Three commercial PBDE mixtures; Penta-BDE, Octa-BDE, and Deca-BDE, have been manufactured. Each mix is comprised of several BDE congeners, but Penta-BDE is predominantly comprised of BDE-47 and BDE-99; Octa-BDE is predominantly comprised of BDE-183, BDE-196, and BDE-197; and Deca-BDE is predominantly comprised of BDE-209 . The European Union banned the use of Penta-BDE and Octa-BDE in 2004 and banned the use of Deca-BDE in 2008 due to concerns for public health. Similarly, PBDE producers in the U.S. phased out production and use of Penta-BDE and OctaBDE in 2004; however, Deca-BDE is still being used in the U.S. . To date, there is no legislation to limit the production or use of PBDEs in Asia . Despite the recent regulation of PBDEs in some countries, these chemicals are likely to persist in the indoor environment due to the ubiquitous presence of PBDE-treated consumer goods which can reside in homes for decades. Globally, PBDE consumption has varied by the quantities and mixtures of PBDEs used. Table 1 shows the regional consumption for three commercial PBDE mixtures reported in 2001 . In 2001, consumption of Penta-BDE, Octa-BDE, and Deca-BDE in the Americas exceeded that of Europe by 47-fold, 2-fold, and 3-fold, respectively. In comparisons between the Americas and Asia, the Americas consumed 47-fold more Penta-BDE but consumed comparable quantities of Octa-BDE and Deca-BDE. Although there is no readily available information regarding the use of PBDEs by country or state, there has likely been substantial regional variation. For example, the U.K. and California have stringent flammability standards that indirectly promote the use of Deca-DBE and Penta-BDE. Several investigators observed that biological PBDE levels in various populations mirror the global patterns in PBDE dust concentrations . Indeed, it is likely that the relatively high levels of PBDEs measured in blood and breast milk from North Americans compared to Europeans are the result of higher dust concentrations of PBDEs in North American residences . Researchers have also measured PBDEs in matched samples of dust and biological material and reported positive associations between subjects’ residential-dust PBDE levels and their corresponding biological levels.

Such associations were observed in geographical regions with both low and high levels of PBDE in dust. In the U.S., concentrations of PBDEs in residential dust were positively correlated with matched levels of PBDEs in serum and breast milk , as well as with various reproductive hormone levels in serum . Likewise, two studies from Europe observed significant relationships between PBDE levels in dust and plasma and one study from Sweden observed an association between PBDE levels in dust and breast milk . In contrast, two studies from the U.S. , two from Europe , and one from Australia were unable to detect positive associations between PBDEs measured in dust and matched biological samples. Two of these studies had only 10 subjects , three did not measure or could not detect BDE-209 in serum, and two observed that dust was a minor contributor to overall PBDE intake . The positive associations observed between PBDE levels in dust and biological samples suggest that dust is an important source of PBDE exposure worldwide. The estimated intake of PBDEs attributed to residential-dust exposure has varied widely within and between regions, but estimates from North America and Asia are generally higher than estimates from Europe .Two studies from Belgium and one from Germany suggest that residential-dust ingestion was likely responsible for less than 3% of overall PBDE exposure in European adults. In contrast, two studies from Canada estimated that dust ingestion contributed 14 and 65% of the total PBDE intake for adults, while two U.S. studies estimated that dust exposure contributed 56 and 82% of adult intake , and an Asian study estimated dust ingestion contributed 79% of adult intake. Based on these estimates, residential dust is expected to be the most important source of PBDE exposure for adults in geographical regions with relatively high PBDE dust levels . Moreover, children worldwide receive an even larger proportion of their total PBDE intake via dust ingestion compared to their adult counterparts due to hand-to-mouth behavior .

