Arsenic behavior in newly drilled wells

In the present paper, inorganic arsenic species and chemical parameters in groundwater were determined to investigate the factors related to the distribution of arsenic species and their dissolution from rock into groundwater. For the study, groundwater and core samples were taken at different depths of two newly drilled wells in Huron and Lapeer Counties, Michigan. Results show that total arsenic concentrations in the core samples varied, ranging from 0.8 to 70.7 mg/kg. Iron concentration in rock was about 1800 times higher than that of arsenic, and there was no correlation between arsenic and iron occurrences in the rock samples. Arsenic concentrations in groundwater ranged from <1 to 171 microg/l. The arsenic concentration in groundwater depended on the amount of arsenic in aquifer rocks, and as well decreased with increasing depth. Over 90% of arsenic existed in the form of As(III), implying that the groundwater systems were in the reduced condition. The results such as high ferrous ion, low redox potential and low dissolved oxygen supported the observed arsenic species distribution. There was no noticeable difference in the total arsenic concentration and arsenic species ratio between unfiltered and filtered (0.45 microm) waters, indicating that the particulate form of arsenic was negligible in the groundwater samples. There were correlations between water sampling depth and chemical parameters, and between arsenic concentration and chemical parameters, however, the trends were not always consistent in both wells.     

Mobilization of arsenic from subsurface sediments by effect of bicarbonate ions in groundwater

Arsenic leaching by bicarbonate ions has been investigated in this study. Subsurface sediment samples from Bangladesh were treated with different carbonate and bicarbonate ions and the results demonstrate that the arsenic leaching efficiency of the carbonate solutions decreased in the order of Na2CO3>NaHCO3>BaCO3>MnCO3. Sodium carbonate and bicarbonate ions extracted arsenic most efficiently; Na2CO3 leached maximum 118.12 microg/l of arsenic, and NaHCO3, 94.56 microg/l of arsenic from the Ganges delta sediments after six days of incubation. The arsenic concentrations extracted in the batch experiments correlated very well with the bicarbonate concentrations. The kinetics study of arsenic release indicates that arsenic-leaching rate increased with reaction time in bicarbonate solutions. Bicarbonate ions can extract arsenic from sediment samples in both oxic and anoxic conditions. A linear relationship found between arsenic contents in core samples and those in leachates suggests that dissolved arsenic concentration in groundwater is related to the amount of arsenic in aquifer sediments. In batch experiment, bicarbonate solutions effectively extracted arsenic from arsenic adsorbed iron oxyhydroxide, reflecting that bicarbonate solutions may mobilize arsenic from iron and manganese oxyhydroxide in sediments that are ubiquitous in subsurface core samples. Carbonate ion may form complexes on the surface sites of iron hydroxide and substitute arsenic from the surface of minerals and sediments resulting in release of arsenic to groundwater. Like in the batch experiment, arsenic and bicarbonate concentrations in groundwater of Bangladesh correlated very well. Therefore, bicarbonate leaching is presumed to be one important mechanism to mobilize arsenic in bicarbonate dominated reducing aquifer of Bangladesh and other parts of the world as well.     

Temporal variability of groundwater chemistry in shallow and deep aquifers of Araihazar, Bangladesh

