This experimental pilot study involved spiking fabrics with lead, laundering the fabrics in residential washing machines, and testing the lead levels of the laundered fabrics. The authors first evaluated the analytical methodology by computing the recovery of known amounts of lead spiked on fabric and determining the accuracy and precision of the method.

The authors then evaluated the levels of lead present on laundered swatches that had been spiked with two forms of lead. The swatches were of three fabric types commonly worn by workers. Along with the fabric, eight pounds of bedsheets and pillowcases were washed to simulate a typical household laundry load (Leverette 2022). The spiked 3 cm × 3 cm swatches were attached to a pillowcase in the laundry load. Levels of carryover lead were also determined in uncontaminated bedsheets and pillowcases that were run in a laundry load with the spiked fabric. The authors cut a 3 cm × 3 cm swatch from a random section of the bedsheet and analyzed it for carryover levels of lead. All bedsheets and pillowcases were purchased new and washed twice before use.

To document other variables that may have influenced lead removal and are pertinent to local laundry situations, both the pH and hardness of the wash water were measured. A common consumer detergent and a common washing machine were used for experiments where swatches were laundered. The washing machines were purchased new. Finally, to measure the levels of cross-contamination, the interiors of the washing machines were tested for residual lead.

This pilot study included three fabrics:

Dickies Pant Fabric (DPF): Dickies 874 Flex Material 65% Polyester/35% Cotton.

Based on anecdotal observations made by the authors on field studies, these fabrics are examples of those often worn by workers in industries where lead exposure is a concern. All items were purchased commercially and washed twice before using them for testing.

Experiments were done with water-soluble lead nitrate [Pb(NO₃)₂] and water-insoluble lead carbonate [Pb(CO₃)₂]. Lead nitrate was obtained from JT Baker. Lead carbonate was obtained from NIST (National Institute of Standards and Technology, Gaithersburg, MD; Standard Reference Material #2589), which is a paint dust with ~9.99% lead. When lead carbonate is mentioned in this study, it refers to lead paint/SRM 2589 and not pure lead carbonate.

Known concentrations of lead nitrate were applied to the fabric swatches using aqueous solutions of lead nitrate or a slurry/paste of lead nitrate solid in deionized water. Lead carbonate was applied to the fabric swatches as a powder, to which deionized water was added. The swatches were folded once and pressed by hand to smear the lead carbonate slurry across the fabric.

A Mettler-Toledo Seven2Go portable pH meter was used once each day of washing machine operation to measure the pH of incoming water into the washing machine. The instrument was calibrated daily when the washing machines were run, using buffer standards at pH 4, pH 7, and pH 10. A sample of the water was analyzed once each day of washing machine operation for a hardness determination. Hardness was based on the sum of calcium and magnesium calculated as calcium carbonate hardness (U.S. EPA 1994).

Fabric swatches were cut into squares approximately 3 cm × 3 cm (9 cm²) in size. A known quantity of lead (9 μg, 900 μg, or 9,000 μg) was spiked on each fabric swatch, dried, and weighed for a final level of 1 μg/cm², 100 μg/cm², and 1,000 μg/cm². These levels span the range of concentrations (in μg/m³) seen in industrial settings (Koh et al. 2015). Lead nitrate was spiked at two levels: 1 μg/cm² and 1,000 μg/cm². Lead carbonate was spiked at three levels: 1 μg/cm², 100 μg/cm², and 1,000 μg/cm². The swatches were then subjected to microwave-assisted digestion using nitric acid and peroxide and closed digestion vessels. The solution was diluted to 20 mL volume with deionized water and analyzed by Inductively Coupled Plasma Mass Spectroscopy using EPA method 200.8 Determination of Trace Elements in Waters and Wastes by Inductively Coupled Plasma—Mass Spectrometry (U.S. EPA 1994).

Recovery experiments were performed on the spiked fabric matrix with lead nitrate (n = 40) and lead carbonate (n = 32). Of the 72 samples, 25 each were spiked at the 1 μg/cm² and 1,000 μg/cm² levels, and 22 were spiked at the 100 μg/cm² level. Percent recoveries of lead at each spike level were calculated by dividing the final mass by the initial mass and multiplying by 100. The percent coefficient of variation (%CV) was reported as a measure of precision. A method with a %CV less than or equal to 20 was deemed precise (Reed et al. 2002).

