Won't Someone Please Think of the Sushi?

Saturday October 07, 2017

•  Earth science •  environmental studies •  food security •  public affairs •  public health •  zoology • 

A friend picked up the kids from the bus stop last night and I met up with them for dinner at the neighborhood sushi restaurant. See, they love sushi. Ducky is 5 and her favorite food is salmon roe, which she calls “bubbles.” She also loves some raw tuna. Chase is 8 and his first solid food, literally, was raw tuna, which he pulled off my plate and started gumming.

Now, why I am talking about this. First, tuna is an apex predator. It eats everything…including things that eat other things. And tuna is so very fatty…that’s what makes it pretty tasty.

As organic compounds drop into the sea, they invariable end up in the plant life and smallest animals. This might be from an oil spill, degrading plastics, or pesticides from runoff. This is not good for them, but it is worse for the next member of the foodchain up. The next fish up will absorb some naturally and accumulate more through eating contaminated food. This works all the way up and the limiting factor is the partition coefficient between water and the body fat in tuna, grouper, mackerel and other fish we eat.

If a chemical, organic or not, is particularly soluble in the body fat, which we approximate with octanol, then the fish can absorb more of it. This is why pregnant women are advised to avoid tuna, due to mercury accumulation. The octanol-water coefficient of a chemical represents how soluble the chemical will be in body fat versus the water and we can estimate how much will end up in our foodstocks.

As troubling as this is, there is good news. Recent observations have shown that there is a decrease in toxins in fish harvested. This is good news for the fish, since they don’t want to be poisoned any more than I do. And it means I can keep giving sushi to the kids.