Health implication among occupational exposed workers in a chromium alloy factory, Thailand.

This study was conducted to assess the occupational exposure and its health impact on the chromium alloy workers. Environmental and biological monitoring, noise and audiometry measurements were done to evaluate the exposure levels in the factory. A total of 112 non-smoking workers were monitored from July 2001 to August 2002. The results showed that most of the chromium and lead exposures in the factory were below the ACGIH-TWA of 50 microg/m3 for chromium(VI) and OSHA-PEL of 50 microg/m3 for lead. The highest chromium (7.25 +/- 0.16 microg/m3) and lead (14.50 +/- 0.29 microg/m3) concentrations were measured in the vibro room. The results indicated that elevated concentrations of chromium and lead were found in both blood and urine samples especially in those areas which were characterized by poor ventilation. The metal contents in blood and urine samples were significantly correlated with airborne metal concentrations in the factory. The result demonstrated that blood and urinary levels among workers were associated with increasing age and duration of exposure. The background noise level of the factory ranged from 67.6 to 89.2 dBA and was frequently higher than the threshold limit value for noise (90 dBA). According to the audiometric test, the exposed workers showed signs of noise-induced hearing loss. Noise at work continued to be an important factor to hearing loss among exposed workers. In our statistical analysis, a significant hearing loss was established on age effect and year of exposure among the workforce.

Benzene and lead exposure assessment among occupational bus drivers in Bangkok traffic.

Four environmental and biological monitoring sites were strategically established to evaluate benzene and lead exposure assessment at various traffic zones of Bangkok Metropolitan Region(BMR). Biological measurement of 48 non air-conditioned, male bus drivers was carried to study the relationship between individual exposure levels and exposure biomarkers. The study group was further subdivided into four age groups(16-25, 26-35, 36-45 and 46-55 years old) to monitor the age-related exposure effects. A total of 12 unexposed persons were deliberately chosen as the control group. Measurement of unmetobolized benzene in blood and analysis of urinary tt-Muconic acid urine and urinary creatinine are recommended as biomarkers of benzene exposure. Measurement of lead in blood and urine is also recommended for the biological monitoring of lead exposure. During the monitoring period, benzene and lead levels at Yaowarat Road was C6H6: 42.46 +/- 3.88 microg/m3 , Pb: 0.29 +/- 0.03 microg/m3 and decreased to C6H6: 33.5 +/- 1.35 microg/m3, Pb: 0.13 +/- 0.01 microg/m3 at Phahonyothin Road. Significant difference was established between the nonsmoking exposed group and nonsmoking control group for blood benzene concentrations (P < 0.001, two-tailed, Mann-Whiteney U test). Strong correlations were also found between trans-trans-Muconic acid concentrations in post shift samples and atmospheric benzene concentrations. Similarly, good correlation between all of biomarkers and lead level in air is established from automobile emissions. The analysis revealed that among the occupational population in the urban sites, the driver groups were found to have the highest risk of benzene and lead exposures derived from automobile emission.

Anti-fouling effect of bentonite suspension in ultrafiltration of oil/water emulsion.

The effect on membrane fouling resistance during ultrafilration of oil/water emulsion with the presence of bentonite suspension is experimentally evaluated. The fouling resistance was analyzed as a function of different membrane types and bentonite concentration. The total membrane fouling was categorized into reversible and irreversible, by adopting an appropriate chemical cleaning technique. The results revealed a 40% flux augmentation with the increase of bentonite concentration up to an optimum value of 300 mg l(-1) for cellulose acetate membrane. Further increase of bentonite concentration led to particle deposition on the membrane surface and reduced the flux. The polysulfone membrane did not show a similar flux improvement. This could be due to its high hydrophobicity. The absorption of oil/water emulsion on bentonite increased TOC removal rate from 65% to 80%, and this effect was the major cause of reduction in gel layer formation on the membrane surface. The extent of irreversible fouling of the hydrophilic cellulose acetate membrane was much smaller than that of the polysulfone membrane. These experiments demonstrated that, presence of bentonite could induce transformation of irreversible fouling caused by oil emulsion to reversible fouling, which could be periodically chemically cleaned.

