Benzene is a carcinogenic unsaturated closed-chain aromatic hydrocarbon compound ( ATSDR, 2007). Benzene has been known as a good organic solvent for various processes in the industry such as the rubber industry, shoes, paint solvents, components in motor fuels, components in detergents, pesticides, and pharmaceutical manufacturing ( Paustenbach et al., 1992; Wijaya, 1993). One informal sector that is often exposed to benzene is the car paint shop. The car painting work area is one of the areas that requires attention due to its increasing number with a large risk of occupational diseases. The car painting process uses solvents containing benzene as the main ingredient in the work process which can have a detrimental effect on health. These materials enter the body through absorption with more presentation through inhalation due to exposure to steam in the process of spray painting ( Coresh et al., 2007).

Continuous benzene exposure can cause health effects. The body is continually exposed to benzene which causes symptoms and signs of chronic poisoning such as headaches, dizziness, nausea to vomiting, and slow-in-pale reactions due to anemia which is often accompanied by bleeding under the skin and mucosa. The clinical effects of benzene systemically cause cardiovascular, respiratory, neurological, gastrointestinal, liver, kidney, endocrine and reproductive systems, dermatology, local effects, hematological, immunological, metabolic, and allergic reactions ( ATSDR, 2007; Cronkite et al., 1989; McHale et al., 2012; Tunsaringkarn et al., 2013).

In 2007 the ( American Conference of Governmental Industrial Hygienists (ACGIH), 2007) issued a benzene chemical threshold of 0.5 ppm and since 1997 benzene has been confirmed to have carcinogenic properties in humans (Al = confirmed human carcinogen). The National Institute for Occupational Health and Safety (NIOSH) in 2010 set a recommended exposure limit or REL (Recommended Exposure Limit) of 0.1 ppm for 8 working hours ( NIOSH, 2010). The threshold value of chemical factors at work according to Minister of Manpower and Transmigration number 13 in 2011 is 0.5 ppm. The benzene exposure pathway enters the human body in three ways, namely absorption through the skin, inhalation, and ingestion. Inhalation is a very important route to consider because benzene has volatile properties ( ATSDR, 2007).

Benzene which enters the body oxidizes to proteins, lipids and produces Malondialdehyde (MDA). An increase in MDA levels is a sign of an increase in free radicals in the blood. Increased MDA levels even become a benchmark to determine the risk of cancer that will occur in workers exposed to benzene. Exposure to benzene in high content causes narcotic effects and irritation to the eyes and airways ( Ho et al., 2006). Long-term exposure to low content can result in bone marrow suppression and can be associated with leukemia events or other blood cell disorders. The population of workers who work in the car painting industry or use benzene can be exposed to the highest exposure levels. For this reason, special attention needs to be paid to workers for occupational safety and health.

Exposure to benzene and alkyl benzene has been linked to kidney and liver injury and kidney cancer ( Brautbar et al., 2006; Henderson, 2001). Other research conducted in Indonesia also stated that as many as 256 child workers in the Cibaduyut Bandung slipper and shoe industry were listed as being threatened by various types of diseases such as liver and/or kidney damage and even leukemia ( ILO, 2004). That is due to bad habits and an unhealthy work environment so workers in the Cibaduyut Bandung sandal and shoe industry inhale and ingest benzene compounds contained in the glue they use to make sandals.

Examination of creatinine level in the blood is one of the parameters used to assess kidney function, because the concentration in plasma and its excretion in urine in 24 hours is relatively constant ( Soedaman, 1995). This serum creatinine reflects the most sensitive kidney damage because it is produced constantly by the body ( Lewis et al., 2014). In addition, high Blood Urea Nitrogen (BUN) levels have been associated with adverse kidney effects suggesting that BUN is a useful marker for predicting the development of kidney disease ( Seki et al., 2019). Therefore, the purpose of this study is to analyze the relationship between benzene concentration and RQ benzene with MDA, BUN, and creatinine levels in workers exposed to benzene in a car painting workshop in Surabaya.

This research is an observational study with a cross-sectional design conducted in two car painting workshops in Surabaya that use benzene as a solvent in the production process, namely in Kalijudan and Jemursari. The population in this study were all workers exposed to benzene in two car painting workshops in Surabaya, totaling 90 people aged 20-65 years in 2019. The research sample was taken using an accidental sampling method involving 30 respondents. Inclusion criteria were workers between 20-65 years old who had worked in the workshop for at least 1 year. Exclusion criteria were workers with a previous history of liver or kidney disease and workers not willing to provide blood samples.

The variables studied included benzene concentration, RQ of benzene (a metabolite of benzene), malondialdehyde (MDA) levels as a marker of oxidative stress, and indicators of renal function such as blood urea (BUN) and creatinine levels. Benzene concentration and benzene RQ were considered as exposures, representing the level of exposure to benzene and its metabolic products. MDA levels were examined as an outcome reflecting oxidative stress status. Renal function parameters (BUN and creatinine levels) are outcomes that indicate potential renal effects. To account for possible influences on these relationships, age, and duration of exposure were considered as possible confounding variables. In contrast, smoking status was considered a modifier effect due to its potential to interact with benzene exposure.

Data measurements were made by sampling workplace air using gas chromatography for benzene concentration and benzene RQ. MDA levels were measured using spectrophotometric assay on blood samples. Renal function markers, BUN, and creatinine levels were assessed through blood tests conducted at a clinical laboratory. An attempt was made to overcome participant selection bias through the incidental sampling method, although this method may introduce some bias due to its non-randomized nature.

