Photoreduction of chlorothalonil fungicide on plant leaf models.

Environmental science & technology (2011-09-29)
S Monadjemi, M El Roz, C Richard, A Ter Halle
ABSTRACT

Photodegradation is seldom considered at the surface of vegetation after crop spraying. Chlorothalonil, a broad-spectrum foliar fungicide with a very widespread use worldwide, was considered. To represent the waxy upper layer of leaves, tests were performed within thin paraffin wax films or in n-heptane. Laser flash photolysis together with steady-state irradiation in n-heptane allowed the determination of the photodegradation mechanisms Chlorothalonil ability to produce singlet oxygen was measured; noteworthy its efficiency is close to 100%. Additionally, chlorothalonil photodegradation mainly proceeds through reductive dechlorination. In these hydrophobic media, a radical mechanism was evidenced. Photochemical tests on wax films under simulated solar light show that formulated chlorothalonil is more reactive than pure chlorothalonil. The field-extrapolated half-life of photolysis on vegetation was estimated to 5.3 days. This value was compared to the half-lives of penetration and volatilization available in the literature. It appears that chlorothalonil dissipation from crops is ruled by both photodegradation and penetration. The relative importance of the two paths probably depends on meteorological factors and on physicochemical characteristics of the crop leaf cuticle.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Heptane, suitable for HPLC, ≥99%
Sigma-Aldrich
Heptane, anhydrous, 99%
Sigma-Aldrich
Heptane, ReagentPlus®, 99%
Sigma-Aldrich
Heptane, HPLC Plus, for HPLC, GC, and residue analysis, 99%
Sigma-Aldrich
Heptane, puriss. p.a., reag. Ph. Eur., ≥99% n-heptane basis (GC)
Supelco
Heptane, analytical standard
Supelco
Chlorothalonil, PESTANAL®, analytical standard
Sigma-Aldrich
Heptane, suitable for HPLC, ≥96%
Sigma-Aldrich
Heptane, biotech. grade, ≥99%
Chlorothalonil, analytical standard
Chlorothalonil, analytical standard
Supelco
Heptane, HPLC grade, ≥99%

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