Evaluation of Potential Exposure to Metals in Laundered Shop Towels

Figures & data

Table 1 Exposure parameters.

Parameter	Acronym	Typical use
Exposure via hand contact
Metals’ load on LST surface	LoadLST (mg/cm^2)		See data in Table 3. LST weight = 1 oz (0.0283 kg) based on mean weight of three LSTs (Beyer et al. 2003).
Surface area of LST (front and back)	SALST (cm^2)	2268	Based on average dimensions for five LSTs (Beyer et al. 2003).
Fraction of LST in contact with hand	FLST (unitless)	75%	Under typical usage, based on professional judgment.
Number of LSTs used daily per person	N (day^–1)	14	Average Exposure—95% UCLM daily use per employee based on forms submitted by managers.
		20	High Exposure—95th percentile daily use per employee based on forms submitted by managers.
LST-to-hand transfer	Tt/h (unitless)	7%	Based on a range of transfer rates from carpet (Lu and Fenske 1999; Wester et al. 1996 as cited in Babich 2006; Camann et al. 1996; Cohen Hubal et al. 2005, 2008; Rodes et al. 2001). Averaged mean transfer rates from moist/wet hands and mean rates from dry hands.
Hand-to-mouth transfer efficiency	HTE (unitless)	6%	Based on median ingestion rate of 12 mg/day (see text), USEPA's recommended soil adherence factor and surface area of both hands (USEPA 2004, 2011a).
General exposure parameters
Exposure frequency	EF (days/year)	250	Standard default for a worker—50 weeks a year, 5 days a week (USEPA 1991).
Exposure duration	ED (years)	25	Standard default for a worker (USEPA 1991). Based on the 95th percentile from the Bureau of Labor Statistics in 1990 (USEPA 1991). The median time spent in a specific occupation, was 6.6 years for all adults (men and women combined) USEPA (2011a).
Bodyweight	BW (kg)	70	Standard default for a U.S. adult (USEPA 1991). Although the average U.S. adult bodyweight is 80 kg (USEPA 2011a), we conservatively used a mean bodyweight of 70 kg, the default value USEPA uses in its risk assessments (USEPA 1991).
Averaging time—non-cancer	AT-NC (days)	9125	Exposure duration × 365 days/yr (USEPA 1991).
Averaging time—cancer	AT-C (days)	25,550	70 years × 365 days/yr (USEPA 1991).

Table 3 Detected concentrations (without outlier data) and estimated load.

	Detected concentrations				Load
		Mean	95%	95th	Average	High
Chemical	% Detected	(mg/kg)	UCLM	Percentile	(mg/cm^2)	(mg/cm^2)
Aluminum	100%	567	670	1200	8.4E-03	1.5E-02
Antimony	98%	12	14	20	1.7E-04	2.5E-04
Arsenic	87%	0.59	0.70	1.3	8.7E-06	1.6E-05
Barium	100%	473	629	1900	7.8E-03	2.4E-02
Beryllium	36%	0.091	0.13	0.41	1.6E-06	5.1E-06
Boron	87%	14	45	20	5.7E-04	2.5E-04
Cadmium	98%	10	33	48	4.1E-04	6.0E-04
Calcium	100%	3052	3566	7040	4.4E-02	8.8E-02
Chromium	98%	72	123	240	1.5E-03	3.0E-03
Chromium (VI)	64%	0.34	0.42	1.0	5.2E-06	1.3E-05
Cobalt	98%	33	53	120	6.6E-04	1.5E-03
Copper	100%	662	836	1980	1.0E-02	2.5E-02
Iron	100%	5102	6551	13,400	8.2E-02	1.7E-01
Lead	100%	112	231	462	2.9E-03	5.8E-03
Magnesium	100%	608	722	1700	9.0E-03	2.1E-02
Manganese	100%	94	106	190	1.3E-03	2.4E-03
Mercury*	90%	0.048	0.16	0.14	2.0E-06	1.7E-06
Molybdenum	98%	60	100	184	1.3E-03	2.3E-03
Nickel	100%	71	97	254	1.2E-03	3.2E-03
Potassium	98%	94	175	208	2.2E-03	2.6E-03
Selenium	98%	1.2	1.9	2.9	2.3E-05	3.6E-05
Silver	98%	5.2	12	26	1.4E-04	3.3E-04
Sodium	98%	507	575	940	7.2E-03	1.2E-02
Strontium	100%	28	33	84	4.1E-04	1.1E-03
Thallium	0%	0.38	ND	0.50
Tin	96%	18	27	53	3.4E-04	6.6E-04
Titanium	100%	48	68	158	8.4E-04	2.0E-03
Vanadium	96%	4.0	6.3	12	7.9E-05	1.5E-04
Zinc	100%	518	627	1120	7.8E-03	1.4E-02
HEM (Oil & Grease)	100%	74,120	86,615	173,500	1.1E+00	2.2E+00
ND—not detected. *Mercury was only analyzed in 29 laundered LST samples due to the low percentage of samples in which mercury was detected.

