An on-site, field-portable analytical method was evaluated (1) (2) and National Institute of Occupational Safety and Health (NIOSH) Method 7701(3) has been published for the determination of lead in workplace air samples. Using ultrasonic extraction (UE) and anodic stripping voltammetry (ASV) analysis, samples can be analyzed on-site with laboratory accuracy within one hour.

A study (4) has demonstrated and NIOSH Method 7700 (5) has been published that allows for a qualitative, rhodizonate-based chemical spot test kit to be used for rapid field screening of airborne particulate samples for lead. Screen test results can then be compared to the Occupational Safety and Health Administration (OSHA) PEL of 50 ug/m3. After screening and if quantitative results are needed, the same samples may subsequently be presented for quantitative analyses.

Based upon the results of the above studies and published NIOSH Methods, it is now possible to obtain acceptable, rapid, on-site evaluations of personal breathing zone and area air samples with respect to this hazardous metal.

Background

Industrial Hygienists (IH), as well as other professionals practicing in the health and safety arena have interest in methods for measuring concentrations of hazardous materials rapidly. The reason for rapid test results is that members of the health and safety professions are charged with the task of protecting people (and other living things) from becoming exposed to environmental health hazards. Many such hazards are not readily detectable by our senses. Yet, they may be present in concentrations that are potentially harmful to the health of anyone exposed to them. Therefore, the health professional needs a means of identifying and quantifying the hazard in as short a time as possible. Only then can informed decisions be made to protect those who might potentially be exposed to that hazard. Indeed, the lack of a proper method to quickly evaluate potential health hazards is an ongoing source of frustration and anxiety to those health professionals and IH's.

The ability to rapidly measure lead in airborne particulate samples has long been a case in point. Traditional lead measurement methods involve laboratory analysis by atomic absorption or emission spectrometry following collection on filter membranes using properly calibrated personal sampling pumps. Sample collection and analytical procedures follow accepted, published guidelines such a NIOSH Methods or ASTM Standards. It is mandatory that the health professional have the analytical results in order to make informed decisions about potential exposure to hazardous lead concentrations. Then he/she can determine what appropriate steps must be taken to adequately protect the individuals at risk.

Other, non health-based reasons for wanting rapid lead testing results right there on the project site center around project timetables and protecting the client from potential future liability or litigation situations. Most lead abatement and renovation jobs are of short-term duration. All involve using expensive equipment and highly paid personnel who must be certified to work on lead projects through specialized training courses mandated by regulatory requirements. Rapid testing and monitoring results of personal breathing zone (PBZ) allows personnel and equipment to continue working. This reduces project costs associated with delays and downtime often encountered when awaiting analytical results from an off-site laboratory. Continuous feedback from monitoring the containment areas and worksite perimeter for airborne lead excursions allows for three protective actions.

1. Excursions detected from containment areas can lead to immediate corrective actions, thus avoiding the spread of contamination beyond the containment area.
2. Monitoring the air along the worksite perimeter not only provides valuable data to combat potential liability situations from off-site neighbors, but provides a "red flag" early on when elevated lead levels are detected so that corrective actions can be implemented.
3. Monitoring of construction workers, a group that is ordinarily overlooked in occupational health monitoring.

The two on-site test methods described in this article represent a long-awaited breakthrough in airborne lead testing. Taken separately, each method provides a rapid, on-site, field portable method for the detection and evaluation of amounts of airborne lead. This, for the first time, allows health and safety decisions relative to lead exposures to be made in a timely manner. Taken together, the methods collectively provide a rapid, two-step procedure for identifying and evaluating the magnitude of the problem. Using the chemical spot test method immediately reveals whether or not the OSHA PEL of 50 ug/m3 is being exceeded. Then, submitting the same sample to the UE/ASV analytical procedure quantifies the lead concentration in the air sample with the accuracy and precision of laboratory methods.  Lead concentrations can then be compared to regulatory guidelines and appropriate action taken. To avoid confusion, this article will discuss the two methods separately.

UE/ASV determination of lead is a relatively new technique available for use by industrial hygienists and environmental health scientists. The UE/ASV method has been evaluated by the NIOSH Laboratory in Cincinnati, Ohio and a new method (NIOSH Method No. 7701) has been added to the NIOSH Manual of Analytical Methods. (3) The UE/ASV method can be used for the determination of lead concentrations in either area or personal breathing zone samples. The intended use is for on-site monitoring of workplace lead, which may be used for Occupational Safety and Health Administration (OSHA) compliance purposes for lead in construction (29CFR 1926.62) as well as for lead in general industry (29 CFR 1910.1025).

