Personal exposure to dust, endotoxin and crystalline silica in California agriculture.
(1/2325)
AIMS: The aim of this study was to measure personal exposure to dust, endotoxin and crystalline silica during various agricultural operations in California over a period of one year. METHODS: Ten farms were randomly selected in Yolo and Solano counties and workers were invited to wear personal sampling equipment to measure inhalable and respirable dust levels during various operations. The samples were analysed for endotoxin using the Limulus Amebocyte Lysate assay and crystalline silica content using X-ray diffraction. In total 142 inhalable samples and 144 respirable samples were collected. RESULTS: The measurements showed considerable difference in exposure levels between various operations, in particular for the inhalable fraction of the dust and the endotoxin. Machine harvesting of tree crops (Geometric mean (GM) = 45.1 mg/m3) and vegetables (GM = 7.9 mg/m3), and cleaning of poultry houses (GM = 6.7 mg/m3) showed the highest inhalable dust levels. Cleaning of poultry houses also showed the highest inhalable endotoxin levels (GM = 1861 EU/m3). Respirable dust levels were generally low, except for machine harvesting of tree crops (GM = 2.8 mg/m3) and vegetables (GM = 0.9 mg/m3). Respirable endotoxin levels were also low. For the inhalable dust fraction, levels were reduced considerably when an enclosed cabin was present. The percentage of crystalline silica was overall higher in the respirable dust samples than the inhalable dust samples. CONCLUSIONS: Considerable differences exist in personal exposure levels to dust, endotoxin and crystalline silica during various agricultural operations in California agriculture with some operations showing very high levels. (+info)
Purification and characterization of rat hippocampal CA3-dendritic spines associated with mossy fiber terminals.
(2/2325)
We report a revised and improved isolation procedure for CA3-dendritic spines, most of them still in association with mossy fiber terminals resulting in a 7.5-fold enrichment over nuclei and a 29-fold enrichment over myelin. Additionally, red blood cells, medullated fibers, mitochondria and small synaptosomes were significantly depleted. We show by high resolution electron microscopy that this subcellular fraction contains numerous dendritic spines with a rich ultrastructure, e.g. an intact spine apparatus, membranous organelles, free and membrane-bound polyribosomes, endocytic structures and mitochondria. This improved experimental system will allow us to study aspects of post-synaptic functions at the biochemical and molecular level. (+info)
Silica dust and lung cancer in the German stone, quarrying, and ceramics industries: results of a case-control study.
(3/2325)
BACKGROUND: A work force based case-control study of lung cancer was performed in non-silicotic subjects exposed to crystalline silica to investigate the association between silica dust and lung cancer excluding the influence of silicosis. METHODS: Two hundred and forty seven patients with lung cancer and 795 control subjects were enrolled, all of whom had been employed in the German stone, quarrying, or ceramics industries. Smoking was used as a matching criterion. Exposure to silica was quantified by measurements, if available, or otherwise by industrial hygienists. Several indices (peak, average and cumulative exposure) were used to analyse the relationship between the level of exposure and risk of lung cancer as odds ratios (OR). RESULTS: The risk of lung cancer is associated with the year of and age at first exposure to silica, duration of exposure, and latency. All odds ratios were adjusted for these factors. Considering the peak exposure, the OR for workers exposed to high levels (>/=0.15 mg/m3 respirable silica dust which is the current occupational threshold value for Germany) compared with those exposed to low levels (<0.15 mg/m3) was 0.85 (95% CI 0.58 to 1. 25). For the time weighted average exposure the OR was 0.91 (95% CI 0.57 to 1.46). The OR for the cumulative exposure was 1.02 (95% CI 0. 67 to 1.55). No increase in risk was evident with increasing exposure. CONCLUSIONS: This study shows no association between exposure to crystalline silica and lung cancer. The exclusion of subjects with silicosis may have led to dilution with respect to the level of exposure and therefore reduced the power to detect a small risk. Alternatively, the risk of getting lung cancer may be restricted to subjects with silicosis and is not directly linked to silica dust. (+info)
Biochemical evolution III: polymerization on organophilic silica-rich surfaces, crystal-chemical modeling, formation of first cells, and geological clues.
(4/2325)
Catalysis at organophilic silica-rich surfaces of zeolites and feldspars might generate replicating biopolymers from simple chemicals supplied by meteorites, volcanic gases, and other geological sources. Crystal-chemical modeling yielded packings for amino acids neatly encapsulated in 10-ring channels of the molecular sieve silicalite-ZSM-5-(mutinaite). Calculation of binding and activation energies for catalytic assembly into polymers is progressing for a chemical composition with one catalytic Al-OH site per 25 neutral Si tetrahedral sites. Internal channel intersections and external terminations provide special stereochemical features suitable for complex organic species. Polymer migration along nano/micrometer channels of ancient weathered feldspars, plus exploitation of phosphorus and various transition metals in entrapped apatite and other microminerals, might have generated complexes of replicating catalytic biomolecules, leading to primitive cellular organisms. The first cell wall might have been an internal mineral surface, from which the cell developed a protective biological cap emerging into a nutrient-rich "soup." Ultimately, the biological cap might have expanded into a complete cell wall, allowing mobility and colonization of energy-rich challenging environments. Electron microscopy of honeycomb channels inside weathered feldspars of the Shap granite (northwest England) has revealed modern bacteria, perhaps indicative of Archean ones. All known early rocks were metamorphosed too highly during geologic time to permit simple survival of large-pore zeolites, honeycombed feldspar, and encapsulated species. Possible microscopic clues to the proposed mineral adsorbents/catalysts are discussed for planning of systematic study of black cherts from weakly metamorphosed Archaean sediments. (+info)
Presence of Campylobacter and Salmonella in sand from bathing beaches.
