Modelling the washoff of pollutants in various forms from an urban catchment.

The exponential washoff model was originally developed based on observations of particulate pollutants, however, its applicability when applied to different forms of pollutants is not well understood. Data from a previous study of 6 stormwater pollutants from 126 events at 12 sites in Singapore was used for event based model parameter calibration using a Monte Carlo technique. The accuracy of the calibrated exponential washoff model was clearly best for particulate pollutant total suspended solids (TSS), and worst for dissolved pollutants Ortho-Phosphate (PO4), nitrate (NO3) and ammonium-nitrogen (NH4). Model accuracy for mixed forms of pollutants total Phosphorus (TP) and total Nitrogen (TN) were in between these two extremes. Relationships between model parameters with rainfall and flow characteristics were also investigated. Statistically significant relationships could only be found for TSS, where the total rainfall depth was identified as being the most significant variable to explain model parameter behaviour. Antecedent dry period (ADP) was shown to have little or no importance across all land uses and pollutant forms. The results showed that the model parameter behaviour could be explained only for particulate pollutants and small (≤10 ha) sub-catchments, and that replicating washoff of mixed or dissolved forms of pollutants as a fraction of solids is likely to lead to misleading results.

Spatial Distribution of Forensically Significant Blow Flies in Subfamily Luciliinae (Diptera: Calliphoridae), Chiang Mai Province, Northern Thailand: Observations and Modeling Using GIS.

Blow flies of the subfamily Luciliinae (Diptera: Calliphoridae) are one of the main forensically important subfamilies globally. In addition to being used to estimate the minimum post-mortem interval (PMImin), assuming colonization occurred after death, blow fly specimens found infesting a human corpse are used to determine if the corpse was relocated or if the individual ingested narcotics prior to death. The presence of these blow flies in a given area is strongly influenced by abiotic and biotic factors, such as temperature, elevation, and habitat. Having this information, along with geographical distributions and the characteristics of preferred habitats, is necessary to better understand the biology of this group. This study aimed to characterize the spatial distribution of Luciliinae throughout 18 sampling sites within six ecozones (disturbed mixed deciduous forest, mixed deciduous forest, mixed orchard, paddy field, lowland village, and city/town) in central Chiang Mai Province, northern Thailand over one year (May 2009⁻May 2010). The purpose of the study was to elucidate the relationship of blow fly species composition with environmental abiotic factors (e.g., temperature, relative humidity, light intensity), and to predict the distribution of the common species within this subfamily using GIS. Adult collections were performed biweekly, baited with one-day-old beef offal. A total of 2331 Luciliinae flies trapped, comprising eight species, of which the four predominant species were Hemipyrellia ligurriens (Wiedemann) (n = 1428; 61.3%), Lucilia porphyrina (Walker) (n = 381; 16.3%), Hemipyrellia pulchra (Wiedemann) (n = 293; 12.6%), and Lucilia papuensis Macquart (n = 129; 5.5%). Population density across species varied seasonally, peaking in August 2009 coinciding with the rainy season. Predicting population composition was based on a model developed with ArcGIS 9.2, which utilized environmental variables (temperature, relative humidity, and light intensity) in conjunction with abundance data. Models indicated H. ligurriens had the most widespread geographic distribution, while H. pulchra was predicted to occur largely in mixed orchards and lowland villages. Lucilia porphyrina and L. papuensis were less widespread, restricted mainly to mixed deciduous forest. This model, along with knowledge of forensic information, may be useful under certain investigations where the corpse may have been relocated.

Predicting Geographic Distribution of Forensically Significant Blow Flies of Subfamily Chrysomyinae (Diptera: Calliphoridae) in Northern Thailand.

Blow flies (Diptera: Calliphoridae) are carrion-breeding flies that are commonly used as evidence in forensic investigation. An adequate knowledge of ecological and geographical data of blow fly has a direct application in forensic science, as far as estimating time of colonization or corpse relocation. The aim of this study was to evaluate the occurrence of four species of Chrysomyinae (Chrysomya pinguis, Chrysomya chani, Chrysomya villeneuvi, and Ceylonomyia nigripes) across six land use types in central Chiang Mai, northern Thailand. Eighteen study sites were selected for sampling across three districts of Chiang Mai province (Mueang Chiang Mai, Mae Rim, and Hang Dong). Adult flies were collected every two weeks using a funnel trap baited with 1-day tainted beef offal. The predicted geographic distributions of forensically important blow fly species were modeled using the computer program ArcGIS, based on selected climatic variables (temperature, relative humidity, and light intensity) recorded at study sites. During the study period, 1298 adult flies were collected, with peak fly occurrence during summer (April⁻May). Seasonal fluctuation patterns varied depending on fly species. Climatic factors displayed diverse impact on associated fly populations. Identified species were restricted mainly to mixed deciduous forests (MDF) especially in the mountainous area. None of these flies were trapped in an urban area.

