快猫短视频

HYDROTHERMAL vents on the ocean floor release mercury into the sea,
geologists have found. The finding raises questions about whether this 鈥渘atural
pollution鈥� contaminates fish.

Mark Hannington of the Geological Survey of Canada, Ottawa, and his
colleagues were studying water and rock samples gathered last year from
hydrothermal vents in the Bay of Plenty off the coast of New Zealand. Analysis
of the samples showed that the vents release mercury from sediments containing
pure mercury and mercury sulphides (Geology, vol 27, p 931). The team
calculates that each hot spring releases up to a kilogram of mercury each
year.

Hannington鈥檚 colleague Bob Garrett points out that these hot springs are home
to bacteria that turn mercury into its organic form, methyl mercury, which is
easily taken up by fish. 鈥淚t starts moving up the food chain, eventually
reaching the top predators,鈥� says Garrett. In humans, methyl mercury damages the
nervous system and in extreme cases is lethal
(快猫短视频, 6 February, p 4).

It is still unclear how much mercury from the New Zealand vents enters the
food chain. But in the 1970s, Japanese fishermen abandoned tuna fishing in the
region when fish there turned out to contain inexplicably high levels of
mercury. The mercury probably came from the seafloor vents.

It is also unclear how many such springs there are worldwide and how much
mercury lies on the seafloor. 鈥淏ut it could be locally significant,鈥� warns
Garrett.