Effect of temperature and moisture on the degradation and sorption of florasulam and 5-hydroxyflorasulam in soil.
The degradation rate and sorption characteristics of the triazolopyrimidine sulfonanilide herbicide florasulam and its principal degradation product 5-hydroxyflorasulam (5-OH-florasulam) were determined as a function of temperature and moisture in three different soils. The half-life for degradation of florasulam ranged from 1.0 to 8.5 days at 20-25 degrees C and from 6.4 to 85 days at 5 degrees C. The half-life for degradation of 5-OH-florasulam ranged from 8 to 36 days at 20-25 degrees C and from 43 to 78 days at 5 degrees C. The degradation rate of both compounds was strongly influenced by temperature, with activation energies ranging from 57 to 95 kJ/mol for florasulam and from 27 to 74 kJ/mol for 5-OH florasulam. Soil moisture content had negligible impact on the degradation rate. Apparent (nonequilibrium) sorption coefficients for florasulam and 5-OH-florasulam at 0 days after treatment (DAT) were 0.1-0.6 L/kg and increased linearly with time for both florasulam and 5-OH-florasulam (r(2) > 0.90) to levels as high as 12-23 L/kg. Heats of adsorption were calculated on one soil as a function of time. Heat of adsorption values for both florasulam and 5-OH-florasulam increased as incubation time increased and the amount of each compound decreased; values were near 0 kJ/mol initially and increased to a maximum of 91 and 66 kJ/mol for florasulam and 5-OH-florasulam, respectively.
Krieger
M S
MS
Dow AgroSciences, Environmental Chemistry Laboratory, 9330 Zionsville Road, Indianapolis, Indiana 46268, USA. mkrieger@dowagro.com
Pillar
F
F
Ostrander
J A
JA
D001673:Biodegradation, Environmental; D006540:Herbicides / Q000032:analysis / Q000737:chemistry*; D006813:Humidity; D011743:Pyrimidines / Q000032:analysis / Q000737:chemistry*; D012987:Soil / Q000032:analysis*; D012988:Soil Microbiology; D013449:Sulfonamides / Q000032:analysis / Q000737:chemistry*; D013696:Temperature
C416663:5-hydroxyflorasulam; D006540:Herbicides; D011743:Pyrimidines; D012987:Soil; D013449:Sulfonamides; C413390:florasulam