BEHAVIOR OF ATRAZINE IN SOILS OF TROPICAL ZONE - DEGRADATION, MOBILITY AND UPTAKE OF ATRAZINE RESIDUES FROM SOILS IN A CROP-ROTATION SYSTEM(MAIZE BEANS)/

Movement and degradation of C-14-atrazine (2-chloro 4-(ethylamino)-6-( isopropylamino)-s-triazine, was studied in undisturbed soil columns (0 .50m length x 0.10m diameter) of Gley Humic and Deep Red Latosol from a maize crop region of Sao Paulo state, Brazil. Atrazine residues were largely confined to the 0-20cm layers over a 12 month period. Atrazin e degraded to the dealkylated metabolites deisopropylatrazine and deet hylatrazine, but the major metabolite was hydroxyatrazine, mainly in t he Gley Humic soil. Activity detected in the leachate was equivalent t o an atrazine concentration of 0.08 to 0.11 mu g/l. The persistence of C-14-atrazine in a maize-bean crop rotation was evaluated in lysimete rs, using Gley Humic and Deep Red Latosol soils. Uptake of the radioca rbon by maize plants after 14-days growth was equivalent to a herbicid e concentration of 3.9 mu g/g fresh tissue and was similar in both soi ls. High atrazine degradation to hydroxyatrazine was detected by tlc o f maize extracts. After maize harvest, when beans were sown the Gley H umic soil contained an atrazine concentration of 0.29 mu g/g soil and the Deep Red Latosol, 0.13 mu g/g soil in the 0-30 cm layer. Activity detected in bean plants corresponded to a herbicide concentration of 0 .26 (Gley Humic soil) and 0.32 mu g/g fresh tissue (Deep Red Latossol) after 14 days growth and 0.43 (Gley Humic soil) and 0.50 mu g/g fresh tissue (Deep Red Latossol) after 97 days growth. Traces of activity e quivalent to 0.06 and 0.02 mu g/g fresh tissue were detected in bean s eeds at harvest. Nonextractable (bound) residues in the soils at 235 d ays accounted for 66.6 to 75% (Gley Humic soil and Deep Red Latossol) of the total residual activity.