Fate and Transport of Alachlor, Metolachlor and Atrazine in Large Columns

Abstract

14C ring-labelled atrazine, alachlor, and metolachlor were surface-applied at 3.14 kg a.i./ha in greenhouse lysimeters containing two soils in an ongoing experiment. Bromide (Br) – a conservative tracer – at 6.93 kg/ha as KBr and nitrate-nitrogen (NO3-N) at 112 kg/ha as KNO3 were mixed with each herbicide and surface-applied. Growth of Red top (Agrostis alba) was established in each column (105 cm long and 29.4 cm i.d.). The experiment consisted of 12 columns (2 soils × 3 herbicides × 2 replicates) each fitted with four sampling ports for leachates, a volatilization chamber, and an aeration and irrigation system. Volatile materials are being trapped directly in solvents. One column replicate was dismantled for soil and plant analyses. Columns of Plainfield sand and Piano silt loam treated with alachlor and metolachlor were sampled after 23 and 28 weeks, respectively; the atrazine columns after 35 weeks. Herbicide residues are determined by liquid scintillation counting, extracted and separated by thin-layer chromatography using autoradiographic detection. Volatilization was ≤ 0.01% of the amount of herbicide applied. The order of herbicide mobility was alachlor > metolachlor >> atrazine. As many as 8 to 12 alachlor metabolites and 2 to 6 metolachlor metabolites were separated in leachates.