Samples were collected every 2-4 weeks from a set of 37 monitoring wells over a period of 2-3 years in Araihazar, Bangladesh, to evaluate the temporal variability of groundwater composition for As and other constituents. The monitoring wells are grouped in 6 nests and span the 5-91 m depth range. Concentrations of As, Ca, Fe, K, Mg, Mn, Na, P, and S were measured by high-resolution ICPMS with a precision of 5% or better; concentrations of Cl were measured by ion chromatography. In shallow wells <30 m deep, As and P concentrations generally varied by <30%, whereas concentrations of the major ions (Na, K, Mg, Ca and Cl) and the redox-sensitive elements (Fe, Mn, and S) varied over time by up to +/-90%. In wells tapping the deeper aquifers >30 m often below clay layers concentrations of groundwater As were much lower and varied by <10%. The concentrations of major cations also varied by <10% in these deep aquifers. In contrast, the concentration of redox-sensitive constituents Fe, S, and Mn in deep aquifers varied by up to 97% over time. Thus, strong decoupling between variations in As and Fe concentrations is evident in groundwaters from shallow and deep aquifers. Comparison of the time series data with groundwater ages determined by (3)H/(3)He and (14)C dating shows that large seasonal or inter-annual variations in major cation and chloride concentrations are restricted to shallow aquifers and groundwater recharged <5 years ago. There is no corresponding change in As concentrations despite having significant variations of redox sensitive constituents in these very young waters. This is attributed to chemical buffering due to rapid equilibrium between solute and solid As. At two sites where the As content of groundwater in existing shallow wells averages 102 microg/L (range: <5 to 648 microg/L; n=118) and 272 microg/L (range: 10 to 485 microg/L; n=65), respectively, a systematic long-term decline in As concentrations lends support to the notion that flushing may slowly deplete an aquifer of As. Shallow aquifer water with >5 years (3)H/(3)He age show a constant As:P molar ratio of 9.6 over time, suggesting common mechanisms of mobilization.     

Seasonal variation of heavy metals in ambient air and precipitation at a single site in Washington, DC

Atmospheric samples of precipitation and ambient air were collected at a single site in Washington, DC, for 7 months (for ambient air samples) and 1 year (for wet deposition samples) and analyzed for arsenic, cadmium, chromium and lead. The ranges of heavy metal concentrations for 6-day wet deposition samples collected over the 1-year period were 0.20-1.3 microg/l, 0.060-5.1 microg/l, 0.062-4.6 microg/l and 0.11-3.2 microg/l for arsenic, cadmium, chromium and lead, respectively, with a precision better than 5% for more than 95% of the measurements. The ranges of heavy metal concentrations for the 6-day ambient air samples were 0.800-15.7 ng/m(3), 1.50-30.0 ng/m(3), 16.8-112 ng/m(3), and 2.90-137 ng/m(3) for arsenic, cadmium, chromium and lead, respectively, with a precision better than 10%. The spread in the heavy metal concentration over the observation period suggests a high seasonal variability for heavy metal content in both ambient air and wet deposition samples.     

Distribution and variability of redox zones controlling spatial variability of arsenic in the Mississippi River Valley alluvial aquifer, southeastern Arkansas

Twenty one of 118 irrigation water wells in the shallow (25-30 m thick) Mississippi River Valley alluvial aquifer in the Bayou Bartholomew watershed, southeastern Arkansas had arsenic (As) concentrations (<0.5 to 77 microg/L) exceeding 10 microg/L. Sediment and groundwater samples were collected and analyzed from the sites of the highest, median, and lowest concentrations of As in groundwater in the alluvial aquifers located at Jefferson County, Arkansas. A traditional five-step sequential extraction was performed to differentiate the exchangeable, carbonate, amorphous Fe and Mn oxide, organic, and hot HNO(3)-leachable fraction of As and other compounds in sediments. The Chao reagent (0.25 M hydroxylamine hydrochloride in 0.25 M HCl) removes amorphous Fe and Mn oxides and oxyhydroxides (present as coatings on grains and amorphous minerals) by reductive dissolution and is a measure of reducible Fe and Mn in sediments. The hot HNO(3) extraction removes mostly crystalline metal oxides and all other labile forms of As. Significant total As (20%) is complexed with amorphous Fe and Mn oxides in sediments. Arsenic abundance is not significant in carbonates or organic matter. Significant (40-70 microg/kg) exchangeable As is only present at shallow depth (0-1 m below ground surface). Arsenic is positively correlated to Fe extracted by Chao reagent (r=0.83) and hot HNO(3) (r=0.85). Arsenic extracted by Chao reagent decreases significantly with depth as compared to As extracted by hot HNO(3). Fe (II)/Fe (the ratio of Fe concentration in the extracts of Chao reagent and hot HNO(3)) is positively correlated (r=0.76) to As extracted from Chao reagent. Although Fe (II)/Fe increases with depth, the relative abundance of reducible Fe decreases noticeably with depth. The amount of reducible Fe, as well as As complexed to amorphous Fe and Mn oxides and oxyhydroxides decreases with depth. Possible explanations for the decrease in reducible Fe and its complexed As with depth include historic flushing of As and Fe from hydrous ferric oxides (HFO) by microbially-mediated reductive dissolution and aging of HFO to crystalline phases. Hydrogeochemical data suggests that the groundwater in the area falls in the mildly reducing (suboxic) to relatively highly reducing (anoxic) zone, and points to reductive dissolution of HFO as the dominant As release mechanism. Spatial variability of gypsum solubility and simultaneous SO(4)(2-) reduction with co-precipitation of As and sulfide is an important limiting process controlling the concentration of As in groundwater in the area.     

