bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative performance of 5 cm2 and 10 cm2 piezocones in a lacustrine clay
Authors: Hird C. C. , Springman S. M.
Published: July 2006

A piezocone investigation has been carried out in a deep deposit of glacial lacustrine clay using piezocones with cross-sectional areas of 5 cm2 and 10 cm2. The piezocone tests formed part of a larger soil characterisation study, but this paper focuses on the relative performance of the piezocones in profiling the clay. It is shown that using a 5 cm2 piezocone rather than a 10 cm2 one significantly improved the detection of relatively thin silt layers within the lacustrine, and occasionally varved, clay. The feasibility of detecting silt layers as thin as 2–4 mm and of matching the piezocone responses associated with silt layers at different test locations, thereby allowing an assessment of their continuity, is demonstrated. There were no significant differences between the magnitudes of the cone resistance and excess pore pressure recorded in the clay with 5 cm2 and 10 cm2 piezocones. Pore pressure dissipation test results were variable but, in a region where no silt layers were detected, similar results were obtained with piezocones of each size.
Modelling circulation and vertical mixing in estuaries
Authors: Liu W.-C.
Published: July 2006

A laterally averaged two-dimensional model of estuarine circulation has been developed and applied to the Danshuei River estuarine system in northern Taiwan to study the changes in estuarine circulation and salinity distribution when certain parameters of the flow are varied systematically. The numerical experiments were conducted with the real geometry of the Danshuei River system. The boundary conditions include a simple harmonic tidal oscillation and salinity forced at the Danshuei River mouth and a constant river discharge applied at the head of the three tributaries. Two internal parameters, the coefficients of vertical turbulent viscosity and diffusivity, Az and Kz, respectively, were taken: (a) as time varying and (b) as constant. It was found that the use of variable coefficients, Az and Kz, instead of constant values, has significant effects on the vertical profiles of current and salinity distributions during a tidal period. Experimental runs with different values of the tidal amplitude, the river discharge and salinity showed the effects of interaction between the tidal-driven and density-driven components. The simulation results reveal that turbulent mixing terms had substantial impact on estuarine circulation and salinity distribution. Comparisons of field data and modelling results with constant and non-constant Az and Kz were also investigated.
Meeting report: Soft coastal cliff: understanding and managing retreat
Authors: Waters B. E. , Payne H. R.
Published: July 2006

This article reports on a seminar held at the Institution of Civil Engineers in May 2004. This, and a previous meeting in 2002, stemmed from Government-funded research into soft cliff erosion. While the previous meeting dealt with the theory, this one dealt with more practical issues by way of four papers. Dr Neil Dixon described work carried out on landsliding of unprotected London Clay cliffs at Warden Point on the Isle of Sheppey. Dr Alan Clark described practical examples of engineering schemes at Lyme Regis and at Castlehaven, Niton and the Military Road on the Isle of Wight. The final two papers described aspects of work on the Norfolk coast: Dr Mike Walkden presented a process-based regional model of shoreline recession while Peter Frew of North Norfolk District Council described the problems faced by his authority in managing a retreating coastline where property is under threat.
On the limits of toxicant-induced tolerance testing: Cotolerance and response variation of antibiotic effects
Authors: Schmitt Heike , Martinali Bennie , Van Beelen Patrick , Seinen Willem
Published: July 2006

Pollution-induced community tolerance (PICT) as an ecotoxicological test system has been claimed to detect pollutant effects highly specifically and sensitively. However, the specificity might be limited by the occurrence of cotolerance. Another limitation of the application of any ecotoxicological test system lies in variation of the measured responses. We tested the variation and the occurrence of cotolerance experimentally, using antibiotics as toxicants, soil microcosms as microbial communities, and tolerance determination in Biolog plates as PICT detection test. Bacteria have been discussed as being prone to multiple tolerances due to the possible accumulation of multiple resistance genes on mobile genetic elements. However, in our experiments, cotolerance occurred only between antibiotics of the same group (oxytetracycline and tetracycline), as expected from their identical mode of action. Cotolerance between oxytetracycline and tylosin in soil microcosms exposed to oxytetracycline was low, as was cotolerance to oxytetracycline in tylosin-exposed microcosms. We conclude that tolerance development to antibiotics in soils reflects the actual selection pressure rather than a general pattern of multiple resistances. Concerning variation, the PICT effect of tetracycline was well reproducible in two consecutive years. The response variation linked to PICT experiments in controlled microcosms was comparable to that of ecotoxicological test systems of equivalent complexity. In conclusion, our results support an application of the PICT methodology as an effective means to study the soil ecotoxicology of antibiotics.
Field evaluation of an avian risk assessment model
Authors: Vyas Nimish B. , Spann James W. , Hulse Craig S. , Borges Shannon L. , Bennett Richard S. , Torrez Martin , Williams Bruce I. , Leffel Robert
Published: July 2006

