Article pubs.acs.org/est
Toxicity of the Insecticide Fipronil and Its Degradates to Benthic Macroinvertebrates of Urban Streams Donald P. Weston*,† and Michael J. Lydy‡ †
Department of Integrative Biology, University of California, Berkeley, California 94720, United States Center for Fisheries, Aquaculture and Aquatic Sciences, Southern Illinois University, Carbondale, Illinois 62901, United States
‡
S Supporting Information *
ABSTRACT: Fipronil is a phenylpyrazole insecticide with increasing urban use. Sixteen urban waterways and municipal wastewater were sampled for fipronil, its environmental degradates, and pyrethroid insecticides. Because findings could not be interpreted with existing data on fipronil degradate toxicity, EC50s and LC50s for fipronil and its sulfide and sulfone derivatives were determined for 14 macroinvertebrate species. Four species were more sensitive than any previously studied, indicating fipronil's toxicity to aquatic life has long been underestimated. The most sensitive species tested, Chironomus dilutus, had a mean 96-h EC50 of 32.5 ng/L for fipronil and 7−10 ng/L for its degradates. Hyalella azteca, a common testing species, was among the least sensitive. The typical northern California creek receiving urban stormwater runoff contains fipronil and degradate concentrations twice the EC50 of C. dilutus, and approximately one-third the EC50 for a stonefly, a caddisfly, and two mayfly species. The present study substantially increases data available on toxicity of fipronil degradates, and demonstrates that fipronil and degradates are common in urban waterways at concentrations posing a risk to a wide variety of stream invertebrates.
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INTRODUCTION The dominant pesticides in agricultural and urban environments change as new compounds are developed or use of existing compounds is restricted by regulatory action, typically because of unforeseen risks to human health or environmental quality. Insecticide use in urban environments provides an example. After most organochlorine insecticides were banned in the 1970s and 1980s, organophosphates, most notably diazinon and chlorpyrifos, became the dominant urban insecticides. However, because of human health concerns, urban-use diazinon and chlorpyrifos products were withdrawn from the U.S. market in the early 2000s. As organophosphates were restricted, pyrethroids took their place. Nonagricultural pyrethroid use doubled in California from 2000 to 2006.1 Pyrethroid use in the state declined from 2006 to 2009, possibly because of factors related to the economic recession, but has since rebounded (Supporting Information (SI) Figure S1). An emerging insecticide in urban environments is the phenylpyrazole fipronil, now used in applications previously reserved for pyrethroids and organophosphates before them. Though used in both agricultural and urban environments elsewhere, there are no approved agricultural uses in California so its presence in surface waters indicates input from landscape maintenance and structural pest control. There was essentially no use of the compound in California prior to 2000, but use has been climbing since, albeit with the same macroeconomicrelated decline from 2006 to 2009 (SI Figure S1). © 2013 American Chemical Society
Mitigating the environmental impact of these insecticides is a challenge because the compounds have received regulatory approval and come into widespread use with significant data gaps regarding their fate and effects, or analytical difficulty in quantifying environmental concentrations. Diazinon caused frequent toxicity in some of California’s largest rivers in the 1990s.2 Analytical quantification of pyrethroids has not been possible until concentrations reach the threshold of acute mortality for sensitive species, and thresholds for chronic toxicity are probably below current detection limits.3 A major challenge with fipronil is degradation into a desulfinyl by photolysis, degradation