ATRAZINE CONTAMINATION OF WATER SUPPLIES FROM AGRICULTURAL USE IN NEBRASKA

Analytical techniques are described which utilize carbon tetrachloride extraction of water and soxhelet-methanol extraction of soil, high pressure liquid chromatography clean-up, and gas-liquid chromatography quantification for the analysis of up to six herbicides simultaneously. Monitoring of subsoil percolation indicated that leaching of surface applications of atrazine {2-chloro-4-(ethyamino)-6-(isopropylamino)-s-triazine} is the predominate route resulting in low level groundwater contamination presently seen in irrigated corn producing areas of Nebraska. Bioassay analysis indicated that the present level of contamination remains well below the threshold necessary to damage sensitive crops. Atrazine dissipation under aquifer conditions is due largely to dispersion and to a small amount of degradation to produce hydroxyatrazine {2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine}. A mathematical model indicates that present levels of contamination may reflect an equilibrium between entry and subsequent degradation. Atrazine and alachlor {2-chloro-2\u27,6\u27-diethyl-N-(methoxymethyl) acetanilide} losses in runoff water and sediment were studied under different water application methods and tillages. Low pressure irrigation systems and till-plant practices enhanced soil crusting and runoff. Herbicides dissolved in runoff water constituted the major avenue of their loss. Total herbicide loss after three consecutive runoff events did not exceed 0.1% of the amount applied even under conditions most favorable for runoff