Telomere length in peripheral leukocytes is a sensitive marker for assessing genetic damage among workers exposed to isopropanol, lead and noise: the case of an electronics manufacturer
Authors: Lu Yao , Liu Xinxia , Zhao Zhiqiang , Ou Xiaoyan , Yang Yarui , Wei Qing , Chen Jingli , Jiang Jun , Sun Yi , Zhao Heping , Wu Sai , He Yun 
Published: December 2021

Abstract
Background
Workers in electronics manufacturers may be exposed to various occupational hazards such as isopropanol, lead, and noise. Telomeres are special segments of cap-like DNA protein complex at end of liner chromosomes in eukaryotic cells. Telomere length is a potential marker of genetic damage. The aim of this study is to evaluate the effect of occupational hazards on the relative telomere length (rTL) of peripheral blood cells of workers in an electronics manufacturer, and to explore whether relative telomere length could be a biomarker for assessing genetic damage in the electronics manufacturing industry.

Methods
We investigated a large-scale electronics manufacturer in the Pearl River Delta Region. We ultimately collected 699 qualified workers (248 with isopropanol exposure, 182 with lead exposure, 157 with noise exposure, and 112 controls). During physical examination of the workers, we gave them questionnaires to understand their health statuses and living habits. We also collected peripheral blood samples from these workers to test exposure levels and rTL in the leucocytes.

Results
The concentrations of air isopropanol in all monitored workshops was 25.3 mg/m3 and air lead smoke was 0.020 mg/m3. The maximum equivalent continuous A sound level noise exposure position was 82.2dB (A). All were lower than those in the Occupational Exposure Limits in Workplaces in China. Urinary acetone in the isopropanol exposed group was 1.04 (0, 1.50) mg/L, and cumulative urinary acetone was 1.48 (0, 5.09) mg-years/L. Blood lead levels (BLLs) were 28.57 (22.77, 37.06) µg/dL, and cumulative blood lead levels (CBLLs) were 92.75 (55.47, 165.13) µg-years/dL. rTL was different between occupational exposed workers and controls: rTL was 0.140 units (95 % CI: 0.022, 0.259) shorter in lead exposed workers and 0.467 units (95 % CI: 0.276–0.658) shorter in noise exposed workers compared to the controls. There is no statistical difference in rTL between isopropanol exposure workers and the controls. In order to elucidate the relationship between rTL and occupational hazards exposure, we divided the isopropanol exposure workers into three groups (0, ~1.43 mg/L, and >1.43 mg/L). None of the rTL difference was statistically significant among exposed workers at different uroacetone levels (P>0.05).
The groups with ≥100 µg/dL blood lead had shorter rTL than the group with blood lead below 100 µg/dL (F=4.422, P=0.013). We incorporated age, gender, birthplace, race, education level, smoking, and alcohol consumption into the linear regression equation. Only blood lead concentration (X) was entered into the regression equation, yielding a multivariate linear regression equation of Y=0.397-0.124X (F=8.091, P=0.005). Workers with different hearing loss also had statistically significant differences in rTL (F=5.731, P=0.004). rTL was a protective factor for the occurrence of noise-induced hearing loss (NIHL). The longer the rTL, the lower the risk of NIHL [OR=0.64 (0.42, 0.98)].

Conclusions
rTL was shorter in lead exposed workers and noise exposed workers, and it was a protective factor for the occurrence of the noise-induced hearing loss. Thus, rTL of peripheral blood may be a sensitive marker of genetic damage among workers in environments with lead and noise exposure.