RESUMO

Analyses of natural waters frequently show elevated levels of total aluminum (Al) attributable to acid extraction of Al from the total suspended solids (TSS) minerals. Hence, there is a need for an analytical method that measures only bioavailable Al. Natural waters high in TSS were collected to study the chronic effects of Al on Ceriodaphnia dubia. In the collected waters TSS ranged from 30 to 411 mg/L; total Al concentrations ranged from 2.0 to 44.8 mg/L. The TSS in natural waters inhibited reproduction of C. dubia up to 40% in comparison to the same filtered waters. This inhibition did not correlate with the concentration of TSS or total Al; it was attributed to nutritional deficiency and was prevented by increasing the food supply. To demonstrate that toxicity can be measured in natural waters, samples with elevated TSS were spiked with soluble Al, and survival and reproduction were measured in chronic studies performed at pH 6.3 and 8.0. To properly characterize the Al concentrations in the toxicity studies, a method was needed that could discriminate bioavailable Al from mineral forms of Al. An extraction method at pH 4 for bioavailable Al was developed and evaluated using C. dubia chronic toxicity studies in the presence of TSS. It is concluded that the proposed method is better able to discriminate chronic toxicity effects attributable to bioavailable Al from mineralized nontoxic forms of Al compared with existing methods using total or total recoverable Al (i.e., extraction at pH ≤ 1.5). We propose that this new method be used when assessing the potential for Al in natural surface waters to cause toxicity. Environ Toxicol Chem 2019;38:1668-1681. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Assuntos

Alumínio/toxicidade , Cladocera/efeitos dos fármacos , Água Doce/química , Minerais/química , Poluentes Químicos da Água/toxicidade , Alumínio/metabolismo , Animais , Disponibilidade Biológica , Cladocera/metabolismo , Poluentes Químicos da Água/metabolismo

RESUMO

The complex chemistry of iron (Fe) at circumneutral pH in oxygenated waters and the poor correlation between ecotoxicity results in laboratory and natural waters have led to regulatory approaches for iron based on field studies (US Environmental Protection Agency Water Quality Criteria and European Union Water Framework Directive proposal for Fe). The results of the present study account for the observed differences between laboratory and field observations for Fe toxicity to algae (Pseudokirchneriella subcapitata). Results from standard 72-h assays with Fe at pH 6.3 and pH 8 resulted in similar toxicity values measured as algal biomass, with 50% effect concentrations (EC50) of 3.28 mg/L and 4.95 mg/L total Fe(III), respectively. At the end of the 72-h exposure, however, dissolved Fe concentrations were lower than 30 µg/L for all test concentrations, making a direct toxic effect of dissolved iron on algae unlikely. Analysis of nutrient concentrations in the artificial test media detected phosphorus depletion in a dose-dependent manner that correlated well with algal toxicity. Subsequent experiments adding excess phosphorus after Fe precipitation eliminated the toxicity. These results strongly suggest that observed Fe(III) toxicity on algae in laboratory conditions is a secondary effect of phosphorous depletion. Environ Toxicol Chem 2017;36:952-958. © 2016 SETAC.

Assuntos

Clorófitas/efeitos dos fármacos , Compostos Férricos/toxicidade , Modelos Teóricos , Fósforo/análise , Poluentes Químicos da Água/toxicidade , Biomassa , Clorófitas/crescimento & desenvolvimento , Ecotoxicologia , Compostos Férricos/química , Água Doce/química , Concentração de Íons de Hidrogênio , Solubilidade , Testes de Toxicidade , Poluentes Químicos da Água/química , Qualidade da Água/normas

RESUMO

Ambient concentrations of metals in surface waters have become an important consideration when establishing water quality criteria and conducting risk assessments. This study sought to estimate amounts of zinc that may be released into freshwater considering ambient concentrations, toxicity thresholds, and bioavailability. Cumulative distribution functions of ambient zinc concentrations were compared statistically for streams and lakes in Europe, North America, and South America to identify differences among mean distribution variables (e.g., slopes, intercepts, and inflection points). Results illustrated that most of the distributions among sites differed significantly. These differences illustrate the variability in ambient zinc concentrations in surface waters because of geographic location, regional geology, and anthropogenic influence. Additionally, water quality data were used to estimate bioavailable zinc concentrations in ambient surface waters (based on predictions using biotic ligand models). The amount of dissolved metal that could be added to surface waters without exceeding toxicity thresholds was calculated by subtracting ambient surface water concentrations from chronic no observable effect concentrations (NOEC; reproduction for Daphnia magna) or 10% effective concentrations (EC10; growth rate for Pseudokirchneriella subcapitata). Because ambient dissolved-zinc concentrations were, on average, below predicted effects thresholds, an average of 57.1 +/- 175 microg/L (+/- SD) of zinc could be added before exceeding the D. magna chronic NOEC or the P. subcapitata chronic EC10. However, numerous sites (17%) were identified as having ambient zinc concentrations in excess of these toxicity thresholds. This article uses existing biotic ligand models for zinc to estimate the potential magnitudes and variabilities of bioavailable zinc concentrations in fresh surface waters from different regions of the world.

