Residues of 14C-chlorpyrifos in coconut using radio-tracer techniques

A coconut tree was root infused with 5 g a.i. chlorpyrifos (Lorsban) plus 1.4 u Ci of 14 C-chlorpyrifos. Samples of both young and mature nuts were taken 24 hr and up to 90 days after root infusion. The maximum uptake of chlorpyrifos equivalents was on the 13th day after root infusion for both mature and young fruit. The residue in water reached the peak on the 20th day after infusion and declined thereafter. A preharvest interval (PHI) of more than 60 days after root infusion will provide nuts for safe consumption. The usual practice of storing copra in treated warehouses until it is processed into oil was simulated in the laboratory to determine the residues absorbed in the coconut meat. Forty kilos of copra with a moisture content of 7-12 percent were stored in an improvised warehouse i.e., 1 m x 1.5 m x 1 m wooden box, which was treated with 100 ml one percent a.i. Lorsban 50 WP plus 100 uCi 14C-chlorpyrifos. Analysis showed that 14C-chlorpyrifos equivalents ranged from 22.6 mg/kg on the 30th day to 8.2 mg/kg on the 90th day with a 63.7 percent reduction in residues. Bound residues were detected on samples stored for 60-90 days, with levels of 1.0 to 0.2 mg/kg 14C-chlorpyrifos equivalents. This is within the maximum residue limit to 2 mg/kg set by FAO/WHO for chlorpyrifos in most agricultural commodities. Chlorpyrifos residues were also determined at various stages of refining and processing of crude coconut oil. It was subjected to alkali refining, bleaching and finally steaming. The residues were reduced by as much as 32.7 percent in spiked residues and 22.1 percent in aged residues. Thin layer chromatographic analysis revealed that chlorpyrifos was intact after alkali refining with an Rsubf value of 0.74 using a developing solvent of 90:25 dioxane/acetic acid. This was degraded after steaming to an unidentified metabolite which is suspected to be 3,5,6 - trichloro pyridinol