Fipronil

Ecotoxicology: 
Algae: EC₅₀ (96 h) for Scenedesmus subspicatus 0.068 mg/l; (120 h) for Selenastrum capricornutum >0.16, Anabaena flos-aquae >0.17 mg/l.Bees:Highly toxic to honeybees, both by direct contact and by ingestion. However, no risk to bees when used as a soil or seed treatment.Birds:Acute oral LD₅₀ for bobwhite quail 11.3, mallard ducks >2000, pheasants 31, red-legged partridges 34, house sparrows 1120, pigeons >2000 mg/kg. Dietary LC₅₀ (5 d) for bobwhite quail Daphnia: LC₅₀ (48 h) 0.19 mg/l; for D. carinata (48 h) 3.8 mg/l.Fish:Acute LC₅₀ (96 h) for bluegill sunfish 85, rainbow trout 248, European carp 430 mg/l.Worms:Non-toxic. 

Environmental fate: 
Fate in soil:
In laboratory studies, fipronil has a half-life of 122-128 days in oxygenated sandy loam soil. In field studies, half-life on soil surfaces ranges from 0.7 to 1.7 months, whilst for soil incorporation it is 3 to 7.3 months. Fipronil has low soil mobility; it binds to the soil and the residues remain in the upper 12 inches of soil. The average K_oc value is 803. There is little potential for groundwater contamination.
Aerobic soil metabolism studies give the half-life of fipronil in sandy loam to be 122 days.
In anaerobic systems, fipronil degrades slowly in water and sediment with a half-life of 116-130 days. In an aerobic metabolism study, fipronil readily partitioned from the aqueous layer into the sediment.
In a field dissipation study in Niger, 25% of the original applied dose of fipronil (8 g ai/ha) was recovered after 3 days. Four degradates were also identified including a sulfide due to reduction in soil, an amide from hydrolysis, and a sulfone from oxidation in soil. A desulfinyl photodegradate was also identified.
Thus in soil, fipronil dissipates by soil binding along with gradual microbial breakdown.

Fate in aquatic systems:
Fipronil is stable to hydrolysis at 22°C at pH 9.1 (DT₅₀ 1100 days) and pH 7.1 (DT₅₀ 1100 days), whereas at 32°C, the half-life is 11.3 days at pH 9.1 and 15.6 days at pH 7.1.
Fipronil undergoes photodegradation in water with a half-life of 3.6 hours. Thus photolysis is a more important pathway for degradation of aqueous fipronil.
Ground water concentrations of fipronil calculated using the SCI-GRO model (shallow groundwater on highly vulnerable US sites) were 0.055 ppb for maize and 0.00804 ppb for rice. Based on environmental fate assessment, fipronil has the potential to move into surface waters. However, when fipronil is used as an in-furrow application, the run-off potential of fipronil residues is expected to be lower than for unincorporated surface application techniques. The maximum fipronil surface water concentrations for acute and chronic exposure based on GENEEC surface water modelling were found to be for corn, acute 2.05 ppb, chronic 0.78 ppb; for rice, acute 1.45 ppb, chronic 0.40 ppb. These values are less than the drinking water lowest levels of concern of 810 ppb and 220 ppb in surface and ground water for acute risk, and 6.67 ppb and 1.77 ppb for chronic risk.