Traditional and emerging organophosphate esters (OPEs) in indoor dust of Nanjing, eastern China: Occurrence, human exposure, and risk assessment

Highlights

• Fifteen OPEs were analyzed in n = 50 Chinese indoor dust samples.

• 4-BPDP and TBPP were detected in environments for the first time.

• ΣOPE concentrations were dominated by EHDPP, TPHP, TDCIPP, TCIPP, and TCEP.

• Dust from electronic product maintenance centers contained the highest ΣOPE levels.

• Dust ingestion of OPEs was less than reference dosage values proposed by USEPA.

Abstract

Here, fifteen OPEs were investigated in n = 50 floor dust samples collected from six types of indoor spaces in Nanjing, eastern China, in the year 2018. Ten OPEs, including tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCIPP), tris(1,3-dichloro-isopropyl) phosphate (TDCIPP), tris(2-ethylhexyl) phosphate (TEHP), tris(2-butoxyethyl) phosphate (TBOEP), 2-ethylhexyl-diphenyl phosphate (EHDPP), triphenyl phosphate (TPHP), tris(methyl-phenyl) phosphate (TMPP), 4-biphenylyl diphenyl phosphate (4-BPDP) and tris(2-biphenylyl) phosphate (TBPP), were detected in at least one of the analyzed samples (>method limits of quantification). Regardless of indoor spaces, EHDPP (34% of Σ₈OPEs, mean: 1.43 μg/g) and TDCIPP (19%, 0.81 μg/g) were the ascendant OPEs in indoor floor dust. 4-BPDP and TBPP were detectable in indoor floor dust samples, but at relatively low detection frequencies with 2% and 10%, respectively. Various indoor microenvironments exhibited different pollution characteristics of OPEs. Floor dust collected from electronic product maintenance centers contained the richest OPE contaminants with highest mean Σ₈OPEs concentration of 7.92 μg/g. On the basis of measured Σ₁₀OPEs concentrations in dust sample, we estimated daily intake via floor dust ingestion to be 1.37, 0.75 and 1.24 ng/kg BW/day for electronic engineers, undergraduates, and graduate students under mean-exposure scenario, respectively. Overall, our study reported the occurrence of 4-BPDP and TBPP in environmental samples for the first time, and demonstrated that indoor floor dust ingestion exposure does values were far less than reference dosage values of oral toxicity proposed by United States Environmental Protection Agency (USEPA) Integrated Risk Information System.

Introduction

Organophosphate esters (OPEs) are a class of chemicals containing the basic chemical structure of phosphate esters, which are usually added into commercial materials (such as plastics, rubber, textiles, paper products and building materials) as functional additives (van der Veen and de Boer, 2012). OPEs could be halogenated and halogen-free esters, which can be found in different industrial applications (Wei et al., 2015). Specifically, halogenated OPEs are predominantly used as flame retardants (FRs) to prevent or slow ignition of materials, whereas halogen-free OPEs are primarily used as plasticizers, stabilizers, antifoaming, or wetting agents (Andresen et al., 2004; Marklund et al., 2003). Most of OPEs are physically added into host materials and not chemically bonded to polymer products (Rodriguez et al., 2006), indicating that OPEs are easily released into the environment throughout their lifecycle, i.e. production, use, and disposal (van der Veen and de Boer, 2012). In recent years, OPEs have been receiving even more environmental attention given that several halogenated flame retardants (HFRs) were listed as Persistent Organic Pollutants (POPs) (UNEP, 2017), and that several OPEs have been proposed as chemical substitutes/replacements for these phase-out HFRs (Iqbal et al., 2017).

Previous studies have addressed adverse effects of OPEs, including carcinogenicity (Wei et al., 2015), genotoxicity (Shen et al., 2019; Su et al., 2014), cardiotoxicity (McGee et al., 2013), dermatitis (Camarasa and Serra-Baldrich, 1992; McGee et al., 2013), as well as reproductive toxicity (Camarasa and Serra-Baldrich, 1992; Li et al., 2015). Specifically, tris(2-chloroethyl) phosphate (TCEP) and tris(2-chloroisopropyl) phosphate (TCIPP) exposure might affect the neurological development of zebrafish embryos/larvae though downregulating the expression of selected genes and proteins related to neurodevelopment (e.g., mbp, syn2a, and α1-tubulin) (Li et al., 2019b). What's worse, triphenyl phosphate (TPHP) at environmentally relevant concentrations was recently reported to cause a reduced successful mating rate and decreased fertilization and hatching rates in Japanese Medaka (Oryzias latipes) (Li et al., 2018b), and exposure to environmentally relevant concentrations of tris(1,3-dichloro-isopropyl) phosphate (TDCIPP) caused a time-dependent change on expressions of genes involved in the hormone/insulin-like growth factor (GH/IGF) axis of female zebrafish (Danio rerio) (Zhu et al., 2017). Given the increasing reports on adverse effects from OPEs, it is critical to consistently identify and monitor the occurrence of OPEs in various environmental samples.

