Environmental behavior of the chiral acetamide pesticide metalaxyl: enantioselective degradation and chiral stability in soil

Racemic metalaxyl is currently being replaced in many countries by metalaxyl-M, the fungicide enantiomerically enriched with the biologically active R-enantiomer. This "chiral switch" is expected to reduce the amount of pesticide released into the environment as well as potential side-effects on nontarget organisms. Detailed knowledge of the environmental behavior of such chiral compounds should include information on the chiral stability (interconversion of enantiomers). In the present study, the degradation/ dissipation of metalaxyl and its primary carboxylic acid metabolite (MX-acid) in soil was investigated under laboratory conditions using enantioselective gas chromatography mass spectrometry (GC-MS). Racemic and the enantiopure R- and S-compounds were incubated in separate experiments. The degradation of metalaxyl was shown to be enantioselective with the fungicidally active R-enantiomer being faster degraded than the inactive S-enantiomer, resulting in residues enriched with S-metalaxyl when the racemic compound was incubated. The relatively high enantioselectivity suggests that degradation/dissipation was largely biological. The data indicated a conversion of 40-50% of metalaxyl to MX-acid, and the remaining metalaxyl being degraded via other pathways. The degradation of MX-acid was also enantioselective. Metalaxyl and MX-acid were both configurationally stable in soil, showing no interconversion of R- to S-enantiomers, and vice-versa. Furthermore, the conversion of metalaxyl to MX-acid proceeded with retention of configuration. Degradation followed approximate first-order kinetics but showed significant lag phases.     

Morphological aspects of particle uptake by lung phagocytes

Macrophages residing on the inner epithelial surfaces of airways and alveoli are the only lung phagocytes exposed directly to the environment. Their phagocytic and microbicidal activities are essential for maintaining this organ in a clean and sterile state. The morphology of these phagocytes can be investigated in situ only after implementing special techniques, which involve intravascular triple-perfusion of aqueous fixatives or instillation of nonpolar ones. Such studies have revealed the engulfment of particles by these cells to be rapid, the process being essentially complete within a day. Particles are entrapped within phagosomes and the host cells eventually transported out of the lungs by mucociliary action, macrophages with higher loads being more rapidly eliminated than those with lower ones. Very small particles or those persisting on the epithelial surfaces may be taken up by the eponymous cells. Translocation of particles into the underlying connective tissue and their subsequent phagocytosis by interstitial macrophages prolongs their retention time in the lungs. The still poorly studied pleural macrophages might be involved in cell-mediated immune responses within the pleural space. Intravascular pulmonary macrophages figure largely in the phagocytosis of circulating particles. The role played by dendritic cells in particle uptake by the lungs is not well understood. Airway and alveolar macrophages are the primary phagocytes of the lung. In nonoverload situations and for particles >1 microm, a small proportion of those recruited suffices to remove material from the epithelial surface before other phagocytes, with an apparently greater immunological potential, gain access to it.     

An evaluation of the Norwegian Salmonella surveillance and control program in live pig and pork

Population data and apparent prevalence data from the Salmonella surveillance and control program in pigs (NSSCP) from 1998 and 1999 were used in a simulation model to evaluate the efficacy of the program. The model consists of three parts: modelling of individual prevalence at the abattoir (abattoir part), modelling of the number of sampled herds of different sizes when carcasses are randomly sampled at the abattoir (sampling strategy part) and finally, modelling of the within herd prevalence (within herd part). A total of 136,550 sows and 2,866,550 finishing pigs slaughtered, 4446 herds and 11 herds positive for Salmonella in 1994/1995-2000 were included in the abattoir part, sampling strategy part and the within herd part of the model, respectively. The abattoir part showed an average estimated prevalence of Salmonella in sows and finishing pigs of (median) 0.4% (5-95 percentiles = 0.03-2%) and 0.1% (0.04-0.2%) respectively. The estimated number of infected sow carcasses that entered the market was 502 (37-2157) while the estimated number of finishing pig carcasses was 2919 (1218-5771). The probability of being sampled for the 10% smallest herds was (mean) 1.9% (1.6-2.2), to 25% (24.7-26.5%) for the 10% largest herds. The within herd prevalence was estimated to be from 1% to 4% for Norwegian pig herds. The conclusions drawn from this evaluation are that the NSSCP does not have any significant consumer protection effect, and that the documentation could be done more effectively using the herd rather than the individual animal as the unit of sampling. Sampling should focus on the larger herds supplying most of the meat on the market and on herds that produce breeding sows and piglets and thus can contribute to the spread of Salmonella among herds.     

Melting behavior of polypropylene fibers studied by differential scanning calorimetry

Polypropylene fibers produced in a compact-spinning process were studied by differential scanning calorimetry (DSC). With unrestrained fibers, the onset of melting increases with decreasing draw ratio, increasing M_w/M_n, decreasing extrusion temperature, increasing annealing ratio, and increasing draw-down ratio. These trends are discussed in terms of restraints and reorganization. The onset of melting is shifted to lower temperatures as the heating rate increases for all combinations of material and processing parameters, indicating suppressed reorganization. At low draw ratios, the height and width of the endotherm are affected by the spinline stress, and a secondary peak or shoulder is observed on the high temperature side of the main peak. The magnitude of the secondary peak increases with decreasing M_w/M_n, increasing draw ratio, decreasing draw-down ratio, and decreasing heating rate, but its position mainly depends on the heating rate. This indicates that the secondary peak may be due to the melting of structures that have been reorganized during the heating scan. As the draw ratio increases, the melting regime broadens, especially towards lower temperatures, and several maxima emerge on the DSC curve. Reorganization and shrinkage during heating may explain these observations. © 1995 John Wiley & Sons, Inc.     

