The evaluation of two extraction procedures for the recovery of organic chemicals from spiked soils

Abstract

Hazardous waste site assessments are based on the results of analytical procedures used to identify and quantify chemicals contaminating the soil. The accuracy of these results is fundamentally linked to the ability of a solvent extraction procedure to desorb and remove contaminants from a sample matrix prior to analysis. The recovery efficiency of an extraction procedure will indeed affect the quality of analytical data and may influence waste site assessments. The objective of this study was to compare the extraction efficiencies of the automatic Soxtec and U. S. EPA SW846 Soxhlet methods. In phases one and two of the experiment, extractions were performed on silicon dioxide matrices and silt-loam soils spiked with benz(a)pyrene, pentachlorophenol, and naphthalene at three concentration levels. Each test sample contained either an individual chemical or a 1: 1: I mixture of all three chemicals. Phase three consisted of extractions performed on a silt-loam soil spiked with a coal tar complex mixture. Soxtec samples were sequentially extracted with dichloromethane and methanol while Soxhlet samples were extracted with dichloromethane., Gas chromatographic results obtained from sample extract analysis were used to calculate percent recoveries of the chemicals. The recoveries of benz(a)pyrene and pentachlorophenol in the Soxtec procedure ranged from 55-88% and 49-88% respectively, For the Soxhlet method, the recoveries ranged from 4673% and 52-87% respectively, Complex mixture recoveries ranged from 50-60% for both procedures. The mutagenic potentials of the solvent extracts were evaluated using Salrnonella typhimtii- ium strain TA98 with and without metabolic activation. Assay results indicated a positive correlation between mutagenic response, assay controls, and the chemical concentrations derived from GC analysis. The data indicate that the Soxtec method which requires 2 hours, is as effective as the traditional 16 hour Soxhlet extraction procedure for recovering organic chemicals from contaminated matrices. The Soxtec method, thus, offered substantial time and cost savings.