Matrix modification to improve the recovery of MMHg from clear water using distillation

The use of distillation from aqueous solution dramatically improves the recovery of methyl mercury (MMHg) from complex water samples, as compared to solvent extraction techniques. However, low and irreproducible spike recoveries are often observed when distillation is applied to very clear water samples (i.e., precipitation, double deionized water (DDW), etc.) or those containing high chloride concentrations. Based upon the observation that recoveries and reproducibility are higher for waters containing strong complexing compounds, such as humic matter, we investigated the potential of matrix modification to improve the reproducibility of MMHg by distillation from more difficult matrices. At sample acid concentrations of less than 0.1M hydrochloric acid (HCl), we found that the addition of complexers such as ammonium pyrrolidine dithiocarbamate (APDC), and aqueous humic substances improved distillation spike recoveries and reproducibility. The use of complexers was also found to suppress the co-distillation of divalent mercury (Hg(II), which, in highly contaminated samples can be an interferant with the MMHg determination. At higher HCl concentrations, irreproducibility was dominated by the interference caused by chloride co-distilled with the water. In these cases, neither the addition of complexing agents, or buffers to bind the free hydrogen ions (H⁺) in solution were effective in improving results.     

Effect of intratesticular inoculation with Aujeszky's disease virus on genital organs of boars

Ten 8-10-month-old Belgian Landrace boars were intratesticularly inoculated with 500 TCID50 of a virulent Belgian Aujeszky's disease virus (ADV) isolate (75V19) in 0.1 ml volume. One control boar was similarly inoculated with phosphate-buffered saline solution. The genital organs of six inoculated boars were examined by virus isolation and immunofluorescence. In spite of high virus titers, the fluorescence in the testicles remained limited to a few small foci in the interstitial connective tissue and tunica albuginea at or close to the inoculation site. Neither virus replication, necrosis nor inflammatory lesions could be demonstrated in the epithelium of the seminiferous tubules. However, virus replication was regularly demonstrated in the serosa covering testicles, plexus pampiniformis, ductus deferens and tunica vaginalis. Virus was also isolated from the scrotal fluid. It is suggested that the serosa is the primary target tissue for ADV. The other four boars were inoculated to study the effect of ADV on semen. Severe morphologic alteration and lowered sperm cell concentrations were observed during several weeks after inoculation or until slaughter at 47, 53 and 58 days post inoculation. Virus was isolated from semen of only two out of four boars examined at 9 and 10 days post inoculation.     

Evaluation of the mayfly <Emphasis Type="Italic">Ephoron virgo</Emphasis> for European sediment toxicity assessment

Purpose  

The mayfly Ephoron virgo plays a key role in the ecological recovery in large European rivers. The larvae spend their life in the sediment and are therefore exposed to contaminants in various ways. In this study, the use of E. virgo as a test species for whole sediment bioassays was evaluated. The sensitivity was compared with Hexagenia limbata (a North American mayfly recommended for standard sediment testing). Lead (Pb) was used as a model contaminant.     

A three-stage symbiosis forms the foundation of seagrass ecosystems

Seagrasses evolved from terrestrial plants into marine foundation species around 100 million years ago. Their ecological success, however, remains a mystery because natural organic matter accumulation within the beds should result in toxic sediment sulfide levels. Using a meta-analysis, a field study, and a laboratory experiment, we reveal how an ancient three-stage symbiosis between seagrass, lucinid bivalves, and their sulfide-oxidizing gill bacteria reduces sulfide stress for seagrasses. We found that the bivalve-sulfide-oxidizer symbiosis reduced sulfide levels and enhanced seagrass production as measured in biomass. In turn, the bivalves and their endosymbionts profit from organic matter accumulation and radial oxygen release from the seagrass roots. These findings elucidate the long-term success of seagrasses in warm waters and offer new prospects for seagrass ecosystem conservation.     

Determination of atmospheric Hg by collection on iodated carbon,acid digestion and CVAFS detection

An established industrial monitoring technique has been refined to allow the accurate determination of total gaseous Hg in air at background levels (1–3 ng·m^?3). Samples are collected under vacuum through a commercially available iodide-impregnated carbon trap. For analysis, the trap is digested in a 7∶3 (v/v) mixture of HNO₃+H₂SO₄, and an aliquot of the digest analyzed by SnCl₂ reduction, dual gold amalgamation, and cold vapor atomic fluorescence spectrometric (CVAFS) detection. The traps exhibit little breakthrough (<5%) under flow rates of up to 1.0 l·min^?1 for periods up to 10 days. The mean value for the blank on the half traps was found to be 0.40±0.16 ng (n=20), resulting in a 3 α detection limit of 0.07 ng·m (1 week sample at 1.0 L·m^?3). Replicate field collections show a between-trap RSD of ± 6.4%, while field intercomparison with gold trapping resulted in 104±20% recovery in the 1–4 ng/m³ concentration range.     

Retinal vascular patterns in domestic animals

In this paper a morphological study of the retinal vascular patterns in various species of domestic animals is reported. A classification of these patterns into four well-defined groups is described. In the domestic ruminants, pigs and carnivores the retina contains a compact plexus of blood vessels located in the major part of the light-sensitive portion of the retina (euangiotic or holangiotic pattern). In other domestic animals blood vessels are present only in a smaller part of the retina. In the rabbit, vessels are confined to a broad horizontal band coincident with the area of dispersion of the myelinated nerve fibres. The larger of these vessels are readily visible macroscopically (merangiotic pattern). In the horse and the guinea pig the retinal blood vessels are minute and restricted to the direct neighbourhood of the optic disc (paurangiotic pattern). The avian retina is completely avascular (anangiotic pattern), but a densely vascularised pecten oculi is attached to the linear optic nerve head and protrudes far into the inferior part of the vitreous body.     

Development of the Retina in the Porcine Fetus A Light Microscopic Study

Morphogenesis of the porcine retina was studied using light microscopy from 4 weeks of gestation until birth (18 to 310 mm crown-rump length), and compared with the adult stage (6 months). Tissue samples were examined from the posterior and peripheral parts of the retina. At 18 mm the retina consists of an inner marginal layer and an outer layer of neuroblastic cells. At 18-40 mm the latter layer is divided into an inner and an outer neuroblastic layer by the transient layer of Chievitz. Subsequently, the development of the different retinal layers begins at the inner retinal border and moves progressively outwards; it also spreads from the posterior to the peripheral part of the neural retina. Many cells of the inner neuroblastic layer are prospective ganglionic cells which migrate inwards, thus forming the ganglion cell layer and the inner plexiform layer at 90 mm. At 120 mm, primitive horizontal cells appear within the outer neuroblastic layer. Separation of this layer into the inner nuclear, outer plexiform and outer nuclear layers is first evident at 180 mm. At this stage all retinal layers are present, except the layer of the photoreceptor cells which is not widespread until at 220 mm. The inner and outer segments of the photoreceptor cells lengthen considerably during the last month of gestation. During the late fetal stage the nerve fiber layer, the inner and outer plexiform layers and the layer of rods and cones all continue to increase in thickness. Concurrently, the ganglion cell layer and the inner and outer nuclear layers have reached their maximal thickness and become thinner. After the total thickness of the neural retina amounts to approximately 180 microns at two to three weeks before birth, it then thins to approximately 160 microns in the adult stage.