Recently I was changing the thermal grease on my PC. I have noticed on the back of box, that the grease is not dangerous when ingested or when touched. But there was specifically stated, that is dangerous to aquatic organisms.

What is so special about aquatic chemistry, that the grease is dangerous to them? I would guess that the chemistry of mammals, reptiles, and birds would be quite similar to that of fish.

  • $\begingroup$ just a guess, but dissolved in water it may coat the gills and prevent proper oxygen/CO2 exchange... $\endgroup$
    – MattDMo
    Jun 5, 2014 at 16:13
  • $\begingroup$ What type of thermal grease are you using? I think it depends on the ingredients. $\endgroup$
    – Mys_721tx
    Jun 7, 2014 at 9:18

1 Answer 1


From some of the MSDS (1, 2) I come across, a major component of thermal grease is aluminum oxide.

Risk Management for Hazardous Chemicals by Jeffrey Wayne Vincoli states in page 101 that aluminum oxide has both acute and chronic toxic effects to aquatic life; it also states that aluminum oxide has a half-life longer than 200 days in water; finally, it acknowledges that the short term toxicity data for non-aquatic animals are insufficient.

From this, the reason thermal greases have special notification regarding to fishes can be attributed to those following points:

  1. The long half life makes fishes exposure to it longer and therefore makes them more susceptible.
  2. We simply do not understand how aluminum oxide effect non-aquatic animals.

(According to Risk Management for Hazardous Chemicals, bioaccumulation in food chain might not be the concern.)

  • $\begingroup$ I have to admit, 'we don't know that it kills land creatures, but it definitely kills fish' is a scary reason to put an aquatic warning on it. $\endgroup$
    – Resonating
    Jun 23, 2014 at 16:36

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