Kinetic field dissipation and fate of endosulfan after application on Theobroma cacao farm in tropical Southwestern Nigeria.

Abstract

Endosulfan, 6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano,2,4,3-benzodioxathiepin-3-oxide, is still a pesticide of choice for most cocoa farmers in Southwestern Nigeria, in spite of its persistence, bioaccumulative, toxicological properties, and restriction. A single treatment of 1.4kgai/ha (0.5% ai) of technical grade endosulfan (Thiodan, 35EC) was applied to 0.0227ha of cultivated Theobroma cacao L. (Cocoa) farm at the Cocoa Research Institute of Nigeria (CRIN). Levels of parent endosulfan (α-, β-endosulfan) and major metabolite (endosulfan sulfate) were determined in vegetation and surrounding matrices at days 0, 7, 14, 21, 28, 42, and 60 using GC-MS. Their kinetic variables were determined. Order of ∑endosulfan distribution at day 0 was dry foliage > fresh foliage > bark > pods > soil (0-15cm). No residual endosulfan was found in cocoa seeds and subsurface soil (15-30cm). Low residual levels in pods on day 0 may be due to endogenous enzymatic breakdown, with α-isomer more susceptible and α/β-endosulfan ratio being 0.90. Fell dry foliage as mulch was predominantly the receiving matrix for non-target endosulfan sprayed. Volatilization was key in endosulfan dissipation between days 0 and 7 from foliage surfaces (> 60% loss), while dissipation trend was bi-phasic and tri-phasic for vegetation and soil, respectively. ∑endosulfan loss at terminal day ranged between 40.60% (topsoil) and 99.47% (fresh foliage). Iteratively computed half-lives (DT'50) ranged from 6.48 to 30.13days for ∑endosulfan in vegetation. Endosulfan was moderately persistent in pods-a potential source for cross contamination of seeds during harvest. Iteratively determined DT'50 and initial-final day DT50 are highly correlated (R = 0.9525; n = 28) and no significant difference (P = 0.05) for both methods.