Hydrogen Sulfide Leak at Japanese Refinery Threatens Seto Inland Sea Ecology

On May 17, a hydrogen sulfide leak occurred at the refinery of Japan’s largest oil company, Citation, in Sakai City, Osaka Prefecture, killing one person and seriously injuring two others. Hydrogen sulfide gas entered Osaka Bay through atmospheric deposition, causing the pH value of surface seawater to plummet to 5.2 (normal range: 7.5-8.6) over an area of approximately 2 square kilometers, resulting in large-scale mortality in shellfish farms. Data from the Seto Inland Sea Fisheries Cooperative Group showed that the mortality rate of scallops and oysters in the surrounding area exceeded 60% within 24 hours of the accident. An environmental science team from Osaka University detected sulfide at a concentration of 0.8 ppm in seawater 3 kilometers away from the accident site, far exceeding the Seawater Quality Standard limit of 0.02 ppm. The Ministry of Health, Labor and Welfare has issued a health alert prohibiting the consumption of seafood from Osaka Bay and the surrounding 10 km.