The lower reporting limit was determined by taking the lowest concentration in the calibration curve divided by the weight of the sample fabric digested and prepared. The volume upon digestion was 20 mL. The lowest concentration of the calibration curve was 0.5 μg/L.

A known amount of lead (9 μg; 900 μg; or 9,000 μg) was spiked on 3 cm × 3 cm (9 cm²) swatches of DPF, TSM, or BJM, for a spike level of 1 μg/cm², 100 μg/cm², and 1,000 μg/cm². Two forms of lead were used: lead nitrate and lead carbonate. The fabric swatches, along with eight pounds of bedsheets and pillowcases, were washed using top- and front-loading washing machines. Two sets of sheets and pillowcases that represented a load of laundry were alternated between them for use in the wash load. These sheets were a combination of king, queen, and twin sizes and included flat and fitted sheets.

Each washing load had six swatches of the same type (two swatches each of 1 μg/cm² and 100 μg/cm²; one swatch of 1,000 μg/cm²; and one blank). All six fabric swatches were attached to pillowcases using a plastic tag applicator. The swatches were then analyzed to determine the amount of lead still present on the spiked swatch following one laundering cycle. The percentage of lead that was removed from each swatch was reported. Table 1 lists the combination of variables used in each of the 18 laundry loads.

In each load, the initial mass of lead was 10,818 μg [(2 × 9) + (2 × 900) +(1 × 9,000)]. The lead in these spikes could redeposit on each other, on the blank swatch, or the 8 pounds of bedsheets and pillowcases. The percentage of lead removed during the laundry process was determined by computing the mass of lead based on the analytical lead result after each wash. The difference between the initial and final mass was divided by the initial mass and multiplied by 100. This was the percentage of lead removed.

Positive and negative controls were included in the analysis as a quality control step. The positive control was a 100 μg/cm² spiked fabric swatch using the same form of lead and the same fabric type as the other fabric swatches in the analytical run, which did not undergo washing. A recovery between 60% and 140% was deemed acceptable. This range accounted for the physical loss of lead and the redeposition of lead from one fabric swatch to another. Negative controls were unspiked fabric swatches. Positive and negative controls were not included in the washing machine loads. There were 18 samples each of positive and negative controls.

The overall mean recovery from 72 spikes was 109.1%. The recoveries ranged from 12% to 612% and had a %CV of 72.2%. Nine samples were below or above the accepted percent recovery criterion of 60% to 140%. Four samples showed less than 20% recovery, and five samples had recoveries between 146% and 612%. Table 2 shows the nine samples that were not within the acceptable recovery criterion. All nine were spiked with lead carbonate.

Table 3 summarizes the mean percent recovery with range and %CV for the three spikes, three fabrics, and two lead sources. The highest amount of lead recovered was when lead carbonate was spiked on a DPF fabric at the 1 μg/cm² level. The lowest amount of lead recovered was when lead carbonate was spiked on a DPF fabric at the 100 μg/cm² level. The authors concluded that the method was accurate and precise for lead nitrate across all three spike levels because all mean recoveries were between 60% and 140% of the expected 100% recovery, and all %CVs were less than 20%. However, the method for lead carbonate was neither accurate nor precise at the 1 μg/cm² level.

The lowest calibration standard was 0.5 μg/L, and the volume upon digestion was 0.02 L. Therefore, the minimum mass of lead was 0.01 μg. The heaviest fabric swatch was 482 mg. Therefore, assuming fabric swatches could weigh up to 500 mg, the detection limit equates to 0.02 mg/kg. The specific detection limit for TSM was 0.07 mg/kg (135 mg), for BJM was 0.03 mg/kg (350 mg), and for DPF was 0.04 mg/kg (250 mg).

The mean percent lead removed was 88.0%, and the median was 96.6% (range: 48.7 to 99.9). The %CV was 18.4%.

Among the three fabrics tested, BJM appeared to have the least amount of lead removed by laundering (70.6%). The amounts of lead removed from DPF and TSM were similar (97.4% versus 95.9%). The variability was higher for BJM (n = 6, %CV = 25.3) than DPF (n = 6, %CV = 2.7) or TSM (n = 6, %CV = 4.5).

