A 52-year-old woman died on Sunday after being exposed to discarded hydrofluoric acid in Hangzhou, local authorities said.

A statement from the Xianlin subdistrict said the woman, identified only by her surname Tu, came into contact with the chemical at a vacant lot on Sept 9. She was taken to a hospital but died on Sunday despite emergency treatment, the statement said.

Police have begun an investigation, and the environment department has decontaminated the site, the statement added.

The cause of the incident remains under investigation, and the case has raised public concerns about the handling and disposal of hazardous chemicals.

On Tuesday afternoon, a range of hydrofluoric acid products in various strengths could be found on multiple domestic e-commerce platforms. Listings showed containers ranging from 500 milliliters to 25 kilograms. Product descriptions commonly suggested uses such as cleaning glass and tiles or removing oxides.

Sellers typically warned that the solution is corrosive and advised users to wear gloves and protective goggles. They recommended rinsing with water and seeking medical attention in case of contact with the skin.

Hydrofluoric acid, the aqueous solution of hydrogen fluoride, is a clear, volatile liquid with a pungent odor. Wang Xisheng, a professor at the School of Chemistry and Chemical Engineering at Guizhou University, said the acid has many industrial and commercial uses. It is widely used in sectors such as industrial manufacturing, electronics, printing, metal casting and glass etching.

Known in some circles as "bone-dissolving water", hydrofluoric acid can cause both local burns and severe systemic poisoning, according to him.

"Hydrofluoric acid is a highly corrosive substance. It can be absorbed through the skin or inhaled as an acid mist, and direct contact can cause severe damage to subcutaneous tissue, bone, and even internal organs. Ingesting about 1.5 grams of hydrofluoric acid can cause immediate death," Wang said.

He added that laboratory work should be carried out by trained personnel and that equipment should be checked regularly for leaks. Wastewater must be handed over to qualified treatment facilities, and casual dumping is strictly prohibited.

Hydrofluoric acid was included in the 2015 catalog of hazardous chemicals issued by the State Administration of Work Safety, which was later integrated into the Ministry of Emergency Management. It is regarded as dangerous to people, facilities and the environment. National standards require hydrofluoric acid manufacturers to maintain protective distances of 100 to 300 meters from residential areas, schools and hospitals, depending on wind speed and production scale.

A 2022 paper, Research Advances on the Treatment of Hydrofluoric Acid Burns, published in the Chinese Journal of Burns and Wounds, described hydrofluoric acid burns as a clinical emergency. The paper warned that even burns covering a small area can be fatal within hours and urged immediate on-site treatment: remove contaminants, irrigate the area, and transport the patient to a hospital without delay.

Wang advised that anyone whose skin has been exposed should immediately and thoroughly rinse the affected area under running water for an extended period.

As the paper points out, rinsing can remove surface residues, but it cannot remove hydrofluoric acid that has already penetrated the skin, so prompt medical treatment is essential.