We conducted two laboratory subacute dietary toxicity tests and one outdoor subacute dietary toxicity test to determine the effectiveness of the U.S. Environmental Protection Agency's deterministic risk assessment model for evaluating the potential of adverse effects to birds in the field. We tested technical-grade diazinon and its D·Z·N® 50W (50% diazinon active ingredient wettable powder) formulation on Canada goose (Branta canadensis) goslings. Brain acetylcholinesterase activity was measured, and the feathers and skin, feet, and gastrointestinal contents were analyzed for diazinon residues. The dose–response curves showed that diazinon was significantly more toxic to goslings in the outdoor test than in the laboratory tests. The deterministic risk assessment method identified the potential for risk to birds in general, but the factors associated with extrapolating from the laboratory to the field, and from the laboratory test species to other species, resulted in the underestimation of risk to the goslings. The present study indicates that laboratory-based risk quotients should be interpreted with caution.
Enantiospecific toxicity of the β-blocker propranolol to Daphnia magna and Pimephales promelas
Authors: Stanley Jacob K. , Ramirez Alejandro J. , Mottaleb Mohammad , Chambliss C. Kevin , Brooks Bryan W
Published: July 2006

Propranolol is a widely prescribed, nonselective β-adrenergic receptor–blocking agent. Propranolol has been detected in municipal effluents from the ng/L to the low-μg/L range. Like many therapeutics and other aquatic contaminants, propranolol is distributed as a racemic mixture ((R,S)-propranolol hydrochloride). Although the (S)-enantiomer is the most active form in mammals (up to 100-fold difference), no information is available regarding the enantiospecific toxicity of propranolol to aquatic organisms. Acute and chronic studies were conducted with Daphnia magna and Pimephales promelas to determine enantiospecific toxicity of propranolol to a model aquatic invertebrate and vertebrate, respectively. Also, enantiospecific effects of propranolol on D. magna heart rate were examined. Propranolol treatment levels were verified using high-performance liquid chromatography/mass spectrometry. Acute (48-h) responses of both organisms were similar for all enantiomer treatments. Chronic P. promelas responses to propranolol enantiomers followed the hypothesized relationship of (S)-propranolol being more toxic than (R)-propranolol, but chronic D. magna responses did not. This is potentially the result of a lack of β-type receptors in cladocerans. No enantiospecific effects on daphnid heart rate were observed in acute exposures. Interestingly, some propranolol enantiomer treatments produced significant increases in reproduction before causing reproduction to decrease at higher treatment levels. To our knowledge, this research represents the first study of enantiospecific toxicity of chiral pharmaceutical pollutants.
Cumulative impacts assessment along a large river, using brown bullhead catfish (Ameiurus nebulosus) populations
Authors: West David W. , Ling Nicholas , Hicks Brendan J. , Tremblay Louis A. , Kim Nick D. , van den Heuvel Michael R.
Published: July 2006

The effects of point-source and diffuse discharges on resident populations of brown bullhead catfish (Ameiurus nebulosus (LeSueur, 1819)) in the Waikato River (New Zealand) were assessed at sites both upstream and downstream of point-source discharges. At each site, the population parameters, relative abundance, age structure, and individual indices, such as condition factor, organ (gonad, liver, and spleen) to somatic weight ratios, and number and size of follicles per female, were assessed. Physiological (blood), biochemical (hepatic ethoxyresorufin-O-deethylase [EROD] and plasma steroids), and other indicators (bile chemistry and liver metals) of exposure or response also were measured. No impacts on brown bullhead health were obvious at individual geothermal, municipal sewage, or thermal discharge sites or cumulatively along the river. Brown bullhead from the bleached kraft mill effluent site showed elevated levels of EROD, decreased numbers of red blood cells, increased numbers of white blood cells, and depressed levels of sex steroids. However, growth rates, condition factor, age structure, and gonadosomatic index suggest that discharges with significant heat or nutrients benefit catfish despite physiological impairment at one site. Consideration of brown bullhead population-level responses to discharges in a monitoring framework revealed three different population-level response patterns resulting from the point-source discharges.
Relative toxicological importance of aqueous and dietary metal exposure to a freshwater crustacean: Implications for risk assessment
Authors: Wilding Joanna , Maltby Lorraine
Published: July 2006

Abstract—Aquatic organisms can take up toxicants from water (aqueous exposure) and from food (dietary exposure), yet current environmental regulations often fail to consider the toxic effects of dietary exposure. Such unrealistic exposure scenarios may lead to ineffective water-quality standards or discharge consents that fail to provide adequate protection of the receiving water. Both dietary and aqueous exposure routes contributed to the bioaccumulation of zinc by Gammarus pulex, and both influenced the lethal and sublethal effects of zinc exposure. However, little concordance was found between body burden and magnitude of effect on feeding rate, and the duration of the postexposure response differed between exposure routes. Feeding inhibition, resulting from water-only or simultaneous aqueous and dietary exposure, persisted after the contaminant was removed, but feeding inhibition resulting from dietary exposure alone did not. These results imply that whereas aqueous exposure resulted in either irreversible or slowly reversible physiological damage, feeding inhibition in response to dietary zinc exposure involved an avoidance response. Water-only exposure studies underestimated the effects of simultaneous exposure to contaminated food and contaminated water. Therefore, regarding compounds for which dietary exposure is important, regulatory toxicity tests should either incorporate dietary exposure routes or be subjected to an additional uncertainty factor.
Toxicity of silver in water and sediment to the freshwater amphipodHyalella azteca
Authors: Call Daniel J. , Polkinghorne Christine N. , Markee Thomas P. , Brooke Larry T. , Geiger Dianne L. , Gorsuch Joseph W. , Robillard Kenneth A.
Published: July 2006