into an amide by hydrolysis under basic conditions, oxidation to a sulfone in aerobic environments, and reduction to a sulfide in anaerobic soils or sediments.4 Little is known about the toxicity of these derivatives. A published 2007 review provided degradate EC50 or LC50 data for two fish and one aquatic invertebrate.4 The U.S. Environmental Protection Agency’s (EPA) 2007 risk assessment in support of fipronil registration contained degradate aquatic toxicity data on two fish and four invertebrates, obtained almost entirely from publicly unavailable reports submitted by the registrants.5 Although recent work has shown fipronil to be commonly found in urban runoff,6 there are very few data on its Received: Revised: Accepted: Published: 1290
October 13, 2013 December 19, 2013 December 24, 2013 December 24, 2013 dx.doi.org/10.1021/es4045874 | Environ. Sci. Technol. 2014, 48, 1290−1297
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Article
to laboratory water for 24 h. Although we generally conducted 96-h tests, preliminary tests with some species produced unacceptable mortality, so tests for those species were limited to 48 h. Tests were done using Milli-Q purified, deionized water made moderately hard by addition of salts.8 Waters were spiked with fipronil, fipronil sulfide, or fipronil sulfone (ChemService, West Chester, PA) dissolved in acetone. Acetone concentrations were 187 >722 >436 >184 113 (94.2−135) >1229 2107 (1218−2668) >2947 >842
1593 (1343−1889) 1725 (1461−2037) >81.5 >81.5 1231 (769−1667) 105 (76.0−146)
34.2 (14.0−48.8)
42.2 (37.1−47.4)
28.5 (18.7−36.5) 177 (146−216)
90
100
96 100
80.3 (53.1−108)
87
EC50 (ng/L) 540 (456−626) 375 (325−433) 9.3 (7.6−11.4) 10.5 (6.7−13.4)
98 100 77 70
CS (%)
fipronil sulfide LC50 (ng/L)
122 (60.2−177) >551
94.5 (66.8−175)
103 (58.7−142)
>717
1356 (1092−1635) 1398 (1145−1716) >62.4 >75.8
95.9 (62.1−126) 47.4 (40.2−55.9) 72.9 (56.5−94.0) 31.3 (23.0−40.1) 73.8 (38.6−140)
100 85 75 96 100
EC50 (ng/L) 271 (237−310) 155 (122−179) 7.5 (5.3−9.2) 7.9 (5.0−10.3) 163 (51−223) >341 143 (80.2−195) 75.0 (44.9−109) 92.6 (56.5−128) 71.7 (52.3−90.6) 159 (106−214)
100 100 87 85 93 100 87 95 87 95 95
CS (%)
fipronil sulfone LC50 (ng/L)
>824 51.5 (37.0−69.1) >626
>261 50.0 (43.1−58.1)
748 (610−915) 426 (346−497) >102 >106 257 (109−362) >341 535 (382−750) >684 330 (188−536) >196 331 (257−426)
a Values in parentheses are 95% confidence intervals. Empty cells indicate test not done because of insufficient number of individuals. bConsidered a species group by the Southwest Association of Freshwater Invertebrate Taxonomists (SAFIT).
163 (107−208) 70.7 (36.5−93.5) 589 (478−742) >436 >184 101 (84.6−119) >1229 602 (417−788) 634 (531−756) 267 (210−338)
100 100 83 87 93 80
EC50 (ng/L) 729 (646−829) 727 (648−816) 35.0 (21.1−41.5) 30.0 (23.3−36.0) 480 (348−603) 51.9 (37.3−72.0)
CS (%)
species
Hyalella azteca (test 1) Hyalella azteca (test 2) Chironomus dilutus (test 1) Chironomus dilutus (test 2) Hexagenia sp. Baetis tricaudatusb (test 1) Baetis tricaudatusb (test 2) Baetis tricaudatusb (test 3) Diphetor hageni Fallceon quilleri Serratella micheneri Ephemeralla excruciansb Taenionema sp. Isoperla quinquepunctata Tricorythodes sp. Hydropsyche sp. Nectopsyche sp. Helicopsyche sp.
fipronil
Table 2. Control Survival (CS) of Each Test Species, EC50, and LC50 Point Estimates for Fipronil, Fipronil Sulfide, and Fipronil Sulfonea
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dx.doi.org/10.1021/es4045874 | Environ. Sci. Technol. 2014, 48, 1290−1297
Environmental Science & Technology
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Table 3. Frequency of Detection and Median and Maximum Concentrations of Pesticide Analytes in Urban Waterbodies during Rain Events (n = 24)a fipronil and degradates frequency of detection (%) median concentration (ng/L) maximum concentration (ng/L) a
pyrethroids
fipronil
fipronil desulfinyl
fipronil sulfide
fipronil sulfone
bifenthrin
cypermethrin
cyhalothrin
permethrin
88 21.2 49.1
83 5.1 11.5
42