Source and release mechanism of arsenic in aquifers of the Mekong Delta, Vietnam

In order to elucidate the arsenic source and its release mechanism into groundwater in the Mekong Delta, Vietnam, groundwater samples were collected from wells at different depths (20 to 440 m) and core samples (from 20 to 265 m depth) were analyzed. Based on the analytical results for groundwater and core samples, the As source in groundwater is considered to be pyrite (FeS(2)) in acid sulfate soil (ASS) under oxidizing conditions and hydrous ferric oxide (Fe(OH)(3)) under reducing conditions. Geochemical modeling demonstrated that As(III) is the dominant species and the presence of As-bearing sulfides, Fe-bearing sulfides and oxides phases may locally act as potential sinks for As. From variation between Fe and As concentrations in groundwater samples, the release mechanism of As is: dissolution of Fe(OH)(3) containing As under reducing conditions and oxidative decomposition of FeS(2) containing As under oxidizing conditions.     

Arsenic in groundwater and sediment in the Mekong River delta, Vietnam

A study of groundwater and sediment during 2007-2008 in the Mekong River delta in Vietnam (MDVN) revealed that 26%, 74%, and 50% of groundwater samples were above the US EPA drinking water guidelines for As (10 μg/L), Mn (0.05 mg/L), and Fe (0.3 mg/L). The range of As, Fe, and Mn concentrations in the MDVN were <0.1-1351 μg/L, <0.01-38 mg/L, and <0.01−14 mg/L, respectively. Elevated levels of As were found in groundwater at sampling sites close to the Mekong River and in wells less than 60−70 m deep. An inverse relationship was found between As and Mn concentrations in groundwater. Sediment samples from An Giang and Dong Thap had the highest As concentrations (18 mg/kg and 38 mg/kg, respectively). Arsenic sediment occurred mainly in the poorly crystalline Fe oxide phases. Reductive dissolution of the Fe oxide phase is not necessarily the dominant mechanism of As release to groundwater.     

Spatial variability of arsenic and chromium in the soil water at a former wood preserving site

Contamination of industrial sites by wood preservatives such as chromated copper arsenate (CCA) may pose a serious threat to groundwater quality. The objective of this study was to characterise the spatial variability of As and Cr concentrations in the solid phase and in the soil water at a former wood impregnation plant and to reveal the fundamental transport processes. The soil was sampled down to a depth of 2m. The soil water was extracted in situ from the vadose zone over a period of 10 months at depths of 1 and 1.5m, using large horizontally installed suction tubes. Groundwater was sampled from a depth of 4.5m. Results showed that arsenic and chromium had accumulated in the upper region of the profile and exhibited a high spatial variability (As: 21-621 mg kg(-1); Cr: 74-2872 mg kg(-1)). Concentrations in the soil water were high (mean As 167 microg L(-1); Cr: 62 microg L(-1)) and also showed a distinct spatial variability, covering concentration ranges up to three orders of magnitude. The variability was caused by the severe water-repellency of the surface soil, induced by the concurrent application of creosote wood preservatives, which leads to strong preferential flow as evident from a dye experiment. In contrast to soil water concentrations, only low As concentrations (<12 microg L(-1)) were detected in the groundwater. High Cr concentrations in the groundwater (approx. 300 microg L(-1)), however, illustrated the pronounced mobility of chromium. Our study shows that at sites with a heterogeneous flow system in the vadose zone a disparity between flux-averaged and volume-averaged concentrations may occur, and sampling of soil water might not be adequate for assessing groundwater concentrations. In these cases long-term monitoring of the groundwater appears to be the best strategy for a groundwater risk assessment.     

