Exceedance of the RfD does not imply that an adverse health effect would necessarily occur. As the amount and frequency of exposures exceeding the RfD increase, the probability of adverse health effects also increases. The largest airborne sources of cadmium in the environment are the burning of fossil fuels such as coal or oil and the incineration of municipal waste materials. Cadmium may also escape into the air from zinc, lead, or copper smelters. Application of phosphate fertilizers or sewage sludge may increase the cadmium levels in soil, which, in turn, can cause increased cadmium levels in food.
Smokers have about twice as much cadmium in their bodies as do nonsmokers.
The amount of cadmium present in blood or urine can be measured by atomic absorption spectrophotometry and used as an indication of cadmium exposure. A single acute exposure to high levels of cadmium can result in long-lasting impairment of lung function. Other effects noted from chronic exposure to cadmium in air in humans are effects on the lung, including bronchiolitis and emphysema. These data also permit calculation of pharmacokinetic parameters of cadmium absorption, distribution, metabolism, and elimination. Oral exposure may cause reproductive effects in humans, but only at high levels of exposure.