Influence of various solvent-water mixtures on the extraction of dieldrin and methomyl residues from radishes.

The effect of organic solvent/water ratios on the extraction of field-incurred residues of dieldrin and methomyl from radishes was determined. 14C-Dieldrin and 14C-methomyl were applied separately to radishes in commercial formulations at rates of 0.2 and 0.9 kg/ha, respectively. Fourteen days post-application, the radishes were harvested and fresh root tissues were extracted using a Polytron homogenizer. Acetone, acetonitrile, and methanol containing 0, 10, 20, 30, 40, and 50% water were used as extraction solvents. For methomyl residues, the optimum water content of acetonitrile-water extraction mixtures was 40-50%; less than 40% water reduced the ability of acetonitrile to extract carbon-14. Methanol and acetone were nearly as efficient as 50% acetonitrile-water and were apparently not influenced by solvent/water ratios. For dieldrin, low water content slightly reduced the extraction efficiency of acetonitrile, with the optimum water content also being 40-50%. Percentage of water appeared to have little overall effect on methanol extraction efficiency. The extraction efficiency of acetone was lower than that of the other 2 solvents, and this effect was independent of the acetone/water ratio. Approximately 20% of the 14C-dieldrin residue was bound to radish roots 14 days post-application.