This deep-sea worm turns two toxins into a harmless mineral

A deep-sea worm survives in toxic conditions around hydrothermal vents by converting arsenic and sulfur into a benign mineral. This natural biomineralisation process allows Paralvinella hessleri to tolerate elevated levels of arsenic and provides the worm with its striking yellow colour.

Hydrothermal vent fluids are rich in numerous substances that are toxic to most species, including heavy metals, arsenic, and hydrogen sulfide. But now a research team led by oceanographer Chaolun Li, from the Chinese Academy of Sciences in Qingdao, has discovered that P. hessleri neutralises arsenic and hydrogen sulfide by combining them into arsenic trisulfide crystals, also known as orpiment. These granules are safely stored within the worm’s epithelial cells and give the worm a distinctive yellow colour.

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Orpiment – a mineral composed of arsenic and sulfur – gives the Paralvinella hessleri worm its bright yellow colour

Source: Wang H, et al., 2025, PLOS Biology, CC-BY 4.0

The orpiment takes the form of small granules that are stored within epithelial cells

Source: Wang H, et al., 2025, PLOS Biology, CC-BY 4.0

Using biomineralisation as a detoxification strategy is unusual, as it is more commonly used for tissue reinforcement

Source: © 2025 Wang et al

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Using advanced microscopy, elemental analysis, genomic and proteomic studies, the researchers revealed how specialised transport proteins and haemoglobins help transfer arsenic and sulfide into intracellular vacuoles, where they are safely immobilised as orpiment. The researchers describe the survival strategy as ‘fighting poison with poison’ due to the way in which two chemical threats are converted into an inert mineral.

Li’s team also points out that P. hessleri’s use of biomineralisation as a detoxification strategy is unusual, as the process is more commonly associated with tissue reinforcement.