bluuebunny/crossref_metadata_2025 huggingface dataset:
Porcine Somatostatin Receptor 2 Displays Typical Pharmacological sst2 Features but Unique Dynamics of Homodimerization and Internalization
Authors: Durán-Prado Mario , Bucharles Christine , Gonzalez Bruno J. , Vázquez-Martínez Rafael , Martínez-Fuentes Antonio J. , García-Navarro Socorro , Rhodes Simon J. , Vaudry Hubert , Malagón María M. , Castaño Justo P.
Published: October 2006

Somatostatin (SRIF) exerts its multiple actions, including inhibition of GH secretion and of tumoral growth, through a family of five receptor subtypes (sst1-sst5). We recently reported that an sst2-selective agonist markedly decreases GH release from pig somatotropes, suggesting important roles for this scarcely explored receptor, psst2. Here, functional expression of psst2 in Chinese hamster ovary-K1 and human embryonic kidney-293-AD cell lines was employed to determine its pharmacological features and functional ability to reduce cAMP, and to examine its homodimerization and internalization dynamics in real time in single living cells. Results show that psst2 is a high-affinity receptor (dissociation constant = 0.27 nm) displaying a typical sst2 profile (nm affinity for SRIF-14≥SRIF-28>cortistatin>MK678>octreotide) and high selectivity (EC50 = 1.1 nm) for the sst2 agonist l-779,976, but millimolar or undetectable affinity to other sst-specific agonists (sst3>sst1>sst5⋙sst4). Accordingly, SRIF dose-dependently inhibited forskolin-stimulated cAMP with high potency (EC50 = 6.55 pm) and modest efficacy (maximum 29.1%) via psst2. Cotransfection of human embryonic kidney-293 and Chinese hamster ovary-K1 cells with two receptor constructs modified with distinct fluorescent tags (psst2-YFP/psst2-CFP) enabled fluorescence resonance energy transfer measurement of physical interaction between psst2 receptors and also receptor internalization in single living cells. This revealed that under basal conditions, psst2 forms constitutive homodimers/homomultimers, which dissociate immediately (11 sec) upon SRIF binding. Interestingly, contrary to human sst2, psst2 rapidly reassociates (110.5 sec) during a subsequent process that temporally overlaps with receptor internalization (half-maximal = 95.1 sec). Therefore, psst2 is a potent inhibitory receptor displaying a unique set of interrelated dynamic features of agonist-dependent dimerization, dissociation, internalization, and reassociation, a cascade of events that might be critical for receptor function.
Genomic splice-site analysis reveals frequent alternative splicing close to the dominant splice site
Authors: Dou Yimeng , Fox-Walsh Kristi L. , Baldi Pierre F. , Hertel Klemens J.
Published: October 2006

Alternative pre-mRNA splicing may be the most efficient and widespread mechanism to generate multiple protein isoforms from single genes. Here, we describe the genomic analysis of one of the most frequent types of alternative pre-mRNA splicing, alternative 5′- and 3′-splice-site selection. Using an EST-based alternative splicing database recording >47,000 alternative splicing events, we determined the frequency and location of alternative 5′- and 3′-splice sites within the human genome. The most common alternative splice sites used in the human genome are located within 6 nucleotides (nt) of the dominant splice site. We show that the EST database overrepresents alternative splicing events that maintain the reading frame, thus supporting the concept that RNA quality-control steps ensure that mRNAs that encode for potentially harmful protein products are destroyed and do not serve as templates for translation. The most frequent location for alternative 5′-splice sites is 4 nt upstream or downstream from the dominant splice site. Sequence analysis suggests that this preference is a consequence of the U1 snRNP binding sequence at the 5′-splice site, which frequently contains a GU dinucleotide 4 nt downstream from the dominant splice site. Surprisingly, ∼50% of duplicated 3′-YAG splice junctions are subject to alternative splicing. This high probability of alternative 3′-splice-site activation in close proximity of the dominant 3′-splice site suggests that the second step of the splicing may be prone to violate splicing fidelity.
An unusual Dicer-like1 protein fuels the RNA interference pathway inTrypanosoma brucei
Authors: Shi Huafang , Tschudi Christian , Ullu Elisabetta
Published: October 2006

RNA interference (RNAi) is an evolutionarily conserved gene-silencing pathway that is triggered by double-stranded RNA (dsRNA). Central to this pathway are two ribonucleases: Dicer, a multidomain RNase III family enzyme that initiates RNAi by generating small interfering RNAs (siRNAs), and Argonaute or Slicer, an RNase H signature enzyme that affects cleavage of mRNA. Previous studies in the early diverging protozoanTrypanosoma bruceihave established a key role for Argonaute 1 in RNAi. However, the identity of Dicer has not been resolved. Here, we report the identification and functional characterization of aT. bruceiDicer-like enzyme (TbDcl1). Using genetic and biochemical approaches, we provide evidence that TbDcl1 is required for the generation of siRNA-size molecules and for RNAi. Whereas Dicer and Dicer-like proteins are endowed with two adjacent RNase III domains at the carboxyl terminus (RNase IIIa and RNase IIIb), the arrangement of these two domains is unusual in TbDcl1. RNase IIIa is close to the amino terminus, and RNase IIIb is located approximately in the center of the molecule. This domain organization is specific to trypanosomatids and further illustrates the variable structures of protozoan Dicer-like proteins as compared to fungal and metazoan Dicer.
Effect of Provider Continuity on Test Repetition
Authors: van Walraven Carl , Cernat Geta , Austin Peter C
Published: October 2006

Background: Provider continuity (PC) occurs when a patient is treated by the same physician over time. A perceived benefit of PC is decreased test repetition. Repeat tests make up a significant proportion of overall laboratory utilization. This study determined whether test repetition increases when PC decreases.

