Impact of imidacloprid treatments for hemlock woolly adelgid on surface water quality: Real or perceived?

Integrated pest management directed at hemlock woolly adelgid (Adelges tsugae[Annand]) (HWA) (Hemiptera: Adelgidae), often use imidacloprid to preserve hemlock resources.  A retrospective study was conducted in Great Smoky Mountains National Park (GRSM) to assess the presence and concentration of imidacloprid and two of its insecticidal metabolites (5-hydroxy and olefin) in streams associated with HWA imidacloprid treatment areas.

Stream water samples were collected from 30 stream locations in GRSM.  Ten streams were sampled both downstream and upstream from areas where imidacloprid soil treatments were applied and ten control streams were sampled.  Liquid chromatography mass spectroscopy (LC/MS) was used to determine concentrations of imidacloprid, 5-hydroxy, and olefin in parts per trillion (ppt).  GRSM personnel provided historical treatment data for integration in data analyses.  A Kruskal-Wallis test (P < 0.05), least significant difference (LSD) and multiple regression (P< 0.05) were used for data analyses. 

Imidacloprid was present in seven downstream locations in concentrations ranging from 28.5 to 379 ppt and metabolites were not detected in streams.  A significant relationship was detected between the total amount of imidacloprid applied to a hemlock treatment area and the concentration of imidacloprid in the associated stream.  All detected concentrations of imidacloprid were below USEPA chronic and acute aquatic life benchmarks for fish and aquatic macroinvertebrates.  Thus, the impact of HWA imidacloprid treatments on surface water quality is minimal.  However, since the amount of imidacloprid applied can affect the concentration of imidacloprid in surface waters, the extent of HWA treatments implemented in a watershed should be carefully considered.