If lead can be measured in the field, on-site, then there is no need to send samples away to a laboratory for analysis. If there is no need to wait for laboratory results, then exposure data can be examined more readily and exposure assessments can be made much more rapidly. It follows, then, that future exposures can be prevented by making rapid decisions regarding personal protective equipment and/or the implementation of engineering controls. The construction industry should find that the ability to perform on-site, near real-time lead measurements using UE/ASV should be especially useful where jobs are frequently short-term and worker turnover is often high. The capability for on-site exposure monitoring can significantly reduce the time required for industrial hygiene work. Reducing this time commitment can reduce associated project costs in job downtime and laboratory analyses. Furthermore, worker exposure to lead hazards can be reduced since the data is available and exposure assessments can be made rapidly.

The UE/ASV testing system, sometimes referred to as a "laboratory in a suitcase", is manufactured by Palintest Ltd. in the United Kingdom. It is available in North America from J & L Environmental Services, Inc., P.O. Box 1167, Elfers, Florida 34680-1167, (727) 376-7258 and costs less than $4,000.

The "laboratory in a suitcase" lead testing system includes the ultrasonicator and the analytical instrument (SA-5000) along with other equipment required to conduct lead extraction and analysis. Expendable supplies, purchased separately, include disposable, screen printed electrodes that may be used for one analysis each. The test system can also be used to test for lead in paint, soil, dust wipes, water and wastes.

HOW IT WORKS

Sample Collection

Area and personal breathing zone samples of airborne particulates are usually collected on 0.8 um pore size, 37 mm diameter cellulose ester membrane filters. The filters are placed inside a 2 or 3 piece cassette placed on-line with a calibrated personal sampling pump operating at a flow rate of 1-4 liters per minute. Collection times are generally for the entire work period to evaluate exposure for an 8-hour time weighted average (TWA). However, short term sampling may also be done in order to investigate exposures from specific area, work practices, or activities.

Ultrasonic Extraction

The filters containing the particulate air sample are removed from the cassette and placed into a 50 ml centrifuge tube. A mechanical pipette is used to transfer 10 ml of a dilute (10 percent v/v) nitric acid solution into the tube containing the sample. The tube is capped and placed into the ultrasonic bath making certain that the water in the bath is adjusted to a level at least 2.5 cm above the level of the liquid within the centrifuge tubes. The sample is then subjected to ultrasonic energy for 30 minutes. Many tubes can be extracted in a sonicator at one time, limited only by the size of the ultrasonicator.

Ultrasonic energy reaches the sample by transmission through the water bath contained in the sonicator into which the sample tubes are placed. This energy generates very high temperatures and pressures within the tubes. Bubbles form, called cavitation, at the interface between the solid phase (containing the lead) and the liquid phase (containing the acid). The combined effect of the physical heat and cavitation causes the solid particles to break up. The acid, in combination with the physical activity, completes the dissolution of the lead from the sample into lead ions (Pb+2) in solution. The resulting solution is referred to as the sample extract and the entire process is called ultrasonic extraction.

ASV Analysis

The Instrument

The Palintest SA-5000 Scanning Analyzer ASV is a portable, light-weight 375 g (13.3 oz) instrument that is battery powered using eight "AA" type batteries. The instrument features solid-state digital electronics and provides a simple menu-driven display which guides the operator through each stage of the analysis setup with easy to understand messages. Test results are stored in memory and can be recalled to the instrument display or downloaded to a computer or printer.

The actual chemical reactions during the lead analysis takes place on a small, disposable electrode attached to the main body of the instrument by an electrode holder, wire and plug.

Testing The Sample Extract

The test solution is prepared by first transferring a 5 ml portion of the sample extract to a 5 ml plastic vial. An electrolyte tablet is added to the solution, crushed and shaken to dissolve completely.

The lead analysis begins as soon as the electrode is introduced into the test solution. A voltage is applied to the solution through the electrode. Lead and other metal ions are deposited onto the electrode surface, just like in the chemistry of electroplating.

Once the plating phase is complete, the scanning phase begins. The analyzer applies an increasing reverse potential to the electrode to strip off the deposited metals. Each metal is stripped in a fixed order and at a precisely known potential (oxidation potential, for you chemists). This "anodic oxidation" reaction produces a current. In this way, lead and other metals are separated from each other and lead concentrations are measured. The entire analysis takes 45 seconds.

