did It Reach Philippine Waters?
Scientists believe the isotope may have traveled southward through large-scale ocean circulation systems, notably the Yellow Sea Coastal Current and the Chinese Coastal Current. These currents feed into broader western Pacific circulation patterns that can transport dissolved substances over thousands of kilometers.
UP MSI emphasized, however, that advanced oceanographic modeling is still required to conclusively map the transport routes and determine how long the isotope took to reach the West Philippine Sea.
No Immediate Health or Environmental Risk
Despite the elevated readings, researchers stressed that the detected iodine-129 concentrations remain well below thresholds that could harm marine ecosystems or human health, including seafood consumers.
“The isotope is present at trace levels only,” UP MSI noted, adding that its significance lies more in what it reveals about long-distance transport of radioactive materials rather than any direct danger.
Call for Stronger Regional Monitoring
The study underscores the need for enhanced regional and international monitoring of radioactive substances, particularly those capable of crossing national boundaries via ocean and atmospheric systems.
Researchers warned that while iodine-129 itself is not currently hazardous, its presence demonstrates how pollutants released decades ago—and continents away—can still be detected in sensitive and geopolitically important waters today.
Funding and Next Steps
The research was funded by the DOST-National Research Council of the Philippines and the DOST-Philippine Council for Agriculture and Resources Research and Development.
UP MSI said follow-up studies will focus on expanded sampling, higher-resolution current modeling, and long-term monitoring, aimed at better understanding how nuclear-related isotopes move through the western Pacific and what they may signal for future environmental surveillance.
While the findings raise important scientific and policy questions, researchers were clear on one point: the iodine-129 detected in the West Philippine Sea is a legacy of global nuclear activity, not a sign of any local nuclear incident.
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