The value of a 2002 1 euro coin might extend beyond its face value, especially when considering its material composition and potential health implications. A study conducted in 2002 investigated the nickel release from 1- and 2-euro coins and revealed surprising results concerning their potential to trigger allergic reactions in nickel-sensitive individuals. This article delves into the findings of this research, shedding light on the unexpected levels of nickel release from these common euro coins.
Skin tests were performed on seven patients with known nickel-contact allergy using 1- and 2-euro coins. These coins were affixed to the patients’ skin with transparent tape for 48 and 72 hours. The results were striking: all seven patients exhibited strong allergic reactions, characterized by erythema (redness), infiltration (swelling), and vesicle formation (blisters). Crucially, these patients showed no reaction to control tests using 1% zinc chloride in Vaseline or 1% copper sulphate in water, indicating the reactions were specifically due to the euro coins.
To quantify the nickel release, researchers employed the European Standard EN 1811, a recognized test for nickel release from materials intended for prolonged skin contact. As anticipated, the 50-cent coin showed no measurable nickel release. However, the 1- and 2-euro coins presented a significant and unexpected finding: they released more nickel than pure nickel itself.
Figure 1: Comparison of nickel release from euro coinage against pure nickel in artificial sweat, as measured by the EN 1811 standard test. The graph emphasizes the unexpectedly high nickel release from the bimetallic 1- and 2-euro coins compared to pure nickel. The inset image visually demonstrates the corrosion observed on a 1-euro coin after immersion in artificial sweat.
This elevated nickel release was particularly pronounced from the inner component, or ‘pill,’ of the 1-euro coin, while the outer ‘ring’ released less nickel. These nickel-release rates were among the highest ever recorded for coins, surpassing even those of pure nickel under the same testing conditions. This discovery raised concerns about the potential for these coins to cause or exacerbate nickel allergy, a common form of contact dermatitis.
The composition of the 1- and 2-euro coins explains this phenomenon. The 1-euro coin consists of a ‘ring’ made of ‘nickel brass,’ a yellow alloy composed of copper (80%), zinc (20%), and nickel (5%). The ‘pill,’ the inner part, is made of ‘cupro-nickel,’ a white alloy of copper (75%) and nickel (25%). Conversely, the 2-euro coin has a cupro-nickel ring and a nickel brass pill. The bimetallic nature of these coins prompted further investigation into galvanic corrosion.
Galvanic potential measurements were conducted by mechanically separating the pill and ring of freshly minted 1- and 2-euro coins and immersing them in artificial sweat and saturated NaCl solution. A difference in electrode potential was found between the two metals, with the yellow metal (nickel brass) being more negative and the white metal (cupro-nickel) more positive. This potential difference, which stabilized at around 40 mV after 24 hours, is a key factor in galvanic corrosion.
Galvanic corrosion, accelerated by an electric current, increases nickel release. In the thin electrolyte layers of sweat on skin, this corrosion is concentrated at the junction between the two metals due to high resistance to lateral current flow. Electrochemical measurements revealed that the yellow metal (nickel brass) corrodes at least five times faster than the white metal (cupro-nickel) in active corrosion conditions. Despite the yellow component containing less nickel than the white component, its nickel release rate is comparable or even higher due to this accelerated corrosion and the similar contact areas with skin.
Visual evidence of corrosion was observed on the 1-euro coin after 36 hours of immersion in artificial sweat. The coin’s colors changed to brown, and the surface structure was damaged. In contrast, a Swiss 1-franc coin, composed of 25% nickel and 75% copper, showed no visible corrosion under the same conditions, highlighting the specific issue with the euro coin composition and design.
The study concluded that the actual nickel release from the 1- and 2-euro coins significantly exceeds the limits deemed acceptable for prolonged skin contact according to European Union directive 94/27. The excess was measured to be between 240 and 320 times the acceptable value. The researchers emphasized that whether this level of release is acceptable depends on the interpretation of “prolonged” contact. They called for further investigation into the epidemiological implications of these high-nickel-releasing coins and the factors contributing to nickel release, particularly the crevice between the pill and the ring, which acts as a potential corrosion site. This study underscores that the material composition and design of even seemingly innocuous items like the 2002 1 euro coin can have significant implications for public health, particularly for individuals with nickel sensitivity.
