2.1. Manufacturing Processes, Uses, and Production-related Information

2.1.1. Manufacturing Processes

The life cycle of antimony trioxide from raw material to consumer product is depicted in Figure 2-1. Antimony(III) trioxide for manufacturing processes may either be imported in that form (second box by the number 1 in Figure 2-1) or produced in the United States by oxidation of imported antimony metal (box 2 in Figure 2-1). Antimony trioxide is used to make various products and may change forms during the manufacturing of those products (see Section 2.1.2) The life cycle for antimony and antimony(III) trioxide often ends at disposal as waste during either production processes or in the final consumer product.

Figure 2-1

Antimony(III) Trioxide Used in Manufacturing Processes

Antimony(III) trioxide is produced primarily by re-volatilization of crude antimony(III) trioxide or by oxidation of antimony metal (EU 2008). The only domestic producer of primary antimony metal and oxide identified is a company in Montana that uses imported feedstock (USGS 2018), as no marketable antimony has been mined in the United States since 2015 (USGS 2018). The most recent U.S. mine production was in Nevada in 2013 and 2014, when about 800 tons of stibnite (Sb₂S₃), the principal antimony ore, was extracted. That mine has been on care-and-maintenance status (i.e., production has ceased but management for public health and safety continues) since 2015 (USGS 2018).

Antimony trioxide changes its chemical form during the formulation and processing stages for many products. The changes in chemical form for antimony are illustrated in Figure 2-1 by the grey shading in the boxes, which indicates the likelihood that antimony(III) trioxide is present at that stage of the process as described in the figure legend.

2.1.3. Production, Consumption, and Trade of Antimony and Antimony(III) Trioxide in the United States

Antimony(III) trioxide, elemental antimony, and several other antimony compounds (e.g., antimony(V) pentoxide, and antimony(III) diamyldithiocarbamate) are high-production-volume chemicals, based on their production in, or import into, the United States in quantities of 1 million pounds or more per year (see Table 2-1 for U.S. antimony(III) trioxide and antimony compound production volumes for 2015 and Table 2-2 for import and export information). Elemental (i.e., metallic) antimony may be converted to antimony(III) trioxide by oxidation, and various forms of antimony, such as antimony(III) trisulfide in brake lubricants oxidize to antimony(III) trioxide at the high temperature achieved during the use of vehicle brakes. Other forms do not generally give rise to the trioxide form except through incineration. The EU (2008) risk assessment report noted that combustion or incineration processes produce antimony(III) trioxide from all forms of pre-incinerated antimony.

Table 2-1

U.S. Antimony(III) Trioxide and Antimony Compound Production Volumes for 2015 Exceeding 1 Million Pounds per Year Ranked by Quantity.

Table 2-2

U.S. Imports and Exports of Antimony Metal and Compounds for 2016^a.

Antimony(III) trioxide accounts for 80% of total antimony use in the United States (NTP 2017a; USEPA 2014). Reports under the U.S. Environmental Protection Agency’s (EPA’s) Chemical Data Reporting rule indicate that approximately 1 million to 10 million pounds of antimony(III) trioxide is produced in the United States (see Table 2-1); however, the actual consumption of antimony(III) trioxide is likely much higher. In 2017, U.S. imports for consumption were approximately 52.8 million pounds of antimony oxide (weight of antimony content) (USGS 2018). EPA (2014) reported that most (approximately 87%) of the roughly 70 million pounds (gross weight) of antimony(III) trioxide consumed in the United States each year between 2007 and 2011 was imported (USEPA 2014). The majority of total antimony (83%) used in the United States is also imported, mostly from China, and the remainder (17%) is recovered from antimony-lead batteries (USGS 2018). In 2012, the U.S. EPA identified three companies manufacturing and ten companies importing antimony(III) trioxide (USEPA 2012).

