Comparison of Zinc and Copper Leached from Coins and Tokens Under Simulated Gastric Environments
In 1982 the composition of United States (USA) pennies was changed from 95% copper (Cu) and 4% zinc (Zn) to 97% Zn and 2.5% Cu.1 Since then many cases of zinc toxicosis have occurred following penny ingestion in animals, including zoo and aquatic species.2,3,4 A few instances of copper toxicosis in animals following the ingestion of copper coins have also been reported.5,6 In addition to coins introduced into their pools or enclosures, animals may be exposed to coins and tokens of various metallic compositions used to operate public feed dispensers.
The objective of this preliminary study was to determine the amounts of copper and zinc released from selected coins and tokens when placed in simulated gastric conditions. Freshly minted 2018 USA pennies (2.5% Cu, 97% Zn, weight = 2.5 grams) and USA quarters (91.67% Cu, 8.33% nickel (Ni), weight = 5.67 grams) were tested along with three different metallic tokens used to operate feed dispensers (Token A 68.86% Cu, 31.08% zinc, weight = 7.1776 grams; Token B 97.628% Cu, 0.1549% Zn, weight = 5.2091 grams; Token C 0.0010% Cu, 0.0003% Zn, 99.926% Ni, weight = 5.2267 grams). Six coins or tokens of each type were separately placed in 100 mL of pH 2.3, 4, or 7 buffer. Blanks and copper and zinc-spiked buffers were used as controls. All test and control samples were placed in a shaking incubator maintained at 39°C. On Days 2, 4, and 7, duplicate sets of each coin and token type, blank, and spiked buffers were removed from the incubator, and a 1 mL portion of buffer solution was sampled from each test vessel for Cu and Zn analysis using inductively coupled plasma mass spectrometry (ICP-MS).
As expected, preliminary data indicated that zinc and copper leaching increased with time and acidity. The USA quarter and Token A leached significant amounts of copper while the USA penny and Token B leached higher amounts of zinc. Token C, containing mostly nickel, leached the lowest amounts of both copper and zinc, so potentially poses the lowest toxicity risk to animals following ingestion. Next steps include repeating the metallic token experiments to obtain additional data points. Future work could look at leaching at lower temperature ranges that would better simulate gastric conditions for fish, reptiles, and amphibians.
* Presenting author
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