More lead was removed in the carbonate form (92.6%) than in the nitrate form (83.4%) by laundering. GLM was used to explore the relationships between the percentage of lead removed and the fabric and lead. Statistically significant differences were found among the fabric and lead explanatory variables (p < 0.05). Significant interaction was also found between fabric and lead (p < 0.05). Table 4 summarizes these findings. The R-squared value was 0.86, which means that 86% of the variability in the percent lead removed can be explained by the model.

Based on an examination of the residual plots, the four assumptions of linear regression (linearity, independence, normality of error terms, and equal variance of error terms) were met.

The recoveries from the 100 μg/cm² positive controls ranged from 84.5% to 188.2%. Four out of 18 positive controls gave recoveries higher than 140% (quality control for loads 3, 4, 10, 12). Only one positive control gave a recovery below 90% (84.5% in Load 17). Therefore, losses of lead were not typical for the positive controls. None of the negative controls were above the limit of detection.

The average ± standard deviation of the pH and hardness of the water were 9.1 ± 0.1 units and 40.4 ± 4.0 mg/L, respectively.

To ensure that the results from each load washed in the machine were not influenced by the prior loads washed, experiments were performed to assess potential carryover between loads. The “sheet control, not washed” represented a bedsheet sample that was not included in the load in the machine. Since each load of laundry had five spiked swatches for a total of 10,818 μg of lead, residues and carryover checks showing <1 μg of lead were considered as evidence of no significant lead levels remaining on the fabric (sheets) or in the washing machine (Table 5).

No analytical method existed for the extraction and analysis of lead from the three fabrics in this pilot study (DPF, TSM, and BJM) at 1 μg/cm², 100 μg/cm², and 1,000 μg/cm². Therefore, the authors adapted and validated an analytical method where fabric samples containing lead were prepared and analyzed by microwave digestion using nitric acid and hydrogen peroxide, and subsequent analysis by ICP-MS (National Institute of Standards and Technology 2021).

The range of lead levels selected is relevant to occupational health as it covers a range of measures typically seen in workplace wipe and air lead samples. A NIOSH health hazard evaluation found between 23 and 940 μg of lead in hand wipe samples (NIOSH 2014). Although airborne lead samples as low as 4 μg/m³ and as high as 4,100 μg/m³ have been reported (NIOSH 2014), most airborne samples in occupational settings with lead exposures are between 60 and 800 μg/m³ (Koh et al. 2015). This translates to 58–768 μg, assuming an 8-hr sample at a nominal flow rate of 2 liters/min. This study intended to mimic the amount of lead that may accumulate on clothing during an employee’s workday in an occupation where lead exposure was possible. Therefore, the spikes of 9 μg, 900 μg, and 9,000 μg spanned the ranges reported in the literature.

Of the 72 samples analyzed for the validation study, the mean percent of lead recovered was 109%. However, since the samples were prepared in the laboratory, there were practical limits impacting accuracy and precision, especially at the low 9 μg level with the lead carbonate from the paint dust. Challenges with the application of trace levels of paint dust caused more variability in the recovery. SRM 2589 is a powdered paint with a certified amount of lead. The presence of other compounds in the paint may have affected the efficiency of the digestion and the lead recovery. Moreover, according to the Certificate of Analysis for SRM 2589, 100 mg is the minimum sample size to use. For the lowest level, this study used less than 1 mg of bulk, which may have affected the homogeneity of the sample, which would have led to lower and more variable recoveries. Therefore, the authors determined an acceptable recovery range between 60% and 140% instead of the more restricted 80% to 120% range (U.S. EPA 1994). The range was determined by spiking the fabric swatches and preparing them for analysis without any laundering.

The validation study initially used two spike levels, each of 1 μg/cm² and 1,000 μg/cm². Spiking the fabric with a known volume of a lead nitrate solution was more controlled compared to working with lead carbonate, which was in the form of a solid powdered paint to achieve the spike level. Because of the challenges with working with the powdered paint for lead carbonate, the additional 100 μg/cm² level was included.

The validation results showed that the quantitative accuracy was not reliable when 9 μg of lead from the lead carbonate form was spiked on a 500 mg swatch. Whereas spiking levels of 100 μg lead as lead carbonate on a 500 mg swatch (or approximately 200 mg/kg) showed acceptable quantitative accuracy. From the results of the two spiking levels, a practical quantitation limit of approximately 100 mg/kg can be inferred from the results for the lead carbonate form. This would equate to about 50 μg lead on a 500 mg swatch. The validation study showed that when using lead nitrate, the method demonstrated improved performance at the low spiking level with an average recovery of 99.0% of lead when 9 μg of lead was spiked on a 500 mg swatch (or approximately 18 mg/kg).

