Particle-facilitated pesticide leaching from differently structured soil monoliths.

The leaching of soil particles and surface applied 14C-labeled glyphosate and pendimethalin from intact soil columns (height: 50 cm; diameter: 30 cm) were investigated, and the relative significance of particle-facilitated pesticide transport was quantified. Investigations were performed with a recently plowed (four columns) and an untilled (five columns) sandy loam soil. Leaching was driven by three irrigation events (15 mm h(-1); 2 h each). Samples of the leachate were filtered immediately (within 1.5 minutes) using 20 nm filters, and the 14C-pesticide content was determined for filtered and unfiltered samples. Pesticide leaching was driven by preferential water flow in macropores. For the plowed structure, 68+/-10% of the leached glyphosate (average of 6 events+/-std.) was bound to particles whereas significantly less glyphosate was bound to particles in leachate from minimally disturbed columns (17+/-12%). Thus, the results suggest that soil structure affected the mode of transport of glyphosate. It is likely that glyphosate sorbed strongly when applied on recently plowed soil (Kd=503 L kg(-1) for the soil), and that it could be mobilized and transported independently of soil particles more easily when applied on the minimally disturbed soil covered in part with crop residues (Kd<1 L kg(-1) for straw). Significantly less amounts of soil particles were leached from minimally disturbed (119-247 mg) than from recently plowed (441-731 mg) columns. The significance of particle-facilitated pendimethalin leaching could not be accurately quantified due to disagreement between control measurements based on both 14C-activity and chemical analyses.

Enfermedad de Darier - White clásica y lineal / Darier white´ s disease classic and lineal

A través de este trabajo se efectúa una revisión bibliográfica acerca de esta tradicional genodermatosis, que comprende un recorrido a través de la historia, epidemiología y fisiopatología desde la intimidad de la genética, pasando por los procesos bioquímicos actuales. Se repasa la clínica en forma exhaustiva, donde se aplica mi experiencia personal en aspectos evolutivos y terapéuticos.

Through this work the authors reviewed the literature about traditional genodermatosis, which includes a journey through history, epidemiology and pathophysiology from the privacy of genetic, biochemical processes through today. The clinic is reviewed exhaustively and is applied my personal experience, in developmental and therapeutic aspects.

Magnetic fluctuations in nanosized goethite (α-FeOOH) grains.

Mössbauer spectra of antiferromagnetic goethite (α-FeOOH) particles usually show an asymmetric line broadening, which increases with increasing temperature, although the magnetic anisotropy is expected to be so large that magnetic relaxation effects should be negligible. By use of high resolution transmission electron microscopy we have studied a sample of goethite particles and have found that the particles contain many defects such as low angle grain boundaries, in accordance with previous studies of other samples of goethite particles. Such defects can result in a magnetic mismatch at the grain boundaries between nanometer-sized grains, leading to a weakened magnetic coupling between the grains. We show that the Mössbauer data of goethite can be explained by fluctuations of the sublattice magnetization directions in such weakly coupled grains. It is likely that the influence of defects such as low angle grain boundaries also plays a role with regards to the magnetic properties in other antiferromagnetic nanograin systems. We discuss the results in relation to Mössbauer studies of α-Fe(2)O(3) and α-Fe(2)O(3)/NiO nanoparticles.

Toxicity and bioaccumulation of xenobiotic organic compounds in the presence of aqueous suspensions of aggregates of nano-C(60).

The potential of C(60)-nanoparticles (Buckminster fullerenes) as contaminant carriers in aqueous systems was studied in a series of toxicity tests with algae (Pseudokirchneriella subcapitata) and crustaceans (Daphnia magna). Four common environmental contaminants (atrazine, methyl parathion, pentachlorophenol (PCP), and phenanthrene) were used as model compounds, representing different physico-chemical properties and toxic modes of action. The aggregates of nano-C(60) formed over 2 months of stirring in water were mixed with model compounds 5 days prior to testing. Uptake and excretion of phenanthrene in 4-days-old D. magna was studied with and without addition of C(60) in aqueous suspensions. It was found that 85% of the added phenanthrene sorbed to C(60)-aggregates >200 nm whereas about 10% sorption was found for atrazine, methyl parathion, and pentachlorophenol. In algal tests, the presence of C(60)-aggregates increased the toxicity of phenanthrene with 60% and decreased toxicity of PCP about 1.9 times. Addition of C(60)-aggregates reduced the toxicity of PCP with 25% in tests with D. magna, whereas a more than 10 times increase in toxicity was observed for phenanthrene when results were expressed as water phase concentrations. Thus, results from both toxicity tests show that phenanthrene sorbed to C(60)-aggregates is available for the organisms. For atrazine and methyl parathion no statistically significant differences in toxicities could be observed in algal and daphnid tests as a result of the presence of C(60)-aggregates. In bioaccumulation studies with phenanthrene in D. magna it was found that the uptake of phenanthrene was faster when C(60) was present in suspension and that a 1.7 times higher steady-state concentration was reached in the animals. However, a very fast clearance took place when animals were transferred to clean water resulting in no accumulation of phenanthrene. This study is the first to demonstrate the influence of C(60)-aggregates on aquatic toxicity and bioaccumulation of other environmentally relevant contaminants. The data provided underline that not only the inherent toxicity of manufactured nanoparticles, but also interactions with other compounds and characterisation of nanoparticles in aqueous suspension are of importance for risk assessment of nanomaterials.