2.2. Occupational Exposure

The highest exposures to antimony(III) trioxide and total antimony occur in the workplace including transportation workers exposed to antimony trioxide in the air. Historic data for the number of workers exposed to antimony were reported for the National Occupational Exposure Survey (NOES) conducted by the National Institute for Occupational Safety and Health (NIOSH) from 1981 to 1983, during which an estimated 209,773 male and female workers were potentially exposed to antimony(III) trioxide (CDC 2017). Although these data are over 30 years old, cancer has a long latency and thus this exposure information is still relevant. In 2010, 273 U.S. facilities likely produced or used antimony(III) trioxide (in flame retardants), based on information from EPA’s Toxics Release Inventory Program (USEPA 2014). Fire fighters may be exposed to antimony in smoke particulates released from combustion of retardant-treated textiles during fires (Fabian et al. 2010).

U.S. monitoring data from the Occupational Safety and Health Administration (OSHA) Chemical Exposure Health Dataset during a period of more than 30 years (1984 to 2017) reported data from 2,126 personal breathing zone samples collected from companies producing or using “antimony and compounds (as Sb)” (forms of antimony not specified) (OSHA 2017). The antimony air levels (measured personal breathing zone values), as total antimony, ranged from 0.2 μg/m³ to 54,500 μg/m³ across all facilities. Facilities with the highest antimony air concentrations were in the following industries: standard industrial classification (SIC) Code 2899, chemicals and chemical preparations, not elsewhere classified (this category would likely include antimony-containing flame retardants) (3.3 μg/m³ to 54,500 μg/m³); SIC Code 3341, secondary smelting and refining of nonferrous metals (this category would likely include antimonial lead refining) (1.8 μg/m³ to 47,700 μg/m³), and SIC Code 3339, primary smelting and refining of nonferrous metals (including antimony) (5 μg/m³ to 18,500 μg/m³). All of these industries are likely to involve exposure to antimony(III) trioxide as either a primary product or through oxidation of elemental antimony during smelting and refining processes; however, the levels most likely reflect other antimony compounds in addition to antimony trioxide.

Workers in the United States and other countries producing or using antimony(III) trioxide, as well as workers in occupations exposed to other antimony compounds, can be exposed to antimony(III) trioxide through inhalation of airborne solid dust or by skin contact resulting in increased excretion in the urine (see Table 2-3). The studies reported in Table 2-3 were identified primarily from the ATSDR (2017) draft toxicological profile for antimony and compounds and supplemented by literature searches. All results are reported from the primary publication cited.

Table 2-3

Air Levels and Urine Levels of Total Antimony in Workers Occupationally Exposed to Various Antimony Compounds in the Air.

Among industries using or producing antimony(III) trioxide, the highest levels (up to 5,000 to 6,000 μg/m³, levels 10 times higher than the threshold limit value [TLV]), are found among smelters or antimony manufacturing industries (see Table 2-3). The European Union (EU) (2008) risk assessment report (RAR) for antimony trioxide (Sb₂O₃) considered metal smelting and refining to be one of the major anthropogenic sources of antimony release to the atmosphere. U.S. air monitoring data specific for antimony(III) trioxide industries come primarily from NIOSH walk-through surveys of a few smelters or antimony(III) trioxide companies conducted largely in the 1970s, which usually were conducted as part of health hazard evaluations (CDC 2016a) or industrial hygiene surveys, the results for two of which were also reported in an epidemiological study (Schnorr et al. 1995) (see Table 2-3). Workers using or producing other types of antimony, such as elemental antimony used in the battery industry, can also be exposed to antimony(III) trioxide because metallic antimony oxidizes to antimony(III) trioxide in the air (EU 2008).

Workers in the transportation industry can be exposed to antimony trioxide from oxidation of antimony sulfide or sulfate in brake pads. Port workers in Valparaiso City, Chile were exposed to elevated air concentrations of antimony from heavy vehicular traffic (Quiroz et al. 2009) that resulted in very high levels of antimony in the blood (average concentration of 27 ± 9 ng antimony/kg), which were 5 to 10 times higher than in two control groups (1) from another part of the city or (2) from a rural area outside Valparaiso.