In summary, the available literature indicates that residential dust is an important contributor to PBDE intake in regions with heavy use of PBDEs. This suggests that levels of PBDEs in residential dust can be useful surrogates of total PBDE exposures in epidemiological studies.PBDEs have been incorporated into a myriad of household goods, including televisions, computers, and various other electric appliances as well as drapes, carpet, and furniture containing foam . PBDEs can be transferred from household items to indoor dust either as miniature fragments of foam or textiles via abrasion and weathering or following vaporization of PBDEs from hot surfaces in electronics with subsequent adsorption on dust particles . Few studies have successfully detected significant associations between levels of PBDEs in residential dust and the number of potentially PBDE-treated items in residences. In fact, of 14 studies that inventoried the number of foam-containing pieces of furniture, the number of electronic devices, and/or the typical use of electronic devices in study residences , only Suzuki et al. reported significant associations between these covariates and PBDE levels in dust. These authors reported significant correlations between total electrical appliance usage and dust concentrations of BDEs across 19 residences and 3 office buildings . One possible explanation for the paucity of positive associations is the wide range of bromination levels in similar consumer products . Allen et al. used X-ray fluorescence to identify bromine-containing household goods and illustrated that by excluding furniture without bromine from counts of PBDE-treated items, it was possible to measure a positive association between the number of electronic items and Deca-BDE congeners as well as between the number of foam containing furniture items and Penta-BDE congeners. Authors have examined other household characteristics ,best way to dry cannabis but have identified few determinants of PBDE dust levels . Stapleton et al. found a significant negative correlation between the residence square footage and the contribution of BDE-209 to the total PBDE dust concentrations. Similarly, de Wit et al. reported that median dust concentrations of BDE-209 were higher in apartments than in houses. In addition, Zota et al. found that dust collected from residences in a low-income community in California had higher PBDE levels than dust collected from residences in a more affluent California community. Because of their non-flammability and electrical insulation properties, polychlorinated biphenyls were used as coolants and lubricants in transformers, capacitors, and other electrical equipment and in a host of consumer products, including fluorescent lights, televisions, and refrigerators .

Due to concerns for human health, PCB production and use were restricted by various international regulations beginning in the 1970s . Still, because of the widespread use of PCBs, their persistence in the environment, and their bio-accumulation through the food chain, these chemicals are still ubiquitous in residences around the world. Three estimates of global PCB manufacture indicate that cumulative world-wide PCB production topped 1 million metric tons in 1980 and reached somewhere between 1.3 – 1.5 million metric tons by the time PCBs were entirely phased out of production in 1993 . Historically, the countries that have manufactured the most PCBs are the U.S., Russia, Germany, France, the U.K., and Japan, which produced 642, 174, 159, 135, 67, and 59 thousand metric tons of PCBs, respectively, by 1993 . Likewise, many of these nations were also major consumers of PCBs; with the U.S. consuming the largest portion of the world’s PCBs, followed by Russia , Germany , Japan , and France . The worldwide restriction of PCB production was implemented at different times in various countries. In 1973, member countries of the Organization for Economic Cooperation and Development , restricted production of PCBs to certain applications . Japan and the U.K. banned production of PCBs in 1972 and 1978, respectively, and in 1976, the U.S. congress passed the Toxic Substances Control Act, which phased out all U.S. production of PCBs by 1979 . In the 1980s, limited PCB production continued in Germany and France ; but a more stringent OECD decision in 1987 led to the cessation of all production, import, export, or sale of PCBs from these countries as well . Russia was the last major producer to phase-out PCB production . Recently, investigators have reported high concentrations of PCBs in dust associated with certain construction materials, such as caulking and wood floor finish , as well as with a PCB-contaminated fluorescent light ballast and a PCB-contaminated carpet pad . The prevalence of these particular PCB sources in residences is unknown; however, they are unlikely to be relevant in most homes. Ratios of indoor to outdoor PCB concentrations suggest that indoor PCB sources contribute substantially to PCB dust levels ; yet, investigators have had little success identifying demographics, household characteristics, or typical household items that have an impact on PCB dust concentrations . Two studies from the U.S. have found evidence that dust from older homes or older floors is more likely to contain high levels of PCBs . Colt et al. reported that, in multi-variable linear regression models, the age of the residence was associated with total PCB dust concentrations , with the highest levels found in residences built before 1960 and the lowest in residences built after 1980. Similarly, in the largest analysis of PCB determinants, Lee et al. reported that PCB concentrations were significantly associated with floor age in dust from 764 Michigan residences. Additionally, Lee et al. identified several factors that were associated with increased concentrations of PCBs in dust, including the presence of high-pile carpet, the presence of a vegetable or flower gardens, and elevated PCB concentrations in outdoor soil. In contrast, having a dog at the residence and increased dust loading , were associated with decreased concentrations of PCBs . Still, even the most comprehensive multi-variable model only explained 37% of the variability of PCB concentrations in residential dust . Polycyclic aromatic hydrocarbons are molecules with two or more fused aromatic rings that are formed as products of incomplete combustion. Humans are exposed to PAHs from a variety of indoor sources including cigarette smoke, wood burning fireplaces, gas appliances, and charred foods, as well as to outdoor sources, including vehicle exhaust and treatment of pavement with coal-tar-based sealants . Seven PAHs that have been classified by the U.S.