Table 2 LST-to-hand transfer studies from carpet to hand.

Reference	Value	Compound	Basis
Dry hands
Midwest Research Institute 1994	8.9%	Pesticide	Mean transfer from three trials immediately after application presented in Table 4–5 of report.
Rodes et al. 2001	6.1%	Dust particles	Average of not embedded (8.7%) and embedded (3.4%) mean surface loading presented in Table 4 of the study.
Lu and Fenske 1999	5.9%	Pesticides	After 3.5 hours, hand press, average of aerosol (4.2% and 8.9%), and broadcast (4.5%) applications presented in Table 4 of the study.
Cohen Hubal et al. 2008	4.8%	Pesticide-tracers	1st contact: average of pressing and smudging using riboflavin and uvitex OB tracer results (Trials 3, 8, 12, and 13) presented in Table S1 of the study.
Cohen Hubal et al. 2005	2.6%	Tracer	1st contact transfer: average of smudging and pressing results (Experiments 1–4) presented in Table 3 of the study.
Midwest Research Institute 1993	1.5%	Pesticide	Mean transfer from three trials presented in Table 7 of report.
Damp/Moist/Sticky Hands
Rodes et al. 2001	18%	Dust particles	Average of embed (16.9%) and no embed (19%) mean surface loading results presented in Table 4 of the study.
Cohen Hubal et al. 2008	10%	Pesticide-tracers	1st contact: average of pressing and smudging using riboflavin and uvitex OB tracer results (Trials 2, 5, 9, and 16) presented in Table S1 of the study.
Cohen Hubal et al. 2005	8.3%	Tracer	1st contact transfer: average of smudging and pressing results (Experiments 9–12 and 17–20) presented in Table 3 of the study.
Camann et al. 1996	2.5%	Pesticides	Average of chlorpyrifos, pyrethrin I, and piperonyl butoxide results based on moistened hands presented in Table 5 (average of 9 results).
Average	5%	Dry hands only
	10%	Moist hands only
	7%	Average of the averages (moist and dry separately)
	7%	Average of all studies

Table 4 Toxicity reference values.

	USEPA RSLs			ATSDR		CalEPA		USEPA MCL
	RfD	RfD		Oral MRL		MADL^2	NSRL^3	MCL^4
Chemical	(mg/kg-day)	Key^1	Notes	(mg/kg-day)	Duration	(mg/kg-day)	(mg/kg-day)	(mg/kg-day)	Notes
Aluminum	1.0E+00	P		1.0E+00	Chronic			1.4E-03	Secondary MCL
Antimony	4.0E-04	I						1.7E-04
Arsenic	3.0E-04	I		3.0E-04	Chronic		1.4E-04	2.9E-04
Barium	2.0E-01	I		2.0E-01	Chronic			5.7E-02
Beryllium	2.0E-03	I		2.0E-03	Chronic		1.4E-06	1.1E-04
Boron	2.0E-01	I	Boron and borates only	2.0E-01	Intermediate
Cadmium	1.0E-03	I	Cadmium diet	1.0E-04	Chronic	5.9E-05		1.4E-04
Calcium
Chromium	1.5E+00	I	Chromium III insoluble salts					2.9E-03
Chromium (VI)	3.0E-03	I		1.0E-03	Chronic	1.2E-04
Cobalt	3.0E-04	P		1.0E-02	Intermediate
Copper	4.0E-02	H		1.0E-02	Intermediate			3.7E-02	Action Level
Iron	7.0E-01	P						8.6E-03	Secondary MCL
Lead						7.1E-06	2.1E-04	4.3E-04	Action Level
Magnesium
Manganese	2.4E-02	I	Manganese (non-diet)					1.4E-03	Secondary MCL
Mercury	3.0E-04	I	Mercuric Chloride and other salts	2.0E-03	Intermediate - Mercuric Chloride			5.7E-05
Molybdenum	5.0E-03	I
Nickel	2.0E-02	I	Nickel soluble salts
Potassium
Selenium	5.0E-03	I		5.0E-03	Chronic			1.4E-03
Silver	5.0E-03	I						2.9E-03	Secondary MCL
Sodium
Strontium	6.0E-01	I		2.0E+00	Intermediate
Thallium	1.0E-05	P	Thallium (soluble salts)					5.7E-05
Tin	6.0E-01	H		3.0E-01	Intermediate
Titanium
Vanadium	5.0E-03	I	Adjusted from Vanadium Pentoxide	1.0E-02	Intermediate
Zinc	3.0E-01	I		3.0E-01	Chronic			1.4E-01	Secondary MCL
HEM (Oil & Grease)
Oral reference dose (RfD), regional screening level (RSL), oral minimum risk level (MRL), maximum allowable dose level (MADL), no significant risk level (NSRL), maximum contaminant level (MCL).
Blank—Not available.
^·1P—PPRTV, I—IRIS, H—HEAST, C—CalEPA as presented in the USEPA RSL table (USEPA 2011b).
^2,3CalEPA's MADL and NSRL in μg/day converted to mg/kg-day, using bodyweight of 70 kg (OEHHA 2011).
^4USEPA Maximum Contaminant Levels (MCLs) unless otherwise noted (USEPA 2011c). MCLs are legally enforceable standards applicable to the public water systems. Secondary MCLs are non-enforceable guidelines regarding contaminants that may cause cosmetic effects (skin/tooth discoloration) or aesthetic effects (taste, odor, or color). Action levels were regulated by treatment techniques requiring systems to control corrosiveness of water and are not necessarily health-based. The following assumptions and equation were used: MCL * Drinking Water Rate (2L/day) * Exposure Frequency (365 days/yr) * Exposure Duration (70 yr)/(Bodyweight 70 kg * Averaging Time 25,550 days).

