Factors influencing the enhanced microbial degradation of pesticides in soil

A recent concern in the widespread use of soil-applied pesticides is the phenomenon of enhanced degradation by soil microorganisms. This study investigated selected factors influencing the enhanced microbial degradation of pesticides. Because hydrolysis is a significant initial step in the degradation of pesticides, the role of hydrolysis metabolites in the induction of enhanced degradation was studied. Salicylic acid, p-nitrophenol, and 2,4-dichlorophenol conditioned the soil for enhanced degradation of their parent compounds, isofenphos, parathion, and 2,4-dichlorophenoxyacetic acid, respectively. Repeated applications of 3,5,6-trichloro-2-pyridinol resulted in increased persistence of its parent compound, chlorpyrifos. Pretreatment of soil with hydrolysis metabolites of carbofuran, diazinon, fonofos, and 2,4,5-T did not have any effect on the degradation of their respective parent compounds;The properties of pesticide metabolites such as toxicity and availability to microorganisms may influence their potential to condition soils for the enhanced degradation of their parent pesticides. Mobility studies using a soil thin-layer chromatography technique indicated that for a pesticide to be susceptible to enhanced degradation, it need not necessarily be very mobile. Because some metabolites are capable of inducing or inhibiting the enhanced degradation process the mobility/availability of hydrolysis metabolites is of practical significance. Soil pH significantly affected mobility of most of the chemicals studied, with increased mobility in soils with higher pH\u27s. Water solubility, by itself, was not a good predictor of mobility and structural similarity does not seem to be an indicator of mobility. The Microtox system was employed to determine the toxicity of pesticides and their metabolites to bacteria. Hydrolysis metabolites of pesticides susceptible to enhanced degradation (isofenphos, diazinon, and carbofuran) recorded higher EC[subscript]50 values, indicating their low toxicity to bacteria;The effect of manuring on the degradation of pesticides was investigated. Manuring for seven years resulted in increased persistence of pesticides or their pesticidal metabolites. This study found no evidence that amending soil with manure encourages the development of enhanced microbial degradation of pesticides

Assay of ethambutol in pharmaceutical preparations

Ethambutol tablets of 200 and 400 mg denominations were assayed by the standard non-aqueous titration method and a simpler calorimetric method. With the titrimetric method, assay values, appreciably higher than the stated content (117% or more), were obtained with the products of 4 companies, while all the values were within 6% of the stated content by the calorimetric method. Rifampicin and pyrazinamide interfered with the estimation of ethambutol by both methods: isoniazid, however, caused an overestimation with the titrimetric method only

Determination of the Transient Dehumidification Characteristics of High Efficiency Central Air Conditioners

A series of tests were performed to assesses the dehumidifying performance of residential central air conditioners (CACs). The performance studies were based on factors such as: (i) dynamic performance (ii) the ASHRAE comfort zone, (iii) control strategy and (iv) published performance characteristic of the units. The units were evaluated on their ability to maintain conditions in the ASHRAE comfort zone in a typical residence and typical summer days in Houston, Texas

Degradation of isazofos in the soil environment

Field and laboratory studies were conducted to investigate the degradation of the organophosphorus insecticide isazofos (0-5-chloro-l-isopropyl-1H-l,2,4-triazol-3-ylO,O-diethyl phosphorothioate) in soil. In a 6-year field study, soil pH was an important factor influencing the degradation of isazofos inasmuch as an increased rate of degradation was observed in soils with previous isazofos applications and pH of 6.9 or more. A laboratory study of [14Clisazofos confirmed the rapid degradation of this insecticide in high pH soils. No increased degradation rate, however, was observed in sterilized high-pH soils. The availability of isazofos to microorganisms, based on sorption of isazofos to soil, seems to be an important factor influencing the degradation of isazofos in soil. Sorption coefficients were negatively correlated with isazofos degradation rate

Calcium ion binding to δ- and to β-crystallins. The presence of the "EF-hand" motif in δ-crystallin that aids in calcium ion binding

Abnormal levels of endogenous calcium ions are known to induce eye lens opacity, and a variety of causative factors has been proposed, including calcium-mediated aggregation and precipitation of the lens proteins crystallins. We have specifically looked in some detail at the interaction of Ca2+ with various crystallins and its consequences. Lenses incubated in solutions containing 10 mM Ca2+ or 5 mM Tb3+ opacified. Fluorescence titration of crystallins with TbCl3 revealed that this ion binds to δ- and β-crystallins in solution. Equilibrium dialysis showed that four Ca2+ ions bind to one δ-crystallin tetramer with an affinity of 4.3 × 103 M-1. Analysis of the amino acid sequence of δ-crystallin reveals the presence of a calmodulin-type "helix-loop-helix" or "EF-hand" calcium ion binding conformational motif in the region comprising residues 300-350. This is a novel feature of the molecule not reported so far. No other crystallins appear to have this motif. β-Crystallin also binds four Ca2+ ions/aggregate unit of mass 160 kDa, with an affinity of 2.6 × 103 M-1, presumably in the midregion of the molecule that is rich in anionic and polar residues. Circular dichroism spectroscopy shows that the binding of calcium ion leads to subtle conformational changes in the molecules, notably in the tertiary structure

An Evaluation of Steady-State Dehumidification Characteristics of Residential Central Air Conditioners, Final Report

This report is the first of two reports on the project "Determination of the Transient Response Characteristics of High Efficiency Commercial Air Conditioners" funded by Houston Lighting and Power Company. The purpose of this report is to present the results from an investigation of the possible relationship between residential central air conditioner efficiency and dehumidification performance. The method used was that of a survey of air conditioners currently manufactured and on the market as of late 1986. Chapter 2 outlines the basic terminology used in evaluating the dehumidification performance of central air conditioners. Chapter 3 provides background to the survey data. Chapter 4 presents results from the survey. Conclusions and recommendations are presented in Chapter 5