Dow AgroSciences. Pesticide Tolerance. FINAL RULE. FIRST-TIME APPROVAL FOR THE USE OF FLORASULAM, a selective triazolopyrimidine sulfonanilide post-emergent herbicide, in or on the following food commodities.:
at 0.01 ppm: Barley, grain; Oat, grain; Rye, grain; Wheat, grain
at 0.05 ppm: Barley, hay; Barley, straw ; Oat, forage ; Oat, hay ; Oat, straw ; Rye, forage ; Rye, straw; Wheat, forage; Wheat, hay; Wheat, straw
The mode of action for florasulam is through inhibition of the plant enzyme acetolactate synthase (ALS). The inhibition of ALS results in retardation of plant growth processes leading to death of the plant. Florasulam was first registered in Israel in 1998.
• Florasulam: Human Health Risk Assessment for Proposed Use on Cereal Grains. May 31, 2007.
-- Developmental Toxicity Studies. In the rat developmental toxicity study, at 750 mg/kg/day, body weights were decreased by 4-6 during GD 6-19, resulting in a 16% decrease in body weight gains during treatment (GD 6-16); food consumption was also decreased (not statistically analyzed) by 6-13% during the treatment period. Additionally at this dose, absolute and relative (to body weight) kidney weights were increased (p<=0.05) by 8 and 12%, respectively. At ≥250 mg/kg/day, slight decreases (3-4%) were observed in fetal body weight, accompanied by delayed ossification (not significant) of the skull, ribs, and sternebrae at 750mg/kg/day. However, both findings were within the historical control range.
ENDPOINTS OF CONCERN in human health risk assessment:
• Acute dietary (Females 13-49 years of age): No appropriate endpoint identified.
• Acute dietary( General population including infants and children): No appropriate endpoint identified.
• Chronic dietary (All populations): Chronic toxicity - dogs. LOAEL = 50 mg/kg/day, based on decreased body weights (17%), decreased body weight gains (68%), and food consumption in the females; adverse liver alterations; slight vacuolation of the zona reticularis and zona fasciculate in the adrenal gland (fatty change) in both sexes.
• Short-term dermal (1 to 30 days) (Residential): No appropriate endpoint identified.
• Inhalation Short-term (1-30 days): 90-day oral toxicity - dogs. LOAEL = 50 mg/kg/day based on increased incidence/severity of hepatic vacuolation in both sexes.
EPA is not establishing the proposed tolerances, as requested by Dow AgroSciences, for barley, forage and rye, hay because EPA does not consider these items to be significant food commodities as noted in Table 1 of the OPPTS 860 guidelines. EPA is also not establishing the proposed tolerances for triticale. Triticale is covered by the tolerance for wheat as specified in 40 CFR 180.1(g).
The 5-OH degradate formed by demethylation of florasulam is by far the predominant environmental residue reaching maximum levels of 70% of applied material in the hydrolysis and metabolism (soil, aquatic) studies. This degradate is assumed to be of comparable toxicity to the parent. On this basis, the residues of concern in drinking water are the parent and 5-OH degradate.
In aquatic systems, florasulam degrades with half-lives of 3-18 days in aerobic systems and half- lives of 2-13 days in anaerobic systems. In aerobic aquatic systems, florasulam is biotransformed to 5-OH-XDE-570, which is then further biotransformed to DFP-ASTCA and STCA (tentative identification). However, 5-OH-XDE-570 degrades much more slowly than the parent, degrading with a half-life of 169 days in one aerobic system and remaining stable in another aerobic system. In anaerobic aquatic systems, 5-OH-XDE-570 is stable. Thus, 5-OH-XDE-570 is expected to be persistent in both aerobic and anaerobic aquatic systems... both florasulam and 5-OH-XDE-570 are very mobile in soil and, thus, have the potential to leach - the potential to leach will be greater when there is excessive rainfall or irrigation. (Page 24 of the Human Health Risk Assessment)