New study confirms concerning heavy metal contamination in cocoa
By: Zackary Grines
November 08, 2025
News Article: https://www.confectionerynews.com/Article/2024/08/05/Heavy-metal-contamination-found-in-cocoa
Peer-Reviewed Article: https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2024.1366231/full
Background:
Heavy metal exposure is a serious medical concern and leads to increased chances of hypertension, heart disease, and malignancy1. Cocoa products have been known to contain heavy metals like cadmium and lead from environmental origins2, cadmium is taken up from the soil by the plant itself while lead dust and dirt gets on the beans from nearby industrial sides while they dry3. While several studies have been done to identify and quantify the metals in cocoa, researchers at the George Washington University School of Medicine and Health Sciences put together a long term study focusing on lead, cadmium, and arsenic found in cocoa products.
Peer-Reviewed Article:
From 2014 to 2022 researchers at the George Washington University School of Medicine and Health Sciences in DC analyzed lead, cadmium, and arsenic contamination in 72 consumer-cocoa containing products. They chose these metals due to their presence in soil and their role as industrial waste products around cocoa processing sites. All the products were obtained domestically and were made in the U.S. or in Europe. This was done in coordination with ConsumerLab.com who purchased the products and enlisted commercial laboratories for testing. The chosen products were also picked by ConsumerLab mostly according to a ranked product survey they take yearly. They did this in 4 cohorts; 2014, 2016, 2019, and 2022.
For arsenic and cadmium analysis the samples were digested with acid (acid and hydrogen peroxide for lead) and then analyzed with ICP-MS. They compared the amounts of these metals in the samples to Prop 65 MADLs (Maximum allowable dose level) which are 0.5𝜇g/day for lead, 4.1 𝜇g/day for cadmium, and 10𝜇g/day for arsenic.
Figure 1. Figure one shows the overall mean, median, min, and max data for the heavy metal contaminants.
Overall, the mean concentration of lead and cadmium per serving was above the Prop 65 MADLs (0.615 𝜇g/serving and 4.358 𝜇g/serving respectively). However, the mean arsenic concentration per serving was compliant at 0.931 𝜇g/serving. 43% of products for lead and 35% for Cadmium (per serving) exceed the MADLs. Outliers did play a large role as the median concentrations of lead (0.375 𝜇g/serving) and cadmium (3.03 𝜇g/serving) were compliant. These values did decrease over time compared to the start of the study in 2014. The median values for lead and arsenic fell below the conservative MADLs and even below the stringent FDA IRLs (interim reference levels), for example lead has a IRL of 2.2𝜇g/day for children under 7 while the median value in the study was 0.375 𝜇g/serving. There are no federal limits for cadmium but the values were above many regulatory recommendations.
Figures 2-4. Figures 2-4 show the % of products at certain 𝜇g/serving levels for the three metals in each cohort.
On average taking individual servings of most samples is fine, but outliers are significant. Another finding in the study was that when comparing product’s labels they found that “organic” products were significantly more likely to have higher levels of cadmium and lead, and that the amount of all 3 heavy metals did not change significantly with the trade certifications of the products.
News Article:
The news article focuses on the 43% of products having more than the MALD for lead and 35% for cadmium statistics. They hook with that then provide some background information about the chocolate industry, like its expected $133.6 billion expected 2024 revenue. The article does describe how this contamination can occur, likely from other metal-polluting industries located near cacao plants, especially consequential when drying the beans. It also includes many quotes from some of the main authors of the study about their views on chocolate and the study. One main quote describes the lead author’s motivation for this study was to see if the levels of metals in cocoa are meaningful from a public health standpoint. They finish up the article by stating that eating chocolate is still safe but that they may be exposed to biologically significant amounts of metals like cadmium with unknown significance.
Analysis:
Overall, the article provides sufficient background information on the topic and keeps the reader engaged by not going too deep into the numbers. They provide an accurate conclusion about the risk of eating chocolate and some concerns with it still. However, they make several errors. They incorrectly state that the scientists recommend staying to one ounce of chocolate a day when the recommendation was one serving, although many chocolate servings are around an ounce it can vary significantly by the product. They also incorrectly claim that the scientists established the MADLs themselves when those are from the infamous California Prop 65. They do not mention that outliers are a significant contribution to the results and that the prop 65 MASLs are quite conservative compared to the federal limits. Although they present the information in a clear way for the average reader, the false statements and lack of any statistical language leads me to give this a 5/10.