Study staff visited all sessions of a required course to explain study objectives and distribute parental consent and student assent forms,how to cure cannabis followed by in-class administration of the electronic survey on computers 1–2 weeks later. As a programmed feature of the survey software , students were randomized at the participant level with equal probability to one of two discrete choice experiments: e-cigarettes or moist snuff smokeless tobacco. Participants randomized to the e-cigarette experiment were presented six pairs of randomly generated hypothetical e-cigarette products under a full factorial design. The composite products differed in device type , flavor , vapor cloud , and nicotine amount . Prior to viewing the computer generated composite e-cigarettes, participants were shown an image containing the possible e-cigarette product characteristics they might see . Participants randomized to the smokeless tobacco discrete choice experiment were presented six separate, consecutive pairs of randomly generated hypothetical moist snuff products under a full factorial design. The composite products differed in brand , flavor , cut , and price . Prior to viewing the computer-generated composite moist snuff products, participants were shown an image containing the possible moist snuff product characteristics they might see . The number of displayed characteristics and their levels were necessarily constrained to avoid excessive cognitive burden. Some characteristics were product specific . Prioritizing which characteristics to retain for each product was based on existing qualitative and quantitative literature on youth tobacco-related perceptions and use motivations. In each experiment, for each pair of product composites, participants were asked which product ‘are you more curious about’, which ‘is more dangerous to health’, which ‘would be easier to use’, and which ‘would give a bigger ‘buzz’ or ‘head rush’’. These outcomes were chosen because of previous work showing associations between tobacco use and/or susceptibility with youth-reported curiosity, perceived danger, and perceived ease-of-use. The outcome ‘buzz’ was introduced to measure perceived physiological effects or potency. Participants could select either composite product within the pair or ‘neither of these options’.

Supplementary file, Figure A3 shows an example question layout. Of 1052 eligible participants, 525 took part in the e-cigarette discrete choice experiment and 522 the moist snuff discrete choice experiment . Participants providing ‘straight-line’ responses with no variation in choosing the left hand-side or right hand-side product were excluded to improve data quality, leaving 495 in the e-cigarette experiment and 508 in the moist snuff experiment.Conditional logistic regression was used to quantify the independent contribution of product attributes to participants’ choices while maintaining the matching of each pair. The position of the composite product on the screen was also included in models to account for possible ordering preference. A positive regression coefficient indicates how much the attribute level in question increased the log-odds of that composite product being chosen relative to the whereas a smaller percentage used smokeless tobacco products . In the e-cigarette experiment , tank-type and pod-type devices garnered more curiosity and were perceived as easier to use than cigalike or dripmod devices. Relative to tobacco flavor, all flavors were associated with more curiosity, less perceived danger, and greater perceived ease-of-use. On the adjusted log-odds scale, where tobacco flavor is the reference, fruit and dessert were most positively associated with curiosity, while mint and unicorn were the flavor options most negatively associated with danger. Smaller vapor cloud e-cigarettes were viewed as less dangerous, offering less buzz, and easier to use. Nicotine amount was strongly associated with perceived danger and buzz. High nicotine devices were viewed with less curiosity, as more dangerous, delivering more buzz, and less easy to use, relative to low nicotine or nicotine-free devices . In the moist snuff experiment , one brand was perceived as the most dangerous but also the easiest to use. Relative to tobacco flavor, all moist snuff flavors were associated with more curiosity, less perceived danger, and greater perceived ease-of use. On the adjusted log-odds scale, fruit and mint flavors were the characteristic levels associated with the most curiosity, while fruit flavor was also viewed as offering the least buzz .

