Novel and Traditional Organophosphate Esters in House Dust from

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Novel and Traditional Organophosphate Esters in House Dust from South China: Association with Hand Wipes and Exposure Estimation Hongli Tan, Da Chen, Changfeng Peng, Xiaotu Liu, Yan Wu, Xue Li, Rui Du, Bin Wang, YING GUO, and Eddy Y. Zeng Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b02933 • Publication Date (Web): 10 Sep 2018 Downloaded from http://pubs.acs.org on September 10, 2018

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Environmental Science & Technology

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Novel and Traditional Organophosphate Esters in House Dust from South China:

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Association with Hand Wipes and Exposure Estimation

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Hongli Tan, † Da Chen, †,* Changfeng Peng, † Xiaotu Liu, † Yan Wu, ‡ Xue Li, § Rui Du, § Bin

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Wang, ||,⊥ Ying Guo, † Eddy Y. Zeng †

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†

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Jinan University, Guangzhou, 510632, China

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‡

School of Environment, Guangdong Key Laboratory of Environmental Pollution and Health,

Cooperative Wildlife Research Laboratory and Department of Zoology, Southern Illinois

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University, Carbondale, 62901, USA

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§

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510632, China

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||

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Health, National Health and Family Planning Commission of the People’s Republic of China,

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Beijing 100191, China

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⊥ Department

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Beijing 100191, China

Institute of Mass Spectrometer and Atmospheric Environment, Jinan University, Guangzhou,

Institute of Reproductive and Child Health, Peking University; Key Laboratory of Reproductive

of Epidemiology and Biostatistics, School of Public Health, Peking University,

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*Corresponding author: Da Chen. E-mail: [email protected]; Phone: +011-86-20-85220949;

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Fax: +011-86-20-85226615.

ACS Paragon Plus Environment

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Abstract. The present study investigated the occurrence of 20 organophosphate esters (OPEs) in

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house dust from 51 South China homes and the risks of human exposure to OPEs via two

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pathways: dust ingestion and hand-to-mouth contact. In addition to several traditional OPEs, five

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out of six novel OPEs, including bisphenol A bis(deiphenyl phosphate) (BPA-BDPP), t-

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butylphenyl diphenyl phosphate (BPDPP), cresyl diphenyl phosphate (CDP), isodecyl diphenyl

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phosphate (IDDPP), and resorcinol-bis(diphenyl)phosphate (RDP), were frequently detected in

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house dust (median concentration: 59.7 – 531 ng/g). Eight out of the 20 target OPEs were

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frequently detected in hand wipes collected from adults and children (n = 51 and 31,

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respectively), which in combination (referred to as Σ8OPEs) had a median mass of 76.9 and 58.9

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ng, respectively. Increasing dust concentrations of Σ8OPEs or three individual substances among

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these eight OPEs, including tris(1-chloro-2-propyl) phosphate (TCIPP), tris(1,3-dichloro-2-

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propyl) phosphate (TDCIPP), and triphenyl phosphate (TPHP), were strongly associated with

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their levels in children’s hand wipes (p < 0.05 in all cases). By contrast, in adults’ hand wipes

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only TPHP exhibited a marginally significant association with dust concentrations (p = 0.04).

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Levels of Σ8OPEs in hand wipes from children, but not adults, were inversely influenced by hand

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washing frequency (p = 0.002), while indoor temperature was inversely associated with hand

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wipe levels of Σ8OPEs from both children and adults (p = 0.01 and 0.002, respectively).

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Exposure estimation suggests that hand-to-mouth contact represents another important pathway

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in addition to dust ingestion and that children are subjected to elevated OPE exposure than adults.