References:
1. Wang, X, Han, X, Guo, S, Ma, Y, and Zhang, Y. Associations between patterns of blood heavy metal exposure and health outcomes: insights from NHANES 2011–2016. BMC Public Health. (2024) 24:558. doi: 10.1186/s12889-024-17754-0
2. Abt, E, Fong Sam, J, Gray, P, and Robin, LP. Cadmium and lead in cocoa powder and chocolate products in the US market. Food Addit Contam Part B. (2018) 11:92–102. doi: 10.1080/19393210.2017.1420
3.Loria, Kevin. (2023, January 31). How lead and cadmium get into dark chocolate. Consumer Reports. https://www.consumerreports.org/health/food-safety/how-lead-and-cadmium-get-into-dark-chocolate-a3299517114
Hi Zackary! This is an interesting topic! I never thought that heavy metals would be in chocolate, let alone organic chocolate. The news article focuses on the the potential for heavy metals to be in dark chocolate, but the peer-reviewed article states that they sampled cocoa products. Did the study compare heavy metal concentrations found in different types of cocoa products (e.g. dark chocolate vs. milk chocolate or different brands)? I also find it interesting that this study was conducted over eight years. The heavy metal concentrations in the cocoa products seem to be consistent across the eight years, but how can we trust the data if outliers were included? Why did the authors not exclude outliers, and what were the QA/QC procedures used in this study? Can you also explain more about Prop 65?
ReplyDeleteHi Shyleigh, the study did not compare different kinds of chocolates or cocoa products, they just picked any kind of cocoa products based on ConsumerLab's yearly customer survey, they did exclude some products which were found to have high amounts of heavy metals from subsequent years tests in order to find more which were healthier. I believe this was due to working with ConsumerLab whose stated mission is helping consumers and healthcare professionals find the best quality health and nutrition products. In general, the trend was that the heavy metals found decreased over time (this is seen in the charts and is fairly consistent outside of Lead 2022. Although because it is not broken down into smaller increments it is harder to notice). While outliers in data can be bad for getting a conclusive result or a reliable average, in this case the outliers were the worst offenders and the unhealthiest, so they were the most significant finds for the study. At the end of the study's methods section, they have 2 paragraphs focused on statistical tests and analysis, I don't know enough about them to confidently explain to others but one part I understand that seems to answer your question is that samples which exceeded the Prop 65 limits were retested at a different independent lab. Prop 65 is a law that was passed in California in 1986, along with protecting the state's drinking water it also requires any products which contain chemicals that are known to cause cancer or reproductive harm to have a warning on them. I used the word infamous to describe it because these warnings are often found on products across the country and use a specific wording along the lines of "this product contains chemicals known to the state of California to cause..." and are found even on products you might expect. In my experience I often see them on electronics where the chemicals mentioned would only cause harm if you disassembled the electronic, ground up a certain part, and ingested it.
DeleteZackary, thank you for sharing this article with us. I know that arsenic and other heavy metals can exist in different chemical forms, and not all of them are equally harmful to humans. For example, seaweed and many types of seafood naturally contain arsenic, but it is the As3+ and As5+ forms that are the most toxic. How did the researchers determine how much of each heavy metal occurs naturally in the cocoa vs. how much comes from post-harvest contamination (such as during drying)? Based on the methods section, it seems they only analyzed cocoa products after purchasing them from stores. If that is the case, how can they determine the original source of the contamination? For instance, how do they know whether contamination occurred during the drying of the beans near industrial areas, rather than later during processing in factories in Europe or the US? I assume the cocoa itself was grown in tropical regions and the shipped for processing, so it seems difficult to pinpoint where contamination occurred.
ReplyDeleteAlso, the study mentions that certain products had higher concentrations of metals than others. Why do you think the researchers chose not to identify those brands so that the consumers could make informed choices?
There have been some studies on cocoa beans, specifically on samples that are freshly harvested compared to processed beans which have found significantly more heavy metals after they were processed. The third reference I have is a different news article covering a research paper that goes over how the different metals get into/on the plant if you are interested in reading more on that. I believe the results of this study were not hidden, it is hard to find information because this is the summary of an 8 year long process, but their collaboration with ConsumerLabs on this makes me think they did in some way make this known since ConsumerLabs aims to find healthy food choices.
DeleteHi Zackary! This was a very interesting blog post. I think it is helpful that the news article included quotes from the main authors of the study. I also liked how the news article provided background on how contamination could occur. Do you think the authors of the news study purposefully left out that the MADLs were from the California Prop 65, and the influence of outliers on the data? Is this possibly a tactic to evoke concern and possibly fear? What are some feasible next steps that can be taken as a result of the data from this study? Are there ways to reduce metal contamination?
