Cadmium, in its elemental form, occurs naturally in the earth's crust. Pure cadmium is a soft, silver-white metal; however cadmium is not usually found in the environment as a metal but as a mineral combined with other elements such as oxygen (cadmium oxide), chlorine (cadmium chloride), or sulfur (cadmium sulfate, cadmium sulfide). These solid compounds are soluble in water. Cadmium has no definite odor or taste. Most cadmium is extracted during the production of other metals such as zinc, lead, or copper.
The largest source of cadmium release to the general environment is the burning of fossil fuels (such as coal or oil) or the incineration of municipal waste materials. Cadmium may also escape into the air from zinc, lead, or copper smelters. It can enter water from disposal of waste water from households or industries. Fertilizers often contain some cadmium
Food and cigarette smoke are the largest potential sources of cadmium exposure for members of the general population. The average person ingests about 30 micrograms (ug) of cadmium from food each day. Smokers absorb an additional 1 to 3 ug per day from cigarettes. Average cadmium levels in cigarettes range from 1,000 to 3,000 ppb. Average cadmium levels in food range from 2 to 40 parts of cadmium per billion parts of food (ppb). The level of cadmium in most drinking water supplies is less than 1 ppb. Air levels normally range from 5 to 40 ng/m3.
Cadmium is a flammable powder. Toxic fumes are produced in a fire.
Cadmium is highly persistent in water, with a half-life of greater than 200 days.
| BENCHMARKS
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Canadian Water Quality Guidelines
| Drinking water
| 0.005 mg/l
| Protection of freshwater aquatic life
| 0.0002-0.0018 mg/l depending on hardness | (under review) Irrigation
| 0.01 mg/l
| Livestock watering
| 0.02 mg/l
| Ontario Water Quality Objectives Protection of freshwater aquatic life
| 0.0002 mg/l
| Interim Objective under development
| 0.0001 mg/l Hardness 0-100 mg/l CaCO3 | 0.0005 mg/l Hardness >100 mg/l CaCO3 U.S. EPA Drinking water
| 5 ppb
| Interim Maximum Contaminant Level (MCL)
| 0.01 mg/L
| Proposed Maximum Contaminant | Level Goal (MCLG) 0.005 mg/L (5 ug/L).
| No cadmium allowed in pesticides.
| U.S. Food and Drug Administration (FDA) Food colors maximum
| 15 ppm
| The Occupational Safety and Health Administration (OSHA) Workplace air
| 100µg cadmium/m3 air as cadmium fumes | 200 µg cadmium/m3 as cadmium dust Legal airborne permissible exposure limit (PEL)
| 0.2 mg/m3 | averaged over an 8 hour workshift 0.6 mg/m3 not to be exceeded during any (15 minute) work period. OSHA is planning to limit all cadmium compounds to either 1 or 5 µg/cubic meter.
| ACGIH Recommended airborne exposure limit
| 0.05 mg/m3 for cadmium dust | averaged over an 8 hour workshift. A concentration of 0.001 mg/l in freshwater hardness above 100 mg/l CaCO3 is considered harmful to aquatic life. LC50 values Rainbow trout
| 0.0036 mg/l
| Daphnia magna
| 0.056 mg/l
| Fathead minnow
| 0.030 mg/l
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HUMAN HEALTH
Cadmium can enter the blood by absorption from the stomach or intestines after ingestion of food or water, or by absorption from the lungs after inhalation. Very little cadmium enters the body through the skin. Usually only about 1 to 5% of what is taken in by mouth is absorbed into the blood, while about 30 to 50% of that which is inhaled is taken up into the blood. However, once cadmium enters the body, it is very strongly retained; therefore, even low doses may build up significant cadmium levels in the body if exposure continues for a long time.
The amount of cadmium needed to cause an adverse effect in an exposed person depends on the chemical and physical form of the element. In general, cadmium compounds that dissolve easily in water (e.g., cadmium chloride), or those that can be dissolved in the body (e.g., cadmium oxide), tend to be more toxic than compounds that are very hard to dissolve (e.g., cadmium sulfide).
By the inhalation route, airborne concentrations of 1 mg/m3 are associated with acute irritation to the lung, and long-term exposure to levels of 0.1 mg/m3 may increase the risk of lung disease. These same levels are also associated with development of kidney injury similar to that observed following oral exposure. Long-term exposure to a level of 0.02 mg/m3 is thought to pose relatively little risk of injury to lung or kidney. It has been estimated that lifelong inhalation of air containing 1 ug/m3 (0.001 mg/m3) of cadmium is associated with a risk of lung cancer of about 2 in1,000.
For soluble cadmium compounds, an oral dose of about 0.05 mg/kg (3.5 mg in an adult) is considered to be the minimum which causes irritation to the stomach. Long-term intake of up to about 0.005 mg/kg/day (0.35 mg/day in an adult) is believed to have relatively little risk of causing injury to the kidney or other tissues.
