METHOD DETECTION LIMITS IN SOLID-WASTE ANALYSIS

A two-part study is presented to assess the applicability of the U.S. EPA's method detection limit (MDL) to the analysis of solid materials. The first part compares MDLs calculated for arsenic, cadmium, molybdenum, selenium, and thallium in soil with the actual method performance on real spiked soils with these analytes at concentrations above and below the calculated MDL. The MDL method is examined to discover its empirical suitability for solid waste analysis and to see if it is the proper theoretical tool for solid matrices. The criteria are the precision and accuracy of results. The results show that the MDL method produces accurate and precise results only in interference-free conditions. This investigation was extended to an interlaboratory study which included the same five soils used above and five other soils spiked with PCBs. A total of 160 accredited environmental laboratories participated in this study. The applicability of the MDL was assessed by measuring the number of qualitative and quantitative errors produced by these laboratories. The results indicate that approximately two-thirds of the reported MDLs produced significant errors.