RESUMEN

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.

Asunto(s)

RESUMEN

To assess worker isocyanate exposures in a variety of processes involving the manufacture and use of surface coatings, polyurethane foams, adhesives, resins, elastomers, binders, and sealants, it is important to be able to measure airborne reactive isocyanate-containing compounds. Choosing the correct methodology can be difficult. Isocyanate species, including monomers, prepolymers, oligomers, and polyisocyanates, are capable of producing irritation to the skin, eyes, mucous membranes, and respiratory tract. The most common adverse health effect is respiratory sensitization, and to a lesser extent dermal sensitization and hypersensitivity pneumonitis. Furthermore, isocyanate species formed during polyurethane production or thermal degradation may also produce adverse health effects. Isocyanate measurement is complicated by the fact that isocyanates may be in the form of vapors or aerosols of various particle size; the species of interest are reactive and therefore unstable; few pure analytical standards exist; and high analytical sensitivity is needed. There are numerous points in the sampling and analytical procedures at which errors can be introduced. The factors to be considered for selecting the most appropriate methodology for a given workplace include collection, derivatization, sample preparation, separation, identification, and quantification. This article discusses these factors in detail and presents a summary of method selection criteria based on the isocyanate species, its physical state, particle size, cure rate, and other factors.

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

The National Lead Laboratory Accreditation Program (NLLAP) recognizes laboratories capable of analyzing lead in paints, soils, and dusts. NLLAP requires successful participation in the Environmental Lead Proficiency Analytical Testing (ELPAT) program. For paint chip analyses, laboratory-to-laboratory variability is about 10% relative standard deviation (RSD) for lead levels near 0.5%, the HUD definition of lead-based paint. For soil analyses, RSDs are about 9 to 10% near relevant federal soil standards and 16% near the lowest state bare soil standard that currently exists. For dust wipe analyses, RSDs range from 10 to 16% for lead levels near relevant HUD standards. Of participating laboratories, 92 to 93% consistently meet ELPAT performance limits. A variety of analytical methods gives similar results. No conclusive significant differences were found among most frequently used hotplate and microwave sample preparation techniques. In addition, several participating laboratories have successfully used ultrasonic extraction methods, a method suitable for use at abatement sites. The three most frequently used instrumental techniques, flame atomic absorption (FAA), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and graphite furnace atomic absorption show no statistically significant differences in ability to meet ELPAT performance limits. However, small statistically significant biases between these methods sometimes occur. The magnitude of biases is less than 5% of the corresponding laboratory mean near relevant federal standards except for lead levels near the lowest HUD lead wipe standard, where biases can be as high as 8%. Other instrumental methods that have been used successfully include ICP-mass spectroscopy, direct current plasma-atomic emission spectroscopy, dithizone spectrophotometry, and anodic stripping voltametry.

Asunto(s)

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

Asbestos fiber counting data reported in the NIOSH Proficiency Analytical Testing (PAT) Program are used in this study to evaluate the analytical performance of participating laboratories and to determine if overall performance has improved during a ten-year period. PAT laboratories have achieved intralaboratory precision of 0.18 to 0.28 relative standard deviation (RSD), and interlaboratory precision of 0.33 to 0.44 RSD. In addition, there was higher variability between PAT laboratories from 1974 to 1978, when the program underwent considerable change and growth than the variability found during previous or subsequent time periods. The improvements in interlaboratory precision by approximately one-third since 1974 and the tendency of laboratories with little PAT experience to have poorer interlaboratory precision than more experienced laboratories raises a concern that interlaboratory precision may deteriorate as large numbers of new laboratories start to enroll in the PAT Program with the increased emphasis on asbestos removal in public buildings.

Asunto(s)