Methods: Cohort study of adults in eastern Ontario, Canada between September 1999 and September 2000 using population-based clinical databases. The primary study outcome was the probability that 7 common laboratory tests (hemoglobin, sodium, creatinine, thyrotropin, total cholesterol, ferritin, and hemoglobin A1C) were repeated at physician visits subsequent to the index test. We determined whether the probability of test repetition changed if the follow-up physician ordered the index test. We adjusted for multiple factors regarding the patient (age, sex, days in hospital, and number of physician visits in previous year), index test (normality and location), follow-up visit (location and time from index test), and follow-up physician (age and specialty).

Results: The study included 881 353 patients, 1 419 438 index laboratory tests, and 7 622 938 follow-up physician visits. After adjusting for other important factors, we found that tests were significantly more likely to be repeated if the follow-up physician ordered the index test (adjusted odds ratio range 2.5–5.9). This association was consistent in most subgroups.

Conclusions: For these common laboratory investigations, PC was associated with increased, not decreased, test repetition. This suggests that increased PC alone will likely not decrease test utilization.
A Novel Real-Time Duplex PCR Assay for Detecting penA and ponA Genotypes in Neisseria gonorrhoeae: Comparison with Phenotypes Determined by the E-Test
Authors: Vernel-Pauillac Frédérique , Merien Fabrice
Published: October 2006

Background: For many years, the pathogenic bacterium Neisseria gonorrhoeae, the etiologic agent of gonorrhea, was generally susceptible to penicillin, until the emergence of resistant strains. Well-characterized genetic variations in the penicillin resistance–determining region correlate with decreased susceptibility to penicillin. At least 5 genes (penA, penB, mtrR, ponA, and penC) are involved in the chromosomally mediated resistance to this antibiotic. To date, no development of multiplex PCR assays targeting a range of gonococcal genes and variations as a means of predicting antibiotic resistance has been reported.

Methods: The aim of this study was to develop a duplex assay using DNA from isolated strains. We describe the development and evaluation on the LightCycler platform of a real-time duplex PCR assay (hybridization probe format) for rapid and specific detection of ponA and penA variations, predicting penicillin susceptibilities.

Results: The real-time duplex PCR assay successfully detected variations in ponA and penA genes by use of distinct melting temperatures from a total of 120 Neisseria gonorrhoeae isolates. Moreover, the variation profiles obtained with the real-time PCR and the melting analysis showed good correlation with the pattern of penicillin susceptibility generated with classical antibiograms. Nucleotide sequencing data were in complete agreement with multiplex assay results.

Conclusions: The presented assay is suitable for the detection of chromosomally mediated resistant strains of Neisseria gonorrhoeae in genotyping studies and could be valuable in the effective antimicrobial strategy to gonococci.
How Biased Household Inventory Estimates Distort Shopping and Storage Decisions
Authors: Chandon Pierre , Wansink Brian
Published: October 2006

The authors develop a model of how consumers estimate the level of product inventory in their households. Two laboratory experiments and two field studies involving 29 product categories show that (1) consumers anchor their estimates on their average inventory and fail to adjust sufficiently; (2) adjustments follow an inelastic psychophysical power function, leading to overestimations of low levels of inventory and underestimations of high levels; and (3) adjustments are more elastic and, thus, more accurate when inventory is salient. Contrary to the assumptions of practitioners and academic modelers, these inventory estimates, not actual inventory levels, drive subsequent purchase incidence. Simulation results further show that biased estimates increase overstocking and spoilage among stockout-averse consumers but increase stockouts and unmet demand among overstocking-averse consumers. By predicting the magnitude, not just the direction, of estimation biases, the model and the results offer new insights into accelerating the consumption of healthy foods and improving the targeting of stockpiling-inducing sales promotions.
Promotion Profitability for a Retailer: The Role of Promotion, Brand, Category, and Store Characteristics
Authors: Ailawadi Kusum L. , Harlam Bari A. , César Jacques , Trounce David
Published: October 2006

The purpose of this article is to quantify the net unit and net profit impact of promotions for a retailer and to understand the key correlates of this impact. Using data on all promotions offered in 2003 by CVS, a leading U.S. drug retailer, the authors (1) quantify the gross promotional lift; (2) decompose this into switching, stockpiling, and incremental lift for the retailer; (3) estimate the extent to which promotion affects sales of other product categories in the store to compute the net unit impact of the promotion; (4) account for promotional and nonpromotional margins and manufacturer funding to compute the net profit impact of the promotion; and (5) examine how promotion, brand, category, and store characteristics influence the net impact. The authors find that approximately 45% of the gross lift is incremental for CVS, and there is also a significant, positive halo effect on sales of other categories. However, on average, the net profit impact of promotions is negative because CVS's promotional margin is often substantially less than regular margin. In the authors' analysis of the correlates of net impact, they find that many promotion and brand characteristics have opposing associations with net unit and net profit impact. Deep, featured promotions on high “consumer-pull” brands generate high net unit impact, but they significantly reduce CVS's promotional margin, resulting in lower net profit impact. Therefore, the retailer must make some difficult trade-offs between revenue and profit objectives in promotion decisions.
The Short- and Long-Term Impact of an Assortment Reduction on Category Sales
Authors: Sloot Laurens M. , Fok Dennis , Verhoef Peter C.
Published: October 2006

