95: Copper

HISTORY AND EPIDEMIOLOGY

Copper exits naturally, either as native copper (elemental copper, Cu^o) or as one of its sulfide or oxide ores. Important ores include malachite (CuCO₃·(OH)₂), chalcocite (Cu₂S), cuprite (Cu₂O), and chalcopyrite (CuFeS₂or Cu₂S·Fe₂S₃). Chalcopyrite, a yellow sulfide ore, is the source of 80% of the world’s copper production. The smelting, or separation, of copper ores began about 7000 years ago; copper gradually assumed its current level of importance at the start of the Bronze Age, around 3000 bc. Smelting begins with roasting to dry the ore concentrate, which, in more modern times, is further purified by electrolysis to a 99.5% level of purity. The sulfide ores have a naturally high arsenic content, which is released during the extraction process, posing a risk to smelters.

Although acute copper poisoning is uncommon in the United States, the historical therapeutic role of copper remains noteworthy. Copper sulfate was used in burn wound débridement until cases of systemic copper poisoning were reported.⁵¹ Interestingly, in one report, each wound débridement procedure was associated with an 8% to 10% fall in the patient’s ­hematocrit. In the 1960s, copper sulfate (250-mg dose, containing 100 mg copper ion) ironically was recommended as an emetic agent, typically for use in children following potentially toxic exposures.⁶⁰ It was recognized for its rapidity of onset and effectiveness, and it compared favorably with syrup of ipecac. However, copper-induced emesis was rapidly identified as a highly dangerous practice, and this use was generally discontinued,^68,111 although fatal cases still occur. Copper salts are administered in religious rituals as a green-colored “spiritual water,” containing 100 to 150 g/L of copper sulfate as an emetic to “expel one’s sins.”^5,110

There is a growing body of knowledge linking copper to the promotion of both physiologic and malignant angiogenesis.⁴⁷ In this latter case, copper may enable tumor expansion, invasion, and metastasis. Additionally, copper binding to amyloid fibers in the brains of patients with Alzheimer disease may lead to local oxidative damage and cause the characteristic neurodegeneration.¹⁹ Copper is also similarly implicated in the pathogenesis of both Parkinson disease and autism.^22,126

Acute or chronic copper poisoning can occur when the metal is leached from copper pipes or copper containers. This occurs frequently when ­carbon dioxide gas, used for postmix soft drink carbonation, backflows into the tubing transporting water to the soda dispensers, creating an acidic solution of carbonic acid that leaches copper from the equipment pipes.¹²² Similarly, storage of acidic potable substances, such as orange or lemon juice, in copper vessels may cause copper poisoning. A particularly dangerous situation occurs when acidic water is inadvertently used for hemodialysis.^35,74 In this circumstance, the leached copper avoids the normal gastrointestinal barrier and is delivered ...