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TOC Art

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INTRODUCTION

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Organophosphate esters (OPEs) represent a group of halogenated and non-halogenated

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compounds sharing a tri-ester structure. They are broadly used as flame retardants in a variety of

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commercial products, including foams, plastics, textile, furniture, and many others.1,2 Some

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OPEs are also used as plasticizers, stabilizers, antifoaming and wetting agents, and as additives

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in hydraulic fluids and lubricants.3 Typical halogenated OPEs include tris(2-chloroethyl)

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phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), tris(1,3-dichloro-2-propyl)

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phosphate (TDCIPP), and tris(2,3-dibromopropyl) phosphate (TDBPP). Additional non-

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halogenated OPEs include tris(2-butoxyethyl) phosphate (TBOEP), tributyl phosphate (TNBP),

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tris(2-ethylhexyl) phosphate (TEHP), triphenyl phosphate (TPHP), tris(3,5-dimethylphenyl)

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phosphate (T35DMPP), tris(2-isopropylphenyl) phosphate (T2IPPP), and 2-ethylhexyl-diphenyl

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phosphate (EHDPHP). A few OPEs (e.g., TDCIPP and TPHP) were listed as High Production

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Volume (HPV) chemicals, although in many regions their contemporary production volumes are

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not well documented.2 Their market demands are expected to be increasing in the past decade,

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following

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hexabromocyclododecane (HBCDD) flame retardants in Europe and the United States (U.S.).

the

discontinuation

of

polybrominated

diphenyl

ether

(PBDE)

and

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In addition to the well-known OPEs listed above, several “novel” OPEs were recently

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identified with commercial applications. These include bisphenol A bis(diphenyl phosphate)

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(BPA-BDPP), t-butylphenyl diphenyl phosphate (BPDPP), cresyl diphenyl phosphate (CDP),

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isodecyl diphenyl phosphate (IDDPP), and resorcinol-bis(diphenyl)phosphate (RDP), which are

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all structurally based on that of TPHP, as well as tetrakis(2-chloroethyl)dichloroisopentyl

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diphosphate (V6). Some new OPEs may be subject to increasing production to replace the

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relevant traditional chemicals that have already attracted mounting environmental and health


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concerns. However, investigations on their environmental occurrences, fate, and human exposure

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risks remain overall limited.4-9

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Various studies have reported the occurrences of traditional OPEs in indoor

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environments.10-24 Mean or median concentrations of total OPEs were reported to range from 0.2

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to 1610 µg/g in in indoor dust from different countries, revealing large variations between

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regions and country-specific contamination profiles.10-24 Dust-associated OPEs represent a

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considerable risk to humans, as they can enter the body via absorption through the skin,

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inadvertent ingestion from hand-to-mouth contact, or inhalation of resuspended dust particles.25

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Reported associations of dust concentrations of TDCIPP and TPHP with their metabolites in

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urine or serum implicate the contribution of dust intake to human exposure to these two OPEs.26-

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with altered hormone levels or decreased sperm concentrations in men.30,31

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associations have not been shown for many other OPEs, suggesting that additional measures

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other than dust concentrations may be stronger indicators for internal exposure.

Meeker et al. also reported associations of TDCIPP and TPHP concentrations in house dust However, the

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The occurrence of novel OPEs in indoor environment and associated human exposure

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risks are not sufficiently investigated. Data are also limited in the simultaneous estimation of

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OPE exposure risks for children and adults from both dust ingestion and hand-to-mouth contact.

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Children may be subjected to elevated indoor exposure than adults as they spend more time in

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home environments and have a higher frequency of hand-to-mouth contact indoors than

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outdoors.32 Therefore, in the present study we investigated the occurrence of 20 OPEs in South

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China house dust and their presence on children and adult hands. Specific objectives were to: (1)

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evaluate the concentrations of six novel OPEs (i.e., BPA-BDPP, BPDPP, CDP, IDDPP, RDP,

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and V6) in house dust and their relative abundances to other OPEs; (2) investigate the types and


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levels of OPEs on adults’ and children’s hands via hand wipe sampling and the predictors of

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continuous OPE levels in hand wipes; and (3) estimate and compare exposure risks via dust

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ingestion and hand-to-mouth contact for adults and children. Hand wipes have been

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demonstrated as an exposure assessment more comprehensive than just the indoor

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environment.8,28,33 Our work contributes to a more in-depth evaluation of indoor OPE

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contamination and related human exposure risks.

