Microbiological aspects of fish grown in treated wastewater

Tilapia, common carp and silver carp were reared in treated domestic wastewater. The most sensitive to this environment was the silver carp, followed by common carp and tilapia. In healthy clean fish, bacteria were not found in the blood or the muscles. They were present in small numbers in various organs and in concentrations of 10⁶–10⁷ g⁻¹ in the digestive tract content. In fish exposed to treated wastewater for the entire growing period, bacteria were found in the muscles. The number of bacteria recovered from various organs ranged between 10⁴–10⁶ g⁻¹ and their concentration in the digestive tract content was 10⁸–10⁹ g⁻¹. The number of bacteria in the pond water determined the presence and concentration of bacteria in the fish. The number of bacteria that caused their appearance in the muscles of fish has been named the “threshold concentration”. Considering the public health aspects, fish can be reared in treated wastewater provided the bacteriological quality of the water is compatible with the “threshold concentration” levels of the fish grown in the ponds. The suitability of E. coli (fecal coliform bacteria) as indicators for the bacteriological quality of fish grown in wastewater-fed ponds is examined.     

Rates of experimental microbiological contamination of fish exposed to polluted water

Fish inhabiting fecally polluted bodies of water are often used for human consumption. Such fish can be contaminated by enteric human pathogens and may pose a potential risk to public health. Controlled experiments with 132 fish of 100 g average weight were conducted to evaluate the rate of contamination of various tissues of fish (tilapia hybrids). The fish were exposed to E. coli introduced into the ambient water at concentrations of up to 10⁶ cfu/ml. Additional experiments were conducted with diluted wastewater containing Aeromonas, enterococci, fecal coliform and F+ coliphages. In another experiment poliovirus I was also added. The highest bacterial concentrations were recovered from the digestive tract (DT), some 5–24 h following exposure, with DT levels essentially similar to those in the inoculated water. In the E. coli experiments, geometric mean levels of about 10² cfu/cm² were recovered from the skin, 26 cfu/g in the spleen and 10² cfu/g in the liver. Most of the muscle samples were not contaminated. Greater contamination was not found under conditions of stress such as high organic load, a water temperature of 37°C or low levels of dissolved oxygen.     

Bacterial quality of tile drainage water from manured and fertilized cropland

Bacterial contamination of tile drainage water in three manured and one non-manured cropped fields was studied over a 4-year period at a large, mixed farm near Ottawa, Ontario, Canada. Concentrations of total coliforms, fecal coliforms (FC), fecal streptococci (FS) and Standard Plate Counts at 20 and 35°C, in both the drainage water and the applied dairy cattle liquid manure varied over a wide range. Bacterial concentrations in long-term winter-stored manure were much lower than in relatively fresh manure. Concentrations of FC and FS in the drainage water from the manured fields were lower than concentrations in the applied manure by 3–5 orders of magnitude. Bacterial concentrations in drainage water from all fields had low geometric mean and median values for all parameters tested. Water quality was satisfactory most of the time for recreational use or for use as a raw water source for drinking water supplies. Factors such as precipitation appeared to have a greater influence on drainage water quality than manure application. Influence of soil type on bacterial concentrations in drainage water from the manured fields was not evident. However, a lower unit-area tile outflow in coarse-textured soil compared to fine-textured soil indicated a greater potential in the former for fecal bacteria reaching groundwater beneath the tile drains.     

Impact of population and latrines on fecal contamination of ponds in rural Bangladesh

A majority of households in Bangladesh rely on pond water for hygiene. Exposure to pond water fecal contamination could therefore still contribute to diarrheal disease despite the installation of numerous tubewells for drinking. The objectives of this study are to determine the predominant sources (human or livestock) of fecal pollution in ponds and examine the association between local population, latrine density, latrine quality and concentrations of fecal bacteria and pathogens in pond water. Forty-three ponds were analyzed for E. coli using culture-based methods and E. coli, Bacteroidales and adenovirus using quantitative PCR. Population and sanitation spatial data were collected and measured against pond fecal contamination. Humans were the dominant source of fecal contamination in 79% of the ponds according to Bacteroidales measurements. Ponds directly receiving latrine effluent had the highest concentrations of fecal indicator bacteria (up to 10⁶ Most Probable Number (MPN) of culturable E. coli per 100 mL). Concentrations of fecal indicator bacteria correlated with population surveyed within a distance of 30-70 m (p < 0.05) and total latrines surveyed within 50-70 m (p < 0.05). Unsanitary latrines (visible effluent or open pits) within the pond drainage basin were also significantly correlated to fecal indicator concentrations (p < 0.05). Water in the vast majority of the surveyed ponds contained unsafe levels of fecal contamination attributable primarily to unsanitary latrines, and to lesser extent, to sanitary latrines and cattle. Since the majority of fecal pollution is derived from human waste, continued use of pond water could help explain the persistence of diarrheal disease in rural South Asia.     