Assessment of treatment alternatives for laboratory cod wastewater: a practical comparison with emphasis on cost and performance.

This study focused on investigation of treatment alternatives for COD wastewater from academic laboratories, using a number of technologies including chemical reduction/precipitation, ion exchange and adsorption by chitosan. Results showed that high concentrations of 375 mg l(-1) chromium, 1,740 mg l(-1) mercury and 993 mg l(-1) silver in COD wastewater can be reduced to 2.34 mg l(-1), 3.65 mg l(-1) and 1.89 mg l(-1) respectively, by the chemical reduction/precipitation process. Results from ion exchange at a flowrate of 20 ml min(-1) showed breakthrough effluent concentrations obtained at 0.59 mg l(-1) chromium, 3.92 microg l(-1) mercury and 0.65 mg l(-1) silver corresponding to 75.6 l at 63 hr, 40.8 l at 34 hr and 33.6 l at 28 hr respectively. Kinetic and isotherm studies revealed that chitosan can adsorb Cr6+, Hg2+ and Ag+ ions most effectively at a flowrate of 20 ml min(-1) and the optimum pH for feed solution is 4. Chitosan column experiments indicated that average effluent concentrations at breakthrough point for chromium, mercury and silver are 0.76 mg l(-1), 6.04 mg l(-1) and 0.51 mg l(-1) respectively with throughput volumes and retention times of 120 l at 100 hr, 60 l at 50 hr and 48 l at 40 hr. Results of solidification experiments for chemical sludge and residual chitosan based on compressive strength and metal leachability tests showed, that the acceptable ranges of the solidification parameters were: sludge/cement = 0.1-1.0 (weight/weight), water/cement = 0.5-0.6 (weight/weight) and sand/cement = 0.5-3.0 (weight/weight). Operating cost per litre of COD wastewater treated, based on the current prices in Thailand was found to be Baht 19.95 for the chemical reduction/precipitation process, Baht 96.35 for ion exchange treatment and Baht 18.29 for chitosan adsorption.

Assessment of benzene and toluene emissions from automobile exhaust in Bangkok.

The use of unleaded gasoline, together with an increase in the number of vehicles in Bangkok, has significantly influenced benzene and toluene concentrations in vehicular emissions and contributes to the air pollution problem. As a matter of practical necessity, a quick test program is done for the measurement of emission concentrations/rates for vehicles driven on the road. Exhaust emission measurement at idle mode was conducted in a fleet of 12 vehicles of different model years and manufacturers. The study revealed that the benzene and toluene concentrations in the exhaust effluent averaged 4.4-22.02 and 12.24-44.75 mg/m3, respectively for 1990-1992 cars and decreased to 0.76-4.14 and 0.89-6.26 mg/m3, respectively for 1994-1995 cars. In another study, exhaust emission measurement on a chassis dynamometer was carried out in a fleet of nine selected, in-use cars. It was observed that benzene and toluene emission rates were considerably higher-in the range of 70.84-85.82 and 354.15- 429.00 mg/km, respectively, for 1990-1991 model year cars. Lower benzene and toluene emission rates of 0.43-95.07 and 2. 15-475.35 mg/km, respectively, were represented by newer cars with model years 1994-1995. These results indicated that there was a significant increase in benzene and toluene emission concentrations and rates with increasing car mileage and model year. The finding also revealed that only 28% of the tested vehicles complied to the approved emission standard.

Diarrhoeal diseases related to sanitation and water supply.

Three Thai communities using river water and three Thai communities utilizing klong water for their domestic consumption were studied to assess the water quality, sanitation and the incidence of diarrhoea in the communities. The incidence of diarrhoeal diseases during a four-month period in the three communities of Bangrasan was 454 per 1000 population and in the three communities of Klongchik was 85 per 1000 population. The relationship between water quality as measured by the MPN coliform index and the incidence of diarrhoeal cases showed that an increase in diarrhoeal cases were accompanied by an increase in MPN value. In general the quality of water seemed to influence the incidence of diarrhoeal cases.