CHAPTER 2-50: CHROMIUM

INTRODUCTION

Chromium is a durable metal used in electroplating, paint pigments (chrome yellow), primers and corrosion inhibitors, wood preservatives, textile preservatives, and leather tanning agents. Chromium exposure may occur by inhalation, ingestion, or skin exposure. Although chromium can exist in a variety of oxidation states, most human exposures involve one of two types: trivalent (eg, chromic oxide, chromic sulfate) or hexavalent (eg, chromium trioxide, chromic anhydride, chromic acid, dichromate salts). Toxicity is associated most commonly with hexavalent compounds; however, fatalities have occurred after ingestion of compounds of either type, and chronic skin sensitivity probably is related to the trivalent form. Chromium picolinate is a trivalent chromium compound often promoted as a body-building agent.

MECHANISM OF TOXICITY

1. Trivalent chromium compounds are relatively insoluble and noncorrosive and are less likely to be absorbed through intact skin. Biological toxicity is estimated to be 10- to 100-fold lower than that of the hexavalent compounds.

2. Hexavalent compounds are powerful oxidizing agents and corrosive to the airway, skin, mucous membranes, and GI tract. Acute hemolysis and renal tubular necrosis may also occur. Chronic occupational exposure to less soluble hexavalent forms is associated with chronic bronchitis, dermatitis, and lung cancer.

3. Chromic acid is a strong acid, whereas some chromate salts are strong bases.

TOXIC DOSE

1. Inhalation. The OSHA workplace permissible exposure limit (PEL, 8-hour time-weighted average) for chromic acid and hexavalent compounds is 0.05 mg/m³ (carcinogen). For bivalent and trivalent chromium, the PEL is 0.5 mg/m³.

2. Skin. Chromium salts can cause skin burns, which may enhance systemic absorption, and death has occurred after a 10% surface area burn.

3. Ingestion. Life-threatening toxicity has occurred from ingestion of as little as 500 mg of hexavalent chromium. The estimated lethal dose of chromic acid is 1–2 g, and of potassium dichromate 6–8 g. Drinking water standards for total chromium are set at 0.1 mg/L (100 ppb).

CLINICAL PRESENTATION

1. Inhalation. Acute inhalation can cause upper respiratory tract irritation, wheezing, and noncardiogenic pulmonary edema (which may be delayed for several hours to days after exposure). Chronic exposure to hexavalent compounds may lead to pulmonary sensitization, asthma, and cancer.

2. Skin and eyes. Acute contact may cause severe corneal injury, deep skin burns, and oral or esophageal burns. Hypersensitivity dermatitis may result. It has been estimated that chronic chromium exposure is responsible for about 8% of all cases of contact dermatitis. Nasal ulcers may also occur after chronic exposure.

3. Ingestion. Ingestion may cause acute hemorrhagic gastroenteritis; the resulting massive fluid and blood loss may cause shock and oliguric renal failure. Hemolysis, hepatitis, and cerebral edema have been reported. Chromates are capable of oxidizing hemoglobin, but clinically significant methemoglobinemia is relatively uncommon after acute overdose.

DIAGNOSIS

Is based on a history of exposure and clinical manifestations such as skin and mucous membrane ...