For the past five years, a team at the University of Chile’s Institute of Nutrition and Food Technology in Santiago, led by Magdalena Araya, has been assessing the response of healthy adults to varying concentrations of copper in drinking water. Their goal is to define safe limits for the early, acute effects of excessive copper exposure via drinking water. Their latest report verifies earlier findings that gastrointestinal symptoms such as nausea, abdominal pain, diarrhea, and vomiting occur when copper concentrations reach 4.0–6.0 milligrams per liter (mg/L) [EHP 112:1068–1073]. This provides the best confirmation to date that the World Health Organization’s (WHO) current drinking water limit for copper of 2.0 mg/L is reasonable.
Copper is an essential nutrient needed to prevent anemia and keep the skeletal, reproductive, and nervous systems healthy. The U.S. National Research Council currently recommends that adults receive 1.5–3.0 mg of copper daily to prevent deficiencies. However, the health effects of high copper intake are poorly understood.
Reports of copper poisoning are uncommon, and are linked to eating fruit sprayed with copper fungicides, cooking food in copper vessels, or ingesting grams of copper sulfate in suicide attempts. In such cases, copper toxicosis damages the liver and kidneys. The copper content of most of the world’s natural water supplies does not exceed more than a few milligrams per liter, although concentrations can be higher in well water and in hard water delivered through newly installed copper pipes.
Araya and colleagues are working to identify markers of early biologically relevant effects of copper deficiency and excess. Past studies have shown that gastrointestinal symptoms are better indicators of acute exposure to copper than biochemical markers, such as blood copper, serum ceruloplasmin, and the activity of liver enzymes. According to Araya, copper absorption from food is unlikely to induce acute gastrointestinal responses, whereas the pH of water favors copper solubilization and absorption, which induce gastrointestinal effects. Therefore, it becomes important to define the copper concentrations in drinking water that cause gastrointestinal symptoms.
The current randomized, double-blind, community-based study monitored 1,365 people from 441 families. The subjects ranged in age from 18 to 60 years. For two months each family’s drinking water was spiked with copper at concentrations of <0.01, 2.0, 4.0, or 6.0 mg/L. The lowest copper intake represented the concentration of copper in Santiago’s tap water. The higher concentrations reflected the WHO guidelines (2.0 mg/L) and levels noted in earlier studies to produce nausea (4.0 mg/L) and vomiting (6.0 mg/L). Participants were told to switch to plain tap water for 48 hours if they experienced any of a list of symptoms. If symptoms recurred after participants resumed drinking the copper-treated water, they were told to permanently switch back to plain water. Each household kept a daily diary of water consumption and symptoms.
About 16% of the participants experienced at least one gastrointestinal symptom, with nausea and abdominal pain described most often. All dosage groups reported some symptoms, although the numbers in the two lowest-dosage groups were not statistically significant. Women reported two-thirds of the symptoms. They also appeared more sensitive to copper than men—for instance, during the first week, women’s symptoms occurred at 4.0 mg/L, compared to 6.0 mg/L for men.
The team’s latest results confirm the findings from their earlier studies, which involved controlled clinical trials with smaller numbers of people. According to the authors, given the lack of statistically significant effects in the lower-dosage groups, the results support the WHO guideline of 2.0 mg/L copper in drinking water as a safe limit.