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21.
Degradation of atrazine and alachlor in saturated aquifer materials and soil was studied in the laboratory. A static aquifer was represented by a set of stagnant flasks and a well-mixed aquifer was simulated by recirculating columns. Water was tested at selected time intervals over six months and analyzed for herbicides and metabolites. Under all conditions, atrazine was more persistent than alachlor. Increased temperature had little effect on atrazine dissipation but did increase alachlor degradation rates, especially in the sterilized treatments. The addition of carbon and nitrogen prolonged the initial period before the onset of degradation in some of the columns. Enhanced mass transfer of the herbicides, nutrients, and oxygen in the recirculating columns dramatically increased dissipation of atrazine and alachlor. The degradation rates of atrazine and alachlor were 2 to 5 times faster in the recirculating columns than in the stagnant flasks. Atrazine was more persistent in the aquifer materials than in the soils, while alachlor dissipation was similar in the soils and recirculating aquifer columns, but was slower in the stagnant flasks. The prolonged persistence of atrazine under static, aquifer conditions (t 1/2 = 206 to 710 days) indicates that natural mechanisms are not sufficient to alleviate the risk of atrazine buildup over time; however, in a well mixed aquifer, atrazine degradation rates should be higher (t 1/2 = 66 to 106 days) and the threat of atrazine accumulation is diminished. Alachlor persistence at low concentrations (< 10 μg L?1) in aquifers should not pose a long-term threat to ground water supplies.  相似文献   
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Atrazine [6-chloro-N-ethyl-N′-(1-methyl)-1,3,5 triazine-2,3-diamine] and alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl) acetamide] are agricultural herbicides used in large quantities and, as a consequence, are common contaminants in groundwater and surface water. The retention of these herbicides in soils and their degradation in aqueous environments is highly dependent upon their adsorption to solid surfaces. The adsorption of atrazine and alachlor was investigated on three typical Kansas and underlying aquifers known to be vulnerable to contamination. More alachlor was adsorbed to the soils and sediments than atrazine. The adsorption coefficients for atrazine were 2 to 5 times higher for soils than for aquifer sediments. For alachlor, the adsorption coefficients were 4 to 20 times higher for soil than for aquifer solids. Both linear and Freundlich isotherms represented the adsorption data well in all cases. The slope of the Freundlich isotherms, 1/n, was close to one, with the exception of alachlor adsorption onto the Topeka aquifer sediment (1/n = 0.67). The K d values found in these studies were comparable to the lower range of those reported in the literature.  相似文献   
23.
Caprine arthritis-encephalitis is a retrovirus-induced disease resulting in lymphoproliferative lesions of the CNS and joints. Peripheral blood leukocytes of chronically infected goats were analyzed for the types of cells present and for their reactivity to viral antigen and polyclonal stimulants. Two of 9 infected goats had abnormal numbers of B lymphocytes--one elevated and the other deficient. Lymphocyte reactivity to viral antigens was transiently detectable by a lymphoblastogenic assay in 5 of the 9 goats. The reactive cells were peanut agglutinin-negative T lymphocytes. Concanavalin A induced more division in T lymphocytes of infected goats than in lymphocytes of noninfected goats, whereas the reactions to phytohemagglutinin, pokeweed mitogen, and bacterial lipopolysaccharide were no different in the 2 goat groups. It is concluded that goats infected by the caprine arthritis-encephalitis virus have antigen-reactive T lymphocytes and that infection promotes the response to a nonspecific T-cell stimulant.  相似文献   
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Trochlear arthroplasty was performed on one stifle in each of 18 Greyhounds; their contralateral pelvic limbs and the pelvic limbs of 2 dogs treated with sham surgery were controls. At 2, 4, 8, and 16 weeks, radiography, glycosaminoglycan histochemical analysis, histologic examination, and scanning electron microscopy of the trochlear surface were done. All dogs used the limb and walked without an observable limp within 2 weeks after surgery. Radiography at euthanasia did not reveal degenerative changes. Well-vascularized, highly cellular, loose fibrous connective tissue was reorganized with time into a dense fibrous connective tissue covering the entire wound. Scanning electron microscopy revealed that the replacement tissue surface was rough, torn, and debris-covered. Differential histologic staining established that change to fibrocartilage had begun deep within the replacement tissue. Histochemical analyses corroborated those observations.  相似文献   
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A qualitative assessment of glycosaminoglycans (GAGs) in the non-chondrodystrophoid canine cervical anulus fibrosus was performed using the Alcian blue/critical electrolyte concentration staining technique. Estimates of GAG concentration were deduced for two groups of dogs (average age four and eight years) by determining the hyaluronic acid, chondroitin sulphates and keratan sulphate 'alcianophilic indices'. Keratan sulphate was the predominant GAG in the four-year-old group of dogs. The concentration of keratan sulphate was equal to that of chondroitin sulphates in the eight-year-old group and the total GAG concentration was decreased. This qualitative assessment indicated that the concentrations of keratan sulphate decreased and chondroitin sulphates increased between four and eight years of age. Similar conclusions have not been reported for anuli in the thoracic and lumbar regions of the canine spine.  相似文献   
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