Hyalella azteca was exposed to Ag as AgNO3 over a 10-d period in water and two lake sediments that were selected on the basis of their differences in metal-binding properties. The median lethal concentrations (LC50s) for waterborne exposures were 5.4 and 4.9 μg/L for total and dissolved Ag, respectively. In the sediment containing a lesser quantity of total Ag-binding ligands (i.e., Bond Lake, Douglas County, WI, USA, sediment), an Ag-amended sediment toxicity test resulted in a 10-d LC50 of 0.084 g (i.e., 84,000 μg) Ag/kg dry sediment or 8.6 μg Ag/L of pore water (PW). The no-observed-effect concentration (NOEC) to lowest-observed-effect concentration (LOEC) range was 0.012 to 0.031 g Ag/kg dry sediment, or less than 5.0 to 6.0 μg Ag/L of PW. In the sediment with a greater quantity of total Ag-binding ligands (i.e., West Bearskin Lake, Cook County, MN, USA, sediment), the 10-d LC50 was 2.98 g Ag/kg dry sediment, and the NOEC to LOEC range was 2.15 to 4.31 g Ag/kg dry sediment. Because “dissolved” concentrations of Ag in PW were less than 5.0 μg/L at the critical exposures in the latter test, the bioavailable and toxic form of Ag may have been a weakly associated coprecipitate or colloidal complex with hydrous iron oxides that competitively partitioned to the surface of the gills.
Predicting effects on aquatic organisms from fluctuating or pulsed exposure to pesticides
Authors: Ashauer Roman , Boxall Alistair , Brown Colin
Published: July 2006

Exposure of aquatic nontarget organisms to pesticides almost always occurs as pulses or fluctuating concentrations. Extrapolation from laboratory to field thus depends on an understanding and ability to simulate effects resulting from these types of exposure. This paper reviews models that may be used to predict effects on aquatic organisms resulting from time-varying exposure to pesticides. We evaluate and compare the theoretical basis of these models and their applicability to the simulation of effects from fluctuating exposures. The many different models rest on only a few basic concepts with differing degrees of mechanistic character. Building on this critical review, we select the most appropriate models and propose modifications. Two process-based models, the threshold hazard model and the modified damage assessment model, represent the optimum descriptions that are available at present. They could facilitate a better understanding of the ecotoxicity of different compound and species combinations and even mixtures of noninteracting compounds. The possibility to model lethal and sublethal effects allows applications in risk assessment, standard setting, and ecological modeling.
Influence of salinity and organic carbon on the chronic toxicity of silver to mysids (Americamysis bahia) and silversides (Menidia beryllina)
Authors: Ward Timothy J. , Boeri Robert L. , Hogstrand Christer , Kramer James R. , Lussier Suzanne M. , Stubblefield William A. , Wyskiel Derek C. , Gorsuch Joseph W.
Published: July 2006

Tests were conducted with mysids (Americamysis bahia) and silversides (Menidia beryllina) to evaluate the influence of salinity and organic carbon on the chronic toxicity of silver. During 7- and 28-d tests conducted at 10, 20, and 30‰ salinity, higher concentrations of dissolved silver generally were required to cause a chronic effect as the salinity of the seawater was increased. The 28-d mysid and silverside 20%-effective concentration values (expressed as dissolved silver) ranged from 3.9 to 60 and from 38 to 170 μg/L, respectively, over the salinity range. This pattern was not observed when the same test results were evaluated against the concentrations of free ionic silver (measured directly during toxicity tests), as predicted by the free-ion activity model. Increasing the concentration of dissolved organic carbon from 1 mg/L to the apparent maximum achievable concentration of 6 mg/L in seawater caused a slight decrease in chronic toxicity to silversides but had no effect on the chronic toxicity to mysids. The possible additive toxicity of silver in both food and water also was investigated. Even at the maximum achievable foodborne concentration, the chronic toxicity of silver added to the water was not affected when silver was also added to the food, based on the most sensitive endpoint (growth). However, although fecundity was unaffected at all five tested concentrations during the test with silver in water only, it was significantly reduced at the two highest waterborne silver concentrations (12 and 24 μg/L) during the test with silver dosed into food and water.
Use of paired fathead minnow (Pimephales promelas) reproductive test. Part 1: Assessing biological effects of final bleached kraft pulp mill effluent using a mobile bioassay trailer system
Authors: Rickwood Carrie J. , Dubé Monique G. , Hewitt L. Mark , Kovacs Tibor G. , Parrott Joanne L. , MacLatchy Deborah L.
Published: July 2006