The instrument reports the analytical results in micrograms (ug) of lead. Simply by dividing the weight of lead in the sample by the volume of air sampled in cubic meters (m3) gives the lead-in-air concentration in ug/m3. The concentration may then be used to compare against published guidelines, such as those found in the OSHA regulations, so that informed decisions can be made.

Calibration and Quality Control

Calibration of the SA-5000 couldn't be easier. The electrodes, produced in large batches, are calibrated against certified standards as the batches come out of production. The resulting calibration curve is translated into a set of numbers called the calibration code, which is assigned to that batch of electrodes. When the instrument is used, the operator keys the calibration code into the instrument, prior to each analysis, corresponding to the batch of electrodes he is using.

It is recommended that other quality control methods be used to check on instrument drift, contamination of media and reagents, and lead recoveries. NIOSH Method 7701 suggested frequency of running quality control samples is one for every 10 field samples.

OSHA PEL SCREEN USING CHEMICAL SPOT TEST KIT

How The Method Works

Chemical spot test kits have been used as a qualitative test for the presence of lead for many years, dating as far back as 1925. A qualitative test result merely indicates the presence or absence of lead in the sample, Yes or No. Most chemical spot test kits on the market today rely upon results based on the chemical reaction between lead (Pb) in the form of the dissolved ion (Pb+2) with a solution containing either the sulfide ion (S-2) or rhodizonate ion. The chemical reaction of positive lead ions with either of these negative ions produces a color which is interpreted by the user as a "positive test" for lead. The reaction of lead ions with sulfide ions produces lead sulfide (PbS), a compound that appears as a black precipitate (solid).

The rhodizonate test kits are based upon the reaction of the positive lead ion with the negative rhodizonate ion to form a colored lead-rhodizonate complex molecule. The color of the lead-rhodizonate complex depends on the pH of the solution. Colors ranging from violet to blue are observed when the reaction occurs in neutral to basic solutions (pH 7 to14). The color changes from pink to red in acid solutions (pH 1 to 7). All commercial rhodizonate test kits on the market today utilize reactions in acid solutions, so the pink to red color test results, using any of the kits, indicates a positive test for lead.

The rhodizonate-based chemical spot test kits are now more widely accepted over their sulfide counterparts due to the formation of toxic compounds using the sulfide tests and the ease with which rhodizonate test results can be interpreted. Fewer interferences to the detection of lead have been observed with rhodizonate than with sulfide, in part because sulfide can form dark precipitates with metals other than lead. The rhodizonate pink-to-red color test result is unique to lead. Also, the use of the rhodizonate spot test has been found to be less subject to operator error and interferences compared to the sulfide kits.

OSHA PEL Screening Procedure

The study (4) and NIOSH Method 7700 (5) cited above were based upon performance parameters provided by a commercially available, rhodizonate-based spot test kit. Both the study and NIOSH Method 7700 state that performance parameters for other rhodizonate-based chemical spot test kits may be different than the one used in the study. Thus, each test kit must be independently evaluated so that the performance parameters are known before being used to screen for lead in air samples using this reference method (NIOSH 7700).

For the purpose of describing the PEL screening procedure in this article, the author will use a rhodizonate-based chemical spot test kit with which he is most familiar - the Lead Alert Kit by PPI Pace. Following the recommendation of NIOSH Method 7700, PPI Pace, the Lead Alert manufacturer, through a third party study and report of results, established the performance parameters of the Lead Alert Kit based upon the NIOSH 7700 reference method (5). The procedure (6) for using the Lead Alert Kit to screen air samples for the OSHA PEL is available and can be obtained by requesting a copy from the author of this article.

In addition, although this article bases the use of the chemical spot test kit for the screening of air samples specifically for comparison with the OSHA PEL of 50 ug/m3, this does not represent the only use of this technique. A major potential advantage of the use of spot tests for airborne particulate samples is that the flow rate, collection time, etc. can be adjusted to obtain measurable quantities of lead. Thus the method may be useful for on-site screening of lead in air for a variety of applications. Lead spot tests could be employed on-site to give an indication of whether personal exposures are in compliance with other applicable federal or state regulations. Knowledge of the test kit performance parameters, provided by a statistical fit of the experimental data (as described in ASTM Standard 1828), may allow for the use of rhodizonate-based spot tests in field screening of airborne lead in a wide range of environments.

Sampling And Screening

Equipment

• Lead Alert Chemical Spot Test Kit - follow manufacturer's instructions except where noted in the procedure below.
• Sampler - Cellulose ester membrane filter, 0.8 um pore size, 37 mm diameter, in a two or three piece cassette with cellulose backup pad.
• Personal Sampling Pump - one to four liters per minute with flexible connecting tube.
• Sealed Plastic Bags.
• Gloves - powderless, plastic.