OPEs are ubiquitous in various environmental media (Bollmann et al., 2012; Giulivo et al., 2017; Li et al., 2019c; Tao et al., 2016; Wang et al., 2018; Zeng et al., 2014) and biotic matrices (Li et al., 2019a; Ma et al., 2019; She et al., 2013; Sundkvist et al., 2010), potentially posing a serious risk to human health regarding exposure to OPEs in environments. Very recently, Zhang et al. (2019) developed an untargeted screening strategy for analysis of possible organic chemicals currently-used in extracts of smartphone screens, and identified three chemicals that shared exact same backbone structures with aryl OPEs. These three chemicals were tri(2,4-di-t-butylphenyl) phosphate (TDtBPP; CAS No. 95906-11-9), 2-biphenylyl diphenyl phosphate (2-BPDP; 132-29-6), and tris (2-biphenyl) phosphate (TBPP; 132-28-5). However, there is a dearth of information regarding their occurrence in real environmental samples. Venier et al. (2018) recently reported the occurrence of TDtBPP in e-waste dust and its application in foam and fabric samples (Wu et al., 2019); so far, there are no known reports on the environmental occurrence of 2-BPDP and TBPP.

As compared to dietary and inhalation exposures, dust ingestion is proposed as a more important pathway of exposure to flame retardants for humans, given that 1) where people live and work is equipped with lots of furniture and electric/electronic instruments that contain high concentrations of FRs; and 2) FRs could be emitted from the equipment through evaporation or abrasion (de Boer et al., 2016). Organophosphate flame retardants (OPFRs) and replacement brominated flame retardants (RBFRs) were ubiquitous in house dust during the polybrominated diphenyl ether (PBDE) phase-out (Percy et al., 2020), and recent studies have reported extremely high concentrations of OPEs in indoor dust samples (Guan et al., 2019; Tan et al., 2018). For instance, geometric mean concentrations of OPFRs in dust collected from the homes of Cincinnati (USA) between 2003 and 2006 were reported to be 2.14 μg/g (TCIPP), 1.84 μg/g (TDCIPP), 1.07 μg/g (TPHP), and 0.67 μg/g (TCEP), respectively, present at approximately one order of magnitude higher than RBFRs (Percy et al., 2020). Two novel groups of OPEs with analogous structure to TPHP, isopropylated and tertbutylated triarylphosphate ester (ITP and TBTPP) isomers, were detected in 100% of house dust from Guangzhou (China) and Carbondale (America). Although the levels of ΣITPs and ΣTBTPPs were generally ten times than those of TPHP in the same dust samples, the broad occurrences of these isomers in house dust from the two locations likely suggested their wide applications in household consumer products (Guan et al., 2019). Again, there is no information regarding the environmental occurrences and human exposure risks of the newly identified 2-BPDP and TBPP so far. However, the novel OPEs are worthy of attention due to their possibly wide applications.

In this study, in allusion to fifteen target OPEs including tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), TDCIPP, triethyl phosphate (TEP), tripropyl phosphate (TPrP), tributyl phosphate (TNBP), tris(2-ethylhexyl) phosphate (TEHP), tris(2-butoxyethyl) phosphate (TBOEP), 2⁃ethylhexyl diphenyl phosphate (EHDPP), TPHP, tricresyl phosphate (TMPP), 2-biphenylyl diphenyl (2-BPDP), 3-biphenylyl diphenyl phosphate (3-BPDP), 4-biphenylyl diphenyl phosphate (4-BPDP), and tris (2-biphenyl) phosphate (TBPP) were analyzed in n = 50 flood dust samples from Nanjing, eastern China. The specific objectives were described following as 1) to examine whether two newly identified OPEs were detectable in real environments or not; 2) to analyze the concentrations and distributions of all fifteen OPEs in n = 50 floor dust samples collected from six indoor places (including electronic product maintenance center, teaching building, laboratory building, hotel, dormitory and residence) collected from Nanjing, eastern China; 3) to characterize compositional profiles of OPEs in six indoor spaces; and 4) to estimate exposure risks of OPEs via dust ingestion for three categories of crowds.