Retrospective nationwide occurrence of fipronil and its degradates in U.S. wastewater and sewage sludge from 2001 - 2016

Abstract The insecticide fipronil is under regulatory scrutiny worldwide for its toxicity to pollinators and aquatic invertebrates. We conducted the first U.S. nationwide, longitudinal study of sewage sludges for fiproles, i.e., the sum of fipronil and its major degradates (fipronil sulfone, sulfide, amide, and desulfinyl). Archived sludges ( n  = 109) collected in three campaigns over 15 years were analyzed by isotope dilution liquid chromatography tandem mass spectrometry, revealing ubiquitous fiprole occurrence (0.2–385.3 μg/kg) since 2001 and a significant increase (2.4 ± 0.3 fold; p p  = 0.275). A geospatial analysis showed fiprole levels in municipal sludges to be uncoupled from agricultural use of fipronil on cropland surrounding sampled municipalities, thus pointing to non-agricultural uses (i.e., spot-on treatment and urban pest control) as a major source of fiprole loading to wastewater. Whereas anaerobic digestion was correlated with increases in fipronil sulfide at the expense of parental fipronil ( p p  = 0.519). Treatment plant effluent available from 12 facilities in 2015/6 contained fiproles at 0.3–112.9 ng/L, exceeding the United States Environmental Protection Agency (USEPA) aquatic invertebrate life benchmark for chronic fipronil exposure (11 ng/L) in 67% of cases. Whereas the USEPA identified fipronil in sludge only recently (2015), retrospective analyses and modeling conducted here show contaminant ubiquity and nationwide increases of fiprole mass (compared to 2001 levels) in U.S. municipal sludge (1140 ± 230 kg in 2015/6), and treated effluent nationwide (1970 ± 390 kg in 2015/6) over the past 15 years.