Are mercury levels in fish and chips safe to consume regularly?

In Britain, we’ve been eating fish and chips since the mid-1800s and so much of it that it’s now widely regarded as our national dish. According to figures from the National Federation of Fish Friers, 22% of Britons visit a fish and chip shop every week, with 80% getting fish and chips at least once a year – indeed, with 382 million meals from chippies sold every year, that’s enough for every single one of 68 million Britons to have 6 annually. All in all, we spend £1.2bn (roughly, 0.5% of GDP!) at chippies every year. So, just how safe is our national guilty pleasure? 

How does mercury get into seafood? 

When it comes to seafood generally, the main toxin of concern is mercury – or more accurately, methylmercury, which is elemental mercury that has been digested by anaerobic bacteria in river-, lake- and ocean-beds. Elemental mercury can find its way into the ocean via rainfall, after having been released into the atmosphere by natural causes like volcanic activity, geothermal venting or mineral erosion, or anthropogenic causes. Research for 2010 found that of that year’s total anthropogenic mercury emissions, artisanal and small-scale gold mining (which uses mercury to bind with gold and separate it from its ore) makes up 37% and fossil fuel combustion accounts for (25%), mostly from coal but some mercury results from the burning of oil and natural gas; the rest comes from the production of non-ferrous metals, like zinc, copper, lead, silver and nickel (the ores of all these metals can have mercury in them) (10%) and cement production (9%), because some of the raw materials like limestone or heating elements like coal contain mercury.¹ In 2013, research concluded that over 50% of elemental mercury in ocean is anthropogenic.²

How much mercury is safe to ingest? 

For humans, methylmercury is a neurotoxin, impacting memory, co-ordination, speech and vision. Highly bioavailable, methylmercury in the human body has a half-life of 50 to 70 days, a fact which most governmental exposure limits take into account. For instance, the entry for methylmercury in the Environmental Protection Agency’s Integrated Risk Information System (IRIS) states 

In general, the RfD is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. 

The reference (or safe) dose established by the EPA is 0.1μg of methylmercury per kg of bodyweight per day. This would mean that the average British man weighing 84kg could safely consume 8.4μg of mercury per day and the average British woman weighing 70kg could consume 7μg. Staying at or below this level should keep methymercury concentrations in the blood below 5.8μg/l, a long-term average level considered by the EPA to be without considerable risk.  

Interestingly, the World Health Organisation takes a more liberal approach, allowing for 0.2μg per kg per day, or 1.6μg per kg per week.³ For the average British man, that’s 17μg per day and 13.4μg per week; for British women, that’s 14μg per day and 11.2μg per week. But even this higher level is considered low by the Organisation, applying mostly to pregnant people and their children, as adults, they claim, face next to no risk from ingesting up to roughly twice this intake.³ In the UK, the Food Standards Agency sets a maximum allowable level of mercury at 0.5mg/kg (or 0.5μg/g) of food.  

How much mercury is in cod? 

In 2016, the fish and chip industry standardised portions, deciding that a regular portion of battered cod fish is 170g or 6 ounces. According to the FDA, commercial cod’s mercury concentration is 0.111ppm, which means 0.111μg/g - already, this is below the Food Standards Agency’s maximum allowable level. But using this figure, we can say that one regular portion (170g) of cod will contain 18.87μg of methyl mercury, putting it above both the EPA and WHO’s recommended daily intake for both men and women.  

However, how likely is it that you’ll have much more than one or two portions of cod a week? Surely, then, the better measure is weekly intake. Under the EPA’s guidelines, an average British man would be allowed 58.8μg of mercury every week, allowing for 3 regular portions of cod each week; an average British woman is permitted 49μg each week, which is 2 portions. But in the eyes of the WHO, an average British man could safely consume a regular portion of cod 6 days out of every 7, whilst an average British woman could do so for 5 days out of 7 – this is even if we limit ourselves to the headline level, though the WHO is fine with doubling this level for non-pregnant adults. 

So, all in all, it seems that we’re all free to keep enjoying a great British past-time: treating ourselves to some fish and chips for a lazy night in. 

¹ Global health effects of future atmospheric mercury emissions. Zhang et al. Nature Communications. 2021. 

² Legacy impacts of all-time anthropogenic emissions on the global mercury cycle. Amos et al. Global Biogeochemical Cycles. 2013. 

³ Exposure to Mercury: A Major Public Health Concern. World Health Organization. 2021.