The Interactive Effects of Temperature and Osmotic Potential on the Growth of Aquatic Isolates of Fusarium culmorum.

The mycelial growth of 10 Fusarium culmorum strains isolated from water of the Andarax riverbed in the provinces of Granada and Almeria in southeastern Spain was tested on potato-dextroseagar adjusted to different osmotic potentials with either KCl or NaCl (−1.50 to−144.54 bars) at 10◦C intervals ranging from15◦ to 35◦C. Fungal growth was determined by measuring colony diameter after 4 d of incubation. Mycelial growth was maximal at 25◦C. The quantity and capacity of mycelial growth of F. culmorum were similar at 15 and 25◦C, with maximal growth occurring at −13.79 bars water potential and a lack of growth at 35◦C. The effect of water potential was independent of salt composition. The general growth pattern of Fusarium culmorum growth declined at potentials below −13.79 bars. Fungal growth at 25◦C was always greater than growth at 15◦C, at all of the water potentials tested. Significant differences were observed in the response ofmycelia to water potential and temperature as main and interactive effects. The number of isolates that showed growth was increasingly inhibited as the water potential dropped, but some growth was still observable at −99.56 bars. These findings could indicate that F. culmorum strains isolated from water have a physiological mechanism that permits survival in environments with low water potential. Propagules of Fusarium culmorum are transported long distances by river water, which could explain the severity of diseases caused by F.culmorum on cereal plants irrigated with river water and its interaction under hydric stress ormoderate soil salinity. The observed differences in growth magnitude and capacity could indicate that the biological factors governing potential and actual growth are affected by osmotic potential in different ways.

Toxicity of ZnO nanoparticles, ZnO bulk and ZnCl2 on earthworms in a spiked natural soil and toxicological effects of leachates on aquatic organisms

The present study assessed the uptake and toxicity of ZnO nanoparticles (NPs), ZnO bulk, and ZnCl2 salt in earthworms in spiked agricultural soils. In addition, the toxicity of aqueous extracts to Daphnia magna and Chlorella vulgaris was analyzed to determine the risk of these soils to the aquatic compartment. We then investigated the distribution of Zn in soil fractions to interpret the nature of toxicity. Neither mortality nor differences in earthworm body weight were observed compared with the control. The most sensitive end point was reproduction. ZnCl2 was notably toxic in eliminating the production of cocoons. The effects induced by ZnO-NPs and bulk ZnO on fecundity were similar and lower than those of the salt. In contrast to ZnO bulk, ZnO-NPs adversely affected fertility. The internal concentrations of Zn in earthworms in the NP group were greater than those in the salt and bulk groups, although bioconcentration factors were consistently <1. No relationship was found between toxicity and internal Zn amounts in earthworms. The results from the sequential extraction of soil showed that ZnCl2 displayed the highest availability compared with both ZnO. Zn distribution was consistent with the greatest toxicity showed by the salt but not with Zn body concentrations. The soil extracts from both ZnO-NPs and bulk ZnO did not show effects on aquatic organisms (Daphnia and algae) after short-term exposure. However, ZnCl2 extracts (total and 0.45-μm filtered) were toxic to Daphnia.

The forced oscillations of submerged bodies

The increasing use of very light structures in aerospace applications are given rise to the need of taking into account the effects of the surrounding media in the motion of a structure (as for instance, in modal testing of solar panels or antennae) as it is usually performed in the motion of bodies submerged in water in marine applications. New methods are in development aiming at to determine rigid-body properties (the center of mass position and inertia properties) from the results of oscillations tests (at low frequencies during modal testing, by exciting the rigid-body modes only) by using the equations of the rigid-body dynamics. As it is shown in this paper, the effect of the surrounding media significantly modifies the oscillation dynamics in the case of light structures and therefore this effect should be taken into account in the development of the above-mentioned methods. The aim of the paper is to show that, if a central point exists for the aerodynamic forces acting on the body, the motion equations for the small amplitude rotational and translational oscillations can be expressed in a form which is a generalization of the motion equations for a body in vacuum, thus allowing to obtain a physical idea of the motion and aerodynamic effects and also significantly simplifying the calculation of the solutions and the interpretation of the results. In the formulation developed here the translational oscillations and the rotational motion around the center of mass are decoupled, as is the case for the rigid-body motion in vacuum, whereas in the classical added mass formulation the six motion equations are coupled. Also in this paper the nonsteady motion of small amplitude of a rigid body submerged in an ideal, incompressible fluid is considered in order to define the conditions for the existence of the central point in the case of a three-dimensional body. The results here presented are also of interest in marine applications.

Simultaneous determination of multiclass emerging contaminants in aquatic plants by ultrasound assisted matrix solid phase dispersion and GC-MS

A multiresidue method was developed for the simultaneous determination of 31 emerging contaminants (pharmaceutical compounds, hormones, personal care products, biocides and flame retardants) in aquatic plants. Analytes were extracted by ultrasound assisted-matrix solid phase dispersion (UA-MSPD) and determined by gas chromatography-mass spectrometry after sylilation. The method was validated for different aquatic plants (Typha angustifolia, Arundo donax and Lemna minor) and a semiaquatic cultivated plant (Oryza sativa) with good recoveries at concentrations of 100 and 25 ng g-1 wet weight, ranging from 70 to 120 %, and low method detection limits (0.3 to 2.2 ng g-1 wet weight). A significant difference of the chromatographic response was observed for some compounds in neat solvent versus matrix extracts and therefore quantification was carried out using matrix-matched standards in order to overcome this matrix effect. Aquatic plants taken from rivers located at three Spanish regions were analyzed and the compounds detected were parabens, bisphenol A, benzophenone-3, cyfluthrin and cypermethrin. The levels found ranged from 6 to 25 ng g-1 wet weight except for cypermethrin that was detected at 235 ng g-1 wet weight in Oryza sativa samples.

Induced Damping on Vibrating Circular Plates Submerged in still Fluid

When a structure vibrates immersed in a fluid it is known that the dynamic properties of the system are modified. The surrounding fluid will, in general, contribute to the inertia, the rigidity and the damping coefficient of the coupled fluid-structure system. For light structures, like spacecraft antennas, even when the fluid is air the contribution to the dynamic properties can be important. For not so light structures the ratio of the equivalent fluid/structure mass and rigidity can be very small and the fluid contribution could be neglected. For the ratio of equivalent fluid/structure damping both terms are of the same order and therefore the fluid contribution must be studied. The working life of the spacecraft structure would be on space and so without any surrounding fluid. The response of a spacecraft structure on its operational life would be attenuated by the structural damping alone but when the structure is dynamically tested on the earth the dynamic modal test is performed with the fluid surrounding it. The results thus are contaminated by the effects of the fluid. If the damping added by the fluid is of the same order as the structural damping the response of the structure in space can be quite different to the response predicted on earth. It is therefore desirable to have a method able to determine the amount of damping induced by the fluid and that should be subtracted of the total damping measured on the modal vibration test. In this work, a method for the determination of the effect of the surrounding fluid on the dynamic characteristics of a circular plate has been developed. The plate is assumed to vibrate harmonically with the vacuum modes and the generalized forces matrix due to the fluid is thus computed. For a compressible fluid this matrix is formed by complex numbers including terms of inertia, rigidity and damping. The matrix due to the fluid loading is determined by a boundary element method (BEM). The BEM used is of circular rings on the plate surface so the number of elements to obtain an accurate result is very low. The natural frequencies of the system are computed by an iteration procedure one by one and also the damping fluid contribution. Comparisons of the present method with various experimental data and other theories show the efficiency and accuracy of the method for any support condition of the plate.