Stability of organochlorine and organophosphorus pesticides when extractedfrom solid matrixes with microwave energy

A stability study of 44 organochlorine pesticides (OCPs) and 47 organophosp horus pesticides (OPPs) was conducted, Compounds were spiked into solvent o nly (hexane-acetone, 1 + 1; methylene chloride-acetone, 1 + 1; methyl tert- butyl ether [MTBE]; and toluene-methanol, 10 + 1), solvent/dry soil suspens ions, and solvent/wet soil suspensions (20% water, w/w). Spiked matrixes we re heated in closed vessels with microwave energy at 2 temperatures (50 deg rees and 145 degrees C) for 5 or 20 min, For comparison and for determinati on of nitrogen blowdown losses, spiked matrixes that had not been exposed t o microwave energy were concentrated by using the blowdown technique and an alyzed for each of the spiked compounds. For OCPs, temperature had the most significant effect on compound recovery, followed by matrix. All 3 pairwis e comparisons of the 3 matrix types were statistically significant. The sol vent factor was also significant, with average recoveries of 97.8% with met hylene chloride-acetone, 96.3% with toluene-methanol, 92.8% with hexane-ace tone, and 92.3% with MTBE, Of the 6 pairwise comparisons among the 4 solven ts, all but 2-methylene chloride-acetone versus toluene-methanol and hexane -acetone versus MTBE-were statistically significant, For OPPs, temperature also had the most significant effect on recovery, followed by matrix. All 3 pairwise comparisons of the 3 matrix types were statistically significant in the same order as for OCPs. The solvent factor was also significant, but average recoveries-89.5% with hexane-acetone, 89.4% with methylene chlorid e-acetone, and 81.5% with either MTBE or toluene-methanol-aar in a slightly different order from that for OCPs, Of the 6 pairwise comparisons among th e 4 solvents, all but 2-hexane-acetone versus methylene chloride-acetone an d MTBE versus toluene-methanol-were statistically significant Compounds tha t appear to degrade under microwave-assisted extraction conditions include TEPP, phosphamidon, trichlorfon, naled, monocrotophos, demeton-O, and demet on-S.