Neonicotinoid and Fipronil Insecticides in Minnesota: A Statewide Survey into the Occurrence, Detection, and Removal of Neonicotinoids and Fiproles in Minnesota Surface Waters ,Groundwater, and Engineered Treatment Systems.

Abstract

Neonicotinoids and fiproles have been used extensively in Minnesota agriculture for the last three decades. Their high mobility in water and longevity in aquatic systems makes them key candidates for transport in surface runoff and groundwater to contaminate Minnesota surface and groundwater systems. Four large field studies of (1) Minnesota groundwater and natural springs, (2) Minnesota surface waters, (3) stormwater and precipitation at stormwater-impacted Saint Paul Lake, and (4) wastewater, drinking water, and compost treatment systems were conducted over three years (2019-2022) to evaluate the state of neonicotinoids and insecticides in Minnesota’s natural waters and the current capacity for removal by existing treatment processes. Shallow unconfined groundwater and natural springs were more susceptible to contamination than deeper groundwater. Clothianidin (41% of springs, 14% of wells) was the most common insecticide detected followed by thiamethoxam (31% of springs, 12% of wells), imidacloprid (22% of springs, 10% of wells), thiacloprid (19% of springs, 2% of wells), acetamiprid (12% of springs, 14% of wells), and fipronil (19% of spring, 1% of wells). Groundwater depth also appeared to limit groundwater contamination to shallow systems with detections increasing with increasing urban land use and watershed imperviousness. Tritium/groundwater age, dissolved oxygen (DO), and total nitrite plus nitrate (total oxidized nitrogen), all correlated to noenicitinoid occurrence. Clothianidin (31% lakes, 60% rivers), thiamethoxam (19% lakes, 44% rivers), imidacloprid (65% lakes, 85% rivers), acetamiprid (29% lakes, 35% rivers), thiacloprid (15% lakes, 13% rivers), and fipronil (32% lakes, 30% rivers) were all detected in surface water lakes and rivers. Thiamethoxam and clothianidin has an association with agricultural watersheds while acetamiprid, thiacloprid, and fipronil were associated with urban watersheds. Increasing watershed catchment size and imperviousness increased the likelihood of contamination but the previous year’s application rates were the largest determining factor in the risk of insecticide contamination. All five neonicotinoid and fipronil were detected in stormwater (6% - 49%) and snow melt (13% - 29%). Stormwater and snow melt concentrations spiked with the “spring flush” during the early spring and summer months. Imidacloprid (17% rain, 47% snow), acetamiprid (6% rain, 33% snow), and clothianidin (44% rain, 39% snow), were all detected in direct rainfall and snowfall samples. Most of the contamination in stormwater (>76% stormwater, >67% snowmelt) was picked up as water moves through the watershed with correlated strongly correlations to application rates and soil and lipophilicity. Neonicotinoids and fipronil were present in drinking water, wastewater, and compost material provided by a commercial composting center. Current wastewater biological treatment technologies did not result in a significant reduction in concentrations. Biologically-activated carbon filtration with and without pre-oxidation provided a substantial reduction in concentrations (86% - 100% removal). Pre-oxidation did generate oxidized transformation products (<3.5% yield) but all transformation products were removed by downstream filtration. Compost was capable of degrading fipronil in both residential and commercial composting operations while clothianidin and acetamiprid were degradable in commercial composting systems and acetamiprid, clothianidin, imidacloprid, fipronil were partially degradable in residential composters. Runoff produced from rainfall at the composting facility with substantial neonicotinoid and fipronil concentrations.