Physico-chemical forms of copper in water and sediments of Lake Pontchartrain basin, USA.

In this study, one of the largest estuaries in the Gulf Coast of USA was investigated for Cu forms and fractionations. Both the water and sediment samples in subsegments of the Lake Pontchartrain basin were collected and Cu forms in dissolved phase and sediment phase were analyzed. The BCR sequential extraction procedure was used to extract Cu in exchangeable, reducible, oxidizable and residual fractions in sediments. The results showed that the residual fraction of Cu was a major contributor in Tangipahoa River and I-10 Bridge sediments, while the residual and oxidizable fractions in the case of oil refinery sediments. Cu partitioning in Lake Pontchartrain basin water showed the decreasing trend of inert > labile > organic in both spring and summer. The release of Cu from the sediments into the water column was greater in summer as compared to spring and vice versa. Lower temperature helps in the adsorption of Cu on the surface of sediments in early spring due to low disturbance and temperature.

Evaluation of phosphorus adsorption capacity of sesame straw biochar on aqueous solution: influence of activation methods and pyrolysis temperatures.

The phosphorus (P) adsorption characteristic of sesame straw biochar prepared with different activation agents and pyrolysis temperatures was evaluated. Between 0.109 and 0.300 mg L(-1) in the form of inorganic phosphate was released from raw sesame straw biochar in the first 1 h. The release of phosphate was significantly enhanced from 62.6 to 168.2 mg g(-1) as the pyrolysis temperature increased. Therefore, sesame straw biochar cannot be used as an adsorbent for P removal without change in the physicochemical characteristics. To increase the P adsorption of biochar in aqueous solution, various activation agents and pyrolysis temperatures were applied. The amount of P adsorbed from aqueous solution by biochar activated using different activation agents appeared in the order ZnCl2 (9.675 mg g(-1)) > MgO (8.669 mg g(-1)) ⋙ 0.1N-HCl > 0.1N-H2SO4 > K2SO4 ≥ KOH ≥ 0.1N-H3PO4, showing ZnCl2 to be the optimum activation agent. Higher P was adsorbed by the biochar activated using ZnCl2 under different pyrolysis temperatures in the order 600 °C > 500 °C > 400 °C > 300 °C. Finally, the amount of adsorbed P by activated biochar at different ratios of biochar to ZnCl2 appeared in the order 1:3 ≒ 1:1 > 3:1. As a result, the optimum ratio of biochar to ZnCl2 and pyrolysis temperature were found to be 1:1 and 600 °C for P adsorption, respectively. The maximum P adsorption capacity by activated biochar using ZnCl2 (15,460 mg kg(-1)) was higher than that of typical biochar, as determined by the Langmuir adsorption isotherm. Therefore, the ZnCl2 activation of sesame straw biochar was suitable for the preparation of activated biochar for P adsorption.

Potential treatments to reduce phorbol esters levels in jatropha seed cake for improving the value added product.

Jatropha seed cake contains high amounts of protein and other nutrients, however it has a drawback due to toxic compounds. The aim of this study was to investigate the methods applied to detoxify the main toxin, phorbol esters in jatropha seed cake, to a safe and acceptable level by maintaining the nutritional values. Phorbol esters are tetracyclic diterpenoids-polycyclic compounds that are known as tumor promoters and hence exhibited the toxicity within a broad range of species. Mismanagement of the jatropha waste from jatropha oil industries would lead to contamination of the environment, affecting living organisms and human health through the food chain, so several methods were tested for reducing the toxicity of the seed cake. The results from this investigation showed that heat treatments at either 120°C or 220°C for 1 hour and then mixing with adsorbing bentonite (10%), nanoparticles of zinc oxide (100 µg/g) plus NaHCO3 at 4%, followed by a 4-week incubation period yielded the best final product. The remaining phorbol esters concentration (0.05-0.04 mg/g) from this treatment was less than that reported for the nontoxic jatropha varieties (0.11-0.27 mg/g). Nutritional values of the seed cake after treatment remained at the same levels found in the control group and these values were crude protein (20.47-21.40 + 0.17-0.25%), crude lipid (14.27-14.68 + 0.13-0.14%) and crude fiber (27.33-29.67 + 0.58%). A cytotoxicity test conducted using L929 and normal human dermal fibroblast cell lines confirmed that most of the toxic compounds, especially phorbol esters, were shown as completely eliminated. The results suggested that the detoxification of phorbol esters residues in the jatropha seed cake was possible while it also retained nutritional values. Therefore, the methods to detoxify phorbol esters are necessary to minimize the toxicity of jatropha seed cake. Further, it is essential to reduce the possible environmental impacts that may be generated throughout the jatropha waste-handling process. However additional tests such as digestibility as well as acceptability of the treated jatropha seed cake should be conducted using both in vivo and in vitro studies before recommending the jatropha seed cake as a source of renewable animal feed and other value-added products.

