Unless the fumes come from a burning cigarette, inhalation exposure primarily occurs in the workplace.Cadmium compounds are inhaled as particulate matter, either as fumes with very small particle size or as dust.
After inhalation exposure, the absorption of cadmium compounds may vary greatly. and depends upon the particle sizes and their solubility. Large particles, dusts, (>10µm in diameter) tend to be deposited in the upper airways, while small particles, fumes, (approximately 0.1 µm) tend to penetrate into the alveoli. While some soluble cadmium compounds (CdCl2 and CdSO4) may undergo limited absorption from particles deposited in the respiratory tree, the major site of absorption is the alveoli. Only about 5% of particles > 10µm in diameter will be deposited, up to 50% of particles <0.1 µm will be deposited, and between 50-100% of cadmium deposited in the alveoli will ultimately be absorbed. Thus particle size, which controls alveolar deposition, is a key determinant of cadmium absorption in the lung.
In humans, figures of 10-30% of absorption rate according to particle size are derived for Cd dusts. For Cd fumes, based on cigarette smoke studies, it can be calculated that the respiratory absorption of Cd fumes is between 25% and 50%.
The respiratory Cd intake can be diverted to the gastro-intestinal tract due to the clearance of Cd deposited on the mucosa of nasopharynx, trachea or bronchi. It can also be deposited in the alveoli and from there be absorbed into the blood.
Depending on the dietary intake and the iron status, it has been estimated that a European or an American adult absorbs cadmium orally at an average rate varying between 1.4 and 25 µg/day. The cadmium absorption from the gastrointestinal tract is usually about 5%. However it varies considerably and subjects with iron deficiency may absorb up to 10%.
For a given individual, the absorption following oral exposure to cadmium is likely to depend on physiologic status (age; body stores of iron, calcium, and zinc; pregnancy history; etc.) and, also, on the presence and levels of ions (Zn) and other dietary components ingested with the cadmium.
Absorption of cadmium through the skin is extremely low (0.5%) and would be of concern only in situations where concentrated solutions would be in contact with the skin for several hours or longer.