You might think you’re doing your bit for the environment by using a bamboo cup - but new research by German consumer group Stiftung Warentest has shown that you might be risking your health in the process.

Stiftung Warentest: “Keep your hands off bamboo cups”

Bamboo cups are officially in vogue: a much-lauded alternative to disposable coffee cups, which are responsible for 36.000 tonnes of waste per year, these “natural” cups are marketed as being environmentally-friendly, ecological and biodegradable.

Therefore, it may come as a surprise that the Stiftung Warentest, a reputable consumer organisation that investigates and compares goods on the German market, has warned people to “keep [their] hands off bamboo cups” and opt for other reusable drinks containers instead.

All bamboo cups contain melamine resin

Testing 12 different bamboo cup brands, Stiftung Warentest found that buyers are generally given the impression that they are buying natural products. With descriptions such as “bamboo mug” or “made from bamboo fibres”, producers gloss over the fact that the cups are made from a powder of finely-ground bamboo fibres that are then glued together.

All of the cups tested contained melamine resin, a kind of plasticky glue made from formaldehyde and melamine. Melamine is suspected of causing damage to the bladder and kidneys, while formaldehyde is a known irritant and can even cause cancer if inhaled. Still, as long as certain conditions are met, melamine resin is not considered a dangerous substance.

Cups unsuitable for hot drinks

One of these conditions, however, is that it is kept under 70 degrees celsius. And these cups are being specifically marketed for hot drinks. So, when the Stiftung Warentest testers simulated the process of adding coffee to the cups, they made a concerning discovery.

The cups were filled with a hot, slightly acidic liquid (akin to coffee) and left for two hours. This process was repeated seven times per cup. After the third and seventh fillings, the liquid in each cup was tested for chemicals.

The results showed that four of the twelve beakers contained “high” levels of melamine after the third filling, and three more after the seventh filling. Many of them were also releasing high amounts of formaldehyde. Even more concerning, the results were sometimes higher after the seventh test, suggesting that the harmful chemicals don’t evaporate but continue to seep into drinks with prolonged use.

Misleading packaging

Stiftung Warentest also slammed the manufacturers for not properly warning about the dangers of placing the bamboo cups in the microwave. When heated to high temperatures, the cup’s material will begin to decompose: as the cup’s surface is destroyed, it will release even more melamine and formaldehyde. One cup’s packaging simply stated that it should be kept out of the microwave to prolong its life.

Many of the cups also suggested that they were “biodegradable” or “recyclable”. Stiftung Warentest maintains that this is a barefaced lie. Of course, natural bamboo fibres will biodegrade over time, but the cups will not rot, even if you give them years. Neither can they be recycled via standard methods - the only option is to burn them.

Their overall advice? Pick a different kind of reusable cup.