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MATERIALS AND METHODS

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Participant Recruitment. A total of 51 families from the city of Guangzhou (South China)

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voluntarily participated in this study from September 2015 to July 2016. These families were

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recruited through verbal spread and social media. The main recruitment criteria include: (1)

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living in the present home for more than one year; (2) only one family recruited from each

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building if the building contains multiple homes; (3) adults’ occupations not directly involved in

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the manufacturing of flame retardants or flame retardant-related products; and (4) adults from

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any two families not working in the same workplaces. To understand hand-to-mouth exposure,

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one adult from each participating family was recruited for hand wipe sampling. Thirty one out of

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the 51 families had at least one child aged 1 – 5 years old. One child from each of these 31

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families was also recruited for hand wipe sampling. Participants were requested not to wash their

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hands during at least two hours prior to hand wipe sampling. Study participants gave informed

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consent before providing samples or personal information and were requested to complete a

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short questionnaire. The questionnaires for children were completed by or with the help from

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their parents. The questionnaire was designed to collect data on age, sex, height, weight,

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occupation (for adults only), dwelling size, the number of electronic equipment in homes, hand


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washing frequency, and hours per day spent in homes. Hand washing frequency was recorded as

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0, 1-2, 3-4, 5-6, 7-8, 9-10, and >10 times/day. Indoor temperature and humidity were also

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recorded by investigators during home visit. Our study was approved by the Institutional Review

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Board of Jinan University. Table S1 in Supporting Information summarizes the characteristics of

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study populations and home environment.

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Sample Collection. A customized nylon bag with a pore size of approximately 25 µm

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was pre-cleaned with acetone. It was attached to the floor attachment of a commercial vacuum

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cleaner (Electrolux, ZMO1511, 1400 W) prior to dust collection.21 After the floors of each

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dwelling’s living room and bedrooms were vacuumed, the nylon bag was detached and wrapped

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with clean aluminum foil. Hand wipes were collected during home visit for dust sampling. Each

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participant had both hands wiped with pre-cleaned sterile gauze pads on the palm and back of the

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hand from wrist to fingertips.33 The gauze pads were pre-cleaned by sonication with high

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performance liquid chromatography (HPLC) grade isopropyl alcohol (repeated three times) and

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then soaked in isopropyl alcohol prior to use. The collected hand wipes were wrapped with pre-

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cleaned aluminum foil and kept in clean glass jars. Pre-cleaned gauze pads and sodium sulfate

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were used as field blanks for hand wipe and dust collection, respectively. Field blank wipes were

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prepared by wrapping the soaked hand wipe with aluminum foil and then placing into a glass jar.

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Field blanks for dust collection were prepared by vacuuming pre-cleaned sodium sulfate and

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then storing the nylon bag in the same way as used for dust collection. A field blank of each kind

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was prepared for every five homes. Dust was removed from the nylon bag and sieved through a

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125-µm stainless cloth sieve (Hogentogler & Co., Inc., Columbia, MD). Sieved dust, hand wipes,

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and field blanks were stored at -20 ºC prior to chemical analysis.


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Chemical Analysis. A total of 20 OPEs were determined in the present study, including

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six novel OPEs (i.e., BPA-BDPP, BPDPP, CDP, IDDPP, RDP, and V6) and 14 traditional OPEs,

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including EHDPHP, TBOEP, TNBP, TCEP, TCIPP, TDCIPP, TPHP, tricresyl phosphate

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(TMPP), TDBPP, triethyl phosphate (TEP), TEHP, tripropyl phosphate (TPP), T2IPPP, and

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T35DMPP (Table S2). Detailed procedures of sample pretreatment and instrumental analysis are

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provided in Supporting Information. In brief, approximately 20 – 50 mg of sieved dust or the

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entire hand wipe sample was transferred to a glass tube, spiked with surrogate standards (i.e.,

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d27-TNBP, d12-TCEP, d15-TDCIPP, d15-TEP, d15-TPHP, and tris(2-butoxy-[13C2]-ethyl)

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phosphate), and extracted with 5 mL of a mixture of hexane and dichloromethane (1:1, v/v)

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under sonication. Extraction was repeated three times (5 min each) and the combined extract was

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cleaned through a Florisil solid phase extraction (SPE) cartridge. The final extract was spiked

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with

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quadrupole mass spectrometry (AB Sciex; Toronto, Canada).