Soil oxidation-reduction in wetlands and its impact on plant functioning.

Soil flooding in wetlands is accompanied by changes in soil physical and chemical characteristics. These changes include the lowering of soil redox potential (Eh) leading to increasing demand for oxygen within the soil profile as well as production of soil phytotoxins that are by-products of soil reduction and thus, imposing potentially severe stress on plant roots. Various methods are utilized for quantifying plant responses to reducing soil conditions that include measurement of radial oxygen transport, plant enzymatic responses, and assessment of anatomical/morphological changes. However, the chemical properties and reducing nature of soil environment in which plant roots are grown, including oxygen demand, and other associated processes that occur in wetland soils, pose a challenge to evaluation and comparison of plant responses that are reported in the literature. This review emphasizes soil-plant interactions in wetlands, drawing attention to the importance of quantifying the intensity and capacity of soil reduction for proper evaluation of wetland plant responses, particularly at the process and whole-plant levels. Furthermore, while root oxygen-deficiency may partially account for plant stress responses, the importance of soil phytotoxins, produced as by-products of low soil Eh conditions, is discussed and the need for development of methods to allow differentiation of plant responses to reduced or anaerobic soil conditions vs. soil phytotoxins is emphasized.

Relationship between sediment clay minerals and total mercury.

A group of 262 sediment samples were collected from various lakes, rivers, reservoirs, and bayous of Louisiana. All samples were analyzed for total mercury. Twenty nine of the samples with total mercury content ranging from 11 to 401 ppb (µg/kg) were analyzed for clay minerals and other sediment physical and chemical properties. Clay content in sediments varied from 3 to 72%. Clay minerals were determined by X-ray diffraction (XRD) technique. Identification of clay minerals was determined by MacDiff software and quantification of clay minerals was obtained by Peak Height Percentage (PHP) calculation. The dominant clay mineral was Hydrated Interlayer Vermiculite (HIV), which represented 51-83% of the total clay mineral. Significant linear correlations were observed between Hg and total clay content (r=0.538**). However Smectite was the only individual clay type correlated (r=0.465**) with mercury in sediment. Cation exchange capacity (r=0.404*), organic matter (r=0.577**), and sulfur (r=0.676**) were also correlated significantly with mercury level in sediment.

Lead distribution and its potential risk to the environment: lesson learned from environmental monitoring of abandon mine.

There are many abandon and existing mines (tin, lead and zinc) in the mountainous areas of Thailand. Toxic elements including heavy metals such as lead (Pb), cadmium (Cd) and arsenic (As) have been released and transported from the mining sites to the adjacent landscape. In Thong Pha Phum District, Kanchanaburi Province, Thailand Pb contamination in the vicinity of the mine has occurred which could lead to potential health problems in downstream communities. To better understand current status of Pb contamination and accumulation in the surrounding environment and potential health impact, surface sediment, soil and plant samples were collected seasonally from representative monitoring sites along the aquatic track or flow regime. Potential health risk was determined using hazard quotient (HQ) as an index for local inhabitants who consume rice. Environmental monitoring illustrated that Pb concentrations in the surface sediment was as high as 869.4 mg kg(-1) dry weight and varied differently among stations sampled. Lead content in agricultural soil ranged between 137.8 to 613.5 mg kg(-1) dry weight and was inversely proportion to the distance from the point source. Moreover Pb was transported from the point source to down hill areas. At the highly polluted monitoring stations (S1, S2, and S3), concentrations of Pb exceeded the maximum allowable concentration for Pb in agricultural soil (300 mg kg(-1)) by 1.7-2 times. The Pb in soil was primarily associated with Fe/Mn oxides bound fraction (46-56%) followed by the organic bound fraction (25-30%). Lead uptake by plant varied and was species dependent. However root and tuber crops like cassava (19.92 mg Pb kg(-1) dry weight) and curcumin (3.25 mg Pb kg(-1) dry weight) could have removed Pb from the soil which suggest growing root crops in Pb contaminated soils should be avoided. However Cd, a co-contaminant at one of monitored stations (S4) yielded rice grain with Cd exceeding the maximum allowable concentration suggesting some potential health risk (HQ = 5.34) if people consume rice grown at this station. Overall result shows a low risk associated with Pb release into the environment.