Identification and significance of phenazone drugs and their metabolites in ground- and drinking water

Residues of three phenazone-type pharmaceuticals have been identified in routine analyses of groundwater samples from selected areas in the north-western districts of Berlin, Germany. Phenazone, propiphenazone, and dimethylaminophenazone have been detected in some wells at concentrations up to the low microg/l-level. Additionally, three phenazone-type metabolites namely 1-acetyl-1-methyl-2-dimethyl-oxamoyl-2-phenylhydrazide (AMDOPH), 1-acetyl-1-methyl-2-phenylhydrazide, and dimethyloxalamide acid-(N'-methyl-N-phenyl)-hydrazide have also been identified in these groundwater samples. The residues are suspected to originate from former production spills of a pharmaceutical plant located in a city north of Berlin. It was observed that with the exception of AMDOPH all other residues were efficiently removed during conventional drinking water treatment. The drug metabolite AMDOPH deriving from dimethylaminophenazone residues was found at concentrations of 0.9 microg/l in finished drinking water. However, a following study on the toxicological relevance of the AMDOPH residues has shown that there is no toxicological harm for humans at the low concentrations of AMDOPH observed in Berlin drinking water.     

Air and groundwater pollution in an agricultural region of the Turkish Mediterranean coast

Air pollution and groundwater pollution in conjunction with agricultural activity were investigated in Antayla province on the Turkish Mediterranean coast. The air pollution was investigated in terms of gas-phase nitric acid (HNO3), sulfur dioxide (SO2), ammonia (NH3), and particulate matter for a 6-month period in the atmosphere using a "filter pack" system, which was developed and optimized in our laboratory. Ozone was measured by using an automated analyzer. Among all of the gas-phase pollutants, HNO3 had the lowest concentration (0.42 microg x m(-3)) followed by NH3. Agricultural activities seem to be the major source of observed NH3 in the air. The current state of water pollution was investigated in terms of organochlorine and organophosphorus pesticides around the greenhouses, in which mainly tomato, pepper, and eggplant are cultivated. Water samples were collected from 40 points, 28 of which were wells and 12 of which were surface water. The pesticide concentrations in water samples were determined by means of solid-phase extraction (SPE) followed by a gas chromatography (GC)-electron capture detector (ECD)/nitrogen phosphorus detector (NPD) system. In general, surface water samples were more polluted by the pesticides than groundwater samples. The most frequently observed pesticides were chlorpyriphos (57%) and aldrin (79%) in groundwater, and chlorpyriphos (75%), aldrin, and endosulfan sulfate (83%) in surface water samples. The highest concentrations were observed for fenamiphos (394.8 ng/L) and aldrin (68.51 ng/L) in groundwater, and dichlorvos (322.2 ng/L) and endosulfan sulfate (89.5 ng/L) in surface water samples. At least one pesticide had a concentration above the health limit in 38% of all the water samples analyzed.     

Arsenic forensic modeling leads to decommission of downgradient/off-site monitoring wells

Arsenic was detected at concentrations exceeding the regulatory limit of 0.010 milligrams per liter (mg/L) in an off-site bedrock monitoring well downgradient of a former electroplating facility in Merrimack, New Hampshire. The bedrock underlying the site is associated with naturally occurring high concentrations of groundwater arsenic. Geochemical modeling was used to evaluate whether the arsenic in bedrock groundwater at the off-site monitoring location was site-related or naturally occurring. The hydrogeochemical signature of the off-site bedrock well did not resemble signatures of site-impacted bedrock wells. Multiple lines of evidence support that the arsenic observed in off-site bedrock groundwater was not a result of adverse impacts from site-related groundwater contamination.     

