Shing Tet Leong

Regional monitoring of lead and cadmium contamination in a tropical grazing land site, Thailand

An investigation was carried out to monitor Pb and Cd contamination in grazing land located near a highway. Environmental media at different distances fromhighway (soil, grass, water, cows forage, fertilizer,manure and milk samples) were collected from three samplinglocations. Soil and grass were characterized by high metalmobility (soil with Pb: 5.25±0.71–14.59±1.17 mgkg-1, dry mass and Cd: 0.038–0.33±0.04 mg kg-1, dry mass and grass with Pb: 0.76±0.05–6.62±0.18 mg kg-1, dry mass and Cd: 0.17±0.01–0.73±0.09 mg kg-1, dry mass). One-way analysis of variane (ANOVA) was applied to find out the correlation between metal (total and bioavailable) concentrationsin the soil and the distance from roadside. In most cases, the finding showed that plants growing nearer to the highway are usually exposed to more heavy metal accumulations than those awayfrom the highway. In addition, a correlation was established between plant available metal concentrations and plant metaluptake concentrations.Analysis of fertilizer and manure showed considerable amountof metals (fertilizer with Pb: 1.53±0.06 mg kg-1 andCd: 0.038 mg kg-1 and manure with Pb: 2.55–3.34 mgkg-1 and Cd: 0.14–0.31 mg kg-1). Long termsimultaneous application of fertilizer and manure on thecommercial farm showed higher metal accumulation in the soiland plants than those of co-operative farm Considerableconcentrations of metals (Pb: 1.60–2.94 mg kg-1 andCd: 0.025–0.19 mg kg-1) were observed in fodder. The finding clearly demonstrated that there are seasonalvariation in total daily metal intake by individual cow (Pb:109.37 mg day-1 (dry), 273.47 mg day-1 (rainy) andCd: 2.02 mg day-1 (dry), 19.62 mg day-1 (rainy)).The provisional tolerable weekly intake of heavy metals incows is 390 μg Pb and 28 μg Cd per kg bodyweight in the rainy season and 156 μg Pb and 2 μgCd per kg body weight in the dry season. The levels of metals (Pb: 0.014 mg L-1 and Cd: not detectable) and bio-transferfactor (10-5–10-4) in raw milk were found to be well below the Codex Alimentarius Commissions Draft (1997). Ouranalysis revealed that improvements on farm management give significant reduction in elevated levels of Pb and Cdin soil and plants, and however leads to minimize the amountof Pb and Cd in consumed milk.

Monitoring and Assessment of Daily Exposure of Roadside Workers to Traffic Noise Levels in an Asian City: A Case Study of Bangkok Streets

Four noise monitoring sites were strategically established to evaluate average noise level and audiometric assessment at various traffic zones of Bangkok Metropolitan Region (BMR). During the monitoring period, noise levels were found to be 72.8–83.0 dBA during day time and 59.5–74.5 dBA during night time. The finding also indicated that traffic noise levels depend on distance from roadside, diurnal variation and character of the traffic and street configuration. Audiometric measurement of 4000 persons was carried by four major hospitals in Bangkok to study the relationship between traffic noise exposure of groups of people working in the streets and hearing loss. Four different categories of occupational people, i.e., drivers, street vendors, traffic officers and dwellers were selected and were further classified into age groups (16–25, 26–35, 36–45 and 46–55 years old) to monitor the traffic noise induced hearing loss throughout their everyday lives. The control group was deliberately chosen to screen out the effects of traffic noise. According to the audiometric investigation, it was revealed that hearing capacity of the daily noise exposure groups living in the three urban sites (Yaowarat Road, Din Daeng Road and Ratchaprarop Road) were noticeably poorer than those who were living in suburban site (Phahonyothin Road). It was noted that the mean hearing threshold level (HTL) of the 16–25 years old groups were found to have better hearing capacity than those older adults of 46–55 years old. In particular the mean HTL dropped at the frequency of 4000 Hz. Among the occupational population who were living in the urban monitoring sites, the driver groups were found to have the highest risk of traffic noise induced hearing loss.

Monitoring and Assessment of Exhaust Emission in Bangkok Street Air

Measurement of the exhaust emission from gasoline-powered motor vehicles in Bangkok were performed on chassis dynamometer. A fleet of 10 vehicles of different model, years and manufacturers were selected to measure the air pollutants in the exhaust effluent. The study revealed that the carbon monoxide and hydrocarbon emissions averaged 32.3–64.2 and 1.82–2.98 g km−1, respectively, for 1990–1992 cars and decreased to 17.8–40.71 and 0.75–1.88 g km−1, respectively, for 1994–1995 cars. A monitoring program for air pollutant concentrations in ambient air was also conducted to evaluate the air pollution problems in Bangkok arising from vehicle exhaust emission. Four air sampling stations were strategically established to cover the Bangkok Metropolitan Region (BMR). Composite air samples in this study area were collected during the day/night times and weekday/weekend. The average concentrations of suspended particulate matter, carbon monoxide, and nitrogen dioxide in Bangkok street air were found to be 0.65 mg/m3 (24 hr ave.), 19.02 mg/m3 (8 hr ave.) and 0.021 mg/m3 (1 hr ave.), respectively. The average concentrations of benzene and toluene in the ambient air of the study area were found to be 15.07–50.20 and 25.76–130.95 μg/mf3, respectively, for 8 hr average. These results indicated that there was a significant increase in air pollutant emissions with increasing car mileage and model year. Subsequent analysis of data showed that there were only 20% of the test vehicles complied to approved emission standard. The finding also revealed that there was a correlation between the average air pollutant concentrations with average traffic speed in each traffic zone of the Bangkok Metropolitan Region (BMR).