Cadmium and zinc are found together in natural deposits and possess similar structure and function in the human body. The zinc-cadmium ratio is very important, as cadmium toxicity and storage are greatly increased with zinc deficiency. Good levels of zinc protect against tissue damage by cadmium. Cadmium is not known to have any beneficial effects, but can cause a number of adverse health effects. Cadmium competes with zinc for binding sites and can therefore interfere with some of zinc's essential functions. It may inhibit enzyme reactions and utilization of nutrients. Cadmium may be a catalyst to oxidation reactions, which can generate free-radical tissue damage. Cadmium may be taken up more readily on a diet low in iron or other nutrients.
Cadmium that enters your body remains in the liver and kidneys. Cadmium is excreted slowly, in urine and feces. Most of the cadmium is stored in a form that is not harmful, but too much cadmium can overload the kidneys' storage system and lead to health problems.
High exposures can cause severe lung damage with shortness of breath, chest pain, cough, and even a buildup of fluid in the lungs. In severe cases death or permanent lung damage occurs. Illness can be delayed for 4 to 8 hours, allowing overexposure without warning.
Non-lethal exposure to high levels of cadmium may cause nausea, salivation, vomiting, cramps, and diarrhea. During heating or grinding operations, cadmium can cause a flu like illness with chills, headache, aching and/or fever.
Emphysema and/or lung scarring can occur from a single high exposure or repeated lower exposures.
Long term exposure can cause anemia, loss of sense of smell, fatigue and/or yellow staining of teeth.
Kidney damage has been observed in people who are exposed to excess cadmium either through air or through the diet. This kidney disease is usually not life-threatening, but it can lead to the formation of kidney stones and effects on the skeleton that are equally painful and debilitating. It may also promote hypertension and heart disease.
Exposure to cadmium (especially cadmium oxide) may increase the risk of lung, prostate, and kidney cancer in humans. There may be no safe level of exposure to a cancer-causing agent.
Cadmium also affects the bones; causing bone and joint aches and pains, a syndrome, first described in Japan, where it was termed the itai-itai ("ouch-ouch") disease. Symptoms of this disease include weak bones that lead to deformities, especially of the spine, or to more easily broken bones. It is often fatal.
Cadmium may damage the testes (male reproductive glands) and may affect the female reproductive cycle.
Cadmium levels in humans tend to increase with age (probably because of chronic subtle exposure), usually peaking at around age 50 and then leveling off.
No cadmium is present in newborns; cadmium does not cross the placenta-fetal barrier nor the blood-brain barrier as lead and mercury do. Exposure during pregnancy may not be toxic to fetuses, nor does it cause the mental and brain symptoms of lead and mercury.
It is a probable teratogen in humans.
Cadmium appears to depress some immune functions, mainly by reducing host resistance to bacteria and viruses.
To protect against cadmium toxicity, avoid cadmium exposure and intake by minimizing smoking and exposure to cigarette smoke, avoiding refined foods, shellfish, coffee, tea, and soft water and maintain good zinc levels by eating high-zinc foods, such as whole grains, legumes, and nuts (oysters are high in zinc but also high in cadmium). Taking additional zinc, 15-30 mg. daily in a supplement, will offer further protection against cadmium problems.
MEDICAL TESTS
Tests are available that measure cadmium in blood, urine, hair, or nails.
The amount of cadmium in blood is a good indicator of recent exposures whereas the amount in urine is a reflection of how much total cadmium is present in the body. Urine tests can indicate kidney damage. The amount of cadmium in hair is not usually considered to be reliable, since cadmium can bind to the outside of hair and give faulty results.
Below 2 ppm in hair and .015 ppm in whole blood are considered current normal ranges for body cadmium levels. The levels of cadmium in a urine test should be less than 10 micrograms per liter of urine.
Another approach is to measure cadmium concentrations in the liver or kidney, using a process called neutron activation analysis. While this method gives a very useful indication of the amount of cadmium in the body, it is usually too costly and inconvenient for routine use.
ANIMAL HEALTH
Animals given cadmium in food or water show iron-poor blood, liver disease, and nerve or brain damage.
Inhaling cadmium causes liver damage and changes in the immune system in rats and mice.
Reproductive and developmental effects have been observed in rats and mice treated with cadmium.
Cadmium has been shown to cause lung and testes cancer in animals.
In rat studies, higher levels of cadmium are associated with an increase in heart size, higher blood pressure, progressive atherosclerosis, and reduced kidney function.
High blood pressure has been observed in animals exposed to cadmium.
Acute toxic effects may include the death of animals, birds, or fish, and death or low growth rate in plants.
Cadmium has high acute toxicity to aquatic life.
The concentration of cadmium found in fish tissues is expected to be much higher than the average concentration of cadmium in the water from which the fish was taken.
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