The volatilization of benzene (C 6 H 6 ), a component of volatile emissions from landfills receiving certain industrial wastes, was characterized in the laboratory using a simulated landfill apparatus. The steady-state vapor diffusion of C 6 H« in soil under isothermal conditions and negligible water flow was directly related to soil air-filled porosity. The volatilization flux of C«H 6 through a soil cover was greatly reduced by increased soil bulk density and increased soil-water content. The actual flux through the soil cover could be predicted from the soil porosity term, P"' 3 P'j, where P a is the soil air-filled porosity and P T is the total porosity. The diffusion coefficient in air for C 6 H 6 calculated from the experimental results was 8.91 x 10" m ! s~', at 20°C, which agrees with other reported data.
Additional Index Words: volatilization, landfills, industrial wastes, air-filled porosity, soil bulk density, soil-water content. Karimi, A.A., W.J. Farmer, and M.M. Cliath. 1987.Vapor-phase diffusion of benzene in soil. J. Environ. Qual. 16:38-43.
1,3-Butadiene is classified as carcinogenic to humans by inhalation. This study aimed to assess cancer and non-cancer risk following occupational exposure to 1,3-butadiene. This cross-sectional study was conducted in a petrochemical plant producing acrylonitrile butadiene styrene copolymer in Iran. Occupational exposure to 1,3-butadiene was measured according to the National Institute for Occupational Safety and Health 1024 method. Cancer and non-cancer risk assessment were performed according to the United States Environmental Protection Agency method. The average occupational exposure to 1,3-butadiene during work shifts among all participants was 560.82 ± 811.36 µg m−3. The average lifetime cancer risk (LCR) in the present study was 2.71 × 10−3; 82.2% of all exposed workers were within the definite carcinogenic risk level. Also, the mean non-cancer risk (hazard quotient (HQ)) among all participants was 10.82 ± 14.76. The highest LCR and HQ were observed in the safety and fire-fighting station workers with values of 7.75 × 10−3 and 36.57, respectively. The findings revealed that values of carcinogenic and noncarcinogenic risk in the majority of participants were within the definitive and unacceptable risk levels. Therefore, corrective measures are necessary to protect these workers from non-cancer and cancer risks from 1,3-butadiene exposure.
Hearing sense is one of the key elements which may have impact on the driver's task quality. This cross-sectional study investigates the hearing status of 500 truck drivers by pure tone audiometry (AC) in one of the cities in Fars province, Iran. Hearing threshold levels of the subjects were measured in frequencies of 500Hz-8000Hz. Screening and determination of permanent threshold shift (PTS) was the first aim of this study. Hence tests were done at least 16 hours after any exposure to noticeable sound. The effect of age as a confounding factor was considered using ISO equation and subtracted from whole hearing threshold. The threshold of 25 dB HL and above was considered abnormal but the calculation of hearing was also carried out using 0 dB HL as reference. Subjects were categorized into two groups on the basis of working experience and the hearing threshold of 25 dB was considered a boundary of normal hearing sense. The results of Pearson Chi-Square test showed that working experience as an independent variable has significant contributing effect on hearing thresholds of truck drivers in frequencies of 500, 1000, 2000 and 4000 Hz (p greater than 0.05). Also, it was shown that currently nine and 12.6 % of truck drivers suffer from impaired hearing sense in left and right respectively (hearing threshold level greater than 25 dB) in mid frequencies (500, 1000, 2000 Hz) and 45% in high frequencies of both ears (4000 and 8000 Hz). The results indicated that hearing damage of professional drivers was expected to occur sooner at 4000 and 8000 Hz than lower frequencies. Finally it was deduced that the occupational conditions of truck drivers may have bilateral, symmetrical harmful effect on hearing threshold sense in all frequencies mainly in frequency of 4000 Hz, so health surveillance programs such as education and periodic medical examinations are emphasized for pre-diagnosing and prevention of any possible impairment and an urgent need to take up some interventions such as better maintenance of roads, automobile industry efforts to reduce the noise level emission of vehicles and reducing number of working hours per day of drivers are highlighted to improve the harmful working conditions of truck drivers.
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