In a collaborative study with a major Dutch retailer, the authors assess the short- and long-term effects of a 25% item reduction on category sales. On an aggregate level, a major assortment reduction can lead to substantive short-term category sales losses but only a weak negative long-term category sales effect. Short-term category sales losses are caused mainly by fewer category purchases by former buyers of delisted detergent items. However, the results also show that the assortment reduction attracts new category buyers. These new buyers partially offset the sales losses among former buyers of the delisted items. The collection of supplemental process data on assortment perceptions and actual search time in the test stores before and after the assortment reduction provides evidence that delisting results in an increase in perceived search efficiency and a decrease in actual search time.
Deferring versus Expediting Consumption: The Effect of Outcome Concreteness on Sensitivity to Time Horizon
Authors: Malkoc Selin A. , Zauberman Gal
Published: October 2006

This work examines consumers' preferences for consumption timing. Specifically, the authors examine how temporal framing (deferring versus expediting) of a decision moderates the sensitivity of consumers' pattern of discounting to changes in time horizon. The results from three experiments show greater decline in consumers' discount rates with time horizon (i.e., greater present bias) when they defer than when they expedite consumption. These results are robust to using monetary and nonmonetary outcomes, as well as to different time horizons (months, days). The authors further demonstrate that the different levels of mental representations (concreteness) triggered by the two decision frames moderate this difference in sensitivity.
Fading Optimism in Products: Temporal Changes in Expectations about Performance
Authors: Monga Ashwani , Houston Michael J.
Published: October 2006

The authors demonstrate that choosing one product from a set of competing alternatives can change expectations about the chosen product such that consumers can become optimistic about the product's performance, and this optimism can then fade away. In five experiments, the authors show that this phenomenon of fading optimism in products is robust across different experimental settings and product categories and is moderated by prior attitude toward the product category and ambiguity of the product's performance.
Customizing Complex Products: When Should the Vendor Take Control?
Authors: Ghosh Mrinal , Dutta Shantanu , Stremersch Stefan
Published: October 2006

Casual observation suggests that firms use contrasting practices and procedures when offering customized products to individual customers. Some firms take a “hands-off” approach and let customers self-select their desired product. In contrast, other firms are proactively involved in designing customized solutions to individual customer needs. The authors call the former “low vendor customization control” and the latter “high vendor customization control.” Despite the strategic importance of customization, no research has shed light on the rationale for using these contrasting approaches to customization and their normative consequences. The authors develop a conceptual model that contends that the appropriate level of vendor control over the customization decision is a function of technology and knowledge considerations. They use data on 304 procurement arrangements for customized products to test their hypotheses and to explore the normative ramifications for three key measures of performance: closeness of the delivered product to customer needs, delivery performance, and the vendor's operating profits. The results show that contracting parties choose the level of vendor control over customization in a strategic and discriminating way to enhance the benefits from customization for both parties. The authors discuss implications for both theory and practice.
Effect of Fluoride on Corrosion of Cooling System Metals in Ethylene Glycol-Based Antifreeze/Coolants
Authors: Yang B , Gershun AV , Marinho FJ , Woyciesjes PM
Published: October 2006

Automotive and light-duty vehicle heat exchangers such as radiators are now predominantly made of aluminum alloys. For over 20 years, a brazing technique known as “controlled atmosphere brazing (CAB) with noncorrosive fluxes” has become the preferred process for producing aluminum automotive heat exchangers for original equipment manufacturers and aftermarket suppliers. Fluoride-based fluxes are typically used in the CAB processes to dissolve the aluminum oxide layer on the surface and inhibit reoxidation during the brazing cycle to allow the clad alloy to flow properly. The flux is generally a mixture of potassium fluoroaluminate, (K3AlF6, K2AlF5, and KAlF4). The flux residue left on the internal surface of heat exchangers after brazing is thought to be insoluble and noncorrosive, hence no removal is necessary. Although external corrosion of brazed aluminum heat exchangers has been studied using salt spray tests, a study addressing the effect of interaction between different antifreeze and flux residues on internal corrosion has not been reported. To the authors' knowledge, few studies on the effect of fluoride in engine coolants on metal corrosion are available. In this paper, laboratory test data are provided to show that flux residue is soluble in commercially available coolants and can generate fluoride ions that enhance cooling system corrosion. Systematic study on the effect of fluoride on metal corrosion in cooling systems and its remedies are also presented and discussed.
New Synthesis Method and Mechanical Properties of Magnesium Matrix Composites
Authors: Zhang X , Wang H , Liao L , Ma N
Published: October 2006

A new method to in situ fabricate magnesium alloy reinforced with 8 wt % of TiB2 and TiC is described. The XRD result revealed the formation of TiB2 and TiC in master alloy magnesium matrix composites. Uniform distribution of fine reinforcement in the matrix material obtained through microstructural characterization. Mechanical characterization revealed that the presence of TiB2 and TiC leads to an increase on microhardness and tensile strength of magnesium matrix composites. Scanning electronic micrographs taken from the tensile fracture surface of magnesium matrix composites revealed typical brittle fracture.
Estimation of Annual Incidence of Lung Cancer Associated with Work Place Exposure to Passive Smoking in France
Authors: Alipour Shahryar , Deschamps Frederic , Lesage Francois‐Xavier , Lebargy Francois
Published: October 2006

