A Decade of Data Reveals Imidacloprid (a common insecticide) is Increasing in American Rivers
Imidacloprid, a commonly used insecticide in both agricultural and urban settings, is reaching rivers and streams across the country, where it can potentially harm the aquatic insects and other organisms that support healthy freshwater ecosystems. A decade‑long USGS study found this insecticide in nearly half of all samples, often at levels above chronic health benchmarks and present throughout the entire year, with half of the sites having an increasing trend in stream concentrations over the decade of sampling. These findings show that imidacloprid is widespread, persistent, and increasing in many regions of the country, highlighting the need for continued monitoring and management to protect aquatic life.
Imidacloprid is a widely used neonicotinoid insecticide that protects crops, lawns, landscaping, and pets from insect pests. Its effectiveness in agriculture and home settings has made it one of the most common insecticides in the United States. When imidacloprid moves off treated fields or developed areas as runoff and enters rivers and streams, however, it can affect the aquatic organisms that support healthy freshwater ecosystems. Aquatic insects help cycle nutrients, maintain water quality, and form the base of food webs that support fish, birds, and other wildlife.
USGS Studies Rivers Across the Nation
A recent USGS study analyzed 12,547 samples from 77 rivers and streams across the nation collected from 2013 to 2022 and found that imidacloprid was detected in 44% of samples, with concentrations often high enough to exceed the U.S EPA chronic aquatic-life benchmark for freshwater invertebrates, even in some of the largest rivers sampled for this study. This benchmark indicates levels where long-term exposure may harm sensitive aquatic insects. The study showed detections in every month of the year, with the highest concentrations in summer, but levels remained above the chronic benchmark even in winter. This pattern indicates that imidacloprid is present in streams year‑round and persists in the environment longer than expected.
Contamination was most common in small and developed watersheds, where concentrations were highest and chronic benchmark exceedances were most frequent. Imidacloprid, however, was also commonly present in agricultural watersheds. This decadal study found that half of the sites exhibited a temporal increase in concentration, even for large rivers such as the Mississippi River. The Mississippi and Atchafalaya Rivers delivered an estimated 129,489 kilograms of imidacloprid to the Gulf of America from 2013 to 2022, showing that this insecticide can travel far beyond the areas where it is applied and unintentionally impact downstream water quality.
Why it matters
Imidacloprid is highly toxic to freshwater invertebrates, which support nutrient cycling, water quality, and food webs. Although this study did not investigate biological effects at the sampled sites, the consistent, year-round presence of imidacloprid above ecologically relevant aquatic-life benchmarks in streams across the nation for an entire decade suggests broad and persistent ecological risk. These exceedances align with national assessments identifying imidacloprid as a major contributor to potential toxicity in aquatic macroinvertebrates, suggesting potential for adverse impacts on sensitive communities.
When their populations decline, entire stream ecosystems can be disrupted. The national scale observations for this decadal study (widespread, year-round detections generally increasing with time) reflects contributions from multiple sources, including agricultural use, urban landscapes, and wastewater pathways. This has implications for resource managers including:
- In waterways already listed as impaired for freshwater invertebrates, the presence of imidacloprid can hinder recovery efforts because even low, chronic exposures can suppress reproduction, reduce emergence, and slow recolonization of sensitive taxa. This makes it more difficult for impaired freshwater invertebrate communities to rebound, even when habitat, flow, or other water-quality conditions are improved.
- In small agricultural or developed watersheds, reducing storm‑driven runoff can help limit rapid transport to streams.
- In larger rivers, where imidacloprid can accumulate or reflect long‑term sources, improvements may require understanding groundwater inputs, legacy contamination, and wastewater contributions.
- Continued year‑round monitoring is needed to track trends and understand mixtures of pesticides, their transformation products, and other contaminants (such as pharmaceuticals, PFAS, antibiotic resistance) which commonly co‑occur in streams.
Overall, the study showed that imidacloprid is present across the country at levels capable of affecting aquatic life throughout the year and generally increasing with time, underscoring the need for ongoing research and management to reduce ecological impacts.
This study has been supported by the U.S. Geological Survey Ecosystems Mission Area, through the Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology), and USGS Water Mission Area (Water Quality Processes Program).
