Lead, cadmium, nickel, manganese, chromium, arsenic, cobalt, and mercury have been found in trace amounts in some nail polish (Ouremi & Ayodele, 2014; Karimi and Parisa, 2015; Iwegbue, 2016; Borowska & Brzóska, 2015; Sipahi et al., 2015; Bocca et al., 2014; Perkin Elmer, 2012). These elements naturally occur in minerals, soil, and water, which can result in trace levels in the manufacturing of pigments and other raw materials used in the making of cosmetics, even if not added intentionally. There are also some instances of colorants (i.e., pigments), used today, that contain metals such as antimony orange (i.e., antimony trisulfide) or manganese violet (i.e., ammonium manganese (III) pyrophosphate) (In-Cosmetics, 2020). Metals such as antimony, arsenic, cadmium, nickel, chromium, cobalt, mercury, and lead are banned as intentional ingredients in cosmetics in the European Union (EU) because of their high neurological and reproductive toxicity, and their inclusion is considered technically avoidable, but this is not the case in the United States (ATSDR, 2012, 2019; Bocca et al., 2014; Bund, 2017; EU Regulations, 2009; FDA, 2020).

Nail polish has been evolving considerably in the last decade, with some nail polish brands adding labels reporting the exclusion of certain toxic ingredients such as lead (Young et al., 2019). New nail polishes, for example, may use metallic effect pigments commonly known as metallic finishes. These new metallic shades in nail polish resemble bronze, copper, gold, and silver, and may contain aluminum, copper, and zinc powders as well as mica and bismuth oxychloride (Eckart, 2020; Koel Colours, 2020; Australian Academy of Science, 2020). Mica is a mineral used as glitter in cosmetics, which may contain iron, aluminum, magnesium, manganese, or barium (Koel Colours, 2020). It is plausible that certain minerals and colorants used in the new finishes could increase metal impurities inadvertently such as lead and cadmium, which are not added as ingredients but can be found in trace amounts in some of the ingredients. Information on metal impurities in nail polish finishes has not been documented in the literature.

In nail salons, dried nail polish from nail filings and chippings likely accumulates on surfaces or indoor dust. There are also new nail products that contain loose fine color powder, commonly used for acrylic nails or gels, which is mixed on-site along with resins right before application. The workers could be exposed to metal-containing dust, from nail polish or color powders, through inhalation, ingestion from hand-to-mouth contact, dermal contact, or contaminated water and food (ATSDR, 2019, 2020). Although metal levels in the blood is an ideal biomarker of exposure, such as blood lead levels (ACGIH, 2019), urine and toenails are often preferred media as they are less invasive and easier to collect, with toenails easily stored at room temperature (Keil, 2011; Grashow, 2014). Urine samples tend to reflec tmore recent exposures (the past few days) compared to toenails (the previous 6–12 months) (Goyer and Clarkson, 2001; Slotnick, 2006; van Dael et al., 2001). The use of metal levels in toenails as a biomarker of exposure for nail technicians has not been documented in the literature.

Nail technicians are exposed to a variety of chemicals from the nail care products used including solvents, acrylics, and plasticizers (Ceballos et al., 2019; Craig et al., 2019). Maternal complications (Quach et al. 2015), respiratory symptoms, neurological, and other adverse health effects (Roelofs et al. 2008) have been a concern to this worker population. It is important then to understand levels of metal impurities present in nail polish that could be contaminating nail salons, exposing nail technicians, and contributing to the burden of exposure and health. Although different, other occupations using paints have presented issues with metal exposures, such as artists Spandorfer et al. 2001), autobody painters (Vitayavirasuk et al. 2005), and other spray painters (Lin et al. 2019).

The specific objectives of this study were to: 1) measure the metal composition of commonly used nail polishes including different types of colors and finishes, 2) assess surface contamination of metals in nail salons, and 3) assess concentrations of metals in the urine and toenail clippings of nail salon technicians.

Besides levels of antimony in nail polish exceeding cosmetics guidelines, we did not find other toxic metals in exceedance of current guidelines in our sample of nail polishes. We also did not find levels on nail salon surfaces or in urine biospecimens from the nail technicians studied to be above existing health and safety guidelines.

Nail polish with finishes had significantly higher concentrations of tin compared to nail polishes without finishes. The elements found in highest concentrations in nail polishes were aluminum, barium, bismuth, iron, and magnesium. Surfaces in the nail salons also contained dust with aluminum, barium, iron, and magnesium. No significant differences on surfaces where nail polishes were stored or used with other surfaces may point at the small workplaces where dust may distribute throughout.