Analysis of anaerobic BTX biodegradation in a subarctic aquifer using isotopes and benzylsuccinates

In situ biodegradation of benzene, toluene, and xylenes in a petroleum hydrocarbon contaminated aquifer near Fairbanks, Alaska was assessed using carbon and hydrogen compound specific isotope analysis (CSIA) of benzene and toluene and analysis of signature metabolites for toluene (benzylsuccinate) and xylenes (methylbenzylsuccinates). Carbon and hydrogen isotope ratios of benzene were between -25.9 per thousand and -26.8 per thousand for delta13C and -119 per thousand and -136 per thousand for delta2H, suggesting that biodegradation of benzene is unlikely at this site. However, biodegradation of both xylenes and toluene were documented in this subarctic aquifer. Biodegradation of xylenes was indicated by the presence of methylbenzylsuccinates with concentrations of 17-50 microg/L in three wells. Anaerobic toluene biodegradation was also indicated by benzylsuccinate concentrations of 10-49 microg/L in the three wells with the highest toluene concentrations (1500-5000 microg/L toluene). Since benzylsuccinate typically accounts for a very small fraction of the toluene present in groundwater (generally <1 mol%), the signature metabolite approach works best at higher toluene concentrations when it is not constrained by detection limits. In wells with lower toluene concentrations (410-640 microg/L), carbon and hydrogen isotopic values were enriched by up to approximately 2 per thousand for delta13C and approximately 70 per thousand for delta2H. This evidence of isotopic fractionation verifies the effects of biodegradation in these low concentration wells where metabolites may already be below detection limits. The combined use of signature metabolite and CSIA data is particularly valuable given the challenge of verifying biodegradation in subarctic environments where degradation rates are typically much slower than in temperate environments.     

Geochemistry of a septic-system plume in a coastal barrier bar, Point Pelee, Ontario, Canada

The major ion and trace metal geochemistry of a septic system plume in a shallow sand aquifer was characterized to assess geochemical processes controlling the transport of nutrients and their release to a nearby wetland. The plume was generated from a 16-year-old tile bed, and is more than 60 m long, 40 m wide and 7 m thick. The groundwater pH at the site is near neutral, but up to 0.4 units lower in the plume core as a result of H⁺ generated from NH₃ and DOC oxidation in the unsaturated zone. The plume can be divided into distinct redox zones, which show differences in nutrient mobility. Proximal to the tile bed, there is a shallow suboxic zone, with intermediate Eh values (>400 mV), low concentrations of dissolved oxygen (<1.0 mg/l), and elevated concentrations of Mn (1–3 mg/l) and nutrients (10–80 mg/l NO₃–N, 1–15 mg/l NH₃–N, 0.1–1.5 mg/l PO₄–P, 6–13 mg/l dissolved organic carbon). At the base of the aquifer, there is a reduced zone (Eh<200 mV) with elevated concentrations of Fe (1–14 mg/l), PO₄ and NH₃, but negligible concentrations of NO₃ (<0.01 mg/l N). Distal from the tile bed, the shallow groundwater is suboxic to oxic, and has elevated concentrations of NO₃ and NH_3, but negligible PO₄. In the lower reduced zone, elevated concentrations of PO₄ occur up to 60 m away. The release of groundwater containing even very low concentrations of PO₄ (<0.02 mg/l P) can lead to the development of eutrophic conditions in surface water bodies. Geochemical calculations indicate that, in the Mn-rich zone, the groundwater is close to saturation or supersaturated with respect to hydroxyapatite, rhodochrosite, calcite and ferrihydrite. In the reduced zone, the groundwater is close to saturation or supersaturated with respect to hydroxyapatite, vivianite, calcite and siderite. Formation of these phases, or related phases, are likely limiting the concentrations of dissolved PO₄, Fe and Mn and controlling the geochemical evolution of the plume.     

