What it is:
- Copper is a soft, ductile and reddish metal found widely in nature as salts such as chlorides, sulfides and arsenides but also as elemental copper.
- Copper forms Cu+1, Cu+2 and Cu+3 compounds with the first two being most common.
- Its atomic weight is 63.54 daltons and its atomic number is 29.
- It is a transition metal even though it has +1 and +2 oxidation states, and its chemistry is quite different from the alkali metals (e.g., sodium) and alkaline earth metals (e.g., calcium).
- The metal has multiple uses and oxidizes in air to a green patina.
Uses of copper:
- The metal is widely used in electrical wiring where its conductivity is second only to silver.
- Its principal uses in the water context are in copper pipe but also in copper/zinc alloy brass fittings.
- Copper has biocidal properties, copper sulfate is used as an algicide in source waters and other copper compounds are used as fungicides and in wood preservatives.
- It has been considered a water disinfectant or bacteriostat since at least 400 B.C., but it is slow acting.
- Copper/silver ionization systems are used for controlling legionella in plumbing.
- Some microorganisms can develop resistance to metal toxicity.
Occurrence and exposure:
- Copper is detected in virtually all drinking water sources, usually at less than a few tenths mg/l, but it can exceed 1 mg/l if the water is corrosive.
- The higher concentrations are usually caused by the action of some waters on a copper pipe or brass fixtures, if the corrosivity is not controlled. This occurs if the water is acidic or in high carbonate waters with alkaline pH.
- Copper is common in many foods at approximately mg/100g levels, e.g., seafood, kale, mushrooms, cashews.
- Copper is an essential dietary micronutrient important for functioning of numerous proteins and metalloenzymes that involve growth, bone, brain and heart maintenance, red cell formation, iron absorption as well as cholesterol and glucose metabolism.
- The Recommended Daily Allowances (RDA) and Recommended Daily Intakes are 2,000 and 900 micrograms per day, respectively. So, there is some uncertainty. Mineral supplements typically contain 0.9 to 2 mg of copper.
- It is very toxic at doses approaching 5 mg/kg body weight/day, and the absorption plateau occurs at about 100 µg/kg/day. Adequate intake ranges about 11 to 34 µg/kg/day, and 8.5 µg/kg/day is deficient.
- About 30 to 40 percent of dietary copper is absorbed in the gastrointestinal (GI) tract with water uptake being more efficient than from foods.
- Wilson’s and Menkes are among several rare hereditary genetic diseases that involve the inability to appropriately manage and use copper.
- The incidence of Wilson’s disease is one per 30,000 births and is now treatable; Menkes is about one per 200,000 and is fatal.
- Copper is analyzed by ICP-MS (EPA 200.8) as well as by graphite furnace atomic absorption (EPA 200.9). Detection levels are low parts per billion (ppb) to sub ppb.
- There are numerous test kits for copper in water that are fast and low in cost per test.
- Copper should be controllable by pH and alkalinity adjustment if the source is copper pipe corrosion.
- Removal techniques include cation exchange water softening; POU reverse osmosis (RO) is also effective.
- The U.S. drinking water SMCL is 1 mg/l; the World Health Organization (WHO) guideline is 2 mg/l. Both are based upon taste and potential gastric upset, which can occur at a few mg/l and are probably exacerbated by consumption in acidic juices.
- The Lead and Copper Rule uses the measurement of lead and copper in one liter, overnight, first-draw stagnant water samples as indicative of excessive corrosivity of the water.
- The Action Level (not MCL) for copper is 1.3 mg/l and lead is 0.015 mg/l.
Dr. Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the U.S. EPA Drinking Water Standards Division.