Olfactory function in workers exposed to moderate airborne cadmium levels

The present study investigated the olfactory function in workers exposed to moderate airborne cadmium (Cd) levels, with the purpose of identifying possible early adverse effects of the metal, not demonstrable with the traditional diagnostic methods.

The exposed group consisted of 33 men employed in cadmium fusion, sintering and alloys lamination. Two reference groups were considered: the first consisted of 39 subjects assigned to manual workings, but not exposed to harmful substances for olfaction (drivers, warehousemen); the second was characterized by 23 subjects exposed to iron and steel welding fumes (iron base alloys), non-specific irritants on the respiratory tract. Olfactory threshold and odor identification ability were separately quantified. Individual occupational exposure was studied by calculating the mean blood and urinary cadmium values (CdB and CdU, respectively) of the five years period during which, for each worker, the highest levels of dose indicators were measured. As indicator of renal tubular damage, urinary beta(2)-microglobulin levels in the same quinquennium were monitored.

Mean olfactory threshold scored significantly higher in Cd workers (-5.26 log(10)v/v, P=0.02) than did in controls (welders: -5.78 log(10)v/v; P=0.26 compared to non-exposed -6.37 log(10)v/v). The odor identification test findings for Cd workers were similar to those of the reference groups. Moderate blood and urine cadmium levels (mean CdB 3.7 microg/l; mean CdU 4.4 microg/g creatinine) accompanied threshold impairment. Olfactory threshold weakening was confirmed in the subgroup of Cd workers in which urinary beta(2)-microglobulin never exceeded 300 microg/l (-5.41 log(10)v/v; P=0.045 compared to non-exposed).

These data suggested that possible early toxic effects of the metal can occur at low levels, close to the limits proposed by the American Conference of Governmental Industrial Hygienists (ACGIH), confirming the hypothesis that primary olfactory neuron may represent the early target for cadmium toxic action. The action of the metal seemed to be due to an elective tropism for the olfactory epithelium and not to a non-specific irritant effect on the nasal cavity. The mechanism of this effect did not appear linearly dose-related. These findings underline the importance of olfactory tests to identify the early effects of xenobiotics even at low-exposure levels, and to contribute to verify the adequacy of the current exposure limits.