The chiral herbicide dichlorprop
(2,4-dichlorophenoxy-2-propionic acid), which is sold and applied as the
racemic mixture, was observed to degrade completely
in soil within 31 days, with a half-life of 6.6 d.
Degradation occurred with enantiomeric selectivity,
indicating biologically mediated reactivity as opposed to strictly abiotic degradation. The
S-(−)-isomer
degraded significantly faster (t
1/2 = 4.4 d)
than the
R-(+)-isomer (t
1/2 = 8.7 d);
this is contrary to other
published results that show selective degradation
of the R-(+)-enantiomer, although in other media.
Soil
samples taken from a field plot at increasing time
intervals after application of Foxtril, a commercial
herbicide formulation, were solvent-extracted and
analyzed for total dichlorprop by capillary zone electrophoresis (CZE), using an acetate buffer at pH 4.7.
Heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin, a
chiral
reagent, was then added to the buffer to effect
separation of the (+)- and (−)-isomers of dichlorprop.
Baseline resolution allowed calculation of relative
concentrations (enantiomer ratios) of the two isomers.
CZE is a fast and efficient technique for the
analysis
of ionic organic species (such as the anion of
dichlorprop), including their enantiomers, in pesticide
formulations as well as in environmental samples.
It thus was possible to analyze Foxtril directly
after
dilution with water for ioxynil (2,6-diiodo-4-cyanophenol) as well as for dichlorprop. Ioxynil also
was detected in the soil extract on the day of application. The hydrolysis product [methyl
2-nitro-5-(2,4-dichlorophenoxy) benzoic acid] of bifenox methyl
ester, another herbicide component of Foxtril, was
detected in the soil samples taken at 17 and 31
d.
The photodecomposition of imazamox, a herbicide of the imidazolinone family, was investigated in pure water. The main photoproducts from the photolysis were followed over time by liquid chromatography mass spectrometry and structures were proposed from exact mass determinations obtained by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The method comprised exact mass determination with better than 0.2 ppm mass accuracy and a corresponding structural visualization taking care of respective isotopes with an adapted van Krevelen diagram that enabled a systematic approach to the characterisation of the elementary composition of each photoproduct. By taking advantage of the high resolving power of FT-ICR MS to make precise formula assignments, the derived 2D van Krevelen diagram (O/C; H/C; m/z) enabled one to structurally differentiate the formed photoproducts and to propose a degradation pathway for imazamox.
Direct degradation of imazapic, an herbicide of the imidazoline family, has been investigated in aqueous solution at different concentrations, pH values, and temperatures. The efficiency of the photodegradation process has been evaluated through degradation rate constants that could be fitted best with pseudo-first-order kinetics ( Ct = C0 e(- kt )). Ultrahigh resolution mass spectrometry (FTICR/MS) was used in electrospray ionization mode as a tool to study the photolysis process on a molecular level, whereas UV-vis and high-performance liquid chromatography/mass spectrometry analysis were used to follow, by time, the evolution of the intermediates. Taking advantage of the high resolving power of FTICR/MS to perform precise formula assignments taking account of the natural abundance of isotopes, we herein propose and demonstrate an approach using 2D-derived van Krevelen visualization (O/C, H/C, m/z) to confirm the formation of imazapic intermediates. Such an approach allows a qualitative analysis of intermediates and elucidates the plausible reaction pathways of the photolysis process. More than eight photoproducts were separated and identified as a phototransformation of the imidazole ring. A mechanistical pathway was proposed.
Insect-pollinated plants are essential for honey bees to feed their brood. In agricultural landscapes, honey bees and other pollinators are often exposed to pesticides used for cultivation. In order to gain more insight into the fluctuation of pesticide loads, 102 daily pollen samples were collected between April and July 2018 in a fruit-growing area in Southern Germany. Samples were analyzed with respect to more than 260 pesticides using a multi-residue pesticide analysis method. Almost 90% of the analyzed pollen samples featured between one and thirteen different pesticides. In total, 29 pesticides were detected at maximum concentrations of up to 4500 ng/g pollen. Maximum residual concentrations of most pesticides were observed during April and the first half of May, as well as during the second half of June. In most cases, serial data of pesticide residuals were detected for approximately 10 subsequent days with two or three maximum values, which were several folds higher than concentrations on the days before and thereafter. The pollen hazard quotient (PHQ) was calculated to estimate the risk of the detected pesticides to honey bees and wild pollinators.
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