Environmental factors influencing remediation of TNT-contaminated water and soil with nanoscale zero-valent iron particles.

This study evaluated the application of nanoscale metallic particles (nanoscale zero-valent iron (nZVI) particles) in the remediation of TNT in contaminated water and soil samples. The effects of treatment dosages of synthesized nZVI particles and reaction time on degradation rate of TNT were determined. The synthesized nZVI particles (99.99% pure) size distribution was between 20-100 nm (average particle size 80 nm), with a surface area of 21.63 +/- 0.24 m(2)/g. The optimum dosage of nZVI for degradation of 10 mg/L TNT in the contaminated water was 2000 mg/L (w/v) at a reaction time 20 min. However, trace level of TNT remained since the BOD(5) and COD levels at the optimum nZVI treatment dosage were 834 +/- 8 mg/L and 1280 +/- 900 mg/L, respectively. The BOD(5)/COD ratio was 0.65, which was higher than the BOD(5)/COD ratios for the other nZVI dosages which supports the beneficial effect of using nZVI particles for enhancing degradation of TNT. The observed first-order degradation rate of TNT at 25 degrees C was 0.137 min(-1) corresponding to a degradation rate of 0.156 L/m(2) h. In experiments using sandy clay loam soil containing 20 mg/kg TNT in slurry form (1:2 soil to solution ratio, the optimum nZVI treatment dosage that resulted in 99.88% TNT removal was 5000 mg/kg soil. Less toxic intermediate products and their concentrations following degradation were 2-ADNT and 4-ADNT at 0.90 and 0.10 mg/kg, respectively. Results of this study indicate it is feasible to use nZVI for the remediation of TNT-contaminated water and soil samples as a pre-treatment step however secondary treatments such as phyto-remediation or other biological processes may be needed to remove any residue or intermediate products of TNT degradation.

Fungal and bacterial mediated denitrification in wetlands: influence of sediment redox condition.

Fungal and bacterial denitrification rates were determined under a range of redox conditions in sediment from a Louisiana swamp forest used for wastewater treatment. Sediment was incubated in microcosms at 6 Eh levels (-200, -100, 0, +100, +250 and +400 mV) ranging from strongly reducing to moderately oxidizing conditions. Denitrification was determined using the substrate-induced respiration (SIR) inhibition and acetylene inhibition methods. Cycloheximide (C15H23NO4) was used as the fungal inhibitor and streptomycin (C21H39N7O12) as the bacterial inhibitor. At Eh values of +250 mV and +400 mV, denitrification rates by fungi and bacteria were 34.3-35.1% and 1.46-1.59% of total denitrification, respectively, indicating that fungi were responsible for most of the denitrification under aerobic or weakly reducing conditions. On the other hand, at Eh -200 mV, denitrification rates of fungi and bacteria were 17.6% and 64.9% of total denitrification, respectively, indicating that bacteria were responsible for most of the denitrification under strongly reducing conditions. Results show fungal denitrification was dominant under moderately reducing to weakly oxidizing conditions (Eh>+250 mV), whereas bacterial denitrification was dominant under strongly reducing condition (Eh<-100 mV). At Eh values between -100 to +100 mV, denitrification by fungi and bacteria were 37.9-43.2% and 53.0-51.1% of total denitrification, respectively, indicating that both bacteria and fungi contributed significantly to denitrification under these redox conditions. Because N2O is an important gaseous denitrification product in sediment, fungal denitrification could be of greater ecological significance under aerobic or moderately reducing conditions contributing to greenhouse gas emission and global warming potential (GWP).

