MANILA, Philippines — Researchers from the Philippines and Malaysia have confirmed the presence of toxic diatoms in Luzon, microscopic algae that could cause serious health issues, including gastrointestinal distress and, in rare cases, permanent memory loss.
Scientists from Ateneo de Manila University’s Department of Biology and Universiti Malaysia Sarawak identified two species of the Pseudo-nitzschia diatom—P. pungens and P. brasiliana—in water samples collected from shellfish farms in Bacoor Bay (Cavite) and Pagbilao Bay (Quezon). Notably, P. brasiliana was detected for the first time in Luzon waters.
Although diatoms generally pose no harm and are a vital food source for marine life, certain species of Pseudo-nitzschia are infamous for producing domoic acid, a potent biotoxin. Domoic acid is responsible for a condition known as amnesic shellfish poisoning (ASP), which can cause symptoms such as vomiting, diarrhea, abdominal cramps, and short-term memory loss. In severe cases, the memory loss may become permanent.
The most well-known ASP outbreak occurred in 1987 in Prince Edward Island, Canada, where four people died after consuming toxic mussels.
Domoic acid is not destroyed by cooking or freezing, and currently, there is no antidote. The only treatment for severe cases is supportive care, such as life support, to help the body flush the toxin from the system.
While the presence of these diatoms in Philippine waters is concerning, experts emphasize that the risk to human health remains low under normal circumstances. According to the Washington State Department of Health, harmful Pseudo-nitzschia species are naturally present in marine environments at very low concentrations. When present in small amounts, they typically do not pose a significant threat to those consuming shellfish in moderation.
The primary risk occurs when Pseudo-nitzschia populations surge, typically during algal blooms or "red tide" events. These blooms can lead to a higher accumulation of domoic acid in filter-feeding shellfish, such as mussels, clams, and oysters, which absorb the toxin from the water as they feed.
"Biotoxins do not harm the shellfish themselves, but their toxin levels rise significantly during algal blooms," said the Washington State Department of Health. "Once the bloom subsides and the concentration of harmful algae decreases, the shellfish flush out the toxin over time. However, it can take anywhere from days to months for the shellfish to become safe to eat again."
The study, led by researchers Lorenzo A. Botavara, Janice A. Ragaza, Hong Chang Lim, and Sing Tung Teng, was published in October 2024 by Taylor and Francis. It highlights a significant gap in the monitoring of toxic diatoms in the Philippines, where knowledge about the Pseudo-nitzschia species and their genetic makeup has been minimal.
Given the prevalence of shellfish consumption in many coastal communities, the researchers stress the importance of monitoring these diatoms as part of broader red tide detection efforts. "Understanding the potential toxicity of these diatoms is crucial to safeguarding public health, especially for communities that rely on seafood," the researchers noted.
They also emphasized that, while the presence of Pseudo-nitzschia does not usually pose an immediate danger, heightened vigilance and further research are needed to establish effective monitoring systems and mitigate risks from harmful algal blooms in Philippine waters.
Though the presence of toxic diatoms in Luzon waters may sound alarming, experts assure the public that the risk remains low under normal conditions. It is essential, however, to continue monitoring for algal blooms and to follow health advisories regarding shellfish consumption during these events.
As scientists continue their research, awareness and early detection remain crucial to preventing potential outbreaks of amnesic shellfish poisoning in the Philippines.