Reproductive effects have been recorded in wild fish in waters receiving pulp mill effluent (PME) since the mid to late 1980s. Laboratory assays with fathead minnow (FHM; Pimephales promelas) have been developed to better understand fish responses to PME. However, observations from laboratory studies have been variable, making it difficult to establish cause/effect relationships. A lack of environmental relevance in these laboratory studies may have contributed to the variability observed. The objectives of the present study were, first, to determine the effects of bleached kraft PME (BKME) on FHM under environmentally realistic conditions (i.e., ambient water and effluent quality) and, second, to determine the suitability of pair-breeding FHM to better link BKME-induced changes in indicators at the biochemical, individual, and population levels. A mobile bioassay trailer was situated on-site at a bleached kraft mill for 60 d, allowing supply of both ambient water (Lake Superior, Canada) and final BKME. The reproductive output of FHM was initially assessed for 21 d to obtain baseline data pre-exposure. At the end of the pre-exposure period, selected breeding pairs were exposed to final BKME (100% v/v and 1% v/v) for 21 d. Results demonstrated a stimulatory response pattern at 1% BKME (e.g., increased egg production) compared to control. In the 100% treatment, spawning events were reduced and fewer eggs were produced during the first two weeks of exposure. Exposure to 100% (v/v) BKME also resulted in ovipositor development in males and development of male secondary sex characteristics in females. Obtaining pre-exposure data and use of pair-breeding FHM in this assay gave a sensitive indication of effluent effects and allowed accurate comparisons of endpoints to be made.
Use of paired fathead minnow (Pimephales promelas) reproductive test. Part 2: Source identification of biological effects at a bleached kraft pulp mill
Authors: Rickwood Carrie J. , Dubé Monique G. , Hewitt L. Mark , Kovacs Tibor G. , MacLatchy Deborah L.
Published: July 2006

Reproductive effects of pulp mill effluents on fish continue to be reported in Canadian waters. Spawning delays, reduced gonad size, and altered levels of sex steroid hormones have been found in both sexes of various fish species exposed to effluents. We initiated a project to identify the source/cause of such effects. In part 1 of this two-part series, we exposed mature adult fathead minnow (FHM; Pimephales promelas) for 21 d to final treated effluent (1% and 100% v/v) from a bleached kraft pulp mill in Terrace Bay (ON, Canada). Results suggested pulp mill effluent from this mill affected reproductive indicators in FHM and effects were dependent on effluent concentration, duration of exposure, and method of data analysis. The main objective of this paper was to use the FHM assay to identify waste stream sources within the mill that affect reproductive indicators. Various process streams were selected, characterized with respect to effluent chemistry and acute toxicity, and a subset was tested on-site with the 21-d FHM bioassay. Results showed that both the combined mill effluent (before secondary treatment) and the combined alkaline stream (CALK) caused both decreased spawning events (∼55% for both streams) and decreased egg production (28 and 74%, respectively), and the CALK stream resulted in significant male ovipositor development. By comparing response patterns we were able to identify the CALK stream as a source of compounds at this mill affecting reproductive indicators in FHM and highlight this stream for further toxicity identification evaluation.
Effect of piperonyl butoxide on permethrin toxicity in the amphipodHyalella azteca
Authors: Amweg Erin L. , Weston Donald P. , Johnson Cathy S. , You Jing , Lydy Michael J.
Published: July 2006

Piperonyl butoxide (PBO) is a synergist of pyrethroid pesticides found in many products for structural pest control, mosquito control, and home and garden uses. Because both PBO and pyrethroid residues potentially co-occur in urban creeks, this study determined if environmental levels of PBO were capable of synergizing pyrethroids in the environment. Three types of toxicity tests were conducted with the amphipod Hyalella azteca to determine the minimum PBO concentration required to increase toxicity of the pyrethroid permethrin: Sediment was spiked with permethrin only; permethrin and overlying water spiked with PBO; and permethrin, PBO, and overlying water spiked with PBO. In tests with PBO added to both water and sediment, PBO concentrations of 2.3 μg/L in water and 12.5 μg/kg in sediment reduced the permethrin median lethal concentration (LC50) nearly 50% to 7.3 mg/kg organic carbon (OC). Higher concentrations of PBO increased permethrin toxicity up to sevenfold. In exposures with PBO in water alone, 11.3 μg/L was required to increase permethrin toxicity. Urban creek sediments from California and Tennessee, USA, had PBO concentrations in the low μg/kg range; only one water sample was above the detection limit of 0.05 μg/L. Wetlands in northern California also were sampled after application of pyrethrins and PBO for mosquito abatement. Sediment and water PBO concentrations within 12 h of abatement spraying peaked at 3.27 μg/kg and 0.08 μg/L, respectively. These results suggest that environmental PBO concentrations rarely, if ever, reach concentrations needed to increase pyrethroid toxicity to sensitive organisms, though available data on environmental levels are very limited, and additional data are needed to assess definitively the risk.
Bioavailability of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) to the prairie vole (Microtus ochrogaster)
Authors: Fellows Robert J. , Driver Crystal R. , Cataldo Dominic A. , Harvey Scott D.
Published: July 2006

