Assessment of heavy metals and radon gas in the urine samples: a comparative study between workers of car mechanics and non-car mechanics

Urine is the best method for monitoring internal exposure to environmental pollutants such as heavy metals and radon gas. This may lead to human exposure to these environmental pollutants, which is associated with potential health risks. Therefore, this study aims to determine concentrations of heavy metals chromium (Cr), cadmium (Cd), and lead (Pb), and radon (²²²Rn) concentrations in 20 urine samples collected from male volunteer workers of car mechanics from Al-Najaf governorate, Iraq. Similarly, 5 urine samples from the non-car mechanics group were collected from several regions in the Al-Najaf governorate. Heavy metals and radon gas were measured using an atomic absorption spectroscopy (AAS) and a nuclear track detector type CR-39, respectively. The mean value of Cr, Cd, Pb, and Rn concentrations for workers was 0.018 ± 0.011 mg/L, 0.083 ± 0.067 mg/L, 0.004 ± 0.002 mg/L, and 24.300 ± 20.906 Bq/m³, respectively. In non-car mechanic individuals, the mean values of Cr, Cd, Pb, and Rn concentrations were 0.010 ± 0.006 mg/L, 0.002 ± 0.001 mg/L, 0.002 ± 0.0007 mg/L, and 4.246 ± 0.489 Bq/m³, respectively. Statistical analysis revealed that cadmium levels were significantly higher in car mechanics (0.083 ± 0.067 mg/L) compared to non-car mechanics (0.002 ± 0.001 mg/L, p < 0.001), while lead concentrations were also elevated in workers (0.004 ± 0.002 mg/L vs. 0.002 ± 0.0007 mg/L, p = 0.010). Radon levels showed a marked increase in car mechanics (24.30 ± 20.91 Bq/m³) compared to controls (4.25 ± 0.49 Bq/m³, p = 0.003). Spearman’s correlation analysis demonstrated significant positive correlations between radon and lead (ρ = 0.511, p = 0.021), as well as a strong correlation between chromium and cadmium (ρ = 0.692, p = 0.001). Accordingly, the mean values of heavy metals and radon concentrations in the urine samples of workers were generally higher than those in the non-car mechanic group. Additionally, no statistically significant correlations were observed between Rn and Cr, Rn and Cd, Cr and Pb, or Cd and Pb among workers. Overall, this study indicates that Cr concentrations were within the commonly reported reference ranges, while Rn concentrations in urine lack well-established standard reference limits. Therefore, radon results should be interpreted with caution in terms of safety assessment, while Cd and Pb concentrations in most urine samples of workers exceeded the permissible limits. The limitations of the study are described, as the findings do not establish causality between radon and heavy metals exposure and the health of car mechanics and non-car mechanics. Due to the cross-sectional design of this study, the results reflect associations rather than causal relationships and cannot be generalized to populations with different environmental conditions and exposure levels.