Mercury adsorption-desorption and transport in soils.

Kinetic sorption and column miscible displacement transport experiments were performed to quantify the extent of retention/release and the mobility of mercury in different soils. Results indicated that adsorption of mercury was rapid and highly nonlinear with sorption capacities having the following sequence: Sharkey clay > Olivier loam > Windsor sand. Mercury adsorption by all soils was strongly irreversible where the amounts released or desorbed were often less than 1% of that applied. Moreover, the removal of soil organic matter resulted in a decrease of mercury adsorption in all soils. Adsorption was described with limited success using a nonlinear (Freundlich) model. Results from the transport experiments indicated that the mobility of mercury was highly retarded, with extremely low concentrations of mercury in column effluents. Furthermore, mercury breakthrough curves exhibited erratic patterns with ill-distinguished peaks. Therefore, mercury is best regarded as strongly retained and highly "immobile" in the soils investigated. This is most likely due to highly stable complex formation (irreversible forms) and strong binding to high-affinity sites. In a column packed with reference sand material, a symmetric breakthrough curve was obtained where the recovery of mercury in the leachate was only 17.3% of that applied. Mercury retention by the reference sand was likely due to adsorption by quartz and metal-oxides.

Transport and deposition of organochlorine pesticides from farmland to estuary under tropical regime and their potential risk to aquatic biota.

In this study, residues of organochlorine pesticides (OCPs) in water, suspended particulate matter (SPM), sediment and oysters from the Chanthaburi estuary were monitored closely in the wet and dry seasons for determining potential environmental risks. In water samples, out of twenty OCPs measured, endosulfan and hexachlorocyclohexanes (HCHs) were the two predominant compounds ranging and concentrations between 0.6-13 ng/L and 1-12 ng/L, respectively. Both compounds were found in higher concentrations during the wet season. The two insecticides were significantly correlated with total organic carbon (TOC) in the water with r values of 0.571 (P < 0.05) and 0.440 (P < 0.1), for endosulfan and HCHs respectively suggesting that these chemicals are strongly bound and concentrated by water-soluble organic carbon. As expected, high concentrations of endosulfan and HCHs were associated with SPM and in the surface sediment (0-5 cm) with a concentration ranging from 25-1,219 microg/kg dry wt and 19-110 microg/kg dry wt for SPM, 4-70 microg/kg dry wt and 0.5-50 microg/kg dry wt for surface sediment, respectively. Sediment quality of the Chanthaburi estuary was also assessed in terms of risk to aquatic biota using concentration found in the sediment compared to published allowable threshold levels (U.S. EPA and New York guidelines). Results suggested that most of endosulfan and HCHs levels in sediment samples exceeded the threshold values. Thus potential and environmental risks may be anticipated from levels found in sediment. Oyster from selected farms cultured at the study area appeared to take up both endosulfan and HCHs in proportion to level presented in the water and SPM. The range of endosulfan and HCHs observed in oyster tissue were from 4-46 microg/kg wet wt, and from non-detectable to 8 microg/kg wet wt. respectively. Human risk from oyster consumption was considered by comparing the value measured with allowable threshold level of concerned chemical. The levels of endofulfan and HCHs measured in oyster showed that oysters from this estuary area were safe for consumption.

Mercury contamination and potential impacts from municipal waste incinerator on Samui Island, Thailand.

In recent years, mercury (Hg) pollution generated by municipal waste incinerators (MWIs) has become the subject of serious public concern. On Samui Island, Thailand, a large-scale municipal waste incinerator has been in operation for over 7 years with a capacity of 140 tons/day for meeting the growing demand for municipal waste disposal. This research assessed Hg contamination in environmental matrices adjacent to the waste incinerating plant. Total Hg concentrations were determined in municipal solid waste, soil and sediment within a distance of 100 m to 5 km from the incinerator operation in both wet and dry seasons. Hg analyses conducted in municipal solid waste showed low levels of Hg ranging between 0.15-0.56 mg/kg. The low level was due to the type of waste incinerator. Waste such as electrical appliances, motors and spare parts, rubber tires and hospital wastes are not allowed to feed into the plant. As a result, low Hg levels were also found in fly and bottom ashes (0.1-0.4 mg/kg and

Cadmium concentration in sea bottom sediment and its potential risk in the upper Gulf of Thailand.