Environmental Monitoring and Impact Assessment of a Solid Waste Disposal Site

The objective of this study is an attempt to conduct an environmentalmonitoring and impact assessment of the On-Nooch solid waste disposal sitein Bangkok, Thailand. Four water and five air sampling stations (2 upwindand 3 downwind directions) were established at the site. Grab water samplesfrom leachate treatment plant and Khlong Song Hong, a nearby stream, werecollected during the rainy and dry seasons. Analytical results of the wastewater discharged by the leachate treatment plant, during dry season showedchemical oxygen demand: 618 mg/l; biochemical oxygen demand: 80 mg/l;suspended solid: 101 mg/l; Total Kjeldahl Nitrogen: 283 mg/l, which werestill higher than standard limit for effluents in Thailand. During the dryseason, results also showed widespread heavy metal pollution from leachate(chromium: 1.03 mg/l; manganese: 1.07 mg/l; mercury: 0.025 mg/l) and werehigher than the allowable level of heavy metals for the Industrial EffluentStandard in Thailand. The direct discharge of untreated leachate into inlandwater will cause considerable water pollution in the study area. Compositeair samples in this study area were collected during the rainy and dryseasons and were analyzed for methane (CH4), carbon dioxide(CO2), carbon monoxide (CO), sulphur dioxide(SO2), nitrogen dioxide (NO2) andsuspended particulate matter (SPM). The average concentration of SPM rangedbetween 0.1–0.36 mg/m3 for 24-hour average, dependingupon the season. The level of CH4 and CO2 inthe ambient air of the study area were found to be 3.48–65.71mg/m3 and 886-1758 mg/m3 respectively which weremuch higher than the normal concentration of CH4 andCO2 in the air (CH4: 2.41 mg/m3;CO2: 585 mg/m3). Hence, adverse health andenvironmental effects could be expected from water and air pollution.

RETRACTED: Indicators of benzene emissions and exposure in Bangkok street

Ambient benzene measurements were conducted for the first time at four air monitoring sites in the Bangkok metropolitan region (BMR), from January to December 2001. Analytical results show that the mean benzene concentrations range from 42.4 micro g/m(3) at the Din Daeng urban site to 15.1 micro g/m(3) at the Chaeng Wattana suburban site. The monitoring results show that at a larger distance from the roadside or a higher level from the street surface, the level of benzene decreases. Analysis of the ambient benzene concentrations was carried out with reference to meteorological influences and traffic density. In traffic analysis, the combined effects of street topography and traffic flows established high impact on the overall benzene concentration in Bangkok. Statistical analysis shows good correlations of blood benzene levels and trans, trans-muconic acid with ambient benzene and demonstrated substantial exposure from traffic.

An Environmentally Sound Method for Disposal of Both Ash and Sludge Wastes by Mixing with Soil: A Case Study of Bangkok Plain

This study reported the test done on ash-sludge mixture foramendment of soil in pot experiments. Ash-sludge mixture ratiostudies revealed that 1:5 fly ash-sludge mixture and 1:10 bottom ash-sludge mixture were the optimum mixture ratio thatminimized toxic element and provided sufficient nutrients. Experiments indicated that ash-sludge mixtures is more suitablefor amendment of acid soil than neutral soil which can increasesoil pH and reduce available heavy metal toxicity. The maximumheavy metal adsorption occurred in a pH range of 4 to 6 for allsoil studied. The finding also revealed that fly ash applicationseemed more effective than bottom ash, due to its higher loadingrate and metal contents. Heavy metal toxicity was monitored usingseed germination test. Marigold and tomato seeds were the two crops selected for this test. Seed germination test result showsthat percentage of seed germination increased in pot experimentswith sludge only and ash-sludge mixtures. In addition, higherpercentages of seed germination were observed to vary with longer incubation time (1–8 weeks). After week 12 of the incubation period, percentage of seed germination began to decline, as a result of reduced soil pH and release of toxic heavy metals.

Assessment of Treatment Alternatives for Laboratory COD Wastewater: a Practical Comparison with Emphasis on Cost and Performance

This study focused on investigation of treatment alternativesfor COD wastewater from academic laboratories, using a number oftechnologies including chemical reduction/precipitation, ion exchange and adsorption by chitosan. Results showed that highconcentrations of 375 mg l-1 chromium, 1,740 mg l-1mercury 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/precipitationprocess. Results from ion exchange at a flowrate of 20 ml min-1 showed breakthrough effluent concentrations obtainedat 0.59 mg l-1 chromium, 3.92 μg 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 andsilver 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 leachabilitytests showed, that the acceptable ranges of the solidificationparameters 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 wasfound to be Baht 19.95 for the chemical reduction/precipitationprocess, Baht 96.35 for ion exchange treatment and Baht 18.29 forchitosan adsorption.

Monitoring Framework for Nitrogen Dioxide Measurement in a Tropical City: A Bangkok Case Study

This study addresses a useful and simple way of assessing nitrogen dioxide (NO2) concentrations measured at six monitoring stations in Bangkok Metropolitan Region (BMR), during January to December 2001. The measurements are further interpreted using corelationship between NO2 concentrations and with traffic characteristics, street geometries, and meteorological parameters. Variations in diurnal and seasonal NO2 levels are also identified. The finding shows that the measured NO2 concentrations range from 55 μg m-3 at the Yaowarat urban site to 26 μg m-3 at the Phahonyothin suburban site. The monitoring method has important implications for general applicability to other tropical cities.