Biomedical subjects

G R Webster

Publications and source records attributed to G R Webster.

At least 19 recordsLinked to original sources

PubMed1982

Analysis of fenitrothion and metabolites in stored wheat.

A simple and rapid method for the analysis of fenitrothion and its metabolites, fenitrooxon, S-methyl fenitrothion, demethyl fenitrothion, demethyl S-methyl fenitrothion, 3-methyl-4-nitrophenol, and dimethyl phosphorothioic acid in stored wheat has been developed. Simultaneous analysis of the extract was conducted using FPD-GLC after derivatization with diazoethane except for 3-methyl-4-nitrophenol which was analyzed directly by EC-GLC. Recoveries of all compounds from wheat fortified at the levels from 0.1 to 5.0 ppm were greater than 90%. The developed method was used to quantitatively determine major metabolites found in grain treated with fenitrothion and stored at 20 degrees C for 12 months. Demethyl fenitrothion, 3-methyl-4-nitrophenol, and dimethyl phosphorothioic acid were the major breakdown products of fenitrothion found in stored wheat. Confirmation of these metabolites was carried out by chemical derivatization plus FPD-GLC and by TLC.

Biotransformation↗

PubMed1982

Fate of permethrin in model outdoor ponds.

In 1979 and 1980, outdoor artificial ponds were treated with 14C-permethrin (labelled at either the cyclopropyl or methylene position) at 0.028 kg/ha (15 ug/L). Uptake of permethrin by duckweed and hydrosoil was monitored by direct combustion, TLC-autoradiography, HPLC, and liquid scintillation counting. Rapid loss of permethrin from the water coincided with the detection of five degradation products in the water at concentrations below 2.0 ug/L. The products were cis- and trans-cyclopropyl acid, phenoxybenzoic acid, and phenoxybenzyl alcohol, and an unknown non-cleaved product of permethrin. Permethrin was readily sorbed by duckweed but was not persistent. Permethrin residues in the hydrosoil, which was the major sink for permethrin added to the ponds, were persistent and were detected at 420 days post-treatment. Cis-permethrin was more persistent in the hydrosoil than the trans-permethrin. The results indicated that permethrin in water was short-lived at an application rate of 15 ug/L because of the rapid degradation of permethrin in the water and sorption of permethrin by the hydrosoil and vegetation. However, at one year post-treatment, permethrin residues were still detected in the hydrosoil at 1.0 ug/kg.

Fresh Water↗

PubMed1982

Acidification of a Solonetzic soil by nitrogenous fertilizers.

Annual applications of (NH4)2SO4, NH4NO3 and urea on a Solonetzic soil at 112 kg N/ha for 10 consecutive years reduced pH levels from 5.6 for the check to 4.4, 4.9 and 5.3, respectively for (NH4)2SO4, NH4NO3 and urea. (NH4)2SO4 generated twice as much exchange acidity as NH4NO3 and four times as much as urea. Net extractable cations leached from the Ap horizon closely approximated the amount of exchange acidity generated by (NH4)2SO4 and NH4NO3 fertilizers. The levels of soil extractable Al and Mn were greatly enhanced by (NH4)2SO4 as were plant contents. Similar acidifying effects to that produced by the (NH4)2SO4 occurred when NH4NO3 was applied at 300 kg N/ha annually for 12 consecutive years in another field experiment on the same soil. Liming samples of the field (NH4)2SO4 acidified soils in the greenhouse, significantly increased yields and lowered the Al and Mn contents of the plants to normal levels.

Aluminum↗

PubMed1980

Loss of chlorpyrifos in pond water: examination of results using three simple mathematical models.

Four outdoor artificial pools were fortified with two formulations of chlorpyrifos (the active ingredient in Dursban insecticide), as emulsifiable concentrate, and a slow-release granular formulation. From concentration-time data collected during summer months, the half life of chlorpyrifos was found to be 5 +/- 3 h and 14 +/- 4 h for the emulsifiable concentrate and slow release formulations respectively. The concentration-time data was analyzed by three mathematical models; the power rate model, the hyperbolic rate model, and an empirical power function. Their average correlation coefficients, determined by linear regression, were respectively, 0.78 +/- 0.08, 84 +/- 0.07, 0.76 +/- 0.16.

Chlorpyrifos↗

PubMed1979