The absorption, tissue distribution, metabolism, and excretion of moxidectin, a new endectocide for the control of internal and external parasites in cattle and sheep, was studied in cattle. Following a single subcutaneous dose of 14C-and 2H-labeled moxidectin of 0.2 mg/kg of body weight, highest 14C residues were present in abdominal fat (898,636, and 275 ppb) and back fat (495,424, and 186 ppb) a t 7, 14, and 28 days posttreatment, respectively. Lower residues were detected in liver (109, 77, and 31 ppb), kidney (42,38, and 13 ppb), and loin muscle (21,10, and 4 ppb), respectively. The administered radioactivity was excreted primarily in the feces, with only 3 % of the dose being eliminated in the urine. The HPLC/14C profiles of the residues extracted from the tissues, fat, and feces were qualitatively similar and showed moxidectin was the major component of the residue. Only two metabolites were present that were more than 5 % (2 ppb) of the total liver residues after 28 days. These were identified as the C-29/30 and the C-14 monohydroxymethyl metabolites by LC/MS and LC/MS/MS analysis of the metabolites isolated from the feces. Proton NMR analysis of the authentic compounds prepared in-uitro from cattle liver microsomal incubation and rat liver homogenate incubation with 14C-labeled moxidectin confirmed the mass spectral results. By LC/MS and LC/MS/MS, several other mono-and dihydroxylated and 0-demethylated metabolites were also identified.Moxidectin is a semisynthetic derivative of nemadectin (Asato and France, 1990), a macrocyclic lactone produced by fermentation in a culture of Streptomyces cyanogriseus.

Arsenal herbicide, the active ingredient of which is imazapyr [2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid], is an imidazolinone type of herbicide. Photodegradation of imazapyr 14C labeled at the carboxyl and 5-oxocarbon positions was carried out separately under borosilicate-filtered xenon arc light at 25 °C in aqueous media. Imazapyr was shown to photodegrade rapidly and extensively in aqueous solution. The decline of imazapyr concentration in the solution followed first-order kinetics. The half-lives were calculated as 1.9-2.3 days in distilled water, 2.7 days in pH 5 buffer, and 2.3 days in pH 9 buffer. The predominant photolysis products derived from carboxyl-14C-labeled imazapyr were 7-hydroxyfuro [3,[4][5][6]pyridin-5(7H)-one and 2,3-pyridinedicarboxylic acid. Decarboxylation was evident as a minor photodecomposition product of carboxyl-14C-labeled imazapyr. Two cyclized compounds, 2,3-pyridinedicarboximide and furo [3,46] pyridin-5(7/i)-one, were also detected as minor degrádales. The one major photolysis product of the 5-oxo-14C-labeled imazapyr was the volatile 14CC>2.

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The imidazolinones are a significant new class of low-use-rate, reduced-environmental-risk herbicides for protection of a wide variety of agricultural crops. Current analytical methodologies for the determinations of individual imidazolinones in water at the 1 ppb level involve processing several hundred milliliters of water through a series of solid-phase extraction cartridges and solvent-partitioning steps. By combining liquid chromatography with electrospray ionization mass spectrometry or electrospray ionization tandem mass spectrometry, all imidazolinones can be monitored simultaneously at the 1 ppb level with only a simple filtration prior to analysis. Recoveries from tap, lake, and well waters were essentially quantitative for each imidazolinone in both modes of analysis. Keywords: Imidazolinone; herbicides; determination; LC/ESMS; LC/ESMS/MS