Background: Inorganic lead can interfere with humoral and especially cell-mediated immunity even at frequently occurring (<50 microg/dl) blood lead (Pb-B) levels. Occupational exposure to lead causes a primary impairment of the chemotactic and phagocytic activities of neutrophil leucocytes.
Objective: To verify whether, after taking into account the main confounding factors, occupational lead exposure is shown to induce changes in the number of blood neutrophil leucocytes, and to assess a possible dose-response relationship between Pb-B and the circulating neutrophil count in exposed workers.
Subjects and methods: The study included 68 male lead-exposed (E) workers and 59 male workers in a food plant, recruited as controls (NE). A standardized questionnaire probing work, social, familial and personal medical history was administered to all the subjects. Blood and urine samples were collected to determine the dose and effect biological indices of lead and the total white blood cell and neutrophil counts.
Results: Pb-B levels were significantly higher in E (geometric mean (GM): 20.5 microg/dl; 3.2-120 microg/dl) than in NE workers (GM: 3.5 microg/dl; 1-11 microg/dl). The mean absolute neutrophil count (ANC) was significantly higher in E workers with respect to NE workers. ANC correlated significantly with the biological lead dose and effect indices. Moreover, there was a dose-dependent increase of ANC with increasing Pb-B levels. The linear relationship between ANC and Pb-B was confirmed even after correction for age, body mass index and smoking habit. We also found an interaction between Pb-B level and smoking habit in increasing the number of blood neutrophils in lead-exposed workers.
Conclusion: Our study is the first to describe a dose-dependent effect of lead on ANC in exposed workers. Our results underline the importance of promoting a further reduction of occupational lead exposure levels, adopting adequate individual protection means, as well as conducting medical campaigns against smoking, at the workplace.