(5/2325)
The purpose of this study was to determine the presence of thermophilic Campylobacter spp. and Salmonella spp. in sand from non-EEC standard and EEC standard designated beaches in different locations in the UK and to assess if potentially pathogenic strains were present. Campylobacter spp. were detected in 82/182 (45%) of sand samples and Salmonella spp. in 10/182 (6%). Campylobacter spp. were isolated from 46/92 (50%) of samples from non-EEC standard beaches and 36/90 (40%) from EEC standard beaches. The prevalence of Campylobacter spp. was greater in wet sand from both types of beaches but, surprisingly, more than 30% of samples from dry sand also contained these organisms. The major pathogenic species C. jejuni and C. coli were more prevalent in sand from non-EEC standard beaches. In contrast, C. lari and urease positive thermophilic campylobacters, which are associated with seagulls and other migratory birds, were more prevalent in sand from EEC standard beaches. Campylobacter isolates were further characterized by biotyping and serotyping, which confirmed that strains known to be of types associated with human infections were frequently found in sand on bathing beaches. (+info)
Immature germ cell separation using a modified discontinuous Percoll gradient technique in human semen.
(6/2325)
The difficulty of identifying immature germ cells in unstained, fresh semen has led most laboratories to use the broad definition 'round cells' to indicate cells other than spermatozoa, thus grouping together both leukocytes and immature germ cells. This is also the case in research andrology, where very little attention has been given to immature germ cells in the semen apart from some rare exceptions, such as the attempts to study meiosis. Here we report on the use of a discontinuous Percoll gradient method modified to enable the best separation possible of immature germ cells from the other cells found in the ejaculate, in order to obtain a cellular suspension free of spermatozoa. Our technique (intra-assay variation in duplicates < 10%) demonstrated a high immature germ cell concentration in gradient fractions with 30% to 45% Percoll with a small contamination (1.5-6%) of leukocytes, confirmed by May-Grunwald-Giemsa staining, immunofluorescence and cytofluorimetry. The concentrations of immature germ cells ranged from zero in obstructive azoospermia to 2.0 x 10(6)/ml in oligozoospermia and genital tract infection. The purified immature germ cell suspensions obtained can be useful for diagnostic and research purposes. (+info)
Comparative evaluation of two density gradient preparations for sperm separation for medically assisted conception.
(7/2325)
To evaluate and optimize the sperm separation efficiency of a novel silane-coated silica bead (Puresperm), serial studies were carried out to compare the various sperm parameters between: (i) three-layer (90%-70%-40%) Puresperm and three-layer (90%-70%-40%) conventional polyvinylpyrrolidone (PVP)-coated silica bead (Percoll) gradients; (ii) three-layer (90%-70%-40%) and two-layer (90%-45%) Puresperm gradients and separately the same for Percoll; and (iii) large (3.0 ml) and small (0.75 ml) semen loading volumes on three-layer Puresperm gradients. Normozoospermic semen samples were treated and analysed in 12 replicates for each experiment. Manual evaluation of concentration, percentage motility, percentage vitality, percentage normal morphology; computer-assisted semen analysis evaluation of concentration, percentage motility, grade of motility, motion characteristics (curvilinear velocity, linearity, amplitude of lateral head velocity, beat cross frequency, percentage hyperactivation); and yields from the initial semen samples were compared. Percoll was found to be superior to Puresperm in concentration, percentage motility, percentage vitality and yields after three-layer density gradient centrifugation. There were no significant differences in sperm parameters between two- and three-layer Percoll gradients, but three-layer Puresperm gradients behaved significantly better than two-layer gradients. Large semen volume loads on three-layer Puresperm gradients resulted in greater sperm concentrations, percentage motility, percentage vitality and percentage normal morphology, but small semen volume loads produced greater yields of good-quality spermatozoa. In the light of Percoll being withdrawn from the shelf for the use of assisted reproduction because of the presence of PVP, three-layer Puresperm gradients with large semen loading volumes appear to be an attractive alternative for sperm separation in medically assisted conception. (+info)
A post-stishovite SiO2 polymorph in the meteorite Shergotty: implications for impact events.
(8/2325)
Transmission electron microscopy and electron diffraction show that the martian meteorite Shergotty, a shocked achondrite, contains a dense orthorhombic SiO2 phase similar to post-stishovite SiO2 with the alpha-PbO2 structure. If an SiO2 mineral exists in Earth's lower mantle, it would probably occur in a post-stishovite SiO2 structure. The presence of such a high-density polymorph in a shocked sample indicates that post-stishovite SiO2 structures may be used as indicators of extreme shock pressures. (+info)