Estimation of Annual Incidence of Lung Cancer Associated with Work Place Exposure to Passive Smoking in France: Shahryar Alipour, et al. Department of Occupational Health, Faculté de Médecine, France—This study attempted to estimate the number of annual new cases of lung cancer from workplace exposure to Environmental Tobacco Smoke (ETS) in France. The number of new lung cancer cases attributable to workplace ETS exposure in France was estimated with regard to the following factors: excess risk of lung cancer from workplace ETS exposure, incidence of lung cancer in non‐exposed non‐smokers, and number of French workers exposed to passive smoking. The excess risk of lung cancer from workplace ETS exposure was estimated as from 0.12 to 0.39 by different references. The French workforce, regularly exposed to ETS in their workplace is about 3.2 millions. The incidence of lung cancer of non‐smokers without exposure to ETS is between 3.7 to 10 per hundred thousand. If these three factors are combined, it is estimated that exposure to workplace passive smoking causes around 14 to 125 new cases of lung cancer each year in France. New lung cancer cases from workplace exposure to ETS represent a few percent of all occupational lung cancers, and a minuscule number in regards to the whole lung cancer annual incidence (14 to 125 for 23,000 lung cancers in France=0.06% to 0.54%)
Giberela do trigo: aspectos epidemiológicos e modelos de previsão
Authors: Del Ponte Emerson M. , Fernandes J. Maurício C. , Pierobom Carlos R. , Bergstrom Gary C.
Published: October 2006

A giberela ou fusariose da espiga é, atualmente, uma das mais importantes doenças da cultura do trigo (Triticum aestivum). Epidemias severas têm sido observadas nos últimos anos em diversas regiões do mundo, promovendo perdas na produtividade e na qualidade dos grãos. No Brasil, a giberela alcançou o status de principal doença nas regiões tritícolas, principalmente no Sul do Brasil. A sua natureza esporádica está associada à dependência climática, sendo as mais severas epidemias observadas em anos com maior freqüência de chuvas, durante a fase de florescimento e enchimento de grãos. Poucas são as cultivares com resistência genética aceitável e essas normalmente falham em anos muito favoráveis a epidemias. Medidas de controle com fungicidas têm sido preconizadas, entretanto, a dificuldade reside no momento e na tecnologia de aplicação, para se obter resultados satisfatórios. O melhor entendimento dos fatores que influenciam a dinâmica da doença pode auxiliar no manejo da cultura visando a minimizar os riscos de epidemias. Aspectos como aerobiologia e tipo de inóculo, distribuição espacial e gradiente espacial da doença podem contribuir no conhecimento da associação e a importância de fontes de inóculo local ou distante ao campo. Recentemente, uma grande atenção tem sido dada ao desenvolvimento de modelos de previsão ou de risco de giberela. Tais modelos podem auxiliar na tomada de decisão no acionamento de medidas de controle bem como alertar níveis epidêmicos da doença em uma determinada região, ou mesmo quanto à alta contaminação do trigo com micotoxinas de Fusarium spp.
Controle da podridão gomosa em melão rendilhado em cultivo protegido por sanitização de ferramenta de poda
Authors: Vida João Batista , Tessmann Dauri J. , Zambolim Laércio , Verzignassi Jaqueline R. , Brandão Filho José Usan T.
Published: October 2006

A podridão gomosa (Didymella bryoniae) é a principal doença para o meloeiro rendilhado (Cucumis melo) cultivado em estufas no Norte do Estado do Paraná e a poda das brotações laterais das plantas tem sido eficiente meio de disseminação do patógeno. Este trabalho teve como objetivo estudar o efeito da desinfestação da tesoura de poda com hipoclorito de sódio (2%), no desenvolvimento da podridão gomosa em meloeiro rendilhado cultivado em estufa plástica. Foram utilizados os híbridos Bônus II e Sunrise em oito estufas, localizadas em diferentes propriedades em Maringá, Paraná. Avaliou-se a incidência da doença através da percentagem de plantas com alguma necrose no caule, a percentagem de plantas mortas e o brix e a produtividade dos frutos. Os resultados mostraram a alta eficiência da técnica de desinfestação da tesoura de poda no controle da doença. Para Bônus II e Sunrise, podados com tesoura desinfestada, a percentagem de plantas com necrose no caule variou de 27,5 a 12,5 e de 20,0 a 7,5, respectivamente. Ainda com esse tratamento, a percentagem de plantas mortas variou de 7,5 a 2,5 e de 10,0 a 2,5, respectivamente, para Bônus II e Sunrise. Para Bônus II, sem desinfestação da tesoura de poda, registrou-se variação percentual de 62,5 a 100 e de 30,0 a 100 de plantas com necrose no caule e de plantas mortas, respectivamente. Já, para Sunrise, a percentagem de plantas com necrose no caule e de plantas mortas, quando a tesoura não foi desinfestada, variou de 42,5 a 100 e de 10,0 a 87,5, respectivamente. O procedimento de sanitização proporcionou elevado incremento no brix e na produção de frutos.
Marcadores RAPD na análise da diversidade genética de isolados de Acremonium strictum
Authors: Teixeira Hudson , Vieira Maria das Graças G. C. , Machado José C.
Published: October 2006