The results showed that there was no significant relationship between concentration, RQ benzene, and MDA levels in workers in a car painting workshop in Surabaya (p> 0.05). This is in line with research conducted on workers in shoe factories that benzene concentrations do not have a significant relationship with MDA levels ( Tualeka et al., 2019). However, according to research conducted by ( Odewabi et al., 2014) in Nigeria, exposure to free radicals especially benzene in gas station workers can increase MDA levels in workers. Research by ( Suparno et al., 2018) also stated that high plasma malondialdehyde (MDA) levels are markers of oxidative stress that will cause DNA and RNA disturbances. Previous research suggests that oxidative stress might be related to pathogenesis and the development of kidney disease, where it is suspected that malondialdehyde might play an important role in the pathogenesis of glomerulosclerosis ( Kuo et al., 2005). In other studies, oxidative stress has progressively increased and is associated with the degree of kidney dysfunction in patients with chronic kidney failure ( Dounousi et al., 2006; Terawaki et al., 2004). Antioxidant activity plays a crucial role in mitigating the oxidative stress induced by benzene exposure in car painting workers in Surabaya. Benzene exposure leads to the generation of reactive oxygen species (ROS) and free radicals, causing oxidative damage to cells and tissues. Antioxidants help neutralize ROS and free radicals, thereby protecting cells from oxidative stress and potential damage.

There was no significant relationship between benzene exposure, BUN levels and creatinine in painting workers in Surabaya (p> 0.05). Research conducted by ( D’Andrea & Reddy, 2018) in children showed no significant differences in serum creatinine levels between groups exposed to benzene and those not exposed. Although BUN levels were found to be significantly reduced in groups exposed to benzene compared with unexposed group (P = 0.001). Although studies related to the effects of benzene exposure specifically on kidney function (creatinine and BUN) are limited, previous studies related to the exposure of organic solvents to kidney function have been conducted to support this study. Research conducted by ( Elfar et al., 1998) found no statistically significant differences between the groups exposed to organic solvents and the control group regarding kidney function and there was no significant relationship between the two and the length of exposure to organic solvents. This opinion is also strengthened by research conducted by ( Kaukiainen et al., 2004) who found a negative relationship between serum creatinine levels and exposure to organic solvents.

Cytochrome P450 enzymes (CYP450) play a crucial role in the detoxification of various xenobiotics, including benzene. CYP450 enzymes are involved in the metabolism of benzene to less toxic metabolites through a process known as biotransformation. In the context of benzene exposure, CYP450 enzymes are responsible for converting benzene into reactive metabolites, which can then be further metabolized and excreted from the body. The detoxification process mediated by CYP450 enzymes helps in reducing the harmful effects of benzene on the body, particularly in preventing the accumulation of reactive intermediates that can lead to oxidative stress and cellular damage. Understanding the role of CYP450 enzymes in benzene metabolism is essential for assessing the detoxification capacity of individuals exposed to benzene and for developing strategies to mitigate the toxic effects of benzene exposure on various organs, including the kidneys.

Hoek et al. (2003) did not find any effect from exposure to organic solvents on effects to the kidneys. The lack of an association between kidney effects and the intensity or duration of exposure can be associated with individual vulnerability. Vulnerability to benzene can vary due to its effects which arise, in part, from genetic variations in metabolism, DNA repair, genome stability, and immune function ( D’Andrea & Reddy, 2018). In the present study, the effects of benzene have not led to impaired kidney function, yet limited to acute exposure. In addition, the presence of toluene exposure inhaled by labor (measured at the same time as the measurement of benzene exposure using the OVM method) has antagonistic properties against benzene toxicity. According to ( Inoue et al., 1988) workers exposed to a combination of benzene and toluene will experience decreased levels of phenol in the urine compared to those exposed to benzene or toluene separately. Therefore, further research can find out whether there is an antagonistic effect between benzene and toluene on creatinine and BUN levels.

There was no significant relationship between benzene RQ, BUN levels and creatinine levels in paint workers in Surabaya (p> 0.05). RQ calculation is calculated by dividing the intake or intake (ink) by reference (RfC). Therefore, one factor that influences the value of RQ is the amount of benzene intake. Based on the theory of ( Louvar & Louvar, 1998) in determining the assessment of exposure (exposure assessment) regarding the amount of chemical intake received by individuals, the exposure time factor, duration of exposure, body weight and frequency of exposure have a significant contribution in determining the intake of xenobiotic material intake at body to cause health effects. Other factors such as duration of exposure, time of exposure, frequency of exposure, nutritional status, etc. can contribute in the event that there is no effect of the benzene RQ variable on kidney function. In this study, benzene intake in workers was relatively small and the work period of the worker was also not long at 8.2 years (<10 years). In sum, the benzene RQ variable in this study was not a determining factor in its effect on the results of BUN and creatinine levels.

In this study, the majority of respondents (77.8%) were exposed to benzene concentrations above the Threshold Value (>0.5 ppm). The majority of workers (92.6%) had RQ≥1 against benzene exposure, which means the majority of workers were affected by benzene exposure. There was no significant relationship between benzene concentration and RQ on MDA level in workers (p>0.05). There was no significant relationship between benzene concentration, BUN level, and creatinine level in workers (p>0.05). There was no significant relationship between benzene RQ, BUN level, and creatinine level in workers (p>0.05).