A review of the SDSs for the nail polishes disclosed ingredients containing highest elements (except bismuth). For example, barium sulfate, aluminum powder, iron oxides, and mica (known to contain magnesium) were disclosed in nail polish SDSs (listed in Table 1). Of those elements in nail polish and nail salon surfaces, aluminum and iron were also detected in toenails, and manganese was detected in both urine and toenails. Also, barium was detected in urine at comparable levels to those of the general population. Although implications for worker health are unclear, these elements are ubiquitous and occupational exposure limits are often set at extremely high levels (ATSDR, 2007b, 2008) that are unlikely in nail salons. In the context of women’s health, these exposures contribute to the overall burden of exposure and should not be ignored.

Our study found traces of 21 of the 27 elements tested in nail polishes. Of the 40 nail polishes analyzed, the antimony guideline of 0.5 μg/g was exceeded in all five samples that detected this element. Our polishes had concentrations up to 15 μg/g of antimony, which is high enough to suggest that antimony was added intentionally as an ingredient. Antimony is a heavy metal, commonly used as a pigment (In-Cosmetics, 2020); although not listed in any of the SDS’s reviewed. Although the German guideline was not based on health risks of antimony but technical feasibility (i.e., that presence is avoidable in the product by not adding ingredients composed of antimony), the European Union classifies antimony as an element that must be eliminated from cosmetics because of its toxicity (In-Cosmetics, 2020). In occupational settings, chronic exposures to antimony may cause respiratory irritation, pneumoconiosis, antimony spots on the skin, and gastrointestinal symptoms but only at extremely high concentrations in air (in the mg/m3, Sundar and Chakravarty, 2010), which are not likely to occur in nail salons. However, is important to note that nail polish guidelines were developed thinking of consumers that have lower exposures than nail technicians.

The presence of antimony along with cobalt, lead, manganese, and tin, in all of the types of sample matrices tested in the present study, suggests that these elements are common in small amounts. Specifically, cobalt and manganese are essential trace metals or metalloids that are important for vital functions in humans and possibly found in food (Gutierrez-Gonzalez et al., 2019). Lead was heavily used in paints and gasoline before the 1970s and is still found in soil and dust, especially in old buildings (ATSDR, 2019a). Tin is a low toxicity metal heavily used in metal alloys as a component of furniture and everyday items including cosmetics (Toxnet, 2020; Johnson et al., 2014). However, guidelines are often set based on single metal toxicity, but since they appear together in cosmetics, we don’t know their potential collective impact on toxicity or health. Specifically, many elements were found simultaneously in the nail polish samples, like in the case for example of manganese and tin (i.e., elements were significantly correlated, Table S7).

We found the highest nail polish concentrations Pre for aluminum, iron, and magnesium. Aluminum, in particular, is an extremely abundant element found in soil and rocks, and important if added as an ingredient or found as an impurity given its neurotoxicity at very high concentrations (ATSDR, 2008). Other studies on nail polish had not measured those elements. However, Karimi and Parisa (2015) found that nail polish in Iran had lead levels up to 24 μg/g, with reds at up to 6 μg/g, while the present study had lead levels only up to 0.4 μg/g of lead with reds at up to 0.027 μg/g. In general, trace elements found in the nail polishes in our study would not be considered a high-risk exposure source in occupational health. However, it is important to acknowledge that the results from the nail polish analysis may be useful for understanding exposures to personal care products in the general population.

Lead and cadmium are important impurities in cosmetics to study given their neurotoxic and carcinogenic qualities to humans (lead IARC group 2A, cadmium IARC group 1, IARC, 2020; ATSDR, 2019). Although our sample of nail polishes did not detect cadmium, we did not sample the universe of all nail polishes used in the salons and it may still be present in other polishes. Median levels of urinary lead and cadmium in the nail technicians studied were comparable to those of the general female US population. As a contrast, lead and cadmium levels in the nail technicians’ toenails were comparable to other studies. However, toenail levels had a wider variability in the results compared to urine samples. There is no data for toenails in the general population for NHANES, so no comparisons to the general public were made.

Toenail levels of lead and cadmium depend on sulfide bonds in toenails for accumulation. The majority of cadmium accumulates in the kidneys and is very slowly eliminated from the body (in decades) compared to a shorter half-life of months in toenails (Keil, 2011). Similarly, the bones are a major storage depot for lead, where it has a half-life of approximately 32 years, and leaves the body very slowly due primarily to lead’s ability to mimic calcium. With the sulfide bonds in toenails, less lead will accumulate in total than in bone (Keil, 2011). Levels of lead in toenails may reflect the reduction of environmental lead pollutants and body stores in the past decade, including the use of nail polishes without lead.