Imidacloprid, a commonly used insecticide in both agricultural and urban settings, is reaching rivers and streams across the country, where it can potentially harm the aquatic insects and other organisms that support healthy freshwater ecosystems. A decade‑long USGS study found this insecticide in nearly half of all samples, often at levels above chronic health benchmarks and present throughout the entire year, with half of the sites having an increasing trend in stream concentrations over the decade of sampling. These findings show that imidacloprid is widespread, persistent, and increasing in many regions of the country, highlighting the need for continued monitoring and management to protect aquatic life.
Imidacloprid is a widely used neonicotinoid insecticide that protects crops, lawns, landscaping, and pets from insect pests. Its effectiveness in agriculture and home settings has made it one of the most common insecticides in the United States. When imidacloprid moves off treated fields or developed areas as runoff and enters rivers and streams, however, it can affect the aquatic organisms that support healthy freshwater ecosystems. Aquatic insects help cycle nutrients, maintain water quality, and form the base of food webs that support fish, birds, and other wildlife.
USGS Studies Rivers Across the Nation
A recent USGS study analyzed 12,547 samples from 77 rivers and streams across the nation collected from 2013 to 2022 and found that imidacloprid was detected in 44% of samples, with concentrations often high enough to exceed the U.S EPA chronic aquatic-life benchmark for freshwater invertebrates, even in some of the largest rivers sampled for this study. This benchmark indicates levels where long-term exposure may harm sensitive aquatic insects. The study showed detections in every month of the year, with the highest concentrations in summer, but levels remained above the chronic benchmark even in winter. This pattern indicates that imidacloprid is present in streams year‑round and persists in the environment longer than expected.
Contamination was most common in small and developed watersheds, where concentrations were highest and chronic benchmark exceedances were most frequent. Imidacloprid, however, was also commonly present in agricultural watersheds. This decadal study found that half of the sites exhibited a temporal increase in concentration, even for large rivers such as the Mississippi River. The Mississippi and Atchafalaya Rivers delivered an estimated 129,489 kilograms of imidacloprid to the Gulf of America from 2013 to 2022, showing that this insecticide can travel far beyond the areas where it is applied and unintentionally impact downstream water quality.
Why it matters
Imidacloprid is highly toxic to freshwater invertebrates, which support nutrient cycling, water quality, and food webs. Although this study did not investigate biological effects at the sampled sites, the consistent, year-round presence of imidacloprid above ecologically relevant aquatic-life benchmarks in streams across the nation for an entire decade suggests broad and persistent ecological risk. These exceedances align with national assessments identifying imidacloprid as a major contributor to potential toxicity in aquatic macroinvertebrates, suggesting potential for adverse impacts on sensitive communities.
When their populations decline, entire stream ecosystems can be disrupted. The national scale observations for this decadal study (widespread, year-round detections generally increasing with time) reflects contributions from multiple sources, including agricultural use, urban landscapes, and wastewater pathways. This has implications for resource managers including:
- In waterways already listed as impaired for freshwater invertebrates, the presence of imidacloprid can hinder recovery efforts because even low, chronic exposures can suppress reproduction, reduce emergence, and slow recolonization of sensitive taxa. This makes it more difficult for impaired freshwater invertebrate communities to rebound, even when habitat, flow, or other water-quality conditions are improved.
- In small agricultural or developed watersheds, reducing storm‑driven runoff can help limit rapid transport to streams.
- In larger rivers, where imidacloprid can accumulate or reflect long‑term sources, improvements may require understanding groundwater inputs, legacy contamination, and wastewater contributions.
- Continued year‑round monitoring is needed to track trends and understand mixtures of pesticides, their transformation products, and other contaminants (such as pharmaceuticals, PFAS, antibiotic resistance) which commonly co‑occur in streams.
Overall, the study showed that imidacloprid is present across the country at levels capable of affecting aquatic life throughout the year and generally increasing with time, underscoring the need for ongoing research and management to reduce ecological impacts.
This study has been supported by the U.S. Geological Survey Ecosystems Mission Area, through the Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology), and USGS Water Mission Area (Water Quality Processes Program).