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#           Multiple lines of evidence point to pesticides as stressors affecting invertebrate communities in small streams in five United States regions      

      January 24, 2024    

Multistressor studies were performed in five regions of the United States to assess the role of pesticides as stressors affecting invertebrate communities in wadable streams. Pesticides and other chemical and physical stressors were measured in 75 to 99 streams per region for 4 weeks, after which invertebrate communities were surveyed (435 total sites). Pesticides were sampled weekly in filtered water, and once in bed sediment. The role of pesticides as a stressor to invertebrate communities was assessed by evaluating multiple lines of evidence: toxicity predictions based on measured pesticide concentrations, multivariate models and other statistical analyses, and previously published mesocosm experiments. Toxicity predictions using benchmarks and species sensitivity distributions and statistical correlations suggested that pesticides were present at high enough concentrations to adversely affect invertebrate communities at the regional scale. Two undirected techniques—boosted regression tree models and distance-based linear models—identified which pesticides were predictors of (respectively) invertebrate metrics and community composition. To put insecticides in context with known, influential covariates of invertebrate response, generalized additive models were used to identify which individual pesticide(s) were important predictors of invertebrate community condition in each region, after accounting for natural covariates. Four insecticides were identified as stressors to invertebrate communities at the regional scale: bifenthrin, chlordane, fipronil and its degradates, and imidacloprid. Fipronil was particularly important in the Southeast region, and imidacloprid, bifenthrin, and chlordane were important in multiple regions. For imidacloprid, bifenthrin, and fipronil, toxicity predictions were supported by mesocosm experiments that demonstrated adverse effects on naïve aquatic communities when dosed under controlled conditions. These multiple lines of evidence do not prove causality—which is challenging in the field under multistressor conditions—but they make a strong case for the role of insecticides as stressors adversely affecting invertebrate communities in streams within the five sampled regions.

## Citation Information

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#### Lisa Nowell

##### Research Chemist

California Water Science Center

lhnowell@usgs.gov

916-278-3096

#### Patrick Moran

##### Biologist

Washington Water Science Center

pwmoran@usgs.gov

253-552-1646

#### Ian R Waite

##### Research Biologist

Oregon Water Science Center

iwaite@usgs.gov

#### Travis S Schmidt, Ph.D.

##### Research Ecologist

Wyoming-Montana Water Science Center

tschmidt@usgs.gov

406-594-9788

#### Paul M Bradley

##### Research Ecologist/Hydrologist

South Atlantic Water Science Center (SAWSC)

pbradley@usgs.gov

####             Barbara J Mahler (Former Employee)          

##### RGEG Hydrologist

Oklahoma-Texas Water Science Center

####             Peter C Van Metre (Former Employee)          

##### Research Hydrologist

Water Resources Mission Area

## Related Content

#### Lisa Nowell

##### Research Chemist

California Water Science Center

lhnowell@usgs.gov

916-278-3096

#### Patrick Moran

##### Biologist

Washington Water Science Center

pwmoran@usgs.gov

253-552-1646

#### Ian R Waite

##### Research Biologist

Oregon Water Science Center

iwaite@usgs.gov

#### Travis S Schmidt, Ph.D.

##### Research Ecologist

Wyoming-Montana Water Science Center

tschmidt@usgs.gov

406-594-9788

#### Paul M Bradley

##### Research Ecologist/Hydrologist

South Atlantic Water Science Center (SAWSC)

pbradley@usgs.gov

####             Barbara J Mahler (Former Employee)          

##### RGEG Hydrologist

Oklahoma-Texas Water Science Center

####             Peter C Van Metre (Former Employee)          

##### Research Hydrologist

Water Resources Mission Area

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####               Sacramento Projects Office (USGS California Water Science Center)          

6000 J Street, Placer HallSacramento, CA95819United States

916-278-3000

916-278-3070

####               Oregon Water Science Center          

601 SW 2nd Ave Ste 1950Portland, OR97204United States

####             Water Resources Mission Area - Headquarters        

USGS Headquarters12201 Sunrise Valley DriveReston, VA20192United States

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