ReplyDeleteHi Kristen, I did get the feeling that the news article was a little purposefully deceitful. They are based around covering news on foods and even have a section on their website dedicated to large brands, so there could be some corporate relations implications going on. The misstatement on Prop 65 seems extremely egregious due to its prevalence, either the news article author was particularly negligent, or they were trying to make the researchers seem more authoritative on this subject. This isn't new information, and it has long been known these metals are in cocoa products, but specific numbers can vary wildly by product. Because most cocoa is sourced from South America and Africa it is hard to regulate the contamination that happens on site in these locations, if anything these news articles and studies bringing attention to the issue is the best that can be done outside of publicly shaming brands that are the worst offenders.
DeleteHi Zackary, this was an interesting read! The connection between pollutants and our food is something that I think doesn't get enough attention, thank you for sharing. I was curious why the researchers focused specifically on cocoa plants. Were these chosen just as an example crop, or is there something about cocoa that makes it especially susceptible to heavy metal contamination? I thought it was surprising that the organic products were found to have higher levels of lead and cadmium. What factors do you think could cause that? is it a reflection of the certification differences, soil treatments, or growing location? I agree with your rating, too. It’s the media’s responsibility to communicate the science accurately, so even small errors in how they report methods or results can really change how the public perceives the findings.
ReplyDeleteHi Talia, the focus on Cocoa was in part due to its use in many different products and because of how it is processed. The beans from the plant are harvested and need to be dried to then be further processed, this is usually done by leaving them out in the open where they are exposed to contamination from many sources. The biggest mentioned are nearby industrial sites that either produce pollutants themselves or have machinery which runs on leaded gasoline which then gets in the air and falls on the beans. I could not find a direct source on why organic products have more lead and cadmium, but it is likely due to the differences in processing which may not remove as many contaminants, or the organic products get their cocoa beans from unique sources that have worse contamination than average.
DeleteHi Zackary, thank you for sharing this interesting research. The finding in the paper that really shocked me was that 'organic' products were significantly more likely to have higher levels of lead and cadmium. That is completely counterintuitive to what most consumers would expect (as I buy organic cacao powder all the time to make tiramisu)
ReplyDeleteGiven your background info that cadmium is taken up from the soil, it really makes me think. I know other crops, like rice, are one of the main sources of mercury besides seafood. I'm just curious, why do different plants, like cacao trees and rice, seem to be so different in the types of heavy metals they accumulate? Does this mean the soils used for organic cacao are just naturally higher in cadmium, or does the 'organic' label not even factor in heavy metal testing?
I am also curious about other heavy metal levels in cacao products. If the research team also took measurements for other metals during this long-term study, that would be even more insightful.
Thanks for sharing this article. I was not familiar with heavy metal contamination in chocolate, so it was interesting to learn about. I am surprised that the organic samples were the ones most contaminated, since often people buy organic food, thinking it is better. I found it interesting to read about the application of ICP-MS in analyzing these heavy metals, as I am familiar with the analytical technique from previous research experiences and the mass spectrometry course I am currently taking. I enjoy making connections across different courses to better my understanding of environmental chemistry in general.
ReplyDeleteHi Zackary, this is a crazy read, especially thinking I had a hot chocolate just yesterday made from cocoa powder... The found mean concentrations of lead and cadmium are especially concerning. Although I get that the median values comply with law standards, I'm surprised more people aren't at least aware of these contaminants in their beverage. Even more significant is the fact that most cocoa powders are bought by families and for young children. I would be interested in this study being extended to test other foods and processed plants like vanilla or tapioca powder. There's also coffee beans. I'd also be interested to see how these results stand up internationally.
ReplyDeleteAlso, I'm curious to see whether working with small batches versus big batches might make a difference in heavy metal concentration. I'm guessing many of the powders studied came from bigger companies, which usually harvest and process in very large batches for cost-efficiency. I wonder if different companies, smaller companies, see lower concentrations and if that is caused from the lack of heavy machinery used and/or more attentiveness to the harvest to packaging process.
The results of this were also surprising to me at first, but I'm not too concerned due to the downward trend over the years and even if I ate chocolate every day, I would have to be quite unlucky to only eat one of the outliers that had a high concentration of lead or cadmium. It's interesting you bring up coffee beans because they are grown in similar places and are also dried out in the open which leaves them vulnerable to the same kinds of contamination. Your idea about larger vs smaller batches may be onto something as in a different comment about the organic differences I brought up how differences in processing could be one of the reasons why organic labeled products had more heavy metals. Although, unless the drying process is completely changed, I don't see the heavy metal contamination from that changing much even if fewer beans are dried at a time.
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