Polybrominated diphenyl ethers in fish and sediment from river polluted by electronic waste

The present study investigated contamination of polybrominated diphenyl ethers (PBDEs) in sediment and fish samples collected from rivers in Guiyu, China where electronic waste (e-waste) is recycled and disposed. PBDE congeners with mono-to hepta-brominated and deca-brominated substitutions were detected using (13)C(12) isotope dilution GC/MS/MS and GC/MS methods, respectively. The total PBDE concentrations ranged from 4434 to 16088 ng/g (dry weight) in Nanyang River bank sediment, from 55 to 445 ng/g in Nanyang River bottom sediment and 51.3 to 365 ng/g in Lianjiang River bottom sediment in Guiyu compared with those from 16.1 to 21.4 ng/g in wastewater discharged from a vehicle repairing workshop in Lo Uk Tsuen in Hong Kong. No PBDE congeners were detected in bottom sediment and fish from Mai Po Marshes in Hong Kong. The mean concentrations of total PBDEs in mixed muscles of tilapia (Oreochromis spp) from Lianjiang River were 115 ng/g wet weight (ww) and from wastewater in Hong Kong were 4.1 ng/g ww. Highest mean PBDE concentration was obtained in liver (2687 ng/g ww), followed by abdomen muscle (1088 ng/g ww) of bighead carp (Aristichthys nobilis) collected from Nanyang River. A significant correlation of concentration of each PBDE congener between sediment and muscle from Guiyu was observed. The present results of total PBDEs in sediment and fish were 10 and 1000 times higher than other studies. Open burning and dumping of e-waste are the major causes of PBDE contamination.     

Indicator bacteria and limnological parameters in fish ponds

The populations of indicator bacteria (mesophilic, coliform and fecal streptococci) together with relevant limnological parameters (temperature, oxygen, BOD and chlorophyll-) were recorded during a 6 year study of three eutrophic ponds. Ecosystems were manipulated with fish (Cyprinus carpio) in 2-year management cycles: in spring of the first year, the pond was stocked with young fish, and in the fall of the second year it was drained and mature fish were harvested. Fish management had a direct influence on bacterial numbers and on the basic parameters of the systems. A statistical analysis using t-tests found significant differences in oxygen concentration, chlorophyll- and BOD during both years of fish management. A water temperature model was calculated on an extensive homogenous data set (197 measurements), by fitting a regression curve. During each season, populations of indicator bacteria increased with increasing water temperature, and maximal numbers of bacteria were recorded during the summer months. Correlation analysis (fitted Spearman correlation coefficient) confirmed that temperature had a positive significant effect on population dynamics. The results demonstrate that fish stocking can affect bacterial population, in the sense that during high fish biomass (second years) the numbers of indicator bacteria as well as BOD and phytoplankton were higher. If pond water quality must be optimised for the purposes of drinking or recreation, the planned fish yield may have to be reduced.     

重庆城市污水粪大肠菌污染源调查

对重庆市几个主要区县的城市污水排放口及医院污水排放口进行了抽样调查,结果显示未经处理的城市污水粪大肠菌值主要处于106~107个/L数量级,最大值与最小值之间相差4个数量级。医院污水处理系统虽设计安装有消毒装置,但运行管理不当,出水粪大肠菌严重超标,主要处于104~105个/L数量级,低于城市生活污水。比较了安装与未安装消毒装置的污水处理厂出水中粪大肠菌值,技术经济比较结果显示,氯法、紫外光和臭氧消毒技术在城市污水排放消毒和回用水消毒、医院污水排放消毒方面各有优缺点,宜根据实际情况单独或组合使用。     

Methylmercury production and distribution in aquatic systems.