Untreated or partially treated waste water discharge from industrial and domestic sources entering the Upper Gulf of Thailand have been reported to increase cadmium concentration in bottom sediment. This study was directed at providing a better understanding of cadmium transformation in the sediment from the area. Sediment samples collected from Chao Phraya River mouth (CPY), Bang Pakong River mouth (BPK) and Klong Dan estuary (KD) located in the Upper Gulf of Thailand were analyzed for cadmium concentration in various sediment particle size fractions. Using laboratory microcosms, cadmium release from sediment as affected by salinity and sediment redox condition was studied. A higher concentration of cadmium (0.2-0.6 microg/g dry weight) was measured in finer sediment particle size fractions (<0.075 mm) as compared to courser fractions at all sampling stations. Cadmium release from the sediment to water was influenced by both salinity and redox condition. Sediment was spiked with 10 ppm cadmium which is the cadmium level in sediment adopted by the Australia and New Zealand sediment quality guidelines which can cause adverse environmental impacts. Experiments conducted showed soluble cadmium concentration at sediment oxidation reduction conditions representative of bottom sediment were at levels that can adversely impact aquatic organisms, according to the PCADMIUM water quality guideline. In Thailand, there is no sediment quality guideline. Based on these experiments, 10 ppm of cadmium in sediment was recommended as a regulatory guidelines for allowable levels of cadmium in sediment in the study area.

Export of dissolved organic carbon from a ponded freshwater marsh receiving diverted Mississippi River water.

A series of diversion projects has been implemented to reintroduce Mississippi River water into Louisiana's coastal wetlands in order to reduce wetland loss. The export of dissolved organic carbon (DOC) was measured in a 3,700-ha ponded freshwater marsh that receives diverted Mississippi River water. Results show that highly organic marsh soil and plant material are a source of DOC. DOC, on average, was 3 mg/l greater in outlet water as compared to the concentration in river water entering the wetland. DOC in water leaving the marsh was higher in summer months, with a concentration up to 18 mg/l. Based on a discharge of 1,000 ft3/sec (28.3 m3/sec), it was estimated that the equivalent of 7,335 kg/day of DOC would be exported from the marsh into Lake Cataouatche, located in the northern portion of the Louisiana Barataria Basin estuary. Results suggest that river diversion would likely increase the export of DOC from the marsh as compared to normal transport associated with rainfall and tidal exchange.

Total Hg, methyl Hg and other toxic heavy metals in a northern Gulf of Mexico estuary: Louisiana Pontchartrain basin.

Concentration of total Hg, methyl Hg, and other heavy metals were determined in sediment collected along a salinity gradient in a Louisiana Gulf Coast estuary. Surface sediment was collected at established coordinates (n = 292) along a salinity gradient covering Lake Maurepas, Lake Pontchartrain, Lake Borgne and the Chandeleur Sound located in the 12,170 km(2) Pontchartrain basin estuary southeastern coastal Louisiana. Lake Maurepas sediment with lower salinity contained higher levels of methyl Hg (0.80 microg/kg) than Lake Pontchartrain (0.55 microg/kg). Lake Maurepas sediment also had higher levels of total Hg (98.0 microg/kg) as compared to Lake Pontchartrain (67.0 microg/kg). Average total Hg content of Lake Borgne and the Chandeleur Sound sediment was 24.0 microg/kg dry sediment and methyl Hg content averaged 0.21 microg/kg dry sediment. Methyl Hg content of sediment was positively correlated with total Hg, organic matter and clay content of sediment. Methyl Hg was inversely correlated with salinity, sediment Eh and sand content. Total Hg and methyl Hg decreased with increase in salinity in the order of Lake Maurepas > Lake Pontchartrain > Lake Borgne/ the Chandeleur Sound. Lake Maurepas containing several times higher amount of methyl Hg in sediment as compared to Lake Pontchartrain and Lake Borgne and the Chandeleur Sound is an area that could serve as potential source of mercury to the aquatic food chain. Methyl Hg content of sediment in the estuary could be predicted by the equation: Methyl Hg = 0.11670-0.0625 x Salinity + 0.05349 x O.M. + 0.00513 x Total Hg - 0.00250 x Clay. Concentrations of other toxic heavy metals (Pb, Cd, Ni, Cu and Zn) in sediment were not elevated and was statistically correlated with sediment texture and iron and aluminum content of sediment.

