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Protecting Workers Exposed to Lead-based Paint Hazards
A Report to Congress
DHHS (NIOSH) PUBLICATION NO. 98-112
JANUARY 1997
Chapter 5
METHODS TO SAMPLE AND ANALYZE ENVIRONMENTAL LEAD
Introduction
Sample collection
Numerous studies conducted by NIOSH and others have found that workplace air and surface dust are the primary sources of occupational lead exposures. Paint and soil are environmental lead sources in residential and commercial environments. These environmental lead sources may become occupational lead hazards when work activities generate airborne dust from lead-contaminated paint, soil, or surface dust.
In order to control worker lead exposures during LBP activities, it is necessary to be able to accurately measure environmental lead. This chapter discusses laboratory-based sampling and analytical methods, on-site lead screening methods, and evaluation of laboratories and field testing methods.
NIOSH bases its recommendations on NIOSH and EPA protocols, and consensus standards developed by the American Society for Testing and Materials (ASTM). All of the sample preparation and analytical methods recommended here meet the performance criteria specified by NIOSH and EPA.1 - 7
The environmental action level for the health risk of interest should be considered when selecting a method, to ensure accuracy and quality of analytical results. The detection limit for the method selected should be at least an order of magnitude below the action level of concern. The range of measured concentrations should extend at least to twice the action level.
Samples collected must be representative of the environmental matrix (e.g., workplace air, paint, soil, and surface dust). Samples should be collected, using consistent techniques, to assure comparability of samples among sites and among different areas at a site. Recommended methods for sample collection are listed in Table 5.1.
Sampling methods for measuring worker exposure use a two-piece filter holder cassette with a 0.8-micrometer (µm) cellulose ester membrane filter. Personal air samples are collected in the worker's personal breathing zone, usually for the duration of the full-work shift. However, shorter periods may be important to assess exposures by task (task-based exposure assessment), or to prevent overloading of sample filters in very dusty environments (e.g., during abrasive blasting).
NIOSH investigators have found that personal air sampling may be inaccurate during abrasive blasting in confined areas on steel structures.8,9 A large percentage of the personal samples may be torn off the workers as they move about in confined areas.10 These environments are usually extremely dusty, and large particles (> 100 µm diameter) of paint or abrasive grit rebounding directly from the substrates may enter sample filter cassettes, biasing the results. Locating the sample at the back of the worker's neck will reduce entry of grit rebound in all but the most confined areas.
Lead in workplace surface dust can be collected by wipe sampling and vacuum sampling techniques. Most of these methods were originally developed to measure lead poisoning risks to children in homes.11 Wipe sampling, which determines surface lead loading (microgram [µg] lead per unit area), is the method currently preferred by HUD for determining surface lead concentrations as part of residential lead risk assessments.12 Wipe sampling requires systematically wiping a measured surface area (or the area within a sampling template) with a pre- wetted wipe. Some widely available commercial hand wipes are suitable for this purpose. Wipes used should have low background lead contamination and be of constituents that can be readily processed in the laboratory.13 Wipe sampling is also used for assessing dermal lead exposures, especially lead dust on hands.14
Vacuum sampling requires systematically vacuuming a measured area. A commonly used portable dust vacuum method is convenient because it uses the same equipment that is routinely used by industrial hygienists for personal air sampling.15 This method is useful for sampling dust on soft surfaces, and it can determine both lead loading and lead concentration (ppm or percent by weight) in the dust when pre-weighed filters or filter cassettes are used.
| Matrix | Collection | Preparation * | Analysis # (all matrices) |
|---|---|---|---|
| Air | NIOSH 7082, 7105,& 7300 ASTM E1553 | Field: EPA Field SOP Lab: NIOSH 7082 &7105 ASTM E1741 |
Field: Portable ASV** EPA Field SOP Lab: NIOSH 7082 NIOSH 7105 NIOSH 7300 EPA Lab SOP EPA SW-846 6010A EPA SW-846 7420 EPA SW-846 7421 ASTM E1613 |
| Dust Wipe | NIOSH 9100 ASTM E1728 |
NIOSH 7082 & 7105 ASTM E1644 EPA SW-846 3050A | |
| DustVacuum | ASTM D5438 ASTM PS46 | NIOSH 7082 & 7105 ASTM E1644 EPA SW-846 3050A EPA SW-846 3051 EPA Lab SOPf | |
| Paint | ASTM E1729 | Field: EPA Field SOP Lab: NIOSH 7082 & 7105 ASTM E1645 EPA SW-846 3050A EPA SW-846 3051 | |
| Soil | ASTM E1727 | NIOSH 7082 & 7105
ASTM E1726 EPA Lab SOP EPA SW-846 3050A EPA SW-846 3051 | |
|
NOTES: NIOSH methods include protocols for sample collection, preparation, and analysis. The EPA and ASTM methods listed are specific for one of these three elements. * Hotplate digestion: NIOSH 7082, NIOSH 7105, ASTM E1741, ASTM E 644, ASTM E1645, EPA SW-846 3050A, EPA Lab SOP. Microwave digestion: ASTM E1741, ASTM E1645, EPA Lab SOP, EPA SW-846 3051. Ultrasonic extraction: EPA Field SOP. # Flame atomic absorption spectrophotometry: NIOSH 7082, ASTM E1613, EPA Lab SOP, EPA SW-846 7420. Graphite furnace atomic absorption spectrophotometry: NIOSH 7105, ASTM ES 35, EPA SW-846 7421. Inductively coupled plasma atomic emission spectrophotometry: NIOSH 7300, ASTM E 1613, EPA Lab SOP, EPA SW-846 6010A.