During day 3 of the validation study using lead carbonate for spiking, four samples at the 100 μg/cm² level returned extremely poor recovery results (under 20%). Review of the instrumental results did not reveal any dilution or calculation errors. There were no differences in how the samples were processed as compared to any other analysis days. A subsequent data set, including six samples at the 100 μg/cm^2, showed an average recovery of 115%. One sample using DPF and one sample using TSM gave high recoveries for the 100 μg/cm² spiking level, at 146%. No difference in preparation or processing occurred for these fabric swatches, and no laboratory justification exists for the elimination of the data points.

On average, 88% of lead was removed from the fabrics; however, no single washing machine cycle completely removed spiked lead from the fabrics. Any lead remaining on the fabrics after washing could be considered a health hazard because when the fabrics are dried, particles of lead on the fabric could become airborne.

The removal mechanism appears to be based more on agitation and physical “soil” removal as compared to dissolution of the lead. This statement draws from the effectiveness of removing lead carbonate, which is insoluble compared to lead nitrate, which is a soluble form of lead. The authors chose to combine three concentration levels (for a total of 10,818 μg) to reduce the length of experimental time and to reduce costs.

Three fabrics were chosen based on observations of the type of clothing often worn by workers. Of the fabrics selected for this study, the BJM represented the most challenging fabric from which to remove lead compared to the DPF and the TSM. This could be due to the denser nature of the denim and the coarse weave of the fabric. The fabric resisted efficient removal during the residential laundry washing. More studies need to be done on lead retention on denim because the weaves of denim can vary. Non-denim fabrics, such as DPF, may be a better choice for avoiding lead build-up within the fabric after washing.

Results indicated that residential washing machines used to launder lead-contaminated fabrics after occupational exposure can remove some, but not all, of the lead contamination.

This study found some level of lead residues in the washing machine between loads. The study also found that small amounts of lead were transferred from the spiked swatches to clean bedsheets. However, the values were less than 0.5 μg. It did not appear that lead built up in the washer after lead-contaminated clothes were washed. However, due to the small number of samples, additional data are needed. Given the limited scope of this study, it is important to continue to follow public health recommendations for preventing lead exposure, such as laundering work clothes separately from other household clothes.

The 1995 NIOSH report to Congress (NIOSH 1995) identified five effective workplace measures to prevent take-home lead exposures: (1) reducing exposures in the workplace, (2) offering employees the opportunity of changing clothes before going home and leaving soiled clothing at work for laundering, (3) storing street clothes in areas separate from work clothes, (4) offering employees the opportunity to shower before leaving work, and (5) prohibiting the removal of toxic substances or contaminated items from the workplace.

However, not all workplaces offer showering and laundry facilities, and many workers may have no choice but to launder their work clothes at home (NIOSH 1995). The impetus behind this study was to develop a better understanding, from a quantitative perspective, of the effectiveness of and challenges to residential laundering to minimize lead exposure to household members. The public health recommendation to “launder lead-contaminated clothing separately” is based on prudent best practices. This study has provided some information to better quantify the effectiveness of residential laundering in removing lead, lead removal from fabrics commonly worn by workers, and the effectiveness of household detergent on lead removal.

Future studies can build on the data presented here. More research is needed, especially in the determination of background levels of lead and other heavy metals in work clothes, the amount of lead and heavy metals removed in a variety of fabrics, the number of washes needed to remove most of the lead and heavy metals, the amount of residue on washing machines, and the varieties of detergent formulations that can remove the greatest amount of lead. In future experiments, it would be helpful to follow a randomized design to mitigate random experimental errors.

Additionally, the pilot study findings suggest that lead may not be fully removed from clothing during residential laundering. Over time, lead may accumulate on clothing (especially on clothing that is used repeatedly in a lead environment) and could potentially contribute to overall occupational exposures. These exposures could occur via skin absorption through direct dermal contact with lead-contaminated clothing or indirectly through contact with a contaminated surface in the home. This potential exposure pathway has not been characterized in the occupational health literature, but understanding this pathway could play an important role in reducing lead exposure in both workers and their households.