Immobilization of aqueous Hg(II) by mackinawite (FeS).

As one of the major constituents of acid volatile sulfide (AVS) in anoxic sediments, mackinawite (FeS) is known for its ability to scavenge trace metals. The interaction between aqueous Hg(II) (added as HgCl(2)) and synthetic FeS was studied via batch sorption experiments conducted under anaerobic conditions. Due to the release of H(+) during formation of hydrolyzed Hg(II) species which is more reactive than Hg(2+) in surface adsorption, the equilibrium pH decreased with the increase in Hg(II)/FeS molar ratio. Counteracting the loss of FeS solids at lower pH, the maximum capacity for FeS to remove aqueous Hg(II) was approximately 0.75 mol Hg(II) (mol FeS)(-1). The comparison of X-ray power diffraction (XRPD) patterns of synthetic FeS sorbent before and after sorption showed that the major products formed from the interaction between FeS and the aqueous Hg(II) were metacinnabar, cinnabar, and mercury iron sulfides. With the addition of FeS at 0.4 g L(-1) to a 1 mM Hg(II) solution with an initial pH of 5.6, Fe(2+) release was approximately 0.77 mol Fe(2+) per mol Hg(II) removed, suggesting that 77% of Hg(II) was removed via precipitation reaction under these conditions, with 23% of Hg(II) removed by adsorption. Aeration does not cause significant release of Hg(II) into the water phase.

Metal concentrations and trace metal Al and Fe ratios in soil of the Chenier Plain, southwest Louisiana coastal zone.

Soil baseline metal concentrations were determined in 220 surface soil samples collected from the Chenier Plain area of southwest coastal Louisiana. Regression relationships between Al, Fe, and various metals were calculated from the data set. The use of these relationships to identify enhanced metal contents in the Chenier Plain soils is presented. Statistical analyses showed an average Al concentration of 1.6% with a maximum concentration of 4.8% and a minimum concentration of 1.3 mg kg(-1). Al concentration in the sediments was positively correlated at the 1% significance level to Cu (r = 0.577**), Pb (r = 0.936**), Cr (r = 0.969**), Ni (r = 0.830**), Cd (r = 0.617**), and Zn (r = 0.506**), but only a 5% significance correlation was found with Mn (r = 0.148*). Average Fe concentration was 1.2% with a maximum value of 3.4% and a minimum concentration of 9.3 mg kg(-1). Fe concentration in the sediments was positively correlated at the 1% significance level to Cu (r = 0.586**), Pb (r = 0.847**), Cr (r = 0.875**), Ni (r = 0.932**), Cd (r = 0.803**), Zn (r = 0.551**), and Mn (r = 0.479**). These relationships were used to evaluate sites for metal contamination. Data from two known contaminated sites, Capitol Lake (Baton Rouge, LA) and Bayou Trepagnier (LA), fell well outside the prediction limits developed with the Chenier Plain Al and Fe metal regression lines for Cr and Zn. Pb and Cd at Capitol Lake were also elevated beyond the metal/Al prediction developed for the Chenier Plain, but the prediction was not out of range when using the metal/Fe regression. Samples from additional sites with no known metal contamination fell within the predictive limits of the regression equations except for Cd and Pb at some sites. Data presented showed that metal/Al and metal/Fe regression relationships can be used as a tool for identifying areas of potential metal contamination in the coastal zone, but must be regionally correlated.

Denitrification in cypress swamp within the Atchafalaya River Basin, Louisiana.