Os fungos Acremonium strictum e Fusarium verticillioides normalmente apresentam algumas similaridades morfológicas, o que dificulta sua diferenciação em sementes de milho (Zea mays), particularmente quando ocorrem simultaneamente. Técnicas moleculares de análise do DNA têm possibilitado o desenvolvimento de métodos rápidos, sensíveis eespecíficos no diagnóstico de fitopatógenos, em complemento à análise morfológica. Este trabalho objetivou caracterizar e dimensionar a diversidade genética de dez isolados de A. strictum obtidos de sementes de milho, provenientes de diferentes regiões produtoras brasileiras, por meio da análise do DNA genômico (RAPD). Objetivou-se ainda, diferenciar os isolados de A. strictum de F. verticillioides por meio da técnica citada. Pela análise do DNA, 25 primers Operon geraram polimorfismos, os quais tornaram possível e seguro o agrupamento de isolados de A. strictum e sua diferenciação de F. verticillioides. Os isolados de A. strictum apresentaram variabilidade intraespecífica entre 3,4% e 44,4%. Para a maioria dos casos não foi possível correlacionar a similaridade genotípica e a origem geográfica dos isolados de A. strictum.
Differential Gene Expression Associated with Migration of Mesenchymal Stem Cells to Conditioned Medium from Tumor Cells or Bone Marrow Cells
Authors: Menon Lata G. , Picinich Sonia , Koneru Rajeth , Gao Hui , Lin Siang Yo , Koneru Mythili , Mayer-Kuckuk Philipp , Glod John , Banerjee Debabrata
Published: October 2006

Distinct signals that guide migration of mesenchymal stem cells (MSCs) to specific in vivo targets remain unknown. We have used rat MSCs to investigate the molecular mechanisms involved in such migration. Rat MSCs were shown to migrate to tumor microenvironment in vivo, and an in vitro migration assay was used under defined conditions to permit further mechanistic investigations. We hypothesized that distinct molecular signals are involved in the homing of MSCs to tumor sites and bone marrow. To test this hypothesis, gene expression profiles of MSCs exposed in vitro to conditioned medium (CM) from either tumor cells or bone marrow were compared. Analysis of the microarray gene expression data revealed that 104 transcripts were upregulated in rat MSCs exposed to CM from C85 human colorectal cancer cells for 24 hours versus control medium. A subset of 12 transcripts were found to be upregulated in rat MSCs that were exposed to tumor cell CM but downregulated when MSCs were exposed to bone marrow CM and included CXCL-12 (stromal cell-derived factor-1 [SDF-1]), CXCL-2, CINC-2, endothelial cell specific molecule-1, fibroblast growth factor-7, nuclear factor-κB p105, and thrombomodulin. Exposure to tumor cell CM enhanced migration of MSCs and correlated with increased SDF-1 protein production. Moreover, knockdown of SDF-1 expression in MSCs inhibited migration of these cells to CM from tumor cells, but not bone marrow cells, confirming the importance of SDF-1 expression by MSCs in this differential migration. These results suggest that increased SDF-1 production by MSCs acts in an autocrine manner and is required for migratory responses to tumor cells.
Uncertainty analysis of single-concentration exposure data for risk assessment—introducing the species effect distribution approach
Authors: Scott-fordsmand Janeck J. , Damgaard Christian
Published: October 2006

In recent years, the inclusion of uncertainty analysis in risk assessment has been much debated. One pertinent issue is the translation of the effects observed with a limited number of test species to a general protection level for most or all species present in the environment. In a number of cases, toxicity data may consist of data from tests employing only a control and one treatment. Given that more species (or processes) have been tested with the same treatment, the treatment can be considered as fixed, and the effect level of the individual species (or processes) can be considered as variable. The distribution of effects can be viewed as a species effect distribution for that treatment. The distribution will represent all organisms and may be used to predict the maximum impact on any fraction of all organisms (e.g., 95% of all species). Hence, it is possible to predict the maximum effect level, with a selected certainty, for a given fraction of all species.
Comparative acute toxicity of potassium permanganate to nontarget aquatic organisms
Authors: Hobbs Melissa S. , Grippo Richard S. , Farris Jerry L. , Griffin Billy R. , Harding Lora L.
Published: October 2006

Potassium permanganate (KMnO4) is used worldwide in freshwater pond aquaculture for treatment and prevention of waterborne external parasitic, bacterial, and fungal diseases. Nevertheless, KMnO4 has not been approved by the U.S. Food and Drug Administration, and insufficient information exists to allow evaluation of the environmental risk of KMnO4 exposures. Limited data exist concerning KMnO4 toxicity to nontarget species in systems receiving aquaculture effluent from treated ponds. The goal of this research is to generate effects data for use in developing an ecological risk assessment of KMnO4. Toxicity tests were used to compare the relative sensitivities of five standard aquatic test species to KMnO4. Acute toxicity test results using synthetic moderately hard water show static 96-h mean median lethal concentration (LC50) values ± standard deviation (SD) of 0.058 ± 0.006 mg/L for Ceriodaphnia dubia, 0.053 ± 0.009 mg/L for Daphnia magna, 2.13 ± 0.07 mg/L for Pimephales promelas, 4.74 ± 1.05 mg/L for Hyalella azteca, and 4.43 ± 0.79 mg/L for Chironomus tentans. Most of these values are below the recommended KMnO4 treatment rate of at least 2.0 mg/L or 2.5 times the water's potassium permanganate demand (PPD; an estimation of the available reducing agents in the exposure water), suggesting significant environmental risk. However, repeating these laboratory tests using pond water resulted in significantly reduced toxicity, with static 96-h mean LC50 values (±SD) of 2.39 ± 0.36 mg/L for C. dubia, 1.98 ± 0.12 mg/L for D. magna, 11.22 ± 1.07 mg/L for P. promelas, 13.55 ± 2.24 mg/L for H. azteca, and 12.30 ± 2.83 mg/L for C. tentans. The PPD of synthetic moderately hard water was 0.329 ± 0.114 mg/L; however, pond water PPD was 5.357 ± 0.967 mg/L. The effective disease-treating dose based on 2.5 times the PPD would thus be 0.823 and 13.392 mg KMnO4/L, respectively, exceeding the LC50 for most of these nontarget organisms, even in pond water, immediately after treatment.
Organohalogen contaminants and reproductive hormones in incubating glaucous gulls (Larus hyperboreus) from the Norwegian Arctic
Authors: Verreault Jonathan , Letcher Robert J. , Ropstad Erik , Dahl Ellen , Gabrielsen Geir W.
Published: October 2006

