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

Biocompatibility and biodegradation studies of a commercial zinc alloy for temporary mini-implant applications

In this study, the biocompatibility and in vitro degradation behaviour of a commercial zinc-based alloy (Zn-5 Al-4 Mg) were evaluated and compared with that of pure zinc for temporary orthopaedic implant applications. Biocompatibility tests were conducted using human alveolar lung epithelial cells (A549), which showed that the zinc alloy exhibits similar biocompatibility as compared to pure zinc. In vitro degradation evaluation was performed using weight loss and electrochemical methods in simulated body fluid (SBF) at 37 degrees C. Weight loss measurements revealed that the degradation of the zinc alloy was slightly lower during the initial immersion period (1-3 days), but marginally increased after 5 and 7 days immersion as compared to pure zinc. Potentiodynamic polarisation experiments showed that the zinc alloy exhibits higher degradation rate than pure zinc. However, electrochemical impedance spectroscopy analysis suggests that pure zinc is susceptible to localized degradation, whereas the zinc alloy exhibited passivation behaviour. Post-degradation analysis revealed localized degradation in both pure zinc and the zinc alloy

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