A part of any inhaled dust may be swallowed. This process of swallowing is called primary ingestion,
and is of particular importance when the dust originates from very toxic substances. In the 1980s it
became clear that the behavior of the worker could be an important parameter in intake of cadmium and
nickel dust [10]. Factors such as frequency of hand–mouth contact and smoking with contaminated
hands may explain up to 74% concentration variance in blood lead (an uptake measure) in cases of lead
exposure, and up to 48% of the variance in urine chromium concentration (an uptake measure) in cases
of chromium exposure [11,12].
Ingestion following unhygienic behavior is called secondary ingestion and may be responsible for
a major share in the intake (uptake) of dust. Workload and time pressure also affect intake (uptake)
[13,14]. The reason for the importance of ingestion exposure for metal dusts is these dusts show a fast
fall-out rate from air. Thus, concentrations of metal dusts in air may be low, while large amounts have
been deposited as a dust layer on all available surfaces. Dust layers may be touched by unprotected
hands and reach the mouth by hand–mouth contact.