Light-dependent
peroxidizing herbicides (LDPHs)
Ref:
Dec 11, 2001 - US EPA.
Revised Environmental
Fate and Effects Division Preliminary Risk Assessment
for the Oxyfluorfen Reregistration
Eligibility Decision Document.
Phototoxic Pesticide.
Light-dependent peroxidizing herbicides
(LDPHs). US EPA identified the herbicides Acifluorfen,
Azafenidin,
Carfentrazone-ethyl, Flumiclorac-penty, Flumioxazin,
Fluthiacet-methyl, Fomesafen, Lactofen, Oxadiargyl, Oxadiazon,
Oxyfluorfen, Sulfentrazone, Thidiazimin as
phototoxic pesticides that
act by inhibiting protoporphyringen oxidase in the heme
and chlorophyll biosynthetic pathway.
[10 out of the 13 pesticides that EPA identified are organofluorines].
SEE http://www.fluoridealert.org/pesticides/phototoxicity.page.htm
Ref: December 11, 2001 - US EPA. Revised
Environmental Fate and Effects Division Preliminary Risk
Assessment for the Oxyfluorfen Reregistration Eligibility
Decision Document (also at:
http://www.epa.gov/oppsrrd1/reregistration/oxyfluorfen/oxyefedchap.pdf
).
J
Environ Qual 2002 Jan-Feb;31(1):268-74
Photochemistry
and photoinduced toxicity of acifluorfen, a diphenyl-ether
herbicide.
Scrano L, Bufo SA, D'Auria M, Meallier
P, Behechti A, Shramm KW.
Dipartimento di Produzione Vegetale, Universita della Basilicata,
Potenza, Italy.
PubMed Abstract: Photochemistry studies can be helpful in
assessing the environmental fate of chemicals. Photochemical
reactions lead to the formation of by-products that can
exhibit different toxicological properties from the original
compound. For this reason the photochemical behavior of
the herbicide acifluorfen (5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic
acid) in the presence of different solvents was studied.
Photochemical reactions were carried out using a high-pressure
mercury arc and a solar simulator. Kinetic parameters and
quantum yields were determined. The
identification of photoproducts was performed by mass spectrometry
and [1H] nuclear magnetic resonance (NMR). Nitrofluorfen,
hydroxy-nitrofluorfen, 2-chloro-4-(trifluoromethyl)phenol,
5-trifluoromethyl-5'-nitrodibenzofuran, and other derivatives
were identified. The photochemical reactions were also carried
out in the presence of either a singlet or a triplet quencher,
and in the presence of either a radical initiator or a radical
inhibitor. Substances used as inhibitors of the excited
levels T1 and S1 showed that photodegradation of acifluorfen
begins from a singlet state S1 through a pi,pi* transition.
The role of free radicals in the photodegradation of acifluorfen
was determined and a radical mechanism was proposed.
Toxicity tests against Daphnia magna Strauss showed that
acifluorfen was not toxic at
a concentration of 0.1 mM; however,
photoproducts formed after 36 h of
UV exposure of the herbicide induced a remarkable toxicity
to the test organism.
