Continuing my series of posts on seashells…
I have always known that seafood can be very very toxic. Large fish (high up on the food chain, like tuna) concentrate the toxicants consumed by all of the smaller fish they eat. Bottom feeders and filter feeders (like lobsters and mussels) concentrate toxicants that are in the water that flows through their bodies. It is for this reason that doctors discourage pregnant women from eating fish (and especially sushi and shellfish.) It is also for this reason that shellfish is not considered Kosher under Jewish law (because it is, by default – not clean.)
What do the numbers mean?
When we talk about finding unsafe levels of toxicants (and specifically heavy metals) in food products, we are generally looking at levels in the range of 5 to 100 parts per billion (and up) as being considered toxic in food and beverages.
- The AAP recommendation is that water in drinking fountains in schools not be greater than 1 ppb Lead.
- Bottled water over 5 ppb Lead is considered unsafe (& illegal).
- 50 ppb Lead is considered the maximum allowable level of Lead in fruit juice.
- Candy that might be consumed by children is considered toxic and illegal if Lead levels are in excess of 100 ppb Lead.
- Dried fruit is also not legally allowed to have more than 100 ppb Lead.
There are 1000 parts per billion in 1 part per million. The range of detection for an XRF instrument is only as low as single-digit parts per million, so it is very rare for a food product to test positive for toxicants using XRF technology.
As a result – when something that is a main component of a food item (like the shell of a mussel) is positive for a toxicant in a detectable level of parts per million (using XRF technology or other testing methodologies) this is a very alarming result — and a food product (or beverage – including water!) with that high a level of detectable heavy metals should not be considered safe to eat (or drink.)
What is Cadmium? What levels of Cadmium are dangerous?
Cadmium is also a known carcinogen. What this means is that it has been well-studied, and proven to cause cancer in humans and other animals. It is a very toxic heavy metal that is mined and refined for use in rust-resistant industrial coatings – and often to create colorant compounds used in many consumer goods (like the brightly-colored enamels in many Le Creuset pots and pans.)
Toys are considered toxic when they test positive for heavy metals in “parts per million“, not in parts per billion. For Lead, for instance, the toxicity threshold is 90 ppm; anything over 90 ppm Lead is considered unsafe for children to use as a toy. For Cadmium, there are two relevant standards (for regulatory limits on XRF-detectable levels of Cadmium):
- Denmark considers consumer goods unsafe for children if the Cadmium level is 75 ppm or more.
- In the U.S., the State of Washington considers consumer goods unsafe if the Cadmium level is over 40 ppm.
So, wait – what… are these shells safe for my kids to play with?
Considering all of the above, including the relevant regulatory standards for consumer goods, I still stand by the statement that intact shells are generally a safe item for children to play with. However, in light of these findings (see specific XRF test results below) it is also very clear how an artist (in this story – link) was poisoned from working with (grinding and cutting) mussel shells, and those sorts of activities should be avoided (by both children and adults).
Takeaway: Even though, in their natural whole state, mussel shells are technically safe (when considered as a consumer good, not as a food), since they are very thin on the edges and crumble and break more easily than other shells – you might also choose (out of an abundance of caution) to keep them out of your child’s collection (especially since all of the other shells I have tested so far were negative – for even trace amounts of XRF detectable Cadmium.)
XRF Test Results for the Shells Pictured Here
Note: these particular shells were found on the Southern California seashore (somewhere between San Diego and Santa Monica) by my son in 2019.
- Cadmium (Cd): 14 +/- 7 ppm
- Bromine (Br): 386 +/- 26 ppm
- Iron (Fe): 456 +/- 131 ppm
- Titanium (Ti): 131 +/- 60 ppm
Tests were done for a minimum of 60 seconds each, and repeated multiple times in order to confirm the levels. An XRF instrument was used in Consumer Goods mode. Test results are accurate, science-based, and replicable.
What does this level (found in the shells) actually mean for the meat of the mussel (if you eat them)?
I have not tested the meat of a mussel – but will report back if I have the opportunity to do that. However even without testing the meat (testing I know many more formalized research studies have done for shellfish) one can easily extrapolate that the meat of the animal will have at least a portion of the toxicants present in the shell. Even if this portion is only 10% that would put the Cadmium level for the meat at 1,400 parts per billion (far above levels that are considered toxic for heavy metals in food – see below). Even if the fraction (of how much Cadmium is in the meat as compared to what is in the shell) is only ONE percent (1%) that would put the potential amount of Cadmium in the meat at 140 ppb – still too high in my opinion.
While it doesn’t appear that the isolated concern of the presence of Cadmium in Mussels (as a food) has been too well studied, when googling “Cadmium Toxicity” and “Mussels” – quite a few related studies did come up. Here’s a sampling:
- Heavy metals concentrations in fish and shellfish from eastern Mediterranean Sea: consumption advisories.
- Too much cadmium and lead in kids’ food according to estimates by FDA
For context: acceptable levels of Cadmium in chocolate (European Standards)
As one possible data set for comparison – I did find the following information from Europe about allowable Cadmium Limits in chocolate (link here):
- Less than 30% chocolate: Maximum of 100 ppb Cadmium allowed
- 30% to 50% chocolate: Maximum of 300 ppb Cadmium allowed
- Greater than 50% chocolate: Maximum of 800 ppb Cadmium allowed
- Cocoa Powder: Maximum of 600 ppb Cadmium allowed
For context: acceptable levels of Cadmium in crab meat (European Standards)
I also found another (perhaps more relevant) bit of information from Europe… in this summary they look at Cadmium in crab meat and are calling 80 ppb an acceptable level, but warning that the “brown meat” in the body of the crab has as much as 8,000 ppb (8 ppm) and this is an unacceptable and dangerous amount of Cadmium.
Given the biology of mussels I would image that the Cadmium levels in their meat might be similar to the levels found in the brown meat of the crabs – and therefore possibly as high as 8,000 ppb. Link here.
While I always knew there was a concern for toxicants in shellfish, I now (with this finding of 14,000 ppb Cadmium in mussel shells) have a heightened appreciation for this concern – and as of the moment of writing this blog post, will no longer be eating mussels (ever); for me the risk is just too high, and I would like to try to avoid all potent carcinogens in my food – thank you very much!
As always, thank you for reading and for sharing my posts.
Please let me know if you have any questions.