Again, I say, if it was safe, there would be no such guidelines. I'm guessing that the WHO has no guidelines for the safe limits of exposure to milk, for instance (Carol)

Milk isn't a good example for two reasons. First, it consists of too many different more elementary compounds and the relative contribution may vary considerably. The policy of the WHO has been to publish safe limits for identifiable elements or more complex chemicals and not for a food. So it would recommend safe limits for mercury in fish but not safe limits for fish (for the amount of mercury can vary a lot).

Second, components of milk of course have a recommended safe limit of exposure. Take the naturally occuring aflatoxin for instance and then you may read in a WHO discussion:

These (the EU countries) delegations noted that aflatoxin M1 was a genotoxic carcinogen, a lower level was needed to
    protect high level consumers of milk and vulnerable populations such as infants and young children (http://www.who.int/fsf/Chemicalcontaminants/AflaM1_32ccfac.htm)

The existence of recommended safe limits is not a good argument for (or against) relative danger.

Wolfgang