Organohalogen contaminants detected globally in avian wildlife, including populations from the Arctic, have been related to various reproductive hormone potencies, and altered hormonal balance and functions. Besides legacy organochlorine (OC) substances, that is, polychlorinated biphenyls (PCBs) and OC pesticides and by-products, endocrine-disruptive properties have been defined for chemicals of new and emerging environmental concern, such as polybrominated diphenyl ethers (PBDEs) and metabolically derived products like methylsulfonyl (MeSO2)- and hydroxyl (OH)-PCBs. We investigated the relationships between plasma concentrations of selected legacy OCs, PBDEs, and MeSO2- and OH-PCB metabolites and the circulating reproductive hormones testosterone (T), 17β-estradiol (E2), and progesterone (P4) in incubating male and female glaucous gulls (Larus hyperboreus) from the Norwegian Arctic. Principal component and regression analyses demonstrated that P4 levels in male glaucous gulls were associated positively with variations of sum (∑) PCB, dichloro-diphenyl-trichloroethane (∑DDT), chlordane (∑CHL), and ∑PBDE concentrations, which were the most recalcitrant organohalogens determined in glaucous gulls. No such relationship was found for female glaucous gulls as well as between concentrations of any of the selected organohalogens and levels of T for both sexes. The E2 was not detected in any plasma samples. Present results were highly suggestive that exposure to high organohalogen concentrations in glaucous gulls, particularly the most persistent compound classes, may have the potential to interfere with steroidogenesis and impinge on circulating P4 homeostasis. Because significant effects were found in males exclusively, it cannot be completely ruled out that male glaucous gulls are more sensitive than females to organohalogen-mediated alteration of P4 synthesis and breakdown.
Effects of dietary methylmercury on reproductive behavior of fathead minnows (Pimephales promelas)
Authors: Sandheinrich Mark B. , Miller Kevin M.
Published: October 2006

We examined the effects of dietary methylmercury on the production of testosterone in and the reproductive behavior of male fish. Juvenile fathead minnows (Pimephales promelas) were fed one of three diets contaminated with methylmercury at concentrations of 0.06 (control), 0.87 (low), and 3.93 (medium) μg Hg/g dry weight. After attaining sexual maturity, fish were paired for mating, and male behaviors were recorded. Carcass mercury and plasma testosterone concentrations also were measured. No significant differences were found in the amount of time spent by male fish in nest preparation or courtship activities, but dietary methylmercury suppressed mating behavior. Fish that were fed control diets spent approximately 5% of their time spawning; fish that were fed methylmercury-contaminated diets spent approximately 0.5% of their time spawning. Total mercury concentration in the carcass was not correlated with any individual reproductive behavior but was correlated with hypoactivity. Fish that were fed the low- and medium-methylmercury diets and with mean carcass concentrations of 0.71 to 4.2 μg Hg/g dry weight spent an average of 19 to 26% of their time being inactive; control fish with an average of 0.07 μg Hg/g dry weight spent only 8% of their time being inactive. No significant difference was found in testosterone concentrations among dietary treatments; however, testosterone was positively correlated with individual nest preparatory, courtship, and spawning behaviors and negatively correlated with the total amount of time spent in all nonreproductive behaviors. The relation between testosterone, reproductive behavior, and spawning success suggests that altered behavior is, in part, responsible for suppression of reproduction in methylmercury-exposed fish. Moreover, reproductive behavior may be more sensitive than steroid hormones to alteration by dietary methylmercury.
Acute to chronic ratios in aquatic toxicity—variation across trophic levels and relationship with chemical structure
Authors: Ahlers Jan , Riedhammer Caroline , Vogliano Michaela , Ebert Ralf-Uwe , Kühne Ralph , Schüürmann Gerrit
Published: October 2006

For fish, daphnids, and algae, acute to chronic ratios (ACRs) have been determined from experimental data regarding new and existing chemicals. Only test results in accord with the European Union Technical Guidance Document (TGD) and validated by authorities were considered. Whereas the median ACRs of 10.5 (fish), 7.0 (daphnids), and 5.4 (algae) are well below the ACR safety factor of 100 as implied by the TGD, individual ACRs vary considerably and go up to 4,400. The results suggest that a safety factor of 100 is not protective for all chemicals and trophic levels. Neither a correlation between ACR and baseline toxicity as modeled through the logarithmic octanol–water partition coefficient nor an ACR correlation across trophic levels exists. Narcosis is associated with a preference for a low ACR; nevertheless, low ACRs are frequently obtained for nonnarcotics. Analysis of chemical structures led to the derivation of structural alerts to identify compounds with a significantly increased potential for a high ACR, which may prove to be useful in setting test priorities. At present, however, life-cycle tests are the only way to conservatively predict long-term toxicity.
DNA damage and external lesions in brown bullheads (Ameiurus nebulosus) from contaminated habitats
Authors: Yang Xuan , Meier John , Chang Lina , Rowan Michael , Baumann Paul C.
Published: October 2006