Assuntos

Água Doce/química , Poluentes Químicos da Água/metabolismo , Poluentes Químicos da Água/toxicidade , Zinco/metabolismo , Zinco/toxicidade , Animais , Disponibilidade Biológica , Daphnia/metabolismo , Europa (Continente) , América do Norte , América do Sul , Poluentes Químicos da Água/química , Zinco/química

Assuntos

Conservação dos Recursos Naturais , Agricultura , Animais , Animais Selvagens , Guatemala , Humanos , Grupos Populacionais

RESUMO

A technique has been developed for cutting single nerve fibers in mammalian spinal cord. In the presence of diaminobenzidine (DAB), a laser microbeam was applied to carbocyanine (Dil) stained sensory fibers in cultured spinal cords of the newly born opossum Monodelphis domestica. Digital images of fluorescent fibers were acquired with an intensified video CCD-camera coupled to an image processor. Laser illumination of two spots on a fiber in the presence of 3 mg/ml DAB cut it, so that following DAB wash out, Dil fluorescence did not return after the intermediate segment was bleached. In contrast, when a similar procedure was carried out without DAB, fluorescence of the bleached segment was recovered within minutes in darkness, by dye diffusion from adjacent regions of the uncut fiber. After exposure to DAB, through-conduction of compound action potentials continued in undamaged fibers. The DAB reaction product remained as a dark precipitate, helping to localize the lesion sites. By illuminating a continuous series of spots it was possible to cut whole nerve roots. Fluorescent fibers extended across the cut segment 24 h later. With minor modifications, the procedure described here allows a precise lesioning of single fibers within an intact nervous system.

Assuntos

3,3'-Diaminobenzidina , Axônios/efeitos dos fármacos , Axotomia/métodos , Carbocianinas , Corantes Fluorescentes , Estimulação Luminosa/efeitos adversos , Fotoquímica/métodos , Medula Espinal/efeitos dos fármacos , 3,3'-Diaminobenzidina/farmacologia , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Animais , Animais Recém-Nascidos , Axônios/efeitos da radiação , Axônios/ultraestrutura , Carbocianinas/farmacologia , Feminino , Corantes Fluorescentes/farmacologia , Gânglios Espinais/citologia , Gânglios Espinais/efeitos dos fármacos , Gânglios Espinais/efeitos da radiação , Lasers/efeitos adversos , Degeneração Neural/fisiopatologia , Regeneração Nervosa/fisiologia , Gambás , Técnicas de Cultura de Órgãos , Estimulação Luminosa/instrumentação , Estimulação Luminosa/métodos , Fotoquímica/instrumentação , Medula Espinal/crescimento & desenvolvimento , Medula Espinal/efeitos da radiação , Raízes Nervosas Espinhais/lesões , Raízes Nervosas Espinhais/fisiologia , Raízes Nervosas Espinhais/cirurgia

RESUMO

The heterophyllous epiphyte Tillandsia deppeana exhibits an atmospheric habit as a juvenile and a tank form as an adult. Both juveniles and adults utilize C3 photosynthesis. This is the first report of an atmospheric form of Tillandsia which does not exhibit CAM. Photosynthetic saturation occurred at approximately 10% of full sunlight in both forms, but the adults exhibited greater rates of photosynthesis at all levels of irradiance. The adults also had a higher and broader photosynthetic temperature optimum than did the juveniles. The adults transpired at greater rates than the juveniles; however, the water use efficiencies of both forms were similar and were high for C3 plants. In both forms the photosynthetic rate decreased in response to a decrease in humidity. After 8 days without water the juveniles were able to fix CO2 throughout the day. The adults, however, exhibited a net loss of CO2 on the second day without water and thereafter. These results indicate that the water-conservative atmospheric juvenile of T. deppeana is well adapted to establishment in the epiphytic habitat.