The Joongang has an article about eating octopus and the amount of cadmium in octopus heads.

First, it should be clear and obvious that fish and other predators, like octopi, will carry more harmful chemicals than herbivores will.  This is true for chemicals that don’t dissolve in water and accumulate in fatty tissue.  DDT is the most famous of these chemicals, but many pesticides and other compounds also have the same characteristics.   A small fish or shrimp contains a small amount of whatever poison.  A larger fish eats ten small fish and now has ten times the poison.  An octopus eats ten of these larger fish and now has one hundred times the poison of the original small fish.  Eating predators is a risker business.

So, the title of the article, “Can octopus heads be hazardous to your health?”, is quickly and easily answered.

The response from restaurateurs and fishermen is more interesting:

The government says two is the maximum, because of heavy cadmium levels found in local and imported octopuses. But that has infuriated restaurateurs and fishermen in South Jeolla, who say the government’s warning has cost them a bundle in lost sales.

…

A group of 30 fishermen from Muan in South Jeolla met Seoul Mayor Oh Se-hoon on Oct. 8 and threatened to sue the city government if it didn’t offer an official apology and compensation for business losses.

And how did the mayor of Seoul react?

Mayor Oh apologized for causing losses but explained, “The intent of the research was to inform people of the health risks of eating internal organs of octopus heads, and it didn’t mean people shouldn’t eat octopus.”

Oh promised he will come up with measures to encourage people to eat octopus to minimize fishermen’s losses.

…

To mend fences with the fishermen, the city government named Oct. 20 as “Seoul Nakji Day” (nakji is Korean for octopus) and served nakji bibimbap, rice mixed with vegetables and stir-fried octopus, for yesterday’s lunch menu at the Seoul City Hall cafeteria for 1,800 civil servants. But the cafeteria removed the internal organs from the octopus heads.

The last point is informative and also interesting.  You might ask what internal organs are in octopus heads, aside from brains?  Well, the ‘head’ is the internal organ sack -the body- of the octopus and holds most of what we have in our chest and stomach.

From Pharyngula:

Right away, you should notice one major peculiarity: the gut runs through the middle of it, separating the brain into a supra- and sub-esophogeal ganglion.

The guts run right through the brain.  Among these internal organs are ones with a higher fat percentage than the body in general; removing these greatly decreases the harmful chemical load one takes in by eating the animal.

So, eat octopus if you want but keep a suspicious mind about those fisherman who only want you to eat it without concern for what lies inside.