SOP = standard operating procedure. | |||
A sensitive method is needed to assess worker exposures to lead in paint and soil. Hazardous occupational exposures have been found to occur even when average paint concentrations are well below the Title X definition of LBP (0.5%) or the Consumer Product Safety Commission (CPSC) definition of lead-containing paint (0.06%).16,17 To measure these levels accurately the sample usually must be analyzed in a laboratory. The recommended method for paint sample collection is ASTM E1729, which requires removing all of the existing paint layers. Field screening methods for testing for lead in paint in-place (in-situ) are mentioned later in this chapter.
The recommended practice for collection of soil samples is ASTM E1727, which involves scooping or coring methods.
Compositing of wipe, vacuum, paint, and soil samples has been suggested to reduce analytical costs. Compositing is generally not recommended by NIOSH for lead risk assessments because it results in a loss of information about environmental variability with relatively little reduction in total project cost. Additionally, compositing of wipe samples can cause serious problems in the sample preparation because the entire sample, including all of the wipes, must be digested.
The recommended sample preparation methods for lead in workplace air, dust, paint, and soil are listed in Table 5.1. Air samples (filters) can be prepared in the laboratory or in the field. Laboratory preparation is done by hotplate- or microwave-based digestion in strong acid, and field preparation is done by ultrasonic extraction in dilute acid. Paint samples are ground to a powder to maximize lead recoveries, then prepared like air samples. Surface dust (wipe) samples are prepared in the laboratory by hotplate digestion in strong acid. Soil samples are sieved to remove stones and other objects, then prepared in the laboratory by hotplate- or microwave-based digestion in strong acid.
Recommended laboratory and field analytical methods for lead in workplace air, dust, paint, and soil are listed in Table 5.1. Analysis methods in the laboratory include graphite furnace atomic absorption spectrometry, flame atomic absorption spectrometry, and inductively coupled plasma atomic emission spectrometry. In contrast to these laboratory methods which use spectrometry, field methods for lead are based on colorimetric or electroanalytical techniques.18,19,20 Higher airflow rates (2 to 4 liters per minute) and a highly sensitive method, such as graphite furnace atomic absorption spectrometry, should be used when performing short-term (<30 minutes) air sampling.
Screening and semi-quantitative methods are used to estimate the lead content of paints and other environmental matrices. Field screening techniques include portable x-ray fluorescence (XRF) and chemical spot test kits.
Portable XRF is the most commonly used method for screening for LBP in residences and is the method recommended by HUD and EPA. NIOSH does not recommend portable XRF instruments for occupational exposure assessment until they have been shown to meet established performance criteria for quantitative analyses.21,22 A method for the determination of lead in workplace air samples using a portable XRF instrument (with cadmium 109 source) is under development.23
Some chemical spot test kits are able to detect very low lead levels in a variety of environmental matrices and, therefore, may prove to be useful for screening for potentially hazardous levels of lead in the workplace.24 A rhodizonate-based chemical spot test kit has been evaluated for screening of lead in workplace air samples.25 ASTM standard E1753 describes the use of qualitative chemical spot test kits for screening of lead in paint, and ASTM E1828 covers the evaluation of test kits for lead in paint.
Additional laboratory and field sample preparation and analytical methods for lead in a variety of sample matrices are under development or evaluation by federal agencies. ASTM is continuing to develop a series of standards dealing with lead hazard identification and mitigation.26
RECOMMENDATIONS FOR PERFORMANCE EVALUATION
NIOSH recommends, and the HUD guidelines require, the use of laboratories recognized by EPA's National Lead Laboratory Accreditation Program (NLLAP) to ensure the consistency and quality of measurement results. The Environmental Lead Proficiency Analytical Testing program (ELPAT) is part of NLLAP and is administered by the American Industrial Hygiene Association (AIHA) in cooperation with NIOSH and the EPA. ELPAT performance criteria are similar to those of the well-established Proficiency Analytical Testing (PAT) program for workplace air samples administered by AIHA and NIOSH. On a quarterly basis, NIOSH evaluates the performance of approximately 400 laboratories located throughout the United States and Canada and publishes the results in the American Industrial Hygiene Association Journal and Applied Occupational and Environmental Hygiene. Over the past three years, the ELPAT laboratories have demonstrated good agreement in lead measurements among the recommended methods for sample preparation and analysis of lead in paint, dust, and soil samples.27
With the advent of new field-portable methods for environmental lead analysis, it is anticipated that more on-site lead determinations will be performed in the future. NIOSH recommends that ASTM E1775 be used for performance evaluation of on-site extraction and analytical methods. ASTM E1583 should be used to evaluate organizations involved in field-based assessments of lead hazards. A system similar to NLLAP is needed to evaluate the quality of analyses of lead in paint, dust, and soil done in-place (in-situ) with portable instruments (e.g., by portable x-ray fluorescence).
Further research is needed to evaluate the utility of chemical spot test kits for assessing worker lead exposures and to develop a sampling method to reliably measure lead exposures in confined abrasive blasting environments.