The nail technicians in this study had toenail median levels of arsenic of 0.13 μg/g, which was higher than the level (0.04 μg/g) found in the Kentucky study (Johnson et al., 2011) and the Health Professionals Follow-up Study (0.048 μg/g) (Mozaffarian et al., 2011). The higher toenail arsenic in our population may be of concern as Mordukhovich et al. (2012) had found an association between higher toenail arsenic and higher systolic blood pressure and pulse pressure in adults without arsenic-related occupational exposures. Arsenic is also an important impurity given its carcinogenic qualities (IARC group 1, IARC, 2020). Although arsenic was not measured in urine in this study for comparison, toenails can capture months of exposure to arsenic.

Other metals in toenails that were slightly higher in nail technicians compared to other studies included chromium, nickel, and mercury. Toenail chromium (median of 0.38 μg/g) in this study was also slightly elevated compared to that reported by the Sisters study (0.21 μg/g, Obrien et al., 2018). Nickel in toenails was 0.31 μg/g in this study, compared to 0.16 μg/g in the Kentucky study. Nickel in particular is an important impurity given its carcinogenic potential in humans (IARC group 1, IARC, 2020). Nail technicians’ toenail mercury of 0.90 μg/g was higher than the reported levels in the Sisters study (0.097 μg/g), the Health Professionals Follow-up Study (0.31 μg/g), and the AMBIS study (0.5 μg/g, Hinners et al., 2012). Some of the mercury differences between these groups could be attributable to cultural differences in fish consumption in the Asian nail technicians, which was 75% of our participants with a higher level in mercury (median of 0.90 μg/g) compared to other participants (median of 0.24 μg/g)although not statistically significant (p = 0.168). The Hinners et al. (2012) study included Japanese residents near Puget Sound in Washington with heavy fish diets and suggested a potential link with diet, although they still had lower values than those of our study participants.

There are several limitations to our study. First, this was a pilot study using a convenient and limited number of samples and without urine samples from all participants, which hindered the possibility to do a more in-depth data analysis to be considered as representative of the industry. Another disadvantage of our pilot study was that we asked limited questions about other potential sources of exposure for nail technicians in their environments at home and at work (e.g., diet, hobbies, home, and other jobs). Another limitation of the study is that most nail technicians used nail polish, so any exposures to components of the nail polish would be from both personal and occupational uses. Surfaces are often also made with many of the elements measured, such as aluminum or iron among others, so it is impossible to discern the contribution of surface materials versus nail polish related dust towards our sampling results. To discriminate the different sources of nail polish exposures, a control population may be needed in future health studies including nail technicians. Future studies could include laboratory analysis of other nail products such as colored acrylic nail powder and long-lasting nail polish, which were not analyzed in our study. Further, understanding of the bioavailability of trace elements in nail products will be important in follow up studies.

As discussed above, several studies have analyzed samples of nail polishes for trace heavy metals. However, to our knowledge, this is the first study to characterize potential nail technicians’ exposures to trace elements found in nail polish. Important in particular is the evaluation of sources from disclosed pigment ingredients in the nail polishes. Further, this is the first study to analyze different types of nail polishes characterizing the novel generation of finishes new to the industry beyond color. It is important to understand the role that certain metals may play in the health of nail technicians given the many health concerns in this worker population. This study provides preliminary information for future health studies in populations that may include nail technicians.

Nail polishes studied did not contain traces of toxic metals above cosmetics’ guidelines, except for antimony. Further, we found trace elements in nail polish samples that were not always listed as ingredients in the product information. Our findings suggest that antimony concentrations in nail polish may not be an immediate health hazard but are avoidable and should be disclosed since the existing international guideline was not based on specific health risks of antimony but technical feasibility.

Color in nail polishes contributes to presence of trace elements and finishes in nail polish seem to be contributing specifically to the levels of tin found in nail polishes. The surface wipe data suggests that dust generated in salons from the use of nail polish may be depositing on surfaces and potentially contributing to nail technician’s overall exposure. Potential contributions to exposure to nail technicians from nail polish use may include aluminum, barium, iron, magnesium, and tin. Although these would only be toxic individually at very high levels not present in nail salons, it is unclear if low-level metals mixtures are of health concern. Regardless, these results provide further evidence of the importance of ventilation and general housekeeping to keep dust levels low in salons and protect the health of nail technicians.

Results from biomarkers of exposure in nail technicians suggest that this vulnerable population may have levels of certain metals including arsenic and mercury that could be related to other factors rather than their work. Toenails may be a useful non-invasive biomarker to understand exposure to trace elements in this worker population.