Urinary excretion of antimony by exposed workers generally increases with the level of exposure, although relatively few studies have reported both exposure and urinary excretion for the same workers. A few studies that reported both parameters are summarized in Table 2-4 together with studies that reported air levels only. The current TLV for elemental antimony and antimony compounds in air is 500 μg/m³ (ACGIH 2017)) and levels above as well as below this value have been reported. Bailly et al. (1991) measured urine and air concentrations of total antimony for workers manufacturing pentavalent antimony compounds (antimony(V) pentoxide and sodium antimoniate(V)) and reported a significant correlation (r = 0.83, p < 0.0001) between airborne antimony concentrations (log value) and both post-shift urinary antimony concentrations (log value) and an increase in urinary antimony concentrations during the work shift (r = 0.86, p= < 0.0001). Air concentrations and pre-shift and post-shift urinary antimony levels are also reported in Table 2-3.

Table 2-4

Antimony(III) Trioxide Occupational Exposure Level Estimates (as Antimony(III) Trioxide).

Extensive and systematic occupational monitoring data specific to antimony(III) trioxide, or exposures converted to antimony(III) trioxide equivalents, were reported by the EU risk assessment report (EU 2008) (Table 2-4). The industrial processes used in Europe are likely similar to those used in the United States, so data from the EU can help inform potential U.S. exposure. In general, the levels reported in the EU risk assessment report fall within similar ranges to those reported for the most recent U.S. data in Table 2-4 although considerable variability exists for reported values. In addition, the EU risk assessment report data are reported as antimony(III) trioxide; however, this represents only about a 20% difference from the estimates based on total antimony due to the adjustment for the atomic weight of oxygen. Also, the data for the United States are older and, thus, in general, U.S. exposure levels for some industries were higher than the European data. Both U.S. and European data indicate the highest exposures are for antimony(III) trioxide production, followed by the flame-retardant industries. Lower exposures are reported for production of crystal glass and pigment industries.

Inhalation exposure can also occur when antimony(III) trioxide powder is used in cement mixing (or cement powder-based product blending) applications (see Section 2.3) (Mapei Group 2017).

2.3. General Population Exposure

Evidence for exposure of the U.S. general population to antimony is provided by biomonitoring data showing its presence in urine, whole blood, and saliva. Data from the National Health and Nutrition Examination Survey (NHANES) indicate low level of exposure to antimony, with antimony (all forms of antimony) geometric means urine concentration of 0.132 μg/L for years 1999 to 2000 and 0.043 μg/L for years 2013 to 2014 (Table 2-5). Although the mean concentration (not considering the samples with antimony at below detection limit) appeared to be decreasing over time, this could reflect the use of more sensitive analytical methods, primarily inductively coupled plasma mass spectrometry (ICP-MS) in recent years, rather than an actual decrease in exposure, an explanation supported by reports of values close to the lower detection limits for the methods used (Filella et al. 2013a). On the other hand, Pang et al. (2016) (see Table 2-5) analyzing urine samples collected from 1998 to 2003 with a sensitive ICP-MS method reported urine antimony concentrations of 0.1 μg/L or higher, suggesting the exposure was higher.

Table 2-5

Ranges of Geometric Mean and 95th Percentile Antimony Levels in Urine, Blood, and Saliva Samples of U.S. Populations.

Based on analysis of NHANES data, higher urinary antimony levels were found in individuals with lower socioeconomic status, defined as either low income or living in economically deprived neighborhoods (Belova et al. 2013; Gonzales et al. 2016; Tyrrell et al. 2013). Slightly higher urinary antimony levels were reported for smokers than non-smokers in 2013 to 2014 data, as well as for younger people (6 to 11 years old, and 12 to 19 years old) than 20 years and older in 1999 to 2000 data and in 2013 to 2014 data. Total antimony measured in urine as the elemental form can be from various forms of antimony, not just antimony(III) trioxide (see Table 2-5). Antimony concentrations in whole blood (Filella et al. 2013a; 2013b; Whitworth et al. 2017) and saliva (Olmez et al. 1998) were available in only few samples, and the concentrations were much higher than that in urine.

Several studies have reported an association between biomonitoring data in the general population (e.g., urinary antimony, cord blood antimony) and adverse biological effects (Scinicariello and Buser 2016) or non-cancer endpoints, such as cardiovascular-related diseases (e.g., Guo et al. (2016); Shiue and Hristova (2014)) and adverse pregnancy outcomes (Zheng et al. 2014), suggesting that chronic exposure to low levels of antimony may be a potential public health concern.