The Comet assay was used to compare levels of DNA damage in brown bullheads (Ameiurus nebulosus) collected from three known contaminated locations, the Cuyahoga River (OH, USA), Ashtabula River (OH, USA; both tributaries to Lake Erie, USA), and Ashumet Pond (Cape Cod, MA, USA), with brown bullheads collected from three paired reference sites, Old Woman Creek (OH, USA), Conneaut River (OH, USA; both tributaries to Lake Erie), and Great Herring Pond (mainland MA, USA), respectively. Blood was sampled from each fish, and the Comet assay was conducted on erythrocytes. The assay results demonstrate that fish from the three contaminated sites each suffered higher DNA damage compared with fish from their respective reference sites. The results also show that the genetic damage was associated with the occurrence of external lesions and deformities in fish. The Comet assay is sufficiently sensitive to detect exposure of natural fish populations to environmental levels of genotoxic contaminants.
Effects of nutrient enrichment, depuration substrate, and body size on the trophic transfer of cadmium associated with microalgae to the benthic amphipod Leptocheirus plumulosus
Authors: Yu Ri-Qing , Fleeger John W.
Published: October 2006

Bioavailability and nutrient effects on the trophic transfer of Cd associated with microalgae to the marine benthic amphipod Leptocheirus plumulosus were investigated. Cadmium assimilation efficiency (AE) of suspension-feeding L. plumulosus significantly varied among three algal species tested (Nitzschia punctata, Thalassiosira weissflogii, and Isochrysis galbana). Depuration substrate greatly influenced Cd AE for L. plumulosus (AE was much higher for nonburrowed amphipods), probably because sediment burrowing allowed L. plumulosus to feed as a surface deposit feeder. The L. plumulosus body size, ranging from 0.5 to 2.0 mm, did not affect Cd AE. Nitrate enrichment from 0 to 180 μM in algal culture significantly increased Cd AE from 9.4 to 18.8% for T. weissflogii, from 10.0 to 27.3% for N. punctata, and from 10.0 to 16.2% for I. galbana; nitrate enrichment from 0 to 60 μM did not influence Cd AE in any algal species tested. Physiological turnover rate constants of Cd in L. plumulosus ranged from 0.016 to 0.025/h for the three species and were independent of nitrate addition. Nitrate enrichment strongly enhanced Cd distribution in algal cytoplasm. Phosphate enrichment (0–7.5 μM) did not significantly affect Cd AEs in L. plumulosus. Overall, a significant linear relationship was observed between the Cd AE of L. plumulosus and the fraction of Cd available in algal cytoplasm. Our work suggests that eutrophication by nitrate enrichment has the potential to enhance the trophic transfer of Cd from microalgae to suspension-feeding benthic invertebrates.
Relating daily solar ultraviolet radiation dose in salt marsh-associated estuarine systems to laboratory assessments of photoactivated polycyclic aromatic hydrocarbon toxicity
Authors: Weinstein John E. , Diamond Stephen A.
Published: October 2006

Estuaries of the southeastern United States not only serve an important nursery function but also are common repositories of polycyclic aromatic hydrocarbons (PAHs) derived from upland activities. Thus, these habitats may be at risk for PAH phototoxicity. To better characterize this risk, a daily survey of ultraviolet-A (UV-A; 320–400 nm) irradiance was performed at Leadenwah Creek (Wadmalaw Island, SC, USA) on June 27 and August 1, 2003. In addition, laboratory assays were completed using two light exposure regimes: One that was typical of historical phototoxicity assessments (continuous light [C-UV]), and a more environmentally realistic regime (ER-UV). On both survey days, irradiance at a depth of 10 cm exhibited a pattern generally similar to that observed at the surface, whereas irradiance at the bottom of the creek was a function of both tidal height and time of day. Total UV-A dose at a 10-cm depth on June 27 and August 1, 2003 was 4.37 and 4.78 J/cm2, respectively. Attenuation coefficients on both days varied as a function of tidal height. In the laboratory, larval grass shrimp (Palaemonetes pugio) exposed to an ER-UV regime for these habitats (photoperiod, 12: 12-h light: dark; total daily UV-A dose, 4.40 J/cm2) exhibited a 2.5-fold decrease in toxicity compared with those exposed to the C-UV regime (photoperiod, 24: 0-h light: dark; total daily UV dose, 1.50 J/cm2), despite a threefold higher UV dose in the ER-UV regime. The lower potency under the ER-UV regime likely is attributable to the presence of a 12-h dark period allowing for recovery. The consequences of these results are discussed in the context of habitat-specific UV-A dose and its relevance to future laboratory assessments of PAH phototoxicity.
Metabolite production in degradation of pyrene alone or in a mixture with another polycyclic aromatic hydrocarbon by Mycobacterium sp.
Authors: Zhong Yin , Luan Tiangang , Zhou Hongwei , Lan Chongyu , Tam Nora Fung Yee
Published: October 2006