Nitrogen has been implicated as a major cause of hypoxia in shallow water along the Louisiana/Texas, USA coasts. Excess nitrogen (mainly nitrate) from Mississippi and Atchafalaya River drainage basins may drive the onset and duration of hypoxia in the northern Gulf of Mexico. Restoring and enhancing denitrification have been proposed to reduce and control coastal hypoxia and improve water quality in the Mississippi River Basin. Sediments were collected from six baldcypress restoration sites within the Atchafalaya River Basin, Louisiana, USA. The acetylene blockage technique was used to measure background and potential sediment denitrification rates. Denitrification fluxes were measured before nitrate addition (background rates) and after nitrate addition of 100mgNl(-1) (potential denitrification) at three seasonal temperatures. Background denitrification was low across all cypress swamp sites ranging from 0.9 to 8.8, 0.6 to 28.5 and 8.8 to 47.5g N evolved ha(-1)d(-1) at water/sediment column temperatures of 8, 22 and 30 degrees C, respectively. After nitrate addition, temperature had a significant effect on sediment denitrification potential. Maximum rates measured at 8, 22 and 30 degrees C were approximately 250-260, 550 and 970gNha(-1)d(-1), respectively. Most of the added nitrate in water columns, incubated at 8 degrees C, was removed after 65d compared to 32d and 17d at 22 and 30 degrees C, respectively. These results indicate cypress swamps have the potential to assimilate and process elevated levels of floodwater nitrate with denitrification being a major removal mechanism.

Assessment of Hg contamination and exposure to miners and schoolchildren at a small-scale gold mining and recovery operation in Thailand.

Gold extracted by Hg-amalgamation process, which can cause both health and environmental problems, is widespread in South East Asia including Myanmar, Laos, Cambodia, and Thailand. Small-scale gold mining operations have been carried out since the year 2000 in Phanom Pha District, Phichit Province, Thailand. Since no data is available for evaluating Hg exposure, an investigation of mercury (Hg) contamination and exposure assessment was carried out at this mine site. Environmental monitoring illustrated the total Hg in water was as high as 4 microg/l while Hg in sediment ranged between 102 to 325 microg/kg dry weight. Both Hg deposition from the air (1.28 microg/100 cm(2)/day) and concentration in surface soil (20,960 microg/kg dry weight) were elevated in the area of amalgamation. The potential of Hg exposure to miners as well as to schoolchildren was assessed. The concentrations of Hg in urine of 79 miners who were directly (group I) or indirectly (group II) involved in the gold recovery operation were 32.02 and 20.04 microg/g creatinine, respectively, which did not exceed regulatory limits (35 microg/g creatinine). Hair Hg levels in both groups (group I and group II) also were not significantly higher than the non-exposed group. In terms of risk factors, gender and nature of food preparation and consumption were the two significant variables influencing the concentration of Hg in urine of miners (P < 0.05). A hazard quotient (HQ) was estimated based on the inorganic Hg exposure of individual miners. The HQ values of group I were in a range 16 to 218 times higher than the safety level set as 1. By comparison the group II HQ index was very low (0.03-0.39). The miners in group I who worked and ate food from this area experienced potentially high exposure to Hg associated with the mining process. In a second Hg exposure assessment, a group of 59 schoolchildren who attended an elementary school near the gold mine site was evaluated for Hg exposure. A slightly higher Hg urine concentration was detected in group I and group II (involved and not involved in gold recovery) at average levels of 15.82 and 9.95 microg/g creatinine, respectively. The average Hg values for both groups were below the established levels indicating no risk from Hg intake. Average Hg hair level in all schoolchildren (0.93 microg/g) was not significantly higher than reference group. There were two variables (gender and personal hygiene) which affected the concentration of Hg in urine of schoolchildren (P < 0.05). The result (HQ) also suggested that schoolchildren were not at risk (< 1). Schoolchildren involved in gold mining activities showed some indirect exposure to Hg from the adults working in mining area.

Mercury emission and distribution: Potential environmental risks at a small-scale gold mining operation, Phichit Province, Thailand.