Procedure (abbreviated)

1. Calibrate the personal sampling pump with a representative sampler on line.
2. Sample at an accurately known flow rate between 1 and 4 liters per minute.
3. Don a pair of powderless gloves.
4. Use the Lead Alert Kit to screen the filter.
5. Open the cassette.
6. Introduce the extraction solution to the filter. (The extraction solution is part of the Lead Alert Kit.)
7. Place the "dot" on the extraction solution drops and hold the dot to the filter for 30 to 40 seconds to allow the reaction to take place. (The "dot" is in the middle of a small square cut from the test card provided in the Lead Alert Kit.)
8. Observe any color development (look for a pink to red color on the dot which indicates a positive test).
9. If quantitative results are needed, return the dot to the filter, re-close and seal the cassette and submit for analysis (i.e.: in the field using UE/ASV analysis).
10. *Evaluate the result from screening the 8 liter sample.
    • If the screen is positive, there is a 95 percent probability that if this exposure continues, the OSHA PEL will be exceeded. Actions should be taken to control/reduce the exposure and protect personnel.
    • If the screen is NEGATIVE, collect a personal air monitoring (PAM) sample of at least 330 liters of air using a flow rate of from 1 to 4 liters per minute.
11. Use the Lead Alert Kit to screen the 330 liter filter by following steps 3 through 9.
12. Evaluate the result from screening of the at least 330 liter sample.
    • If the screen is negative, there is a 95 percent probability that if the sample conditions continue, the PEL will not be exceeded,
    • If the screen of the minimum 330 liter sample is positive and the 8 liter screen was negative, the exposure may not be screened by this procedure.
    • This procedure assumes that the sampling period yields exposures that are representative of the entire workday.

Conclusion

The primary use of chemical spot test kits for airborne particulate sample screening for lead is to give an indication of whether personal exposures are in compliance with applicable federal or state regulations. The test can be performed and results revealed in minutes allowing the health professional to make rapid evaluations. The added advantage is that the same sample can subsequently be analyzed to produce quantitative results.

UE/ASV presents a method of field portable, on-site analyses of airborne particulate samples. Due to its acceptable performance, the method may be used in the field to assess compliance with OSHA regulations regarding workplace lead exposures. Additionally, the method could be employed for on-site monitoring of lead in other environmental media that are of concern in the residential lead hazard mitigation arena.

Field-based analyses using portable ASV may offer cost savings because decisions regarding worker exposures may be made on-site in the field. Hence there is no need to await laboratory results before determining whether to proceed with a given work practice or job. Costly project delays and downtime due to lead hazard exposure evaluations are significantly reduced.

References

1. Ashley, K.; Mapp, K. J.; Millson, M.: Ultrasonic Extraction and Field-Portable Anodic Stripping Voltammetry for the Determination of Lead in Workplace Air Samples, AIHA Journal (59): 671-678 (1998)
2. Ashley, K.: On-Site Extraction and Anodic Stripping Voltammetric Determination of Lead, Appl. Occup. Environ. Hyg. (13): 94-98 (1998)
3. National Institute for Occupational Safety and Health: Method No. 7701. In: NIOSH Manual of Analytical Methods, 4th ed. NIOSH (1994), Cincinnati, OH (suppl. 1998)
4. Ashley, K.; Fischbach, T. J.; Song, R.: Evaluation of a Chemical Spot-Test Kit for the Detection of Airborne Particulate Lead in the Workplace, AIHA Journal (57): 161-165 (1996)
5. National Institute for Occupational Safety and Health: Method No. 7700. In: NIOSH Manual of Analytical Methods, 4th ed NIOSH (1994), Cincinnati, OH (suppl. 1996)
6. PPI Pace: Lead in Air by Lead Alert Chemical Spot Test Kit, 1-4 (1998)

J. Lee Seaman MA, REM, CEA is an environmental professional with more than 35 years experience in chemistry, both as an instructor and in applied environmental work. Lee is a member of ASTM subcommittee E06.23 on lead. He is an active member of AIHA, IAQA, ASHRAE, NAEP and NREP and is president of J & L Environmental Services Inc. in Elfers, Fla. He represents manufacturers of chemical spot test kits (Lead Alert by PPI Pace), ASV instruments (Palintest - SA-5000) and indoor air quality instruments (GrayWolf DirectSense 100). You may reach him by calling (727) 376-7258 or by e-mail at jleeseaman@worldnet.att.net.