Extracellular and intracellular volume variations during postural change measured by segmental and wrist-ankle bioimpedance spectroscopy

Extracellular (ECW) and intracellular (ICW) volumes were measured using both segmental and wrist-ankle (W-A) bioimpedance spectroscopy (5-1000 kHz) in 15 healthy subjects (7 men, 8 women). In the 1st protocol, the subject, after sitting for 30 min, laid supine for at least 30 min. In the second protocol, the subject, who had been supine for 1 hr, sat up in bed for 10 min and returned to supine position for another hour. Segmental ECW and ICW resistances of legs, arms and trunk were measured by placing four voltage electrodes on wrist, shoulder, top of thigh and ankle and using Hanai's conductivity theory. W-A resistances were found to be very close to the sum of segmental resistances. When switching from sitting to supine (protocol 1), the mean ECW leg resistance increased by 18.2%, that of arm and W-A by 12.4%. Trunk resistance also increased but not significantly by 4.8%. Corresponding increases in ICW resistance were smaller for legs (3.7%) and arm (-0.7%) but larger for the trunk (21.4%). Total body ECW volumes from segmental measurements were in good agreement with W-A and Watson anthropomorphic correlation. The decrease in total ECW volume (when supine) calculated from segmental resistances was at 0.79 l less than the W-A one (1.12 l). Total ICW volume reductions were 3.4% (segmental) and 3.8% (W-A). Tests of protocol 2 confirmed that resistance and fluid volume values were not affected by a temporary position change.     

Remediation of alpha-methylnaphthalene-contaminated sediments using peroxy acid

Laboratory experiments have been conducted to elucidate the degradation of alpha-methylnaphthalene in lake sediments using an advanced oxidation process (AOP) employing peroxy-acids as oxidizing agents. Abiotic degradation of alpha-methylnaphthalene was observed in sediment samples exposed to a 1:1:1 v/v/v mixture of water/organic acid/hydrogen peroxide solution. Sediment samples were collected from Lake Macatawa (Holland, MI) and ranged in total organic carbon content from 2.1% (sandy sediment sample III) to 12.8% (silty-clay sediment sample I) and surface area, which ranged from 3.2m(2)/g (sandy sediment sample III) to 22.0m(2)/g (silty-clay sediment sample I). Analytical measurements performed by gas chromatography revealed varied rates of degradation, depending on the type of acid and the characteristics of the sediment sample. Within 24h, alpha-methylnaphthalene was reduced to 70% and 100% of its original concentration when propionic acid and acetic acid were used as the organic acids, respectively. The formation of products was explored using a gas chromatograph equipped with a mass spectrometer and indicated mainly the formation of lower molecular weight compounds, such as alkyl chains. This AOP method of PAH degradation in sediment/liquid slurry was fast acting and products were most likely biodegradable.     

Human peroxisomal disorders

Peroxisomes are single membrane-bound cell organelles performing numerous metabolic functions. The present article aims to give an overview of our current knowledge about inherited peroxisomal disorders in which these organelles are lacking or one or more of their functions are impaired. They are multiorgan disorders and the nervous system is implicated in most. After a summary of the historical names and categories, each having distinct symptoms and prognosis, microscopic pathology is reviewed in detail. Data from the literature are added to experience in the authors' laboratory with 167 liver biopsy and autopsy samples from peroxisomal patients, and with a smaller number of chorion samples for prenatal diagnosis, adrenal-, kidney-, and brain samples. Various light and electron microscopic methods are used including enzyme- and immunocytochemistry, polarizing microscopy, and morphometry. Together with other laboratory investigations and clinical data, this approach continues to contribute to the diagnosis and further characterization of peroxisomal disorders, and the discovery of novel variants. When liver specimens are examined, three main groups including 9 novel variants (33 patients) are distinguished: (1) absence or (2) presence of peroxisomes, and (3) mosaic distribution of cells with and without peroxisomes (10 patients). Renal microcysts, polarizing trilamellar inclusions, and insoluble lipid in macrophages in liver, adrenal cortex, brain, and in interstitial cells of kidney are also valuable for classification. On a genetic basis, complementation of fibroblasts has classified peroxisome biogenesis disorders into 12 complementation groups. Peroxisome biogenesis genes (PEX), knock-out-mice, and induction of redundant genes are briefly reviewed, including some recent results with 4-phenylbutyrate. Finally, regulation of peroxisome expression during development and in cell cultures, and by physiological factors is discussed.     

Developmental differences in implicit learning of spatial context.

The authors examined whether a form of implicit memory that has been unambiguously dissociated from conscious awareness--learning of spatial context on the contextual cuing task introduced by M. M. Chun and Y. Jiang (1998)--is mature in childhood as predicted by an evolutionary view of cognition. School-aged children did not show reliable learning relative to adults who performed the same version of the task or another version that slowed responses to match those of children. Thus, unreliable learning in childhood was mediated by immature implicit representations of spatial context rather than by slower baseline response speed. The present finding is inconsistent with the prediction of the evolutionary view of cognition but consistent with incomplete maturation of medial temporal lobes known to mediate contextual learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)