Behaviour and biodegradation of sulfonamides (p-TSA, o-TSA, BSA) during drinking water treatment

Three sulfonamides -para-toluenesulfonamide (p-TSA), ortho-toluenesulfonamide (o-TSA) and benzenesulfonamide (BSA) - have recently been detected in groundwater within a catchment area of one drinking water treatment plant (DWTP), which is located downstream of a former sewage farm. The degradation pathways of p-TSA, o-TSA and BSA were investigated during drinking water treatment with incubation experiments and an experimental filter. Incubation experiments showed that p-TSA is removed during the treatment by microbiological processes. Removal of p-TSA is performed by adapted microorganisms only present in polluted groundwater. The elimination in an experimental filter of 1.6m length applying filtration velocities from 2 to 6 m h(-1) was approximately 93% of p-TSA. The microbial degradation rates in the incubation experiment were approximately 0.029 microg l(-1) h(-1) (zero order reaction). In the experimental filter, the reaction rate constants were around 0.0063 s(-1) for all filtration velocities (1st order reaction). Drinking water treatment does not reduce the concentration of o-TSA and BSA under conditions encountered in Berlin. p-TSA, o-TSA and BSA were only measured in the low microg l(-1) concentrations range in the purified water.     

Occurrence of sulfonamide antimicrobials in private water wells in Washington County, Idaho, USA

Samples from six private wells formerly used as sources for drinking water by the residents of Washington County (Weiser, Idaho) were collected to assess the impact of a nearby confined animal feeding operation (CAFO) on the quality of the local groundwater. All six samples were found contaminated by two veterinary antimicrobials, sulfamethazine (at concentrations from 0.076 to 0.22 μg/l) and sulfadimethoxine (at concentrations from 0.046 to 0.068 μg/l). These groundwater samples also contained elevated concentrations of nitrate and ammonium. Three of the sampled wells have nitrate levels that exceeded the maximum contaminant level set by the US Environmental Protection Agency for drinking water, with nitrate concentration as high as 39.1 mg/l. All but one well showed nitrate, which instead contained ammonium at 1.22 mg/l. Analysis of the nitrate and ammonium in these samples by isotopic ratio mass spectrometry indicated δ¹⁵N characteristic of an animal or human waste source. Results from this study underscore the role of CAFO as an important source of antibiotic contamination of groundwater.     

Quaternary stratigraphy, sediment characteristics and geochemistry of arsenic-contaminated alluvial aquifers in the Ganges-Brahmaputra floodplain in central Bangladesh

This study focuses on the Quaternary stratigraphy, sediment composition, mineralogy, and geochemistry of arsenic (As)-contaminated alluvial aquifers in the Ganges-Brahmaputra floodplain in the central Bangladesh. Arsenic concentrations in 85 tubewells in Manikganj area, 70 km northwest of Dhaka City, range from 0.25 microg/L to 191 microg/L with a mean concentration of 33 microg/L. Groundwater is mainly Ca-HCO(3) type with high concentrations of dissolved As, Fe, and Mn, but low level of SO(4). The uppermost aquifer occurs between 10 m and 80 m below the surface that has a mean arsenic concentration of 35 microg/L. Deeper aquifer (>100 m depth) has a mean arsenic concentration of 18 microg/L. Sediments in the upper aquifer are mostly gray to dark-gray, whereas sediments in the deep aquifer are mostly yellowing-gray to brown. Quartz, feldspar, mica, hornblende, garnet, kyanite, tourmaline, magnetite, ilmenite are the major minerals in sediments from both aquifers. Biotite and potassium feldspar are dominant in shallow aquifer, although plagioclase feldspar and garnet are abundant in deep aquifer sediments. Sediment composition suggests a mixed provenance with sediment supplies from both orogenic belts and cratons. High arsenic concentrations in sediments are found within the upper 50 m in drilled core samples. Statistical analysis shows that As, Fe, Mn, Ca, and P are strongly correlated in sediments. Concentrations of Cd, Cu, Ni, Zn, and Bi also show strong correlations with arsenic in the Manikganj sediment cores. Authigenic goethite concretions, possibly formed by bacteria, are found in the shallow sediments, which contain arsenic of a concentration as high as 8.8 mg/kg. High arsenic concentrations in aquifers are associated with fine-grained sediments that were derived mostly from the recycled orogens and relatively rapidly deposited mainly by meandering channels during the Early to Middle Holocene rising sea-level conditions.     

Environmental fate and bioavailability of wood preservatives in freshwater sediments near an old sawmill site.