No U.S. data on total antimony concentrations in breast milk were found, but concentrations (arithmetic means) measured outside the United States ranged from below the detection limit to 13 ng/g [13 μg/L] (Filella et al. 2013a).

The general population is potentially exposed to antimony directly from consumer products (Section 2.3.1)or indirectly from the environment by inhaling contaminated air (Section 2.3.2)or by consuming contaminated food or drinking water (Section 2.3.3)Because antimony can change its form in the environment, the form of antimony to which people are exposed may not be the same form initially released into the environment.

Table 2-6 and Figure 2-1 summarize exposure sources to antimony compounds from exposure to products manufactured with antimony(III) trioxide and the final forms of antimony to which people are exposed.

Table 2-6

Sources of Antimony(III) Trioxide and the Final Forms of Antimony (Antimony(III) Trioxide and Others) to Which People Are Exposed.

2.3.1. Consumer Products

Consumers are potentially exposed to antimony from consumer products as a result of the use of antimony(III) trioxide as a synergist with flame retardants or in PET containers. Exposure of the general population from consumer products is generally to antimony(III) trioxide by inhalation of dust from these products although some exposure could also occur orally to antimony(III) trioxide or other forms of antimony. Exposure is likely higher for children, especially infants, because of their direct skin contact with carpet material containing antimony(III) trioxide as a flame-retardant synergist while crawling, their mouthing of other fabrics containing flame retardants or toys with antimony-containing paint or plastic, and their potential to inhale more dust containing antimony from carpets because they are closer to the floor than adults (see Table 2-7). A 1998 study (Jenkins et al. 1998) reported that antimony could be detected in infant cot mattress covers containing polyvinyl chloride (PVC), and antimony was present in the leachate (extraction fluids) from mattress material.

Table 2-7

Estimated Consumer Exposure to Antimony (as Antimony(III) Trioxide) Directly and Indirectly from Products Containing Antimony(III) Trioxide.

Because antimony(III) trioxide can change its form during the manufacture of many products, exposure may be to other forms of antimony. For instance, if antimony is released in liquid (e.g., water, sweat, or saliva) at near-neutral pH, it will exist as hydrolyzed forms in solution (see Figure 1-1 in Section 1), Sb(III) as Sb(OH)₃ or H₃SbO₃ and Sb(V) as Sb(OH)₆⁻ or H₂SbO₄⁻ rather than as antimony cations (ATSDR 1992). The antimony in house dust is mainly antimony(III) trioxide (from wear and tear of flame-retardant-treated fabric) (EU 2008). Table 2-7 shows exposure levels for consumer products evaluated in the EU antimony trioxide (i.e., antimony(III) trioxide) risk assessment report, which converted all exposure levels to the equivalent mass of antimony(III) trioxide (i.e., converting measured antimony to corresponding antimony(III) trioxide based on molecular weight).

The only U.S. data on indoor air antimony levels are from an elementary school in Arizona (Majestic et al. 2012), where the particles <1 μm in diameter (PM₁) fraction of air samples averaged 0.017 μg antimony/m³. Antimony in air was most likely resuspended from flame-retardant-treated carpet by foot traffic.

A study measuring antimony in costume cosmetic products purchased in the San Francisco Bay area reported measurements of antimony in eyeshadows (mean = 0.34 mg/kg; range = 0.13 to 0.57 mg/kg; N = 5) and in body paint (mean = 1.5 mg/kg; range = 0.12 to 6.2 mg/kg; N = 5) (Perez et al. 2017).

A study in the United Kingdom measured antimony in 750 consumer products (rubber, textile, and foamed materials) (Turner and Filella 2017), and detected antimony in 18% of over 800 measurements of those products at approximately 60 μg/g to 60,000 μg/g. Antimony was also detected in another study in the United Kingdom that measured antimony and other toxic metals in paints on public playground structure surfaces; levels ranged from 273 μg/g to 16,000 μg/g (Turner et al. 2016). Similar products in the United States would likely have similar levels.

