Laboratory evaluations were conducted for 94 weeks to compare, under static conditions, residue levels maintained in water treated with three polyvinyl chloride pellet formulations of fenitrothion. The results showed that foamed formulation (polyvinyl chloride + dioctyl phthalate + Triton X-100 + ammonium carbonate + citric acid + water + fenitrothion) gave the highest rates in the percentage of fenitrothion released followed by expanded formulation (polyvinyl chloride + dioctyl phthalate + Triton X-100 + fenitrothion), while non-expanded formulation (polyvinyl chloride + dioctyl phthalate + fenitrothion) gave the least.
The records indicated that increasing both the exposure time of formulations tested into the water and the percentage of active ingredient in the present formulations increased the amount of fenitrothion released from these formulations. However, all tested formulations gave low-initial rate of release.
The results showed that there were two rates of release of fenitrothion. In the first step, the non-expanded formulation gave a slow rate of release, expanded formulation gave a moderate rate of release, and foamed formulation gave a fast release. In the second step, the release rate of fenitrothion was slow for all tested formulations.