Friday, March 18, 2011

Why Miley Cyrus and Shrek are toxic to your kids

They have both been in the news recently but not for the reasons you may think.

Companies like Wal-Mart and McDonalds were forced to recall thousands of items, such as Miley Cyrus jewelry and Shrek promotional glasses, because of the presence of cadmium. And it’s not too uncommon now that you hear on the news of some product made in China tainted with a toxic heavy metal like lead and cadmium. The most common culprit? Cheap jewelry, specifically, children’s jewelry. But is the cadmium present in these items bioavailable? Meaning, what is the risk to the consumer and just how much cadmium in these products can be potentially taken up by the user’s body? Researchers asked just that.

Cadmium (Cd) has broad industrial applications so it is a common environmental contaminant that is studied. Chronic cadmium exposure in humans can lead to kidney damage as well as osteotoxicity, where the bones become soft and less dense leading to increased fractures as well as general pain and weakness. Chronic exposure at any level is likely unsafe because it is not readily removed from the body and bioaccumilates, persisting in the body for a very, very long time. For example, the half-life of cadmium concentration in the kidneys is between 10 to 30 years. Yikes!

Certain cohorts tend to be more sensitive to cadmium as well. Smokers for example directly absorb cadmium from the inhalation of cigarette smoke, leading to a much more direct route of exposure. The group of most concern through is children. Children have been shown to have increased gut absorption of cadmium compared to adults, especially females (anyone know the reason for this? I’d be interested to know). However current guidelines for safe levels of cadmium exposure do not exist for children, so using the recommendation for adults (0.1 µg/kg bw/day) is likely an overestimate of safe levels for a child. In addition, there are no regulatory limits for cadmium levels in jewelry products.

To test whether there is a risk of cadmium exposure from children’s jewelry, in a coming issue of EHP, researchers went out and bought a bunch of cheap bracelets, charms and pendants. No more than $12 an item, most under $10 and many of the items manufactured in China. In order to determine the risk associated with these items, researchers had to simulate the most common pathways a child would be exposed to the cadmium found in these products and determine whether or not the metal is bioavailable. To simulate a child mouthing or sucking on their jewelry, the items were placed in saline for 6hrs. And to simulate the swallowing of one of these items, the jewelry was placed in HCl for on average 24hrs. The US Consumer Product Safety Commission (CPSC) recommends a maximum cadmium level of 18 µg/6hr saline extraction and 200 µg for the acid extraction.

Of the 612 pieces of jewelry purchased for this experiment, more than 270 contained more than 10,000 ppm (1%) cadmium, with 70 of those containing more than 10% cadmium. There did not seem to be any correlation between the amount of cadmium present in the items and the amount of cadmium extracted from the above methods. This is likely due to the different manufacturing of each item (different items made of different alloys, different coatings etc.) which also lead to a high variability between items. But none the less, both extraction methods yielded very high amounts of cadmium. In the mouthing scenario, up to 2200 µg Cd was leached into saline, and 10 of the 48 items tested were above the 18 µg CPSC recommended threshold.

The HCl extraction yielded even more interesting results because the amount leached into the acid increased linearly over time, tested up to 96hrs. A third of the jewelry tested leached more than the 200 µg recommended amount after just 24 hrs and the highest content measured at 20,000 µg. In addition, some jewelry that was damaged with 1-2mm cutss to simulate normal wear yielded 30 times more cadmium than undamaged replicates. But the differences in damaged versus undamaged jewelry were item specific in both the saline and acid extractions which just highlights the difficulty and complexity of trying to simulate and ultimately regulate the risk associated with cadmium tainted jewelry.

The authors raise an interesting point about whether the time points which are recommended are representative enough of actual ingestion exposure. In another study of children swallowing foreign objects, the “transit time through the digestive tract” (read: poop) was 6 days, but varied from 1 to 46 days (eewww). So maybe 6 or 24hrs time points are not long enough to replicate potential absorption. It would appear to me that the acid digestion utilized in this study would only account for cadmium leached while in the stomach and may not take account any enhanced absorption while passing through the intestines. But there are limitations on any simulation.

Overall though, this study really shows how difficult it is to calculate bioavailability of cadmium when the application and usage is so diverse, even when dealing with a specific subset of products like cheap children’s jewelry. But still, researchers were able purchase items that were both really high in cadmium content but also leached about to 100 times the recommended amount. So the danger is out there on the store shelves right now. As if the dreadful pop music and animated movies weren’t enough reason to avoid Miley Cyrus and Shrek, exposure to toxic cadmium can now be added to the list.

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