What should we be cautious of when we put drinks in metal canteens?

If metal containers and metal cooking tools are damaged or incorrectly used, such as from storage of acidic drinks for a long period, then some metallic elements may dissolve into the foods or drinks, causing unexpected accidents.  In the past, there was a poisoning case caused by internal damage in the surface of a metal canteen.
When you put drinks in a metal canteen, it is important to read the instruction manual well and use the canteen correctly.

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< What is a poisoning case caused by a metal container?>

• When containers and cooking tools made of metals such as aluminum, copper, and iron, come into contact with acidic foods, the metals may dissolve.
• In an ordinary case, the quantity of metal dissolving in a short time is extremely small.  In order to prevent metals from dissolving excessively, various ideas are applied, including coating the internal surfaces of containers and cooking tools so as to prevent metals coming into direct contact with foods.
• However, if the containers and the metal cooking tools are damaged or incorrectly used such as in storage of acidic drinks for a long period, then the metal elements may dissolve into the foods and drinks, causing unexpected accidents.  In particular, ingestion of a large amount of copper may cause poisoning.

< What should we pay attention to?>

• Carefully read the manuals and precautions of containers and drinks and do not keep highly acidic drinks or foods in metal containers for long periods of time.  In case you have kept something in a metal container for a long time, sufficiently check if the taste and/or the color of the food have changed from the normal state.
• Carefully check if the inside of the container has any rust or damage.  With rust and/or damage, the internal parts that do not normally come in contact with drinks or foods may be exposed, causing the metal elements to dissolve.  If a container falls or impacts on something, it may be damaged inside even if the outside appearance looks normal.  Check it carefully prior to use.
• Old containers may have damage inside due to degradation.  Periodically replace them with new ones to prevent unexpected accidents.

[Reference 1] What is included in acidic drinks?

• Drinks containing large amounts of carbonic acid, lactic acid, vitamin C, and citric acid (contained in citrus and other fruits), such as, carbonated drinks, lactic acid drinks, fruit juice drinks, and sport drinks, tend to have high acidities.

[Reference 2] Are there any actual poisoning cases?

• Please let us introduce a poisoning case caused by a canteen with internal damage.

A health center in Tokyo reported that six persons drinking sport drinks said they tasted bitter and thereafter displayed symptoms such as headache, dizziness, and nausea.
The color of the sport drink ingested by the patients should have been milky white but actually changed to blue green and the internal surface of the canteen had many small spots with brown material attached.  As a result of inspection, a high concentration of copper (880 ug/g (ppm)) was detected from the remaining drink and it was made clear that the major component of the brown material that was attached inside the canteen was copper.
The above-mentioned sport drink was prepared by dissolving sport drink powder into water and put in the canteen at around AM 7:30 that day.  It was kept as it was until around PM 2:00, when it was actually consumed.  The inside of the canteen did not look damaged at a glance but the simulation test showed that blue-green liquid gathered inside.  The health center contacted the manufacturer of the canteen and clarified that the canteen wall was of a double structure for heat insulation and copper was used as part of the interior double structure which ordinarily did not come into contact with drinks.
The possible cause of this case is the fact that the inside of the canteen was damaged.  Because the canteen was left for a long time with an acidic sport drink kept inside, the acids penetrated into the copper interior of the lining, and thus, dissolving the copper that was used in the heat insulation structure.  (Case in 2008)