What it is:
- Cadmium is a silvery white metal found in ores in combined forms concurrently with other metals, especially zinc.
- It is present in plants, rocks and foods in small amounts and in the air from combustion.
- The oxide is formed and dispersed into the air when fossil fuels and municipal wastes are combusted.
- It is in the same chemical family as zinc and they have similar chemical properties, but cadmium is significantly more toxic than zinc.
- Its atomic number is 48 and its atomic weight is 112.4 g/mole.
- Cadmium forms numerous salts, e.g., cadmium chloride, CdCl2, which is soluble in water, and cadmium sulfide, CdS, which is insoluble.
- Because of their chemical similarities zinc, including galvanized coatings, often contains small amounts of cadmium.
The uses of cadmium:
- Cadmium is used as the anode in nickel cadmium rechargeable batteries.
- It is used in electroplating as a coating on screws and bolts, in solar cells and plastic stabilizers.
- There are several cadmium-based pigments in glass, plastics, ceramics and paints that provide bright yellow, orange, red and maroon coloring.
Occurrence and exposure:
- Recent U.S annual production is about 600 metric tons per year, which is declining.
- Occupational exposure to cadmium mostly by inhalation is significant in many manufacturing activities including metal refining and welding.
- Many foods including plants, animal livers and kidneys contain traces of cadmium.
- Daily intake from food in the U.S. is in the range of 8 to 30 micrograms (0.008 to 0.030 mg/day).
- Water is a minor source of exposure; only two of 983 groundwaters exceeded the 0.005 mg/l MCL in the 1988 National Inorganics and Radionuclides Survey, and 979 of 983 supplies had less than 0.002 mg/l.
- Tobacco is an important source; two to four micrograms are inhaled by smoking a pack of cigarettes.
Health considerations:
- Cadmium compounds are considered to be carcinogenic by inhalation but not by ingestion.
- It is estimated that only two to six percent of ingested cadmium is taken up by the body compared to 30 to 64 percent of inhaled cadmium.
- The kidney is the general target organ where it accumulates, as well as the lung from inhaled cadmium.
- Cumulative exposure to cadmium is tracked by its concentration in urine.
- Irreversible kidney damage occurs from excess acute and chronic exposure, leading to kidney failure and also indirect consequences of kidney damage such as hypertension, muscle weakness and gout.
- Itai-itai disease in Japan was associated with cadmium in the 1960s and is one of the frequently cited examples of disease from environmental contamination. However, it probably occurred for over 100 years because of uncontrolled mining and manufacturing waste releases in the area.
Analytical methods:
- Cadmium is analyzed by ICP-MS (EPA 200.8) as well as by graphite furnace atomic absorption spectrometry (EPA 200.9). Detection levels are low, parts per billion (ppb) to sub ppb.
- Cadmium can also be analyzed by ion chromatography.
Water treatment:
- Cadmium is removable by conventional drinking water treatment and lime softening.
- Cation exchange water softening POE and POU reverse osmosis (RO) would also be effective.
Regulation:
- The drinking water MCL is 0.005 mg/l; the WHO guideline is 0.003 mg/l.
- The Drinking Water Health Advisories for short-term exposure are 0.040 mg/l for one- and 10-day exposures and 0.005 mg/l for lifetime exposure.
- Very few drinking water supplies have been reported to be exceeding the MCL — e.g., one in California.
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.