Associations of modest magnitude suggested that fine cut products were perceived as less dangerous and offering less buzz. Higher price products were viewed with more curiosity, as more dangerous, offering a greater buzz, and being less easy to use . Among all responses, the probability of choosing ‘neither of these options’ rather than selecting one of the two composite products varied by product and the question being asked. In the e-cigarette experiment, participants indicated ‘neither’ most often when asked about which of the two products they were more curious . ‘Neither’ was less often selected when asked about ease of use , buzz , and danger . Similarly,cure cannabis in the smokeless tobacco experiment, ‘neither’ was indicated most often when asked about curiosity , followed by ease-of-use , buzz , and danger . There was no statistically significant interaction by gender in the e-cigarette experiment . In contrast, having ever used an e-cigarette was associated with differences in all four perception outcomes . E-cigarette ever users held stronger perceptions about device types, viewing tank-type and pod-type devices with more curiosity relative to cigalike devices than did never users. Both e-cigarette ever and never users perceived flavored products with more curiosity and as easier to use compared to tobacco flavored products, but only never users believed that flavored products delivered less buzz than tobacco flavored e-cigarettes. Likewise, only never users were less curious about higher nicotine content e-cigarettes . In the moist snuff experiment, the direction and magnitude of associations were similar by gender, but there was nominally statistically significant interaction for the outcomes curiosity and danger, as male participants indicated more curiosity about higher price products . Only 44 smokeless tobacco ever users completed the moist snuff experiment, limiting statistical power to detect differences in association by product use. Generally, brand perceptions were stronger among smokeless tobacco ever users. Only never users viewed flavored products as offering less buzz and as easier to use, whereas only ever users associated pouched products as easier to use .This study provides quantitative evidence that specific characteristics of non-cigarette tobacco products independently shape how youth perceive these products. As hypothesized, for both e-cigarettes and moist snuff smokeless tobacco, flavored products were viewed with more curiosity and as being less dangerous, less potent and easier to use compared to non-flavored products. Associations of flavors with greater curiosity and ease of use and less perceived danger held for all non-tobacco flavors, including mint and wintergreen. Thus, evidence from this cross sectional study population suggests that mint varieties should be included alongside fruit and dessert in flavor restrictions intended to reduce youth tobacco use9 . Other product characteristics, such as e-cigarette device type, vapor amount and moist snuff price, also appear to shape product perceptions, which could inform tobacco control policy.

In January 2020, citing concern over growing youth e-cigarette use, the FDA announced a policy to prioritize enforcement of premarket authorization requirements for some types of e-cigarettes, but exempted mint and menthol flavors18. The present results suggest that youth perceive the properties of mint and wintergreen flavored tobacco similarly to fruit, dessert, and other flavors, which could undermine the effectiveness of the FDA policy. No such enforcement policy exists for conventional smokeless tobacco, but the present results demonstrate similar flavor association for moist snuff as observed for e-cigarettes. This finding is consistent with tobacco industry documents suggesting that flavored, lower priced, lower nicotine ‘starter products’ are used to target novice users before later ‘graduation’ to established use through a series of higher nicotine products. Use of flavored tobacco, including menthol, is more common among youth than adults8 and is the predominant way youth and young adults consumed tobacco across all tobacco products. A review of qualitative studies reported that flavored tobacco is viewed favorably by consumers, who associate flavors with less danger and often report that flavors contributed to their own tobacco experimentation and initiation10. Given the evidence that flavors contribute to youth use for all tobacco products8,9, current policies should consider not only restricting all non-tobacco flavors in cigarettes and e-cigarettes but in all forms of tobacco. Pod-type e-cigarettes, such as market-leading brand JUUL, have become the most popular type of e-cigarette among US youth21. Independent of nicotine content and flavor, participants in the present study viewed pod devices with more curiosity and as easier to use than other device types but not necessarily as less dangerous. However, participants also associated low nicotine content e-cigarettes with less danger, more curiosity, and greater ease of use. Research suggests that youth may not recognize that pod-type e-cigarettes contain nicotine at high concentrations; a misperception potentially reinforced by the nicotine amount printed on JUUL product packaging. Prior applications of discrete choice methods in tobacco control have focused on adults and/or recruited participants through online panels. Previously reported findings include a preference for non-tobacco flavors both in e-cigarettes and water pipe tobacco, as well as identifying warning labels as a factor reducing product interest. Consistent with the present study, Shang et al.reported that adolescents least prefer tobacco-flavored e-cigarettes and cigalike closed-system devices. The present study expands such work to moist snuff products, finds e-cigarette vapor cloud size and podtype devices as independent contributors to youth perceptions, and assesses the additional outcomes of perceived danger and ease of use. Furthermore, the present study shows no gender difference regarding e-cigarette perceptions, although beliefs associated with certain moist snuff product attributes were stronger among male participants, likely reflecting higher use and male-targeted marketing. Not all perceived qualities observed in the present study aligned with actual product properties. Participants correctly associated higher nicotine content with stronger physical effects . Other perceptions, such as flavored tobacco or small vapor cloud e-cigarettes being less dangerous, are not supported by scientific consensus. This discordance between perceived and actual effects represents a possible area for corrective public messaging or for greater regulatory vigilance for potentially misleading marketing practices. Of note, and not unexpectedly, product ever users held stronger perceptions about device type and brands than did product naïve participants. In a cross sectional setting, it cannot be distinguished to what extent experience shaped perceptions or that existing attention to product attributes contributed to use initiation.For example, danger could refer to either long-term or short term health effects. Meanwhile, ease of use could refer to concealability, access, adverse reactions, or social acceptance.