A Correlative Study on Red Blood Cell Parameters and Urine Trans,Trans-Muconic Acid in Subjects with Occupational Benzene Exposure

Abstract

Benzene is of particular concern because of recent research indicating that benzene exposure can result in toxicity. The hematotoxic effect of benzene is mentioned. However, there is little knowledge about the correlation between the biomarker of benzene exposure and changes in red blood cell parameters. Here, the correlation between the urine trans, trans-muconic acid (ttMA) level and red blood cell parameters were studied in 30 Thai subjects at risk. The regression analysis shows no significant correlation between urine ttMA and any studied red cell parameters (Hb, MCV or MCH). Based on our hematologic data, we proposed that only investigation for the urine ttMA might be not sufficient in detection of alteration in red blood cell parameters in the exposed population. Combinations between biomarker and hematological test are recommended.

Introduction

Benzene is of particular concern because recent research indicating that benzene exposure can result in toxicity (Chocheo, 2000). At present, work with benzene is subject to the Control of Substances Hazardous to Health (COSHH) Regulations (Agency for Toxic Substances and Disease Registration, 1997). Hence, benzene exposure is of particular concern because of ongoing exposure to thousands of workers in the industrial plants. Monitoring for benzene exposure among the at-risk workers is recommended and of several biomarkers, urine trans, trans-muconic acid (ttMA) determination is a helpful test for monitoring (Dor et al., 1999; Suwansaksri and Wiwanitkit, 2000; Wiwanitkit et al., 2001). Presently, urine ttMA level is a good indicator of exposure level to benzene (Dor et al., 1999; Suwansaksri and Wiwanitkit, 2000; Wiwanitkit et al., 2001).

Symptoms of benzene intoxication include headache, dizziness, fatigue, muscular weakness, drowsiness, and poor coordination with staggering gait, skin paresthesia, collapse, and coma (Ross, 1996). The hematotoxic effect of benzene is mentioned (Kalf, 1987). Anemia is a common hematological manifestation due to benzene intoxication (Kalf, 1987). However, there is little knowledge about the correlation between the biomarker of benzene exposure and changes in red blood cell parameters. In this study, the authors aimed to determine the correlation between urine ttMA level among a sample of exposed subjects to the red blood cell parameters.

Materials and Methods

Subjects

Thirty healthy Thai volunteers were included in this study. These subjects had to work daily in the same workplace in an urban area of Bangkok, namely the Pathumwon subdistrict. All subjects gave informed consent. The Faculty of Medicine, Chulalongkorn University, approved the study. Each subject provided a urine sample and an EDTA blood sample for laboratory analysis.

Laboratory Analysis

Urine Sample

All collected samples in this study were sent to the laboratory for further analysis for ttMA level. Determination of ttMA level was performed using the method described by Wiwanitkit et al. (2001b). All laboratory analysis were performed at the standard laboratory (Special Laboratory, Bangkok, Thailand)

Blood Sample

All collected samples in this study were sent to the laboratory of for further analysis for red blood parameters (hemoglobin: Hb, mean corpuscular volume: MCV and mean corpuscular hemoglobin: MCH). The automated hematology analyzer Technicon H*3 RTC was used in laboratory analysis.

Statistical Analysis

Data from all laboratory examinations in this study was systematically comprehensively collected for further statistical analysis. The statistical analysis of the results was carried out using the SPSS 7.0 for Windows Program. The correlation between urine ttMA level and each red blood cell parameter was assessed. For comparison of the value of ttMA, the unpaired t–test was used. Statistical significant difference was accepted at p value ±0.05.

Results

The averages (mean ± SD) of urine ttMA and red blood cell parameters of the volunteer subjects were shown in Table 1, respectively. The results from correlation study are shown in Table 2.

Discussion

Benzene is of particular concern because recent research indicates that benzene exposure can result in several toxicities (Ross, 1996). Benzene exposure must be of particular concern because of ongoing exposure to thousands of workers in the industrial plants. The international organizations such as Agency for Toxic Substances and Disease Registry (ATSDR, 1997) have well documented benzene toxicity and recommend monitoring of benzene exposure for the risk group.

Although benzene may not cause cancer as carcinogen does, however, repeated or prolonged contact with the liquid may cause removal of natural lipids from the skin, resulting in dry, fissured dermatitis. Also, prolonged exposure can cause chronic toxicity (Ross, 1996). Similar to other hydrocarbon solvent exposure, anemia in combination with thrombocytopenia or leukocytosis with decreased enzyme activity of the granulocyte alkaline phosphatase can be seen in the subjects exposed to benzene (Hristeva-Mirtcheva, 1998). The mechanism of benzene-induced anemia remains unclear, but is likely to involve: (a) metabolism of benzene in the liver; (b) transport of metabolites to the marrow and their secondary activation to toxic quinones and free radicals by peroxidase enzymes; (c) induction of apoptosis, DNA damage and altered differentiation in early progenitor cells; and (d) depletion of the stem cell pool (Smith, 1996).

In occupational medicine, urine ttMA is measured to diagnose benzene accumulation. It is a good and easy-to-perform biomarker for measure of both acute toxicity and chronic exposure: high urine ttMA means higher exposure. However, there is no correlative study between the level of urine ttMA and the red blood cell parameters. Here, the authors report the correlation between the urine biomarker for benzene exposure, ttMA and the red blood cell parameters.

Here, we can detect no significant correlation between urine ttMA and Hb, MCV or MCH in our volunteers. Classified into two groups using the reported upper normal limit of urine ttMA (0.11 mg/gCreatinine) (Wiwanitkit et al., 2003), the subjects with high urine ttMA also presented no significant difference of red blood cell parameters comparing to those with low urine ttMA level (Table 3). Although the higher urine ttMA means a higher benzene exposure, no correlation between this urine biomarker and the observed hematological change in red blood cell among our subjects

Indeed, Hristeva-Mirtcheva (1998) proposed no definite relationship between changes in peripheral blood elements and length of service of the workers. Based on our hematologic data, we proposed that only investigation for the urine ttMA might be not sufficient in detection of alteration in red blood cell parameters in the exposed population. Combination between biomarker and hematological test are recommended. Further studies with larger sample size focusing on the details of pathogenesis of red blood cell disorders are also recommended.