acetylcholinesterase inhibitors, the organophosphorus compounds, and methylcarbamates. Environmental fate The main routes of dissipation of imidacloprid in the environment are aqueous photolysis (half-life = 1–4 hours) and plant uptake. The major photometabolites include imidacloprid desnitro, imidacloprid olefine, imidacloprid urea, and five minor metabolites. The end product of photodegradation is 6-chloronicotinic acid (6-CNA) and ultimately carbon dioxide. Since imidacloprid has a low vapor pressure, it normally does not volatilize readily. Although imidacloprid breaks down rapidly in water in the presence of light, it remains persistent in water in the absence of light. It has a water solubility of .61 g/L, which is relatively high. In the dark, at pH between 5 and 7, it breaks down very slowly, and at pH 9, the half-life is about 1 year. In soil under aerobic conditions, imidacloprid is persistent with a half-life of the order of 1–3 years. On the soil surface the half-life is 39 days. Major soil metabolites include imidacloprid nitrosimine, imidacloprid desnitro and imidacloprid urea, which ultimately degrade to 6-chloronicotinic acid, CO2, and bound residues. 6-Chloronicotinic acid is recently shown to be mineralized via a nicotinic acid (vitamin B3) pathway in a soil bacterium. In soil, imidacloprid strongly binds to organic matter. When not exposed to light, imidacloprid breaks down slowly in water, and thus has the potential to persist in groundwater for extended periods. However, in a survey of groundwater in areas of the United States which had been treated with imidacloprid for the emerald ash borer, imidacloprid was usually not detected. When detected, it was present at very low levels, mostly at concentrations less than 1 part per billion (ppb) with a maximum of 7 ppb, which are below levels of concern for human health. The detections have generally occurred in areas with porous rocky or sandy soils with little organic matter, where the risk of leaching is high — and/or where the water table was close to the surface. Based on its high water solubility (0.5-0.6 g/L) and persistence, both the U.S. Environmental Protection Agency and the Pest Management Regulatory Agency in Canada consider imidacloprid to have a high potential to run off into surface water and to leach into ground water and thus warn not to apply it in areas where soils are permeable, particularly where the water table is shallow. According to standards set by the environmental ministry of Canada, if used correctly (at recommended rates,