Degradation of pyrene (PYR) alone and in the presence of phenanthrene or fluoranthene by Mycobacterium sp. strain A1-PYR isolated from mangrove sediments was investigated. When PYR was the only polycyclic aromatic hydrocarbon compound and the sole carbon source, only 33% of the added PYR was slowly degraded during 7 d of incubation. Seven metabolites were obtained, including four-ring metabolites (monohydroxypyrene and three different dihydroxypyrenes) and three-ring metabolites (dihydroxyphenanthrene, 4-phenanthrene-carboxylic acid, and 4-phenanthrol), of which more four-ring metabolites accumulated compared with three-ring metabolites. To our knowledge, this is the first report in which PYR was initially attacked by Mycobacterium sp. to form three different dihydroxypyrenes. Pyrene degradation was significantly stimulated when mixed with phenanthrene or fluoranthene. In the presence of fluoranthene, PYR was rapidly degraded (up to 57%), and significant amounts of dihydroxypyrene were formed within 3 d of incubation, followed by a period of minimal PYR degradation from 3 to 7 d with disappearance of fourring metabolites and accumulation of three-ring metabolites. In contrast, PYR was removed completely, and little evidence of metabolites was detected in the presence of phenanthrene. These results showed that PYR was degraded to a larger extent when mixed with another polycyclic aromatic hydrocarbon concomitant with a higher turnover of PYR metabolites. The induction of complex enzyme systems and increase in biomass possibly affected the transformation of PYR metabolites in the mixture with phenanthrene or fluoranthene.
Estimation of polychlorinated biphenyl fugacity ratios
Authors: van Noort Paul C.M.
Published: October 2006

On the quantitative comparison of solubilities or vapor pressures of homologous series, the variation in the effect of crystal structure on solid properties may substantially influence the outcome of the comparison. Usually, the effect of this variation is eliminated by comparing values of the liquid state. The ratio of solid to liquid properties is called the fugacity ratio. Fugacity ratios are usually calculated from fusion thermodynamic data. For 41 polychlorinated biphenyls (PCBs), fusion enthalpy was found to be correlated with fusion entropy. Highly linear correlations were observed for non-ortho-PCBs, mono-ortho-PCBs, and di-ortho-PCBs. Fugacity ratios estimated from the fusion enthalpy-entropy linear regression parameters were equal, within 10% on average, to fugacity ratios calculated from fusion enthalpy for ortho- chlorinated PCBs with melting points below 380 K and for non-ortho-PCBs. For ortho chlorinated PCBs with melting points above 380 K, fugacity ratios were better estimated from a nonlinear regression of fugacity ratios against the melting point and the system temperature. For all 209 PCB congeners, fugacity ratios at 298 K are listed on the basis of experimental fusion data or estimates from the regressions.
Measured partitioning coefficients for parent and alkyl polycyclic aromatic hydrocarbons in 114 historically contaminated sediments: Part 1. KOC values
Authors: Hawthorne Steven B. , Grabanski Carol B. , Miller David J.
Published: October 2006

Polycyclic aromatic hydrocarbon (PAH) partitioning coefficients between sediment organic carbon and water (KOC) values were determined using 114 historically contaminated and background sediments collected from eight different rural and urban waterways in the northeastern United States. More than 2,100 individual KC values were measured in quadruplicate for PAHs ranging from two to six rings, along with the first reported KOC values for alkyl PAHs included in the U.S. Environmental Protection Agency's (U.S. EPA) sediment narcosis model for the prediction of PAH toxicity to benthic organisms. Sediment PAH concentrations ranged from 0.2 to 8,600 μg/g (U.S. EPA 16 parent PAHs), but no observable trends in KOC values with concentration were observed for any of the individual PAHs. Literature KOC values that are commonly used for environmental modeling are similar to the lowest measured values for a particular PAH, with actual measured values typically ranging up to two orders of magnitude higher for both background and contaminated sediments. For example, the median log KOC values we determined for naphthalene, pyrene, and benzo[a]pyrene were 4.3, 5.8, and 6.7, respectively, compared to typical literature KOC values for the same PAHs of 2.9, 4.8, and 5.8, respectively. Our results clearly demonstrate that the common practice of using PAH KOC values derived from spiked sediments and modeled values based on n-octanol–water coefficients can greatly overestimate the actual partitioning of PAHs into water from field sediments.
Quantitative structure-activity relationships for toxicity of nonpolar narcotic chemicals to Pseudokirchneriella subcapitata
Authors: Hsieh Shih-Hung , Hsu Chih-Hsiung , Tsai Din-Yu , Chen Chung-Yuan
Published: October 2006

This study presents data for 27 nonpolar narcotic compounds regarding toxicity to Pseudokirchneriella subcapitata as evaluated using a closed-system algal toxicity test with an exposure time of 48 h. Two test endpoints, dissolved oxygen production and algal growth rate, were used to assess the toxicity of nonpolar narcotic chemicals on algae. Hydrophobicity (1-octanol-water partition coefficient [KOW]) provided satisfactory descriptions for the toxicity of nonpolar narcotic compounds, and quantitative structure–activity relationships based on log KOW were established. The relative sensitivity of various aquatic organisms to nonpolar chemicals was as follows: P. subcapitata > Vibrio fischeri ≥ Nitrosomonas sp. > fathead minnow > Daphnia magna > polytox > activated sludge. In addition, linear relationships were found between the toxicity observed in P. subcapitata and other aquatic organisms, except in the case of Nitrosomonas sp. Therefore, for nonpolar toxicants, the closed-system technique applied in the present study can be an ideal surrogate for other tests, such as fathead minnow and D. magna, that are either time-consuming or labor-intensive. However, because the current toxicity database is based primarily on the conventional batch tests, it cannot provide adequate assessment regarding the effects of various organic toxicants. Therefore, more extensive research is needed to revise the database for the toxicity of organic compounds on phytoplankton using the closed-system technique.