| Abstract: | Residues of gamma-HCH and chlorpyrifos-methyl in Ponderosa pine bark (Pinus ponderosa Laws.) were determined 7-300 days after spray treatment, by a rapid extraction method using ethyl acetate and sodium sulphate, and analysis by gasliquid chromatography using either an electron-capture or nitrogen-phosphorus detector. The residue data were fitted into a power curve equation, Y = axb, to determine the rates of insecticide disappearance. The half-life values (μg cm?2), as interpolated from the power curve, indicate that 50% disappearance occurred in 43 (± 9) days for gamma-HCH and 102 (± 26) days for chlorpyrifos-methyl. When half-life values, however, are computed from extrapolated initial deposits, 50% disappearance occurred in 6 (± 1) days for gamma-HCH and 15 (±4) days for chlorpyrifos-methyl. |