Table 5 Metals with exceedances by health-based criterion and comparison of results with and without outlier data.

	Without outlier data	With outlier data
Criterion	Hand contact	Hand contact
Average-exposure scenario
Oral RfD/Heast	Co (2.2)	Co (2.5), Cd (3.0)
ATSDR MRL	Cd (4.2), Cu (1.1)	Cd (30.2), Cu (1.2)
CalEPA MADL	Cd (7.2), Pb (409)	Cd (51.5), Pb (3,529)
CalEPA NSRL	Pb (4.9)	Pb (42)
USEPA MCL/AL	Al (5.9), Cd (2.9), Fe (9.7), Pb (6.8)	Al (6.3), Cd (21.7), Fe (10.3), Pb (58.8), Mn (1.3)
High-exposure scenario
Oral RfD/Heast	Co (7.2)	Co (7.2), Cd (1.5)
ATSDR MRL	Cd (8.7), Cu (3.6)	Cd (15.3), Cu (3.8)
CalEPA MADL	Cd (14.8), Pb (1,170)	Cd (26.1), Pb (1,697)
CalEPA NSRL	Be (1.9), Pb (14)	Be (2.5), Pb (20.2)
USEPA MCL/AL	Al (15.2), Sb (2.1), Cd (6.1), Cr (1.5), Fe (28.3), Pb (19.5), Mn (2.4)	Al (19.4), Sb (2.1), Cd (10.7), Cr (1.7), Fe (30.3), Pb (28.3), Mn (2.4)
Al: aluminum, Be: beryllium, Cd: cadmium, Cr: chromium, Co: cobalt, Cu: copper, Pb: lead, Sb: antimony, Fe: iron, and Mn: manganese. Exceedance ratio = Intake/Toxicity Reference Value. Blank—no exceedances.
Bold and italics = exceedances that were dropped when the outliers were removed from data.

Figure 1 Unused shop towel. (Color figure available online.)

Figure 2 Laundered shop towel with area selected for analysis. (Color figure available online.)

Figure 3 Composition of selected particles from area selected for analysis in Figure 2. (Color figure available online.)

Figure 4 Spectrum from area selected for analysis in Figure 2. (Color figure available online.)

Table 6 Impact of alternative exposure assumptions on likelihood of exceeding toxicity criteria.

Parameter with	Likelihood of exceeding
uncertainty	toxicity criteria
Metals’ loading on LST surface	Increase or decrease
Daily LST use	Increase or decrease
Fraction of LST in contact with hands	Slightly decrease
LST-to-hand transfer	Increase or decrease
Hand-to-mouth transfer efficiency	Increase
Bioavailability	Decrease

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