Impacts of an old contaminated sawmill site located in Eastern Finland were studied, with emphasis on transportation and bioaccumulation of wood preservatives in the surrounding water system. To assess the transportation of chlorophenols and chromated copper arsenate (CCA) from the sawmill to the nearby lake, the concentrations of these compounds in selected sediment samples were analyzed. To assess the contribution of a pulp mill further upstream, the concentration of extractable organic halogens (EOX) was analyzed. Bioaccumulation of wood preservatives from sediments was examined using Lumbriculus variegatus as test organism. In sediments collected from the sawmill area, concentrations of chlorophenols, arsenic, chromium and copper were high. In the surrounding area the concentrations of these compounds were slightly elevated at some sampling points but were mostly within the natural range of variation. Thus, it can be concluded that transportation of wood preservatives from the sawmill area to its surroundings is fairly low. However, 60 microg/l of arsenic and 50 microg/l of copper were found in water taken from a brook that runs through a landfill area of the sawmill to the nearby river, and the concentration of arsenic in the surface sediment at one sampling point in the lake was slightly elevated. The total amount of organohalogens in sediment was higher in the river and the lake than in the sawmill area. Of all the wood preservatives studied, only arsenic was found to bioaccumulate in present conditions, reaching a tissue concentration of 362 microg/g dw in organisms exposed for 28 days to sediment from the brook. High concentration of arsenic in oligochaeta tissue was related to high concentration of arsenic in the pore water.     

The acute and chronic toxicity of lanthanum to Daphnia carinata

The rare earth elements (REEs) are increasingly being used as trace supplements in agriculture. This study measured the acute and chronic toxicity of one REE, lanthanum (La), to Daphnia carinata. The 48-h EC50 of La to Daphnia was measured in three media of differing composition and hardness. Lanthanum was most toxic to Daphnia in soft tap water (TW) with an acute 48-h EC50 of 43 microg/l compared with 1180 microg/l in ASTM hard water (ASTM). In the third daphnid growth medium (DW), based on diluted sea water, the acute 48-h EC50 was 49 microg La/l, however, there was significant precipitation of La in this media. The chronic toxicity of La to Daphnia was measured in the DW and ASTM media. Nominal exposure concentrations were 100, 200, 400, 600, 800, and 1000 microg La/l. Mortality was a more sensitive endpoint than growth or reproduction in both chronic experiments. Very little La was detected in either media after 24 h and the measured concentrations below were estimated by logarithmic mean of nominal and measured values. There was 100% mortality at concentrations > or = 80 microg La/l (400 microg/l nominal) by day six of the experiment using DW media, but no effect on survival growth or reproduction at lower concentrations. In the ASTM media, La caused significant mortality to Daphnia at concentrations > or = 39 microg/l (200 microg/l nominal), however, at least one animal survived to the end of the study at each of the tested concentrations. There was no effect of La on growth of surviving daphnids at concentrations < or = 57 microg/l (400 g/l), however, second brood clutch sizes were significantly increased at 30, 39, and 57 microg/l (100, 200, 400 g/l nominal) compared with controls. Lanthanum also caused a delayed maturation in Daphnia.     

Effects of chlorpyrifos on reproductive performances of guppy (Poecilia reticulata)

Guppy (Poecilia reticulata) was selected to investigate the effects of chlorpyrifos on reproductive performances. Male and female guppy with proven fertility were selected from our own colony and the groups of fish (n=72/group) were exposed to pre-determined chlorpyrifos concentrations (0.002 microg/l, 2 microg/l) based on the 96-h LC50 for guppy. Mating behavior of males was recorded on the 2nd day of exposure. Offspring were counted and survival recorded on the 14th day. Gonopodial thrusts (8/15 min) in 0.002 microg/l and (4/15 min) in 2 microg/l were significantly different from the control group (11/15 min). Similarly, live birth reduced significantly to 8/female in 2 microg/l compared to 27/female in the control group. Survival of offspring after 14 days was reduced to 47% in the 2 microg/l group compared to 94% of survival in the control. Our findings demonstrate that low soluble concentrations of chlorpyrifos affect mating behavior, number of offspring and offspring survival of guppy.