2.3.3. Food and Drinking Water

Levels of antimony (form not specified) in food in the United States range from not detectable (limit of detection not reported) to 1.7 μg/g of dry weight (Belzile et al. 2011). Antimony(V) is the most prevalent antimony species in drinking water, as the result of oxidative treatments (chlorination or ozonation) used in water disinfection processes. Antimony levels in U.S. drinking water range from 0.02 μg/L to 9.6 μg/L. The value of 9.6 μg/L was reported for bottled water heated in PET bottles at 80°C for 48 hours.

Exposure to antimony can result from consumption of contaminated food or drinking water (see Table 2-8). However, the EU risk assessment report (EU 2008) noted that antimony(III) trioxide in solution will produce the antimony(III) ion, which hydrolyzes to either the trivalent form as neutral Sb(OH)₃, or the pentavalent form as charged Sb(OH)₆⁻ (see Section 1.2).

Table 2-8

Antimony (as Antimony(III) Trioxide Equivalents) Typical and Worst-case Exposure Levels from Food, Breast Milk, and Drinking Water Based on Data Measured in Europe.

2.4. Summary and Synthesis

A significant number of people in the United States are exposed to antimony(III) trioxide (Sb₂O₃), as evidenced by occupational exposure data and supporting data on production, consumption, and releases into the environment and exposures from consumer products. In addition to exposure to antimony(III) trioxide in the workplace from its use as a synergist with flame-retardant chemicals, as a catalyst in production of PET plastic, as a pigment and fining agent in glass production, and as a colorant and opacifier in pigments for paints and ceramic glazes, people are potentially exposed from using consumer products containing antimony(III) trioxide, and by breathing contaminated air, or a combination of these sources. The chemical form of antimony changes during manufacturing, in the environment, and in vivo, and detection methods typically measure total antimony rather than specific forms of antimony, so identifying exposure specifically to antimony(III) trioxide is presently difficult.

The highest occupational exposure to antimony(III) trioxide occurs in workplaces that produce or use antimony(III) trioxide (e.g., smelting and refining operations and production of antimony(III) trioxide). During the 1970s, reported levels ranged from 50 to 5,000 μg/m³, compared with the current threshold limit value (TLV) of 500 μg/m³. In the United States, roughly 70 million pounds of antimony(III) trioxide are used annually as a synergist for halogenated flame retardants in plastics, rubber, and textiles, as a catalyst in PET production, and as an additive in optical and art glass, pigments, paints, and ceramics. Workers at an estimated 273 U.S. facilities (based on information from EPA’s Toxics Release Inventory) were exposed to antimony(III) trioxide in 2010. More than 200,000 workers were exposed to antimony(III) trioxide in the 1981 to 1983 U.S. National Occupational Exposure Survey, indicating extensive past exposure to antimony(III) trioxide.

The highest occupational exposure to antimony(III) trioxide in the United States, exceeding current regulatory levels by at least 10-fold, occurred during smelting and refining operations and production of antimony(III) trioxide in the 1970s and 1980s. Antimony is no longer mined in the United States and smelting and refining of metallic antimony and production of antimony(III) trioxide was limited to one company in the United States in 2017. More recent European data suggest that the highest exposure to antimony(III) trioxide occurs during production of antimony(III) trioxide, followed by the flame-retardant industry. Lower levels of exposures occur during the use of Sb₂O₃ in the glass and PET industries.

Biomonitoring for antimony in urine and environmental data provide evidence of widespread exposure to antimony; however, the proportion that results from exposure to antimony(III) trioxide is usually not known. Antimony in air is expected to be mainly in the form of antimony(III) trioxide with the highest concentrations near facilities, such as mines and smelting operations, that release antimony(III) trioxide into the air. People can also be exposed to antimony(III) trioxide in the air from oxidation of various forms of antimony, such as antimony(III) trisulfide in brake lubricants which is heated to a high temperature during the use of vehicle brakes, various antimony compounds in burning of coal and petroleum, and various forms of antimony in waste that is burned or incinerated. Household products that contain antimony(III) trioxide, particularly flame-retardant-treated textiles, plastics, and rubber, can release particles containing antimony(III) trioxide to the air or dust and antimony ions in liquids leading to dermal or oral exposures, e.g., through mouthing of these products by infants or small children.