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Elemental iodine hazards
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James Offline

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Elemental iodine hazards

Health Hazards

A. General

Iodine is an essential constituent in the diet and is required for normal function of the thyroid gland. Dietary iodine reaches the circulation in the form of iodide (I−) (Hardman et al., 1996). Long-term ingestion of iodine in amounts that exceed dietary requirements may lead to iodism (see chronic effects section C). The direct acute toxicity of iodine is due to its irritant properties (NAS, 1980). In excessive amounts, elemental iodine (I2) is corrosive and irritates tissue via all routes of exposure (inhalation, ingestion, and skin contact). Airborne iodine is an irritant of the respiratory system, eyes, and skin, and may have adverse effects on the central nervous system and cardiovascular system (Genium, 1999). Pharmaceutical solutions applied to the skin or ingested generally have low toxicity. However, in rare instances, an individual may display hypersensitivity to skin contact with iodine. Symptoms of hypersensitivity include fever and generalized skin reaction (Hardman et al., 1996).

B. Acute Effects

Acute toxicity may result from short-term exposure to a high concentration or a large amount. In adults, an average fatal dose of ingested iodine crystals or powder has been estimated to be two
to four grams. Ingestion causes burns in the mouth, vomiting, abdominal pain, and diarrhea. Severe intoxication may result in headache, delirium, and a drop in blood pressure. Inhalation causes eye and nose irritation and tightness in the chest. Skin contact causes burns, irritation, and rash (Genium, 1999).

C. Chronic Effects

Repeated ingestion of iodine in amounts that exceed dietary requirements results in a toxic syndrome called iodism. Initial symptoms of iodism are an unpleasant brassy taste, burning of the mouth and throat, and soreness of the teeth and gums. Increased salivation, inflammation of mucous membranes of the nose (rhinitis), eye and mouth, sneezing, laryngitis, bronchitis, and skin rashes are frequently observed (Hardman et al., 1996). Prolonged intake of very large amounts of iodine (approximately ten times the recommended daily dietary allowance) can lead to enlargement of the thyroid, a condition called goiter (NAS, 1980). Studies of the effects of long-term inhalation of iodine vapors by humans are not available. Studies in laboratory animals indicate that long-term inhalation of iodine vapor disrupts thyroid function and reduces the ability of the lungs to take up oxygen. Adverse changes in the lungs of exposed animals include edema, scaling of bronchial epithelium, and bleeding (HSDB, 2001).

D. Skin Contact

Contact with iodine produces irritation and damage. In rare instances, skin contact with iodine produces a sensitization reaction, characterized by generalized skin eruptions and fever. Contact with strong iodine solutions may cause burns (AIHA, 2002). Small amounts of iodine may be absorbed through the skin (NAS, 1980).

E. Eye Contact

Eye contact with saturated iodine vapor causes brown staining of the outermost cell layer of the cornea (the corneal epithelium) followed by spontaneous loss of these cells. However, recovery is usually complete in 2-3 days. Eye contact with 4% iodine solution (tincture) initially produces
pain and inflammation, with subsequent loss of the corneal epithelial cells, but recovery from the initial injury is generally complete within a few days. Exposure to iodine vapor at a concentration of 1.6 ppm for just two minutes is sufficient to cause eye irritation. The threshold for eye irritation
is reported to be 0.2 ppm (2 mg/m3), which is significantly below the odor threshold (0.8 ppm, or 9 mg/m3) (AIHA, 2002).

F. Inhalation

Inhalation of iodine vapor is extremely irritating to the respiratory tract, causing tightness in the chest and sore throat. Iodine vapors increase airflow resistance in the lungs (AIHA, 2002). Inhalation may result in spasm, inflammation, and fluid accumulation (edema) in the voice box,
upper airways, and lungs (Aldrich, 2001). Lung edema may be delayed (Genium, 1999). Symptoms may include coughing, wheezing, laryngitis, and shortness of breath (Aldrich, 2001). Some individuals may develop hypersensitivity to inhaled iodine vapor.

G. Ingestion

Ingested iodine reportedly has a metallic taste and stains oral mucous membranes brown (HSDB, 2001). The toxic effects of ingested iodine are primarily due to its corrosive action on the gastrointestinal tract (Hardman et al., 1996). Ingested iodine may cause vomiting, a drop in blood pressure, headache, and delirium. Food in the stomach inactivates iodine by converting it to iodide (I-), which is significantly less toxic (HSDB, 2001). Iodine is an essential micronutrient in the diet. The iodine in food is generally present in the form of iodate (IO3−), which has a low order
of toxicity. Major sources of dietary iodine are iodized salt, bread, milk, marine fish, and seafood (NAS, 1980). The recommended daily dietary allowance for iodine intake by adults is 150 µg/day; slightly higher intakes are recommended for women who are pregnant or lactating, 175 and 200 µg/day, respectively (Hardman et al., 1996).

H. Predisposing Conditions

Pre-existing conditions that have the potential to increase susceptibility to iodine toxicity include diseases of the thyroid, lungs, and kidneys.

I. Special Concerns for Children

Iodides diffuse across the placental barrier and into breast milk. Infant death from respiratory distress secondary to goiter (enlargement of the thyroid) has been reported as a result of mothers taking medications containing iodides (Meditext, 2003). Compared to adults, children have a
greater ratio of lung surface area to body weight. Similarly, the ratio of respiratory minute volume to body weight is greater in children than adults. Therefore, at any given concentration of iodine in air, children will probably receive a larger dose than adults will. The vapor density of iodine is much greater than that of air. Therefore, higher concentrations of iodine are likely to be found closer to the ground. Because of their short stature, children may be exposed to higher concentrations of iodine vapor than adults. Children may be more susceptible to the toxic effects of iodine vapor because they are often less likely to leave an area where iodine vapor is present.
06-24-2012 07:48 PM
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