Testing
Testing of CT Rivers and Groundwater Show Harmful Levels of Neonics
The UConn report, Connecticut Waters: Surface Water, Groundwater, and Threats to Aquatic Ecosystems, compiles all the available data in CT on neonics in streams and rivers showing us where these pesticides are ultimately showing up in the environment.
Data on Neonics in CT is Sparse but What We Have is Important
Unfortunately, assessing how much of any specific pesticide is being used in Connecticut and where, is extremely difficult for two reasons:
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The state database system which captures amounts of pesticides applied by licensed applicators cannot be searched by pesticide name. Applications are filed under the applicator’s last name only.
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The use of neonic-treated seeds, which came on the market in 2004 and are widely used prophylactically by CT farmers, are not tracked as pesticides due to an EPA decision that once coated on a seed, such coatings are not considered to be a pesticide.
About 71 to almost 100 percent of corn seed in the US is treated with a neonic seed coating (Douglas and Tooker, 2015, US EPA 2017).
We do have information on where neonics are showing up in our environment, however, from two sources:
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Two decades of US Geological Survey testing
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A 2024 targeted water quality testing project, the Clean Rivers Project. In addition, we have three decades of periodic testing of river insect populations from the CT Dept. of Energy and Environmental Protection.
US Geological Survey Testing
The majority of the pesticides water testing data available in Connecticut was collected from October of 2001 to January of 2024 by the United States Geological Survey (USGS), which tested a total of 662 water samples (600 surface water and 62 groundwater samples) from Connecticut for a range of pesticides including the neonicotinoid, imidacloprid (Table 1). Surface water samples were collected from 66 sites associated with 23 rivers and streams in Connecticut (Table 1; Figure 1). The USGS first collected surface water samples to test for imidacloprid in 2001 and 2002, but regular testing of surface water for imidacloprid did not commence until December of 2009, with at least a dozen samples from surface water tested for imidacloprid every year (with the exception of 2011). Although the total number of surface water samples tested for imidacloprid is considerable (600), over 200 samples were from a single location on the Connecticut River (Thompsonville), and the majority of the remaining samples are from Fairfield County (Figure 1), demonstrating a need for more comprehensive testing throughout the state.
Figure 1 Locations of Surface and Ground Water Samples in Connecticut
The 2024 CT Clean Rivers Project
In 2024, the Clean Rivers Project, facilitated by CPR member organizations, tested 10 streams in southwest CT that run near, or through, large expanses of manicured lawns. Testing took place above and below the landscaped areas during July and August, times of heavy pesticide use. In total, 56 surface water samples were collected and tested for six neonicotinoids by analytical laboratories of the Center for Environmental Sciences and Engineering at the University of Connecticut. These are the only samples from Connecticut that UConn researchers know of that have been tested for neonicotinoids other than imidacloprid. In the chart below, blue dots represent no detection of neonics, orange represent levels exceeding EPA aquatic life benchmarks for chronic exposure, and red represents levels exceeding aquatic life benchmarks for acute exposure.
of those 56 samples. Once in the environment, thiamethoxam breaks down into clothianidin. In general, thiamethoxam is now the most common neonicotinoid used for agricultural purposes (Simon-Delso et al., 2014), whereas imidacloprid remains the most common neonicotinoid used in urban or suburban settings such as lawn or golf course care (Hladik and Kolpin, 2015).With the exception of the sampling conducted for the Clean Rivers Project during 2024, sampling has not targeted times or locations in which imidacloprid use is expected to be likely.
Analyses of the 56 samples revealed considerable differences in the prevalence of different neonicotinoid compounds. Four neonicotinoids (i.e., acetamiprid, nitenpyram, thiacloprid, and thiamethoxam) were never detected in any samples, and clothianidin was detected in a single sample from the Noroton River in Darien. In contrast, imidacloprid was detected in 30 (54%)
2024 Clean Rivers Project Testing Locations
Connecticut Department of Energy and Environmental Protection Macroinvertebrate Data
Data was collected from 17 different locations along the Norwalk River and its tributaries between 1989 and 2020. This testing was not designed to evaluate effects of neonicotinoids on aquatic life–the samples for insect life and for neonics were not collected at the same places and times–therefore scientists can’t make definitive conclusions from comparing the two datasets. However, this is the best data we have in Connecticut and it can serve as a starting point for understanding the effects on insects exposed to levels on neonics that exceed aquatic life benchmarks. Findings show that while some aquatic insect populations have remained steady or even risen over the last 30 years as the Norwalk River water quality has improved overall, insects most sensitive to neonics, like mayflies, have shown dramatic decreases in abundance and in richness of species diversity.