Avermectin B1a metabolism in celery: a residue study

Photodegradation of avermectin B1a thin films on glass

“…The UV spectra of C4B (exactly as 10,ll-2 standard in Figure 9C) and C6 ( Figure 9A) reflect diene alterations relative to B1A consistent with previous studies (Maynard and Maynard, 1989;Moye et al, 1990). The presence of the 8,9-2 analogue after exposure of B1A to sunlight observed in the present studies and previously by others (Moye et al, 1990) is interesting since this photoisomer would apparently require 220-270-nm light for formation. Recent photoisomerization studies (O'Shea and Foote, 1988) of 2,4-hexadiene in solution in the presence of a sensitizer strongly suggest singlet oxygen involvement in intraconversion of the E$, E,Z, and Z,Z forms.…”

“…The geometric isomers at the 10,ll (C4B) and 8,9 (C6) double bonds have been reported as photoproducts of B1A in solution (Mrozik et al, 1988); C6 has been described as a degradate in plants (Moye et al, 1990;Maynard and Maynard, 1989). The UV spectra of C4B (exactly as 10,ll-2 standard in Figure 9C) and C6 ( Figure 9A) reflect diene alterations relative to B1A consistent with previous studies (Maynard and Maynard, 1989;Moye et al, 1990).…”

“…Time Figure 12B) is similar to that in previous plant metabolism studies (Moye et al, 1990). The polar residues contribute approximately 80% or greater to the total 14C residue when the parent compound is approximately 10% or less of the total residue with the remainder split approximately equally between moderately polar and nonpolar residues (data not shown).…”

“…An isocratic CIS HPLC method (method I, elution with 85% methanol at a flow rate of 1 mL/ min, Zorbax CIS column) was used to broadly classify and quantitate B1A residues as polar [retention times ( t~) 0-0.6 of BlA] and moderately polar ( t~ approximately 0.6-0.95 of BlA), similar to previous studies of avermectin degradation in plants (Moye et al, 1990). A second Cl8 HPLC method (method 11), used for assay of B1A and ita photodegradates, consisted of the Zorbax Cl8 column eluted at 1.5 mL/min with methanol/water at the following proportions: 0-50 min, 79% methanol; 50-60 min, 79-100% methanol.…”

“…Although abamectin is rapidly degraded on plants, limited characterization of residues has been performed (Bull et al, 1984;Iwata et al, 1985;Maynard et al, 1989a,b;Moye et al, 1990). The task of isolating and identifying degradates of avermectins in treated crops for determination of the terminal toxic residue has proven to be a significant undertaking due to the very low application rates (approximately 10 g/acre) and rapid breakdown under field-use conditions to a complex residue (Wislocki et al, 1989).…”