Concerns have been raised over potential bioavailability and biotransfer of energetic materials such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The present study assessed plant-incorporated [14C]RDX and plant-derived [14C]RDX-metabolite ingestion by the prairie vole (Microtus ochrogaster). The animals were fed labeled chow (maximum, ≤ 10 g/d) for 5 or 7 d, followed by a 6- or 4-d chase period. More than 95% of all label presented was recovered in the summed excreta, with 74% of this in the fecal nonabsorbed bulk. Greater than 20% of the presented [14C]RDX and plant-derived [14C]RDX metabolites were absorbed by the animals' digestive tracts. These materials were either metabolized to 14CO2 (8–10% of the total label) or removed as nitrogenous waste through the kidneys (10–14%). Both 14C-urine and 14CO2 excretion continued after the feces cleared, indicating ongoing metabolism of the labeled material. Approximately 4% was retained within the tissues at death, with the highest total activity in the liver and the highest specific activity in the testes. Other labeled tissues included the lung, heart, brain, spleen, skeletal muscle, bone, and pancreas. All these tissues containing [14C]RDX-derived materials are available to subsequent predators, indicating a potential for transfer to a higher trophic level.
Chronic sublethal sediment toxicity testing using the estuarine amphipod,Melita plumulosa(Zeidler): Evaluation using metal-spiked and field-contaminated sediments
Authors: Gale Sharyn A. , King Catherine K. , Hyne Ross V.
Published: July 2006

The present study describes the development of a 42-d chronic sublethal sediment toxicity test using the estuarine amphipod Melita plumulosa (Zeilder). This test was shown to predict the toxicity of metal-contaminated sediments previously found to adversely affect benthic community structure. Metals initially were tested individually by spiking reference sediment under conditions that ensured low metal concentrations in pore waters. Fertility was the most sensitive sublethal endpoint for copper- and zinc-spiked sediments, whereas cadmium-spiked sediments were not toxic to M. plumulosa, despite their high bioaccumulation of cadmium. The 42-d chronic sediment test was reproducible; however, variation between reference sediments collected from the same field location over time or from different locations did affect the reproduction of M. plumulosa. Sensitivity of M. plumulosa to metal-spiked sediments suggested that the interim sediment-quality guidelines (ISQGs) were too conservative. However, toxicity testing of sediments collected from field sites known to affect community assemblages significantly (p < 0.001) reduced the fertility of M. plumulosa, reflecting benthic community survey results and supporting the ISQGs. Bioaccumulation of cadmium and copper by M. plumulosa was elevated following chronic exposure to both laboratory and field-contaminated sediments; however, zinc bioaccumulation could be measured only in M. plumulosa exposed to field-contaminated sediments.
Linking feeding activity and maturation of Daphnia magna following short-term exposure to fenvalerate
Authors: Reynaldi Sebastián , Duquesne Sabine , Jung Klaus , Liess Matthias
Published: July 2006

Feeding activity and maturation were investigated in Daphnia magna exposed to fenvalerate for 24 h. The feeding activity was monitored by measuring filtration rates and 15N-traced food assimilation. Exposure resulted in individuals with reduced feeding activity and smaller body size at concentrations of 0.3 μg/L or greater as well as delayed maturation at concentrations of 0.6 μg/L or greater. Filtration rates recovered within 2 d of the exposure, but long-term effects of reduced feeding activity, such as growth retardation, occurred. Because D. magna needs to reach a minimum size to mature, growth retardation may explain the observed delay in maturity. The proposed causal relationships suggest that exposure to fenvalerate reduces feeding activity, resulting in growth retardation, which leads to delayed maturity. In cases of exposure to such toxicants, the monitoring of feeding activity may predict long-term effects on population parameters.
Comparing cytotoxicity and genotoxicity in HaCaT cells caused by 6-aminochrysene and 5,6-chrysenequinone under ultraviolet A irradiation
Authors: Zhang Yi , Hwang Huey-Min , Ekunwe Stephen
Published: July 2006

Chrysene is one of the basic polycyclic aromatic hydrocarbons that are toxic environmental pollutants. The photoproducts of 6-aminochrysene (6AC) include 5,6-chrysenequinone (5,6-CQ) along with some minor products. In this study, cytotoxicity and genotoxicity of 6AC and 5,6-CQ to a human skin cell line, HaCaT, were measured with the fluorescein diacetate uptake (FDA) test and comet assay, respectively, in the presence or absence of ultraviolet A (UVA) irradiation. The FDA test result showed that HaCaT cell viability decreased dose dependently after exposure to UVA irradiation in both 6AC (0, 0.1, 0.5, 1, 5, 10, 50 μM) and 5,6-CQ (0, 0.05, 0.25, 0.5, 2.5, 5, 25 μM) groups, with the 6AC group having lower cell viability at the same substrate concentrations; therefore, 6AC was more cytotoxic. Results of the comet assay showed that the extent of DNA damage was also dose dependent after the combined UVA and 6AC treatment (0, 0.05, 0.1, 0.5, 1 μM), although no DNA damage was detectable in the 6AC group without UVA irradiation. In addition, no DNA damage was found in the 5,6-CQ group with or without UVA irradiation. Our study indicated that 5,6-CQ, the major photoproduct of 6AC, was less photocytotoxic than the parent compound and was not photogenotoxic to HaCaT cells under the experimental conditions.
Multisubstrate biodegradation kinetics for binary and complex mixtures of polycyclic aromatic hydrocarbons
Authors: Knightes Christopher D. , Peters Catherine A.
Published: July 2006