Mercury methylation and partitioning between sediment, water and fish were studied in river sediment spiked with mercuric chloride at levels of 1, 5 and 10 ppm as Hg. Maximum methylmercury production in the sediment occurred during the first week of incubation, with concentrations reaching 45.5 ng/g (dry wt.). Equilibrium conditions were established 3-4 weeks after the contamination of the sediment with mercury. Methylmercury partitioning between sediment and water yielded methylmercury levels of 25-154 ng/l in the fish aquariums and 0.26 ng/l in the fish-free control after 1 week of incubation. Equilibrium levels were 1.5-5.5 ng/l and 0.53 ng/l, respectively, during the 7th week. Over 50% of the methylmercury in whole water were in soluble form or associated with colloidal particulate < 1 micron. Mercury concentration in fish increased almost exponentially from 30 ppb to an average of 345 ppb within 3 weeks. Mercury uptake rates by fish were in the range of 10-18 ng/g per day during the 2nd and 3rd weeks, high rates occurring in water with methylmercury to total mercury ratios > 0.45. The partition coefficients for total mercury and methylmercury between fish and water (Kf-w) were 5000-7000 and 10,000-22,000, respectively. Large differences were observed in methylmercury production in sediment-water incubation with fish and the fish-free control. Equilibrium methylmercury concentrations in sediment were in the range 15-32 ng/g in the aquariums containing fish and 3-4.5 ng/g in the fish-free control. The significance of fish in mercury methylation in the aquariums still remains to be clarified as fish itself cannot methylate mercury in vivo.     

The persistence and removal of enteric pathogens in constructed wetlands

Sedimentation is thought to be one of the mechanisms of microbial reduction from wetlands used for wastewater treatment. This study compared the occurrence and survival of enteric indicator microorganisms and pathogens in the water column and sediments of two constructed surface flow wetlands in Arizona. On a volume/wet weight basis the concentration of fecal coliforms and coliphage in the water column and sediment was similar. However, on a volume/dry weight basis the numbers were one to two orders of magnitude higher in the sediment. Giardia cyst and Cryptosporidium oocyst concentrations were one to three orders of magnitude greater in the sediment compared to the water column. The die-off rates of all the bacteria and coliphage were greater in the water column than the sediment. The die-off rates of fecal coliforms in the water and sediment were 0.256log(10)day(-1) and 0.151log(10)day(-1), respectively. The die-off rates of Salmonella typhimurium in the water and sediment were 0.345log(10)day(-1) and 0.312log(10)day(-1), respectively. The die-off rates of naturally occurring coliphage in water column and sediment were 0.397log(10)day(-1) and 0.107log(10)day(-1), respectively, and the die-off rates of and PRD-1 in water and sediment were 0.198log(10)day(-1) and 0.054log(10)day(-1), respectively. In contrast Giardia die-off in the sediment was greater compared to the water column. The die-off rates of Giardia in water and sediment were 0.029log(10)day(-1) and 0.37log(10)day(-1), respectively. Coliphage survived the longest of any group of organisms in the sediment and the least in the water column. In contrast Giardia survived best in the water column and least in the sediment.     

Temporal and spatial distributions of sediment mercury at salt pond wetland restoration sites, San Francisco Bay, CA, USA

Decommissioned agricultural salt ponds within south San Francisco Bay, California, are in the process of being converted to habitat for the benefit of wildlife as well as water management needs and recreation. Little is known of baseline levels of contaminants in these ponds, particularly mercury (Hg), which has a well established legacy in the Bay. In this study we described spatial and short-term temporal variations in sediment Hg species concentrations within and among the Alviso and Eden Landing salt ponds in the southern region of San Francisco Bay. We determined total Hg (Hg_t) and methylmercury (MeHg) in the top 5 cm of sediment of most ponds in order to establish baseline conditions prior to restoration, sediment Hg_t concentrations in a subset of these ponds after commencement of restoration, and variation in MeHg concentrations relative to sediment Hg_t, pH, and total Fe concentrations and water depth and salinity in the subset of Alviso ponds. Inter-pond differences were greatest within the Alviso pond complex, where sediment Hg_t concentrations averaged (arithmetic mean) 0.74 μg/g pre and 1.03 μg/g post-restoration activity compared to 0.11 μg/g pre and post at Eden Landing ponds. Sediment Hg_t levels at Alviso were fairly stable temporally and spatially, whereas MeHg levels were variable relative to restoration activities across time and space. Mean (arithmetic) sediment MeHg concentrations increased (2.58 to 3.03 ng/g) in Alviso and decreased (2.20 to 1.03 ng/g) in Eden Landing restoration ponds during the study. Differences in MeHg levels were related to water depth and pH, but these relationships were not consistent between years or among ponds and were viewed with caution. Factors affecting MeHg levels in these ponds (and in general) are highly complex and require in-depth study to understand.     

