Paul C. Schlecht

Field screening test methods: performance criteria and performance characteristics

Field-portable test methods may be quantitative, semi-quantitative, or qualitative and screening methods are often used in the field to determine if the concentration of a toxic substance exceeds regulatory or recommended standards or action levels. For on-site analysis, accurate quantitative tests for field measurements may not be available, depending on the analyte(s) or specific field situation. Thus, in lieu of more definitive test methods, screening tests which are based on qualitative or semi-quantitative methods are often used for making immediate decisions in the field, e.g. for compliance or risk assessment. Also, quantitative methods may be used for screening purposes in many instances. To ensure the quality of these screening tests and the decisions that are made based upon their results, screening methods need to be evaluated with sufficient data and should meet basic performance criteria prior to their being employed for decision-making purposes. Although quantitative, semi-quantitative and qualitative methods demonstrate different characteristics, it is desired that the performance criteria for all three method categories be consistent. If there is consistency, then one can have a sound basis for selecting the most appropriate test(s) for a given application. In order to unify the performance criteria for the different types of methods, a performance function is used to characterise both qualitative and semi-quantitative methods; in turn, this performance function is related to that for quantitative methods. False negative rates, false positive rates, sensitivity and specificity are key characteristics of screening methods that can be determined from the pertinent performance curves. The performance characteristics of each method are related to the uncertainty region that is associated with each method and the applicable uncertainty regions can be gleaned from the performance curves. Also, various options for using multiple test results to improve decisions based on test results are provided.

Ultrasonic extraction and portable anodic stripping voltammetric measurement of lead in paint, dust wipes, soil, and air: An interlaboratory evaluation

Recent studies have demonstrated the utility of ultrasonic extraction (UE), followed by portable anodic stripping voltammetry (ASV), for the on-site determination of lead in environmental and industrial hygiene samples. The aim of this work was to conduct an interlaboratory evaluation of the UE-ASV procedure, with a goal of establishing estimates of method performance based on results from collaborative interlaboratory analysis. In this investigation, performance evaluation materials (PEMs) with characterized lead concentrations were used for interlaboratory testing of the UE-ASV procedure. The UE-ASV protocol examined has been promulgated in the form of two separate national voluntary consensus standards (one for UE and another for electroanalysis, which includes ASV). The PEMs consisted of characterized and homogenized paints, soils, and dusts (the last of which were spiked onto wipes meeting national voluntary consensus standard specifications), and air filter samples (mixed cellulose ester membrane) generated using characterized paints within an aerosol chamber. The lead concentrations within the PEMs were chosen so as to bracket pertinent action levels for lead in the various sample matrices. The interlaboratory evaluation was conducted so as to comply with an applicable national voluntary consensus standard that can be used to estimate the interlaboratory precision of a given analytical test method. Based on the analytical results reported by the participating laboratories, relative standard deviations (RSDs) for repeatability and reproducibility were computed for three different lead contents of the four PEMs. RSDs for repeatability were 0.019-0.100 for paints; 0.030-0.151 for soils; 0.085-0.134 for dust wipes; and 0.095-0.137 for air filters. RSDs for reproducibility were 0.127-0.213 for paints; 0.062-0.162 for soils; 0.085-0.134 for dust wipes; and 0.114-0.220 for air filters. With the exception of one of the air filter samples and one of the paint samples, the precision estimates were within the +/- 20% precision requirement specified in the US Environmental Protection Agency National Lead Laboratory Accreditation Program (NLLAP). The results of this investigation illustrate that the UE-ASV procedure is an effective method for the quantitative measurement of lead in the matrices evaluated in this study.

Phase Contrast Microscopy Asbestos Fiber Counting Performance in the Proficiency Analytical Testing Program

This report evaluates 20 years (1972-1992) of asbestos fiber count reporting for the Proficiency Analytical Testing (PAT) program, which is operated by the American Industrial Hygiene Association (AIHA) in cooperation with the National Institute for Occupational Safety and Health (NIOSH). Estimates were obtained for total, intracounter, and intercounter variability. Results show that total variability of counting chrysotile asbestos fibers improved by approximately 35% in recent years when compared with the variability found during 1975-1977, at the lowest filter fiber densities used in the PAT program. Total, intercounter, and intracounter variability for counting amosite and chrysotile asbestos fibers also were compared over a six-year period starting in 1986. PAT program laboratories achieved about one-quarter lower intracounter variability and about one-third lower total and intercounter variability when counting amosite fibers versus chrysotile fibers. In addition, amosite intercounter variability improved by about one-third, with large improvements occurring in the first year that amosite was included in the program. Factors affecting performance, such as changes in phase contrast microscope fiber counting methods, PAT participation, the AIHA Laboratory Accreditation Program, and PAT sample production, are discussed as possible factors affecting variability.

Interlaboratory and Intralaboratory Variabilities in the Environmental Lead Proficiency Analytical Testing (ELPAT) Program

The Environmental Lead Proficiency Analytical Testing (ELPAT) Program evaluates over 400 laboratories that perform lead measurements in paints, soils, and dusts. A previous National Institute for Occupational Safety and Health study, based on the ELPAT data over a 3-year period (1992-1995), found no large biases among common hotplate and microwave digestion techniques, but did detect small consistent bias between two common instrumental methods. This study expands on the earlier study by examining the total sample variability and its variation components (interlaboratory and intralaboratory). A correlation model was used to separate the variation components by estimating a variation ratio. The correlation model leads to a more general approach than a sample pairing technique developed by Youden. This study found no significant evidence that the relative contribution of intralaboratory and interlaboratory variability to total variability changes with lead loading levels. There were no significant differences in the relative contribution of variation components among three most commonly used analytical methods (combinations of sample preparation techniques and instrumental methods). The interlaboratory relative standard deviation is about 1.7 times the intralaboratory relative standard deviation. Both variation components are important parts of total variation although the laboratory-to-laboratory (including analyst-to-analyst) difference is greater than the within laboratory (including sample-to-sample) variation.

Performance of laboratories analyzing organic solvents in the proficiency analytical testing program

The Proficiency Analytical Testing (PAT) program is operated by the American Industrial Hygiene Association in cooperation with the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, under a Cooperative Research and Development Agreement. Currently more than 300 laboratories in the program report annually over 15,000 analyses for organic solvents on charcoal sorbent tubes. The evaluation of organic solvent determinations reported here covers almost 20 years of the PAT program (1974–92). Estimates are obtained for total variability, intraanalyst variability, and interanalyst variability. Each of these components is shown to have improved since the early rounds of the PAT program. For the most recent data, four analytes (chloroform, 1,2-dichloroethane, o-xylene, and trichloroethylene) have total relative standard deviations less than 0.10 relative standard deviation (RSD). Analytes collected at the lowest loadings (benzene and carbon tetrachloride) and toluene...