Biodegradation kinetics were studied for binary and complex mixtures of nine polycyclic aromatic hydrocarbons (PAHs): Naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, 2-ethylnaphthalene, phenanthrene, anthracene, pyrene, fluorene, and fluoranthene. Discrepancies between the observed biodegradation rates and those predicted by a sole-substrate model indicate that significant substrate interactions occurred in both the binary and complex-mixture experiments. For all compounds except naphthalene, biodegradation was enhanced. The observations were compared to predictions from two multisubstrate biodegradation kinetic models: One that accounts for competitive inhibition, and one that does not. Both models are fully predictive in that parameters had been determined from an independent set of sole-substrate experiments. In the binary experiments, the major multisubstrate effect was biomass enhancement as a result of growth on naphthalene. Substrate interactions were orders of magnitude larger for most compounds in the complex mixtures, but significant competitive inhibition effects counteracted some of the biomass enhancement effect. The present study has demonstrated that the sole-substrate model is inadequate to describe multisubstrate biodegradation kinetics for a broad range of PAH mixtures. Whereas the multisubstrate model without inhibition did an adequate job of predicting the observed effects in some cases, we advocate the use of the multisubstrate model with inhibition for similar modeling efforts in light of the evidence that the model was correct more often than not. Theory supports its use because of the common enzyme pathways for biodegradation of PAHs.
Acute toxicity of copper and silver toCeriodaphnia dubiain the presence of food
Authors: Kolts Jason M. , Boese Connie J. , Meyer Joseph S.
Published: July 2006

Food is added to exposure solutions in cladoceran chronic toxicity tests and sometimes in acute toxicity tests, but its effects on the bioavailability of toxicants have not been studied extensively. We compared the toxicity of waterborne Ag and Cu to Ceriodaphnia dubia in the presence or absence of food (a mixture of a yeast–Cerophyll®–trout chow slurry and a green alga) in two series of acute toxicity tests. In the first series, we added food to Ag or Cu exposure solutions 0, 30, 60, or 120 min before transferring C. dubia into the solutions. In the second series, we exposed C. dubia to waterborne Ag or Cu for 30, 60, and 120 min in the absence of food. Adding food before transferring C. dubia into the exposure solutions greatly decreased the toxicity of Ag, but had less effect on the toxicity of Cu. In contrast, adding food after transferring C. dubia into the exposure solutions did not alter the toxicity of Ag considerably and did not alter the toxicity of Cu as much as the reverse sequence. Median effects concentrations (EC50s) for 30-, 60-, and 120-min unfed Ag tests were within the range of EC50s for 48-h unfed Ag tests, suggesting most uptake that contributes to acute Ag toxicity to C. dubia occurs within the first 30 to 60 min. However, uptake that contributes to acute Cu toxicity to C. dubia appears to occur over more than 2 h. Therefore, standard food decreases the toxicity of waterborne Ag and Cu to C. dubia, and the timing of adding food to exposure solutions is especially important in Ag tests.
Genotoxicity of polar fractions from a herbicide-contaminated soil does not correspond to parent contaminants
Authors: Kubátová Alena , Dronen Laura C. , Hawthorne Steven B.
Published: July 2006

Fractionation with biological and chemical analysis has been proposed to characterize the risk associated with complex samples. Thus, we have employed hot pressurized water for fractionating a herbicide-contaminated soil. Genotoxicity was found in polar and midpolarity fractions extracted from a historically herbicide-contaminated soil. However, the parent herbicides as well as organic solvent extracts (consisting of herbicides) were not genotoxic. Thus, polar organics formed by natural degradation of herbicides may be responsible for the genotoxic response. For correct assessment of the toxicity of complex matrices such as soils, both contaminated and uncontaminated samples need to be studied for their toxicological impact.
A comparison of the effects of single and repeated exposure to an organophosphate insecticide on acetylcholinesterase activity in mammals
Authors: Long Sara M. , Dawson Alistair , Shore Richard F.
Published: July 2006

Exposure to organophosphate (OP) pesticides can occur in free-living mammals in treated areas. Risk to nontarget animals from OPs usually is assessed with acute exposure data, but exposure of wild animals is likely to be intermittent and chronic. We compared the effects of single or repeated (hourly and daily) exposure to dimethoate on acetylcholinesterase (AChE) activity in laboratory mice to assess the suitability of standard laboratory tests for assessing risk. Mice were exposed either to a single dose (10 or 30 mg/kg) or to short-term repeated (three hourly doses of 10 mg/kg) intraperitoneal doses of dimethoate, and brain and serum AChE activity were measured. No significant difference was found in the degree of inhibition of AChE activity following acute and short-term repeated exposure. In a second experiment, mice were given three daily doses of 10 or 20 mg/kg of dimethoate, and both AChE activity and hepatic cytochrome P450 enzyme activity were measured. Daily exposure resulted in a dose-dependent decline in brain and serum AChE activity, and inhibition increased progressively with successively repeated exposures. However, this effect was relatively small compared to the effect of dose. Cytochrome P450 enzyme activity (CYP2B) was inhibited in the dimethoate-dosed mice. Our results indicate that acute dose–response toxicity studies are suitable models for predicting the likely occurrence of adverse effects from either short- or longer-term exposure of wild mammals to anticholinesterase compounds. Likely differences in exposure pattern between the laboratory and the natural environment are unlikely to bias the predictive power of these studies significantly.
Comparison of selenium bioaccumulation in the clams Corbicula fluminea and Potamocorbula amurensis: A bioenergetic modeling approach
Authors: Lee Byeong-Gweon , Lee Jung-Suk , Luoma Samuel N.
Published: July 2006