A laboratory model for evaluating the behavior of heavy metals in an aquatic environment

A dynamic biological system capable of simultaneously distinguishing between bioaccumulation and biomagnification through successive trophic levels in an aquatic ecosystem is described. The organisms used in the system were algae, predominantly Scenedesmus sp., Daphnia magna, fresh water mussels (Ligumia sp. and Margaritifera sp.) and the fathead minnow, Pimephales promelas.Thiosulfate complexed mercury and silver were each studied at two concentrations. The water and organisms were analyzed for the metals periodically during the 10-week tests. Both mercury and silver can be bioaccumulated by fish. The concentration factors for mercury are greater than for silver. Further, mercury is biomagnified by fish whereas silver is not. Fresh water mussels were found to be poor indicator species for metal contamination.     

Mercury transport and bioaccumulation in riverbank communities of the Alvarado Lagoon System, Veracruz State, Mexico

The Alvarado Lagoon System (ALS) is located within the Papaloapan River Basin in southern Veracruz, Mexico. The ALS is a shallow system (2 m) connected to the Gulf of Mexico through a narrow sea channel. There are a large number of riverbank communities within the ALS that are dependent upon its biological productivity for comestible and economic subsistence. The purpose of this project was to determine the levels of mercury in water, sediment, fish, and hair samples from within the Papaloapan River Basin and to characterize the risk of Hg exposure to the individuals that reside in these communities. Water and fish samples were collected during the wet (September 2005) and dry (March 2003 and 2005) seasons. Hair samples, dietary surveys, and sediment samples were obtained during the wet and dry seasons of 2005. Total Hg in the water column ranged from 1.0 to 12.7 ng/L. A strong correlation (R(2)=0.82; p<0.001) between total Hg and total suspended solids in the water column suggests that particulate matter is a transport mechanism for Hg within the lagoon system. Total Hg in the sediments ranged from 27.5 to 90.5 ng Hg/g dry weight with no significant difference between the 2005 wet and dry seasons. There was a mild, but significant, correlation between total Hg and % carbon for the March 2005 sediment samples (R(2)=0.435; p=0.020), suggesting that Hg is associated with organic matter on the solid phase. Concentrations of total Hg in fish and shellfish harvested from the ALS ranged from 0.01 to 0.35 microg Hg/g wet. The levels of total Hg in hair ranged from 0.10 to 3.36 microg Hg/g (n=47) and 58% of the samples were above 1.00 microg Hg/g. The findings from this study suggest that individuals who frequently consume fish and shell fish containing low levels of Hg (<0.3 microg/g) can accumulate low to moderate body burdens of Hg, as indicated by hair Hg concentrations>1.0 microg/g, and may be at risk for experiencing low dose mercury toxicity.     

Quantification of fecal coliform inputs to aquatic systems through soil leaching

In order to assess the fecal contamination of rivers in the Seine watershed through soil leaching, 78 small streams located in rural areas were sampled upstream from any wastewater outfall. Culturable fecal coliforms (FC) and beta-D-glucuronidase activity (specific of Escherichia coli) were measured in the samples. Data showed a significant correlation between both estimates of fecal contamination. In the two different areas of the Seine river watershed investigated, most of the small streams were significantly contaminated by fecal bacteria. In general, the streams flowing through areas partly or fully covered with pastures were more contaminated than those flowing through forest and cultivated areas. Rainfall increased the suspended solid content of small streams as well as their fecal contamination, as an important fraction of FC was adsorbed on particles. Calculations showed that, at a large watershed scale, the input of FC in rivers through soil leaching was very low when compared to the input through the discharge of treated domestic wastewater but this could not be true at local scale.     

Detection of potential carcinogens and toxicants in tap and reclaimed water by the golden hamster cell transformation assay

A transformation assay using primary golden hamster embryonic cells was used for detection of potential carcinogens in water. The system also gave an indication of toxicants present in water and proved to be highly sensitive, because no concentration or extraction procedures were required as in the case of the Ames Salmonella/microsome assay.

Direct reclamation of secondary treated wastewater proved to be highly effective when tested by the golden hamster transformation assay. Reclaimed water showed less transforming activity than a high quality tap water derived from conventional treatment of surface water.     

