Mercury Rising – The Federal Fish Advisory

In a recent post, I discussed the findings from the Environmental Protection Agency (EPA) stating that 300,000 newborns may have been overexposed to mercury through their mothers’ consumption of fish. Based in part on these concerns, the Food and Drug Administration and EPA recently published a fish advisory for mercury. The advisory recommends eating up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury. Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish. Another commonly eaten fish, albacore ("white") tuna has more mercury than canned light tuna. So, when choosing two meals of fish and shellfish, the advisory notes that you may eat up to 6 ounces (one average meal) of albacore tuna per week.

I am registered with an online fitness forum that addresses topics including strength training, diet and cardiovascular exercise. A member recently asked about mercury in tuna; tuna packets are a convenient way to get protein into your diet when you’re on the go. In response, I ran the calculations for estimating the mercury exposure associated with eating 12 ounces/week of tuna (corresponds to 48.5 grams/day). The average concentrations of mercury in tuna (based on the EPA’s Mercury Report to Congress, book 1 and book 2) is:

Albacore – 0.264 ug/g
Skipjack – 0.136 ug/g
Yellowfin – 0.218 ug/g

The daily intake rates from eating 12 ounces/week then look like this:

Albacore – 12.8 ug/day
Skipjack – 6.6 ug/day
Yellowfin – 10.6 ug/day

The NHANES mercury exposure survey published this year notes that the 95th percentile value for mercury intake from fish ingestion for women ages 16 to 49 ranges from 4.5 to 13 ug/day. When normalized for body weight, the intake rates range from 0.09 to 0.19 ug/kg-day (micrograms mercury per kilogram body weight each day).

Using the available data on mercury concentrations in tuna, the fish advisory consumption rates and an assumed body weight of 120 pounds (representing a women of child-bearing age), I get intake rates normalized for body weight ranging from 0.12 to 0.24 ug/kg-day for different tuna species, with skipjack being the lowest and albacore (white) being the highest. So, it looks like the fish advisory was set so that the exposures are kept close to EPA’s Reference Dose (RfD) of 0.1 ug/kg-day for methyl mercury. The RfD is intended to protect newborns and young children from adverse neurodevelopmental effects (more will be said about the RfD in another post).

The advisory attempts to balance the role of fish and shellfish as important parts of a healthy diet with reducing the risks from mercury exposure. Fish and shellfish contain high quality protein, are low in saturated fat and contain omega-3 fatty acids. A well balanced diet that includes a variety of fish and shellfish can contribute to heart health and children's proper growth and development. Thus, the advisory appears to set fish consumption rates as high as feasible without significantly incurring risks of excess mercury exposure.

However, there are a few questions that remain. Is consumption of 12 ounces/week of fish adequate for good nutrition? Also, there are other toxicants potentially associated with neurodevelopmental effects in children (dioxins, PCBs and brominated fire retardants) that are also found in fish. The fish advisory is designed to reduce exposure to mercury. What is not known is whether or not there are additive effects from the combined exposures. If so, the fish advisory may not necessarily protect newborns and young children from neurodevelopmental effects.