Chinese fishermen have been pouring cyanide into the waters around the Spratly Islands, threatening the marine environment, the Philippine Navy personnel stationed aboard the BRP Sierra Madre at Ayungin Shoal, and the livelihood of Filipino fisherfolk, a National Security Council (NSC) official revealed on Monday.

Speaking at a press conference at the Philippine Coast Guard WPS Transparency Office in Manila, NSC assistant director general and spokesperson Cornelio Valencia said the poisoning of the waters began last year around the Second Thomas Shoal in the Spratly chain, an area near vital shipping lanes that is believed to be resource-rich.

Cyanide is a highly toxic chemical that can cause severe and irreversible damage to humans and marine ecosystems.

“The use of cyanide on Ayungin Shoal is a form of sabotage that seeks to kill local fish populations, depriving Navy personnel of a vital food source,” Valencia said.

He said it also threatens the personnel through exposure to contaminated water and poisoned fish, while damaging coral reefs.

Valencia said bottles recovered by the Philippine Navy from Chinese sampans operating near the Sierra Madre tested positive for cyanide. Sampans are flat-bottomed wooden boats used for transport and fishing.

“Laboratory analysis conducted by the National Bureau of Investigation’s Forensic and Scientific Research Service has conclusively established that the yellow bottles seized from the sampans contained cyanide,” he said.

The Navy seized the bottles during operations in February and October 2025.

Valencia said the use of cyanide raises concerns over illegal practices that threaten personnel, damage marine life, and affect Filipino livelihoods.

“Such actions, if proven intentional, constitute a violation of Philippine environmental laws and international maritime norms under UNCLOS,” he said.

He warned that cyanide could also damage coral reefs supporting the grounded warship, potentially affecting its stability.

“If the reef is severely damaged, it not only threatens the ship’s stability, it also allows Beijing to fabricate an environmental crisis which it can then blame on the Philippines,” Valencia said.

He emphasized that Ayungin Shoal lies within the Philippines’ exclusive economic zone.

“The operation of Chinese vessels involving hazardous substances in this area is irresponsible and unacceptable,” he added.

The NSC has directed the Armed Forces, Philippine Coast Guard and other agencies to strengthen patrols and maritime awareness to prevent further environmental harm.

At the same briefing, Philippine Navy spokesperson Rear Admiral Roy Vincent Trinidad said Filipino personnel seized 10 cyanide bottles in several operations in 2025 and observed continued dumping activities near the shoal, with tests confirming the contamination.

None of the personnel aboard the BRP Sierra Madre have tested positive for cyanide exposure, he added.