Agency for Toxic Substances and Disease Registry 
Case Studies in Environmental Medicine (CSEM) 
Chromium Toxicity
What Are the Routes of Exposure for Chromium?

Learning Objectives

Upon completion of this section, you will be able to

• identify the routes of exposure to chromium.

Introduction

The entry routes of chromium into the human body are inhalation, ingestion, and dermal absorption. Occupational exposure generally occurs through inhalation and dermal contact, whereas the general population is exposed most often by ingestion through chromium content in soil, food, and water.

Inhalation

After human exposure to Cr(III) by inhalation, urinary concentrations of chromium were found to be increased indicating respiratory absorption [Aitio, Jarvisalo et al. 1984; Foa, Riboldi et al. 1988; Dayan and Paine 2001].

Data from a few animal experiments indicate that with equal solubility, Cr(VI) compounds are absorbed more readily than Cr(III) compounds, probably because Cr(VI) readily penetrates cell membranes [Mertz 1969; Wiegand, Ottenwalder et al. 1984].

Cr(VI) is reduced to Cr(III) in the lower respiratory tract by the epithelial lining fluid and by pulmonary alveolar macrophages [Dayan and Paine 2001]. One study showed that at equivalent numbers of cells, the reducing efficiency of alveolar macrophages by biochemical mechanisms was significantly greater in tobacco smokers than in nonsmokers [Petrilli, Rossi et al. 1986].

Ingestion

In general, Cr(VI) compounds are better absorbed through the intestinal mucosa than the Cr(III) compounds. However, due to the actions of stomach acid and other components within the gastrointestinal tract, most of an ingested Cr(VI) dosage is converted to Cr(III) [Cohen, Kargacin et al. 1993]. In humans and animals, less than 1% of inorganic Cr(III) and about 10% of inorganic Cr(VI) are absorbed from the gut; the latter amount is slightly higher in a fasting state [Donaldson and Barreras 1966; Dayan and Paine 2001].

Skin

Data from volunteers and indirect evidence from occupational studies indicate that absorption of Cr(VI) compounds can occur through intact skin [Baranowska-Dutkiewicz 1981]. Studies in experimental animals showed poor absorption of Cr(III) compounds following dermal route [Dayan and Paine 2001].

Key Points

• Occupational exposure generally occurs through inhalation and dermal contact, whereas the general population is exposed most often by ingestion through chromium content in soil, food, and water.
• The majority of Cr(VI) that enters the body via inhalation or ingestion is quickly reduced to Cr(III).

Progress Check

To review relevant content, see Introduction in this section.