Removal of bacterial fecal indicators, coliphages and enteric adenoviruses from waters with high fecal pollution by slow sand filtration

The aim of the present study was to estimate the performance of slow sand filtration (SSF) facilities, including the time needed for reaching stabilization (maturation), operated with surface water bearing high fecal contamination, representing realistic conditions of rivers in many emerging countries. Surface water spiked with wastewater was infiltrated at different pore water velocities (PWV) and samples were collected at different migration distances. The samples were analyzed for phages and to a lesser extent for fecal bacteria and enteric adenoviruses. At the PWV of 50 cm/d, at which somatic phages showed highest removal, their mean log₁₀ removal after 90 cm migration was 3.2. No substantial differences of removal rates were observed at PWVs between 100 and 900 cm/d (2.3 log₁₀ mean removal). The log₁₀ mean removal of somatic phages was less than the observed for fecal bacteria and tended more towards that of enteric adenoviruses This makes somatic phages a potentially better process indicator than Escherichia coli for the removal of viruses in SSF. We conclude that SSF, and by inference in larger scale river bank filtration (RBF), is an excellent option as a component in multi-barrier systems for drinking water treatment also in areas where the sources of raw water are considerably fecally polluted, as often found in many emerging countries.     

Relationships between Bacteroides 16S rRNA genetic markers and presence of bacterial enteric pathogens and conventional fecal indicators

Occurrence and prevalence of different bacterial enteric pathogens as well as their relationships with conventional (total and fecal coliforms) and alternative fecal indicators (host-specific Bacteroides 16S rRNA genetic markers) were investigated for various water samples taken from different sites with different degrees of fecal contamination. The results showed that a wide range of bacterial pathogens could be detected in both municipal wastewater treatment plant samples and in surface water samples. Logistic regression analysis revealed that total and human-specific Bacteroides 16S rRNA genetic markers showed significant predictive values for the presence of Escheriachia coli O-157, Salmonella, heat-labile enterotoxin (LT) of enterotoxigenic E. coli (ETEC), and heat-stable enterotoxin for human (STh) of ETEC. The probability of occurrence of these pathogenic bacteria became significantly high when the concentrations of human-specific and total Bacteroides 16S rRNA genetic markers exceeded 10(3) and 10(4) copies/100 mL. In contrast, Clostridium perfringens was detected at high frequency regardless of sampling sites and levels of Bacteroides 16S rRNA genetic markers. No genes related to Shigella spp., Staphylococcus aureus and Vibrio cholerae were detected in any samples analyzed in this study. Conventional indicator microorganisms had low levels of correlation with the presence of pathogens as compared with the alternative fecal indicators. These results suggested that real-time PCR-based measurement of alternative Bacteroides 16S rRNA genetic markers was a rapid and sensitive tool to identify host-specific fecal pollution and probably associated bacterial pathogens. However, since one fecal indicator might not represent the relative abundance of all pathogenic bacteria, viruses and protozoa, combined application of alternative indicators with conventional ones could provide more comprehensive pictures of fecal contamination, its source and association with pathogenic microorganisms.     

Modeling the dry-weather tidal cycling of fecal indicator bacteria in surface waters of an intertidal wetland

Recreational water quality at beaches in California and elsewhere is often poor near the outlets of rivers, estuaries, and lagoons. This condition has prompted interest in the role of wetlands in modulating surface water concentrations of fecal indicator bacteria (FIB), the basis of water quality standards internationally. A model was developed and applied to predict the dry-weather tidal cycling of FIB in Talbert Marsh, an estuarine, intertidal wetland in Huntington Beach, California, in response to loads from urban runoff, bird feces, and resuspended sediments. The model predicts the advection, dispersion and die-off of total coliform, Escherichia coli, and enterococci using a depth-integrated formulation. We find that urban runoff and resuspension of contaminated wetland sediments are responsible for surface water concentrations of FIB in the wetland. Model predictions show that urban runoff controls surface water concentrations at inland sites and sediment resuspension controls surface water concentrations near the mouth. Direct wash-off of bird feces into the surface water is not a significant contributor, although bird feces can contribute to the sediment bacteria load. The key parameters needed to accurately predict FIB concentrations, using a validated hydrodynamic model, are: the load due to urban runoff, sediment erodibility parameters, and sediment concentrations and surface water die-off rates of enteric bacteria. In the present study, literature values for sediment erodibility and water column die-off rates are used and average concentrations of FIB are predicted within 1/2 log unit of measurements. Total coliform are predicted more accurately than E. coli or enterococci, both in terms of magnitude and tidal variability. Since wetland-dependent animals are natural sources of FIB, and FIB survive for long periods of time and may multiply in wetland sediments, these results highlight limitations of FIB as indicators of human fecal pollution in and near wetlands.     