Leaded Paint in Cambodia-Pilot-scale Assessment.

BACKGROUND: Lead is a heavy metal that is well known to pose a threat to human health. Although the sale and use of lead paint has been banned in much of the developed world, lead is still commonly used in enamel paints in the developing world, including Cambodia. As Cambodia's economy grows, this may increase the purchase and use of lead-based paints, thus potentially exposing more of the population to the toxic effects of lead. OBJECTIVE: This study was performed to evaluate the concentration of lead in enamel paints in Cambodia using a method that is quick, effective, and cost-efficient. METHODS: A handheld X-ray fluorescence analyzer was used to evaluate 21 samples of enamel paint, including 8 replicates that were randomly purchased from three shops in Phnom Penh, Cambodia to evaluate the level of metals. All of the paint samples in the current study were manufactured in Thailand. DISCUSSION: Ninety percent of the enamel paints sampled in Cambodia exceeded the voluntary standard of 100 µg/g lead of the producing country, Thailand. The mean and median levels for lead were 11,833 µg/g, and 4,961 µg/g, respectively. CONCLUSION: Based on our pilot-scale assessment, high levels of lead appear to be common in enamel paints in Cambodia, and a fuller assessment of the situation is warranted. Import and production of such toxic products should be avoided and appropriate labeling and public warnings should be provided.

Mercury Contamination of Skin-whitening Creams in Phnom Penh, Cambodia.

BACKGROUND: In Cambodia, there is widespread use of skin-whitening creams containing levels of mercury that exceed Association of Southeast Asian Nations (ASEAN) guidelines by up to 35,000 times. Mercury in skin-whitening creams threatens to compromise the health of Cambodians. OBJECTIVES: It is important to provide essential information on sources of mercury so that Cambodians can avoid exposure to elevated levels of mercury and to support informed management of consumer goods. METHODS: Students were directed to buy selected skin-whitening creams that were then sampled with replication in 2011 and 2015 and processed with X-ray fluorescence (XRF) at the University of Health Science (UHS), Phnom Penh, Cambodia. DISCUSSION: The analysis of skin-whitening creams in Phnom Penh in 2015 was compared to analyses in 2008 and 2011 and showed that several creams produced in Asia no longer contain mercury. However, skin creams produced in Phnom Penh continue to use mercury and counterfeit products also are contaminated with mercury. Vendors occasionally identified Vietnam as a source of counterfeit products, but often the source was unknown. Mercury continues to be the metal of greatest concern in skin creams. Creams with more than 1,000 µg/g of mercury are a common cause of dermatitis (27% of cases). A new XRF analyzer was also able to detect more lead and arsenic than that used in analyses performed in 2011, and these two metals also exceeded ASEAN guidelines. Arsenic contamination also reflected the presence of bismuth in creams. CONCLUSION: Some producers of skin-whitening creams in Thailand, China and Taiwan appear to be aware of the risks of mercury contamination and have modified their products. However, other producers of skin-whitening creams continue to use mercury. XRF analysis allows for rapid screening of mercury in cosmetics and should be used to gather additional information on mercury content in cosmetics in support of public health efforts to stem the import, export and sales of skin creams containing mercury.

Impact of abiotic factor changes in blowfly, Achoetandrus rufifacies (Diptera: Calliphoridae), in northern Thailand.

Understanding how medically important flies respond to abiotic factor changes is necessary for predicting their population dynamics. In this study, we investigated the geographical distribution of the medically important blowfly, Achoetandrus rufifacies (Macquart) (Diptera: Calliphoridae), and ascertained the response to climatic and physio-environmental factors in Chiang Mai, northern Thailand. Adult fly surveys were carried out every 2 weeks from May 2009 to May 2010 at 18 systematically randomized study sites in three districts of Chiang Mai province (Mueang Chiang Mai, Mae Rim, and Hang Dong), using reconstructable funnel traps with 1-day tainted beef offal as bait. During the study period, 8,861 adult A. rufifacies were captured, with peak densities being observed at the end of winter (i.e., late February) and throughout most of the summer (May to March). Population density had a weak but significant (α = 0.05) positive correlation with temperature (r = 0.329) and light intensity (r = 0.231), and a weak but significant (α = 0.05) negative correlation with relative humidity (r = -0.236). From the six ecological land use types (disturbed mixed deciduous forest, mixed deciduous forest, mixed orchard, lowland village, city town, and paddy field), greater fly densities were observed generally in the disturbed mixed deciduous forest and lowland village, but not in the paddy fields. In conclusion, A. rufifacies are abundant from the end of winter and throughout most of the summer in northern Thailand, with population density being weakly positively correlated with temperature and light intensity, but weakly negatively correlated with relative humidity. The greatest densities of this fly species were collected in disturbed mixed deciduous forest and lowland village land uses. The prediction of annual and season specific distributions of A. rufifacies were provided in each season and all-year patterns using a co-kriging approach (ArcGIS9.2).

