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Dissipation of Carbaryl and the 1-Naphthol Metabolite in Flooded Rice Fields¹

ABSTRACT

Field and laboratory experiments were conducted under flooded rice (Oryza sativa L.) culture to evaluate persistence of carbaryl (1-naphthyl-N-methyl carbamate) and the 1-naphthol metabolite. Treatments consisted of two rates of carbaryl (1.12 and 5.60 kg ha^–1) super-imposed on two irrigation management schemes (i.e., intermittent and continuous flow) to determine their potential for environmental contamination. Results showed that foliarly applied carbaryl was washed from the rice canopy into plot water and subsequently degraded via chemical and biological mechanisms. Time of sample collection and application rate had a highly significant influence on the residual levels of carbaryl in the flood water for each of the 3 yr tested. The effect of irrigation management was statistically significant in two of the three seasons studied, with greater levels of carbaryl residues observed for the intermittent irrigation scheme. Carbaryl residues in plot water were greatest in those years when a rainfall event occurred within 24 h following the foliar spray application. A significant first order interaction between time and application rate was observed in 1973 and 1975, when measurable rainfall was recorded prior to the 24-h sampling period. The 1-Naphthol recovered in the plot water was proportional to the contamination level of the carbaryl spray formulation and did not reflect the quantities of dissipated carbaryl. Field results and laboratory experiments suggested that 1-naphthol was degraded more rapidly under flooded soil conditions than carbaryl.

Key Words: Sevin • pesticide • irrigation return flow • simulated rainfall • anaerobiosis

¹ Contribution of the Texas Agric. Exp. Stn., College Station, Texas, and the Texas Agricultural Extension Service. This work was sponsored in part by EPA Grant no. S-802008.

² Former research scientist and professor, respectively, Dep. of Soil & Crop Science, Texas A&M Univ., College Station, TX 77843; agricultural chemist, Texas Agric. Ext. Serv., College Station, TX 77843; and associate professor, Texas Agric. Exp. Stn. at Beaumont, TX.

Received for publication December 24, 1983.