The residual dynamic of polycyclic aromatic hydrocarbons and organochlorine pesticides in fishponds of the Pearl River delta, South China

Hong Kong and South China are the most developed regions within China. The industrialization in these areas has resulted in severe environmental problems. Sediment and biotic samples including tilapia (Oreochromis mossambicus), bighead carp (Aristichthys nobilis), grass carp (Ctenopharyngodon idellus), crucian carp (Carassius auratus) and mandarin fish/fresh water grouper (Siniperca chuatsi) were collected from different fishponds in the Pearl River Delta (Tanzhou, Sanjiao, Guangzhou, Shipai, Changan and Mai Po) for the analysis of polycyclic aromatic hydrocarbons (PAHs) and organochlorine (OC) pesticides. Mandarin fish, which belongs to the highest trophic level, accumulated the highest concentrations of PAHs and DDTs among all fish species. The levels of DDTs in fish samples ranged from 1.5 to 62ng g-1 (wet wt.), with more than 30% of the fish samples exceeding the limit of 14.4ng g-1 (wet wt.) for human consumption recommended by US EPA (2000). Levels of PAHs in fish samples ranged from 1.91 to 224.03ng g-1 (wet wt.), but the potency-weighted total concentrations of PAHs in all muscle tissues were below the guideline value of 0.67ng g-1 (wet wt.) for human consumption set by US EPA (2000). The guideline value calculated was based on a tissue consumption rate of 142.2g day-1 (4-5 meals per week), which is a more protective rate for populations with a high consumption of fish, like Chinese and Asians. The effect of lipid content in PAHs and DDTs accumulation in fish tissue was not significant in general.     

Health assessment for mercury exposure among schoolchildren residing near a gold processing and refining plant in Apokon, Tagum, Davao del Norte, Philippines

Artisanal gold-mining activities in the Philippines have proliferated since the early 1980s. Presently, environmental and health monitoring conducted by several governmental agencies is limited to the determination of total mercury only. Previous studies undertaken focused mainly on the exposure of adults and workers to mercury during mining/processing operations. However, in one area in Mindanao, mined ores are brought down and processed in the lowlands where residential communities are exposed to environmental pollutants resulting from gold processing/refining operations. The area of study is Apokon, Tagum, Davao del Norte, which has 29 gold processing and refining plants. Health complaints among schoolchildren in Apokon Elementary School were received by the Department of Health and were attributed to the mercury pollution in the environment. As part of a collaboration with the Health Department, UP-National Poisons Control and Information Service, the National Institute for Minamata Disease (NIMD), Japan, provided technical assistance in the analytical determination of mercury in biological and environmental samples. Elevated mercury concentrations were noted in some of the river systems up to 15 km from the mining areas. Environmental quality monitoring showed T-Hg sediment levels ranged from 0.553 to 66.471 microg/g dry wt. while water samples from river systems exhibited mercury levels from 72.8 to 78.4 ng/ml. Twenty-seven sediment samples from river systems near mining operations and seven water samples were also brought to the Institute for analysis. Fish samples collected showed levels ranging from 1.07 to 438.8 ng/g for total mercury and 0.71-377.18 ng/g for methylmercury. Methylmercury content in fish is predominant. All water and sediment samples collected from three sampling sites have elevated T-Hg level while three fish species have elevated T-Hg and methylmercury levels (WHO/CDC, 1994). Blood and hair samples from 162 schoolchildren aged 5-17 years were collected and analyzed at the NIMD for mercury analysis. Analytical procedures used in the NIMD for mercury testing were applied. Laboratory results showed that total mercury hair samples ranged from 0.278 to 20.393 microg/g while methylmercury hair results were from 0.191 to 18.469 microg/g. Methylmercury in hair showed levels from 45.96 to 99.81%. Total blood mercury levels ranged from 0.757 to 56.88 microg/l while Me-Hg blood levels ranged from 1.36 to 46.73 microg/l. It was determined that 10 children had elevated T-Hg blood levels while one child had high total and methylmercury levels in hair. A summary of physical examination results showed that the predominant findings include under-height, gingival discoloration, adenopathy, underweight and dermatologic abnormalities among children examined.