Environ. Sci. Technol. 2008, 42, 9453–9454
Comment on “Alternate and New Brominated Flame Retardants Detected in U.S. House Dust” Stapleton et al. (1) reported levels of nonpolybrominated diphenyl ether and brominated flame retardants (BFRs) in dust and concluded “...children living in homes where the dust levels of these BFRs are >90th percentile may be receiving significant exposures.” Herein, we provide an evaluation of the “significant exposures” to which Stapleton et al. (1) refer. Further, we place the reported values into context from a toxicology and risk assessment standpoint. The highest value reported by Stapleton et al. (1) was for hexabromocyclododecane (HBCD) at 130,200 ng/g of dust (Table 1, column 3). Though not mentioned by the authors, the United States (U.S.) National Academy of Sciences (NAS) calculated a reference dose (RfD) for HBCD of 200,000 ng/ kg-day (2). Note that an RfD is defined as follows: “[a]n estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime” (3). Therefore, using the NAS RfD, a 15-kg child may consume up to 3,000,000 ng/day of HBCD without an appreciable risk. This value equates to a 15-kg child consuming about 23 grams per day of the dust with the highest reported level of HBCD (i.e., 130,200 ng/g dust). Obviously, this value is far in excess of any level of dust that a child may consume in a single day; however, the U.S. Environmental Protection Agency (EPA) has published recommended soil ingestion values for children that may be used as surrogates for dust ingestion, given that inhaled dust will ultimately be expectorated or ingested. EPA recommends using a soil ingestion value of 100 mg/ day for children, as well as a conservative estimate of 200
mg/day (4). Using the EPA’s conservative soil ingestion estimate, the daily dose of ingested dust for a 15-kg child was calculated for each compound (Table 1, column 4) based on the levels reported by Stapleton et al. (1). A comparison of the NAS RfD for HBCD (Table 1, column 5) with the highest level (i.e., 26,040 ng/day) reported by Stapleton et al. (1) showed that the latter levels are 115 times lower than the NAS RfD. For the BFRs for which formal RfDs have not been issued, surrogate values were used based on the structural comparisons made by Stapleton et al. (1) (5) [i.e, bis(2-ethylhexyl)phthalate (DEHP) for bis(2-ethylhexyl) 3,4,5,6-tetrabromophthalate (TBPH) and 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB)] or highly conservative estimates were calculated [e.g., applying a composite uncertainty factor (UF) of 3,000 to the lowest reported no-observed-adverse-effect level (NOAEL)]. As shown for DEHP (TBPH and TBB), the EPA’s Integrated Risk Information System (IRIS) published an RfD of 20,000 ng/kg-day (6). Thus using the EPA’s conservative soil ingestion estimate, Stapleton et al.’s (1) highest reported values for TBPH and TBB are 141 and 99 times lower, respectively, than the IRIS RfD for DEHP. Similar evaluations do not indicate risk for 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), and decabromodiphenyl ethane (DBDPE) at the levels reported by Stapleton et al. (1) (Table 1). Though not the primary focus of this comment, we take issue with Stapleton et al.’s (1) statement that “[l]ittle information is available regarding the exposure and potential toxicity of these compounds to humans and wildlife; such data are needed given their presence and log-normal distribution in indoor dust” (1). For HBCD, the NAS reported “...the subcommittee concludes that no further research is needed for assessing health risks from HBCD” (2). This conclusion was made after the subcommittee evaluated the extensive toxicology database that exists for this compound
TABLE 1. Estimated Daily Dose of BFRs for a 15-kg Child Based on Stapleton et al.’s (1) Findings Compared to oral RfDs daily dose for a 15-kg child (ng/day) BFR levels in dust (ng/g), as reported in Stapleton et al. (1)
BFR
at dust levels reported by Stapleton et al. (1)a
at the RfD
HBCD
median range
230
