 If you intentionally expose people to mercury by feeding them fish like tuna for 14 weeks and then stop, this is what happens to the level of mercury in their bloodstream. It goes up, up, up, and then as soon as you stop the fish, it drops back down, such that you can detox down half in about 100 days. So the half-life of total mercury in their blood is approximately 100 days. So even if you eat a lot of fish, within a few months of stopping, you can clear much of it out of your blood. But what about out of your brain? Modeling studies are all over the place, suggesting half-lives, similar to blood, at 69 days, all the way up to 22 years. But when you put it to the test, autopsy studies suggest it may even be longer still. Once mercury gets into your brain, it can be decades before your body can get rid of even half of it, so better than detoxing is to not tox in the first place. That's the problem with these fish advisories, where they tell pregnant women to cut down on fish. For pollutants with long half-lives, like PCBs and dioxins, temporary decreases in fish consumption, daily contaminant intake, will not necessarily translate to appreciable decreases in maternal, persistent, organic pollutant body burden, which is what helps determine the dose that the baby gets. For example, here's how much exposure an infant gets to a tumor-promoting pollutant called PCB 153. If their mom ate fish, but if for one year mom ate only half the fish, or no fish at all, it wouldn't budge levels much. Only if mom cut out all fish for five years before, do you see a really substantial drop in infant levels. So that's the fish consumption caveat. The only scenarios that produced a significant impact on children's exposures were cried mothers to eliminate fish from their diets completely for five years before their children were conceived. Substituting plant foods instead of fish would reduce prenatal and breastfeeding exposures by 37% each, and subsequent childhood exposures by 23%. So a complete ban on fish consumption may be preferable to targeted, life-stage-based fish consumption advisories. But if you are going to eat fish, which is less polluted wild caught or farmed fish? In this recent study, researchers measured the levels of pesticides like DVT, PCBs, polycyclic aromatic hydrocarbons, and toxic elements like mercury and lead in a large sample of farmed and wild caught seafood, and in general they found farmed was worse. Think of the suspect as farmed and dangerous. The measured levels of most organic and many inorganic pollutants were higher in the farmed seafood products, and consequently intake levels for the consumer if such products were consumed. So, for example, this is for polycyclic hydrocarbons, persistent pesticides and PCBs, significantly more contamination in all the farmed fish samples for all the contaminants, the salmon and sea bass, though it didn't seem to matter for crayfish and the wild caught mussels were actually worse. And if you split adult and child consumers into only eating farmed seafood or only eating wild caught seafoods, the level of pollutant exposure would be significantly worse from the farmed seafood. Overall, they investigated a total of 59 pollutants and toxic elements and taking all these data as a whole, and based on the rates of consumption of fish and seafood in the population in Spain, where the researchers hailed from, the results indicate that a theoretical consumer who chose to consume only farmed fish would be exposed to levels of pollutants about twice as high than if they would have chosen instead wild caught fish. So, you could eat twice the amount if you stuck to wild caught. Easier said than done, though. Mislabeling rates for fish and other seafood in the U.S. is between 30 and 38%, so the average fraud rate is like 1 in 3.