Hazard
Moderately toxic by skin contact. Low tox-icity by ingestion and inhalation.
Description
Kresoxim-methyl is a strobilurin fungicide.
1 It inhibits conidial germination of
V. inaequalis isolates from apple orchards (EC
50s = 0.00033-0.0078 mg/L). Kresoxim-methyl also inhibits mycelial growth (EC
50 = 0.240 mg/L) and is fungicidal against
Saprolegnia (MIC = 1 mg/L).
2 It increases intracellular calcium levels and disrupts the mitochondrial membrane potential in mouse cortical cultures in a concentration-dependent manner.
3 Kresoxim-methyl is toxic to goldfish (
C. auratus; LC
50 = 0.807 mg/L).
2
Definition
ChEBI: A carboxylic ester that is the methyl ester of (2E)-(methoxyimino){2-[(2-methylphenoxy)methyl]phenyl}acetic acid. A fungicide for the control of scab on apples and pears and other fungal diseases on a wide range of crops.
Metabolic pathway
By hepatocyte suspensions prepared from goats, pigs,
hens, and rats that have been cryopreserved and
thawed, BAS 490 F is metabolized via the same
pathways as observed using fresh rat hepatocytes.
The rate of hydrolysis of 14C-BAS 490 F leading to a
carboxylic acid derivative seems to be constant
between the cryopreserved and fresh hepatocytes
except for goats. The oxidation reaction at the methyl
group of the phenoxy ring, leading to the
hydroxymethyl analog of the carboxylic acid of BAS
490 F, significantly decreases after cryopreservation,
whereas the formation of (E)-2-methoxyimino-2[2-(4-
hydroxy-2-methylphenyloxymethyl)phenyl] acetic acid
by hydroxylation at the 4-position of the phenoxy ring
remains at a constant rate. In pig hepatocytes, the two
hydroxylated metabolites of the phenoxy ring, carboxy
BAS 409 F and (E)-2-methoxyimino-2-o-
hydroxymethylphenyl acetic acid, are formed to a
lesser extent after cryopreservation.
Metabolism
Kresoxim-methyl is rapidly metabolized in mammalian
systems to the virtually inactive carboxylic acid, accounting
for its low toxicity and high level of selectivity. Atharvest
residues in cereals and top fruit are <0.05 mg/kg
and <1 mg/kg in grapes and vegetables. The soil DT50 =
<3 days, and the Koc is 219 to 372. For the main metabolite,
the Koc is 17 to 24. Hydrolytic stability tests indicate
a DT50 of 34 days at pH 7 but only 7 h at pH 9.
Degradation
Kresoxim-methyl is a stable crystalline solid with limited water solubility.
It is stable in the pH range 3-8 but it is hydrolysed to the carboxylic acid
(2, see Scheme 1) in base. DT50 values (25 °C) at pH 5,7 and 9 were 875,34
and 0.29 days, respectively. The product (2) was stable under these
conditions.
Kresoxim-methyl undergoes rapid photodegradation in water when
irradiated with UV light. Its DT50 was 3 days and several products were
formed, one of which was the Z-isomer. Details of the other products are
not available. Under conditions of simulated sunlight the compound was
degraded with a DT50 of 37 days in pure water and 19 days in natural
pond water.
Toxicity evaluation
Kresoxim-methyl has an acute oral LD50 > 5,000
and an acute dermal LD50 > 2,000 mg/kg in rats. The
NOEL for rats is 800 ppm, and the ADI = 0.4 mg/kg bw
(body weight). Kresoxim-methyl is not a skin or eye
irritant, is nonmutagenic and nonteratogenic. It shows
toxicity to aquatic organisms (fish 96-h LC50 = 0.681
to 1 mg/L) but does not cause permanent damage.
Other nontarget organisms show the following levels
of sensitivity: bird: 14-day LD50 = 2,150 mg/kg; bee: 48-
h LD50 ≥ 20 μg/bee; worm: LC50 ≥ 937 mg/kg; Daphnia:
48-h EC50 = 0.186 mg/L; and algae 0- to 2-h EC50 =
63 μg/L.