Patterns of ecosystem metabolism in the Tonle Sap Lake, Cambodia with links to capture fisheries.

The Tonle Sap Lake in Cambodia is a dynamic flood-pulsed ecosystem that annually increases its surface area from roughly 2,500 km(2) to over 12,500 km(2) driven by seasonal flooding from the Mekong River. This flooding is thought to structure many of the critical ecological processes, including aquatic primary and secondary productivity. The lake also has a large fishery that supports the livelihoods of nearly 2 million people. We used a state-space oxygen mass balance model and continuous dissolved oxygen measurements from four locations to provide the first estimates of gross primary productivity (GPP) and ecosystem respiration (ER) for the Tonle Sap. GPP averaged 4.1±2.3 g O2 m(-3) d(-1) with minimal differences among sites. There was a negative correlation between monthly GPP and lake level (r = 0.45) and positive correlation with turbidity (r = 0.65). ER averaged 24.9±20.0 g O2 m(-3) d(-1) but had greater than six-fold variation among sites and minimal seasonal change. Repeated hypoxia was observed at most sampling sites along with persistent net heterotrophy (GPP

Do climatic and physical factors affect populations of the blow fly Chrysomya megacephala and house fly Musca domestica?

The blow fly, Chrysomya megacephala (Fabricius), and house fly, Musca domestica L., are medically and forensically important flies. The population dynamic of these flies is essential for both control and forensical aspects. The aim of this study was to investigate the climatic and physical factors affecting the population trend of both species in Chiang Mai province, northern Thailand, using the Geographic Information System (GIS). Based on systematic random sampling, 18 study sites were selected in three districts (Mueang Chiang Mai, Mae Rim, and Hang Dong). Six land use types were involved in the study sites, i.e., disturbed mixed deciduous, mixed deciduous forest, mixed orchard, lowland village, city, and paddy field. Adult flies were sampled every 2 weeks using an in-house prototype reconstructable funnel trap. Two types of bait were used--one with fresh beef viscera for luring M. domestica and the other with 1-day tainted beef viscera for luring C. megacephala. Collections were conducted from May 2009 to May 2010, and analysis of climatic factors (temperature, relative humidity, and light intensity) was carried out. Correlation bivariate analysis was performed initially to determine the relationship between climatic factors and the number of flies. Consequently, an ordinary co-kriging approach, in ArcGIS 9.2, was performed to predict the spatial distribution of flies with land use and climatic factors as co-variables. A total of 63,158 flies were captured, with C. megacephala being the most common species collected (68.37%), while only 1.3% were M. domestica, thus proving that C. megacephala was the most abundant species in several land use types. A significantly higher number of females than males was found in both species. Fly populations can be collected throughout most of the year with a peak in late summer, which shows a positive relation to temperature but negative correlation with relative humidity. C. megacephala was predicted to be abundant in every land use type, from lowland to forested areas, while the density of house fly was association with altitude and land use types.

Field investigation of Bithynia funiculata, intermediate host of Opisthorchis viverrini in northern Thailand.

A survey of freshwater snail, Bithynia funiculata, was conducted in four locations, Doi Saket, Mueang, Saraphi and Mae Rim Districts of Chiang Mai Province, northern Thailand, between June and October, during the rainy season of 2004. A total of 2,240 snails was collected and classified into 7 families and 15 genera; of which 352 B. funiculata were obtained. B. funiculata was found most abundant in July and September. The infection rate of trematode cercariae in B. funiculata was 9.6% (19/352), while that of pleurolophocercous was 0.3% (1/352). Virgulate cercaria was the most common type, followed by lophocercous, monostome and pleurolophocercous. B. funiculata prefers habitats with clear water, which was less than 30 cm depth, temperatures between 24.48 and 31.78 degrees C, dissolved oxygen 2.03-7.66 mg/l, saturated dissolved oxygen 26.70-95.00%, conductivity 0.000-0.2642 mS/cm, turbidity 16.00-288.00 NTU and pH 6.58-7.56. Geographic Information System (GIS) analysis using loose soil mixed with clay revealed that the breeding grounds of this snail species was in the paddy fields and village environs of the Ping, Kuang and Fang river basins.