Drinking Water
USGS Surveys Show Neonics in CT Groundwater but More Testing of Wells is Needed
This section is taken from the UConn report (Presley, 2025). In contrast to the regular sampling of surface water, groundwater testing by the USGS has been sporadic, including only 62 samples from 46 wells throughout the state (Figure 1). Only 16 groundwater samples have been tested for neonicotinoids during the past 20 years. Even more concerning, no groundwater samples have been tested during the past 7 years. Because rural residents in Connecticut typically rely on private wells for residential water, the lack of knowledge of neonicotinoids in Connecticut groundwater represents a potential human health risk. USGS testing of groundwater for imidacloprid occurred between 2002 and 2004, and then again in 2017, with no recent USGS groundwater testing of neonicotinoids from anywhere in the state.
Figure 1 Locations of Surface and Ground Water Samples in Connecticut
This has led to a large disparity in the number of samples tested for imidacloprid in surface versus ground waters. In addition, the groundwater samples have come almost exclusively from the central part of the state, with effectively no testing of groundwater for any neonicotinoid in the northwestern, eastern, or coastal portions of the state. The lack of information about neonicotinoids in the groundwater of large swaths of suburban parts of the state, as well as the lack of any information about neonicotinoids other than imidacloprid in Connecticut groundwater, are concerning.
To understand the frequency with which imidacloprid infiltrates groundwater, representing a potential threat to human health given the high number of residential wells that are in use in Connecticut, as well as how long it persists once in groundwater, a protocol must be established that more consistently samples and tests groundwaters throughout the state. The current groundwater data are not sufficient to draw strong conclusions. However, in contrast to its frequent occurrence in surface water, imidacloprid appeared in only 10-20% of ground water samples each year, with the exception of 2014, for which there was only one sample. Although imidacloprid is effective at infiltrating ground waters in sandy soil, the geology of Connecticut mitigates this potential issue in parts of the state where sandy soils are less pervasive. The lack of groundwater data for the time period (2012-present) during which imidacloprid was more frequently found in surface waters is concerning however.
An additional concern that applies to groundwater more than to surface water is the ability of neonicotinoids to persist for extended periods of time when not exposed to sunlight. Whereas the half-life of imidacloprid is a few hours to a few days in shallow surface waters (Lu et al., 2015), resulting in quick degradation and amelioration of potential chronic effects, imidacloprid can persist in shallow soils for over 100 days (Anhalt et al., 2007), and potentially much longer in deep drilled wells like those typically used in rural regions of Connecticut. However, without regular testing of groundwaters throughout the state, it will be difficult to know how pervasive or serious the risks are to humans from chronic exposure to neonicotinoids in drinking water. Once detected in a well, repeated testing is required to determine how long neonicotinoids persist. Moreover, once detected, remediation efforts can remove neonicotinoids via use of nanocomposite hydrogels (Alammar et al., 2020).