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

Edebi N. Vaikosen, Bamidele I. Olu-Owolabi, Lorraine T. Gibson, Kayode O. Adebowale, Christine M. Davidson, Uche Asogwa

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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 1.4 kg ai/ha (0.5% ai) of technical grade endosulfan (Thiodan, 35EC) was applied to 0.0227 ha 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 (0–15 cm). No residual endosulfan was found in cocoa seeds and subsurface soil (15–30 cm). 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 30.13 days 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 DT 50 are highly correlated (R = 0.9525; n = 28) and no significant difference (P = 0.05) for both methods.

Original languageEnglish
Article number196
JournalEnvironmental Monitoring and Assessment
Volume191
Issue number3
Early online date27 Feb 2019
DOIs
Publication statusPublished - 1 Mar 2019

Keywords

  • Endosulfan
  • Half-life
  • Kinetics
  • Persistence
  • Theobroma cacao

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