Selenium uptake from food (assimilation efficiency) and dissolved phase (influx rate) as well as loss kinetics (efflux rate) were compared between two bivalves, Corbicula fluminea and Potamocorbula amurensis. The effects of salinity and temperature on these kinetic parameters for both clam species also were evaluated. The Asiatic clam, C. fluminea, more efficiently assimilated Se associated with algae (66–87%) than Se associated with oxic sediments (20–37%). However, no consistent difference was found between Se assimilation efficiencies from both food types (19–60%) for P. amurensis. The temperature and salinity had a minor influence on the Se assimilation from ingested food. However, the effects of temperature and salinity were more evident in the uptake from dissolved sources. The influx rate of Se(IV) increased by threefold with the increase of temperature from 5 to 21°C for C. fluminea. The increase of salinity from 4 to 20 psu decreased the uptake rate constant (ku) of Se in P. amurensis from 0.011 to 0.005 L/g/h, whereas salinity change (0–8 psu) had a negligible effect on the Se influx rate of C. fluminea. The Se influx rate of P. amurensis decreased by half with the 3.5-fold increase in tissue dry weight. The rate constant of loss was greater for P. amurensis (0.029/d at 8 psu) than for C. fluminea (0.014/d at 0 psu and 0.01/d at 8 psu). A bioenergetic model suggests that dietary uptake is the dominant pathway for Se bioaccumulation in the two clams in San Francisco Bay and that interspecies differences in Se bioaccumulation can be explained by differences in food ingestion rates.
Isolation and partial characterization of proteins involved in maternal transfer of selenium in the western fence lizard (Sceloporus occidentalis)
Authors: Unrine Jason M. , Jackson Brian P. , Hopkins William A. , Romanek Christopher
Published: July 2006

Selenium from dietary exposure is efficiently transferred from mother to offspring in oviparous vertebrates, where it can cause severe teratogenic effects. We isolated and partially characterized proteins involved in maternal transfer of selenium in the oviparous lizard Sceloporus occidentalis using size-exclusion chromatography, inductively coupled plasma–mass spectrometry, and polyacrylamide gel electrophoresis. Selenium from dietary selenomethionine exposure was incorporated into at least three egg proteins. One of these proteins was lipovitellin. The other two proteins may be part of a previously unknown mechanism of maternal transfer of Se that is independent of vitellogenesis or albumin secretion. Our results suggest at least three pathways for maternal transfer of Se in vertebrates that may vary in importance depending on the species.
Inhibition of aquatic toxicity of pyrethroid insecticides by suspended sediment
Authors: Yang Weichun , Spurlock Frank , Liu Weiping , Gan Jianying
Published: July 2006

The use of pyrethroid insecticides is increasing in both agricultural and urban environments. Although pyrethroids display very high acute toxicities to water column organisms in laboratory tests, environmental water samples typically contain suspended sediment (SS) that can reduce the freely dissolved concentration of pyrethroids, hence their bioavailability. Consequently, phase distribution could play an important role in pyrethroid aquatic toxicology. In this study, we evaluated the effect of SS on the acute toxicity of four widely used pyrethroid insecticides to Ceriodaphnia dubia. In all assays, median lethal concentrations (LC50s) consistently increased with increasing SS, demonstrating the pronounced inhibitory effects of SS on pyrethroid toxicity. The LC50s in the 200 mg/L SS solutions were 2.5 to 13 times greater than those measured in sediment-free controls. Solid-phase microextraction (SPME) was used to determine the apparent distribution coefficient Kd for the pyrethroids in the water samples. Under the assumption that only the freely dissolved fraction is bioavailable, the measured Kd was used to predict C. dubia LC50s in the water samples. The predicted LC50s were within a factor of two of the measured values for 95% of the treatments. Results from this study suggest that the inhibitory effect of SS can be highly significant and must be considered in estimating exposures to pyrethroids in aquatic systems. The SPME methodology could be used effectively to measure bioavailable concentration and to predict the actual ecotoxicologic effects of pyrethroids.
Macro-Level policy and Micro-Level planning
Authors: Barkhuizen Gary , Knoch Ute
Published: July 2006

This article reports on a study which investigated the language lives of Afrikaans-speaking South African immigrants in New Zealand. Particularly, it focuses on their awareness of and attitudes to language policy in both South Africa and New Zealand, and how these influence their own and their family’s language practices. Narrative interviews with 28 participants living in towns and cities across New Zealand reveal that while living in South Africa they were generally aware of macro-level language policies in the country, and were able to articulate how these policies influenced language practices at work and within their families. The absence of an explicit national language policy in New Zealand means that these immigrants, on arrival in New Zealand, base their understanding of the linguistic context in the country on the language practices that they observe in their day-to-day lives. It is these observations which guide their decision-making with regard to their own and their family’s language practices.
Student expectations of TESOL programs
Authors: Bordia Sarbari , Wales Lynn , Pittam Jeffery , Gallois Cindy
Published: July 2006