Mercury (Hg) contamination was assessed in environment near an amalgamation gold recovery operation located at a small scale mining operation (Phanom Pha) in Phichit Province, Thailand. Total mercury (THg) concentrations was determined in water, sediment, bivalves in the aquatic environment and as dry deposition or atmospheric fallout on surface soil and leaves of Neem tree (Azadirachta indica Juss. var. siamensis Valeton) near the mining operation. THg in surface soil, Neem flowers (edible part) and rice grain in surrounding terrestrial habitat and with distance from the mining area were also evaluated for possible contamination. Potential environmental risks were evaluated using the hazard quotient equation. Hg analyses conducted in the aquatic habitat showed that THg in water, sediment and bivalves (Scabies cripata Gould) ranged from 0.4 to 4 microg L(-1), 96 to 402 microg kg(-1)dry weight (dw) and 15 to 584 microg kg(-1) wet weight (ww), respectively. High concentrations of THg in water, sediment and bivalves were observed in the receiving stream near the mining operation which was located near the Khao Chet Luk Reservoir. Whereas the THg concentration in water, sediment and bivalves from monitoring stations outside the gold mining operation (upstream and downstream), were considerably lower with the values of 0.4-0.8 microg L(-1), 96-140 microg kg(-1) dw and 88-658 microg kg(-1) dw, respectively. The elevated concentration of Hg found in the sediment near the mining operation was consistent with Hg accumulation measured in bivalves. The elevated Hg levels found in living bivalves collected from highly contaminated sites suggested that the sediment bound Hg was bioavailable. THg in surface soils, brown rice grain (Jasmine rice #105) and Neem flowers of terrestrial habitats were in the range of 16 to 180 microg kg(-1) dw, 190 to 300 microg kg(-1) dw, and 622 to 2150 microg kg(-1) dw, respectively. Elevated concentrations of mercury were found in Neem flowers with the concentration greater than 600 microg kg(-1) ww, which exceeds the maximum permissible concentration reported for biota tissue (500 microg kg(-1) ww). An evaluation of air and soil pollution near the mining operations showed high concentrations of THg in dry deposit from atmospheric fallout (139 microg m(-2) d(-1)), and in surface soil (10,564 microg kg(-1) dw) at station near where open burning of gold ore extracts using the amalgamation process occurred. High or elevated concentration of THg (1172-1301 microg kg(-1) dw) in leaves of Neem tree was also measured near the mining operations. A survey of Hg in surface soil showed elevated Hg concentrations near the site which corresponded to the elevated THg concentration in dry deposition. These results suggested that atmospheric fallout is a major source of Hg to the area surrounding the mining or gold ore extraction. Results also suggest that Hg emitted into the air (estimated to be 60-150 g d(-1)) from the gold mining activities (over the past 10 years) contaminated air, the aquatic environment, surface soil and biota in the area surrounding the gold mining operation.

Partitioning and removal of Cd and Mn using a simulated mangrove wastewater treatment system.

A greenhouse experiment was conducted to study the partitioning and removal of Cd and Mn from wastewater using constructed mangrove (Kandelia candel) wetland treatment system. Three different strengths of artificial wastewater passed through the system in fixed quantities. Artificial seawater was used as a control. Three different compositions were natural wastewater concentration (C1), medium wastewater concentration (C5) and concentrated wastewater concentrations (C10). C1 had the characteristics and strength similar to natural municipal wastewater while C5 and C10 contained five and ten times of the nutrients and heavy metals in C1, respectively. Results showed that the major portion of the Cd and Mn entering the simulated wastewater treatment system entered the sediment pool where approximately 88% to 95% of the Cd, and between 63% and 89% of Mn, was retained. The amount of added Cd and Mn in the wastewater found in plants were between 0.16% to 1.1%, and 1.7% to 13.9%, respectively. Within the total plant pool, roots accounted for between 30% and 39% of Cd, and from 0.65% to 7.3% of Mn; leaves contained between 19.9% to 30.5% of Cd, and from 7.8% to 41.0% of Mn; litterfall contained 12.3% to 20.6% of Cd, and from 15.2% to 70.3% of Mn, respectively. The averaged accumulative coefficients concentration in plant tissues/concentration in sediment in plant for Cd and Mn were 1.22 to 2.40 and 0.02 to 0.08, respectively. Assimilated Cd and Mn were stored in non-activity plant zones such as cell wall, supplimentary cells of the lenticel, stone cells, cell gaps in root and stem, etc. Kandelia candel seedlings had a relative high toxicity resistance to the two heavy metals.