Objectives Benzene is a well-known haematological toxin causing aplastic anaemia and leukaemia. Recent studies showed that low level benzene less than 1ppm disturbs the hematopoietic system. However, other studies did not show consistent results. The aim of the present study was to examine the relationship between low level benzene exposure and blood cell counts in Korean workers.

Method Blood cell counts of benzene exposed workers were retrieved from a nationwide Worker’s Health Examination Database from 2003 to 2008. If a worker did not take a blood test for benzene during 2003–2004, the worker was regarded as a first exposed. Personal air benzene monitoring records were retrieved from nationwide Work Environment Monitoring Database from 2004–2008. Mean benzene levels were calculated and assigned for the various combinations of factory/industry/process codes. Mixed-effects models were employed to examine associations between benzene level, and the numbers of WBC, RBC, platelet, segmented neutrophil, lymphocyte and monocyte.

Results 11 281 workers took blood tests during 2005–2008 for the first time. 8679 personal benzene measurements during 2004–2008 across industries were collected. RBC counts showed a significant negative association with low level benzene exposure with a dose-response relationship. WBCs also showed negative association, but did not show a dose-response relationship. Among WBCs, lymphocyte showed a stronger association with low level benzene than other cell types.

Conclusions Our findings support the hematotoxicity of low level benzene exposure. Further study with direct benzene measuring for first exposed workers is needed to confirm the low level benzene toxicity in Korean workers.