Pesticides in ground water beneath irrigated farmland in Nebraska, August 1978.

During the 1978 irrigation season, 14 ground water samples were collected in the Central Platte region of Nebraska, an area known to have high nitrate-nitrogen (NO3--N) levels, and analyzed for the presence of 13 pesticide residues. Atrazine levels ranged from 0.06 microgram/liter to 3.12 microgram/liter and were correlated to NO3--N concentrations with a coefficient of r = +0.55. Nitrate-nitrogen concentrations were measured as indicators of deep percolation from irrigated lands and ranged from 17.1 mg/liter to 34.3 mg/liter. Alachlor levels ranged from less than 0.01 microgram/liter to 0.71 microgram/liter. The amounts of 2,4-D were indeterminate because of experimental problems. Levels of the herbicides silvex and EPTC were below the limits of detectability. Levels of the organochlorine insecticides endrin, gamma-BHC (lindane), dieldrin, DDT and its primary metabolite DDE, heptachlor and its primary derivative heptachlor epoxide, and methoxychlor were all below the detectable limits of 0.005-0.010 microgram/liter.