Most practitioners teaching English to speakers of other languages (TESOL) will agree that students come with some expectations about course content and teaching methodology and that these expectations play a vital role in student motivation and learning. However, the study of student expectations has been a surprising omission from Second Language Acquisition research. In the studies reported here, we develop a model of student expectations by adapting the Expectation Disconfirmation paradigm, widely used in consumer psychology. Student and teacher perspectives on student expectations were gathered by interviews. Responses shed light on the nature of expectations, factors causing expectations and effects of expectation fulfilment (or lack of it). The findings provide new avenues for research on affective factors as well as clarify some ambiguities in motivational research in second language acquisition. The model presented here can be used by teachers or institutions to conduct classroom-based research, thus optimising students’ learning and performance, and enhancing student morale.
Land Use Change Effects on Forest Carbon Cycling Throughout the Southern United States
Authors: Woodbury Peter B. , Heath Linda S. , Smith James E.
Published: July 2006

We modeled the effects of afforestation and deforestation on carbon cycling in forest floor and soil from 1900 to 2050 throughout 13 states in the southern United States. The model uses historical data on gross (two‐way) transitions between forest, pasture, plowed agriculture, and urban lands along with equations describing changes in carbon over many decades for each type of land use change. Use of gross rather than net land use transition data is important because afforestation causes a gradual gain in carbon stocks for many decades, while deforestation causes a much more rapid loss in carbon stocks. In the South‐Central region (Texas to Kentucky) land use changes caused a net emission of carbon before the 1980s, followed by a net sequestration of carbon subsequently. In the Southeast region (Florida to Virginia), there was net emission of carbon until the 1940s, again followed by net sequestration of carbon. These results could improve greenhouse gas inventories produced to meet reporting requirements under the United Nations Framework Convention on Climate Change. Specifically, from 1990 to 2004 for the entire 13‐state study area, afforestation caused sequestration of 88 Tg C, and deforestation caused emission of 49 Tg C. However, the net effect of land use change on carbon stocks in soil and forest floor from 1990 to 2004 was about sixfold smaller than the net change in carbon stocks in trees on all forestland. Thus land use change effects and forest carbon cycling during this period are dominated by changes in tree carbon stocks.
Soil Organic Carbon Sequestration in Cotton Production Systems of the Southeastern United States
Authors: Causarano H. J. , Franzluebbers A. J. , Reeves D. W. , Shaw J. N.
Published: July 2006

Past agricultural management practices have contributed to the loss of soil organic carbon (SOC) and emission of greenhouse gases (e.g., carbon dioxide and nitrous oxide). Fortunately, however, conservation‐oriented agricultural management systems can be, and have been, developed to sequester SOC, improve soil quality, and increase crop productivity. Our objectives were to (i) review literature related to SOC sequestration in cotton (Gossypium hirsutum L.) production systems, (ii) recommend best management practices to sequester SOC, and (iii) outline the current political scenario and future probabilities for cotton producers to benefit from SOC sequestration. From a review of 20 studies in the region, SOC increased with no tillage compared with conventional tillage by 0.48 ± 0.56 Mg C ha−1 yr−1 (H0: no change, p < 0.001). More diverse rotations of cotton with high‐residue‐producing crops such as corn (Zea mays L.) and small grains would sequester greater quantities of SOC than continuous cotton. No‐tillage cropping with a cover crop sequestered 0.67 ± 0.63 Mg C ha−1 yr−1, while that of no‐tillage cropping without a cover crop sequestered 0.34 ± 47 Mg C ha−1 yr−1 (mean comparison, p = 0.04). Current government incentive programs recommend agricultural practices that would contribute to SOC sequestration. Participation in the Conservation Security Program could lead to government payments of up to $20 ha−1 Current open‐market trading of C credits would appear to yield less than $3 ha−1, although prices would greatly increase should a government policy to limit greenhouse gas emissions be mandated.
Effects of Land Use on Soil Inorganic Carbon Stocks in the Russian Chernozem
Authors: Mikhailova Elena A. , Post Christopher J.
Published: July 2006

Little is known about changes in soil inorganic carbon (SIC) stocks with depth and with land use in grassland ecosystems. This study was conducted to determine SIC stocks under different management regimes in the Mollisol, one of the typical soils in grasslands. Four sites were sampled: a native grassland field (not cultivated for at least 300 yr), an adjacent 50‐yr continuous fallow field, a yearly cut hay field in the V.V. Alekhin Central‐Chernozem Biosphere State Reserve in the Kursk region of Russia, and a continuously cropped field in the Experimental Station of the Kursk Institute of Agronomy and Soil Erosion Control. All sampled soils were classified as fine‐silty, mixed, frigid Pachic Hapludolls. Significant differences occurred in SIC stocks between cultivated and grassland soil. The inorganic carbon stocks in the top 2 m were 107 Mg ha−1for the native grassland, 91 Mg ha−1for the yearly cut hay field, 242 Mg ha−1for the continuously cropped field, and 196 Mg ha−1for the 50‐yr continuous fallow. The SIC was in the form of calcium carbonate and was mostly stored below the 1‐m depth. The largest difference between inorganic carbon stocks was observed between the continuously cropped field and native grassland. The increase in inorganic carbon in the continuously cropped field and continuous fallow was attributed to initial cultivation and fertilization. Soil inorganic carbon in Mollisols is not accounted for in the current global carbon estimates.