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C18-TPHP and determined on an Agilent 1260 HPLC coupled to a 3200 Q Trap triple

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An analyte with a response below the instrumental detection limit (IDL; a response three

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times the standard deviation of the noise) was considered non-detectable (nd). The limit of

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quantification (LOQ), defined as an analyte response 10 times the standard deviation of the

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noise, ranged from 2 to 14 ng/g dry weight (dw) for dust analysis and 0.1 – 1.2 ng for hand wipe

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analysis. To confirm the presence of BPA-BDPP, CDP, and RDP, dust composite extract was

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analyzed on ultra HPLC-high resolution MS and the results are provided in Supporting

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Information (Tables S3-S4; Figure S1).

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To ensure data quality, a number of quality assurance and control (QA/QC) procedures

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were undertaken, which included the evaluation of background contamination in field blanks and


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laboratory procedural blanks, the recoveries of target analytes in spiking experiments, and the

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recoveries of surrogate standards in authentic samples. Detailed description of QA/QC practices

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and the resulting data are summarized in Supporting Information.

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Exposure Assessment. Our study investigated human exposure risks from two

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approaches: dust ingestion (EDI) and hand-to-mouth contact (EHTM).

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exposure to OPEs via indoor dust ingestion was determined using the following equation:10,34

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‫ܧ‬஽ூ =

஽ூோ×஼×ூாி

The estimated daily

(Eq. 1)

஻ௐ

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Where EDI is the estimated daily exposure via dust ingestion (ng/kg body weight/day), C is the

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concentration of a FR chemical in house dust (ng/g), IEF is the indoor exposure fraction (hours

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spent over a day in homes), DIR is the dust ingestion rate (g/day), and BW is body weight (kg).

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Exposure via hand-to-mouth contact was estimated using the below equation:35

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‫ܧ‬ு்ெ =

ெೞೠೝ೑ ×்ா×ௌ஺஼×ாி ஻ௐ

(Eq. 2)

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Where EHTM represents estimated exposure via hand-to-mouth contact (ng/kg bw/day), Msurf is

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the mass of a chemical on the hands (ng), TE is transfer efficiency (%; i.e., fraction of the mass

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of a chemical transferred at each contact), SAC is the proportion of the hand area contacted each

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time (%), and EF is the frequency of contact during a day (day-1).

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Data Analysis. Reported levels of OPEs were corrected based on the recoveries of

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relevant surrogate standards and expressed as ng/g dw in dust or ng in hand wipes. A half LOQ

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was assigned for statistical analyses if a measurement was below LOQ. The Kolmogorov-

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Smirnov test was used to determine whether dust or hand wipe levels followed a normal

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distribution. Non-normally distributed data were subjected to logarithmical transformation (base-


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10) to approximate a normal distribution prior to statistical analyses. Given that the number of

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hand wipe samples differed between adults and children, we used both Independent-Samples T

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Test to determine the difference in hand wipe OPE levels between adults (n = 51) and children (n

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= 31) and Paired-Samples T Test for matched adult and children hand wipes from the same

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homes (n = 31 each). Spearman’s correlation analyses were used to determine the correlations of

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OPE levels between house dust and hand wipes. Linear regression models were employed to

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determine predictors of continuous OPE levels in hand wipes for adults and children separately.28

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The beta coefficients were exponentiated to produce the multiplicative change in hand wipe

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levels relative to the reference group for categorical variables or the per-unit change for

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continuous variables (age only in the present study).28 Dust concentrations were categorized into

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tertiles as predictors of OPE levels in hand wipes, while other categorical variables (i.e., sex,

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hand washing frequency, hours per day spent in homes, dwelling size, indoor temperature,

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indoor humidity, and the number of electronic equipment in homes) were dichotomized.

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Statistical analyses were conducted using PASW Statistics 18.0 (IBM Inc.). The level of

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significance was set at α = 0.05.

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RESULTS AND DISCUSSION

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Concentrations and Compositions of OPEs in Indoor Dust. In addition to the 10 traditional

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OPEs (i.e., EHDPHP, TNBP, TBOEP, TMPP, TCEP, TCIPP, TDCIPP, TEP, TEHP, and TPHP),

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five novel OPEs of interest (i.e., BPA-BDPP, BPDPP, CDP, IDDPP, and RDP) were also

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frequently detected (detection frequency = 77 – 100%) in South China house dust (Table 1). V6

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was only detected in 8% of the samples. The total concentrations of these six novel OPEs ranged

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from 142 – 16,550 ng/g (median: 1,230 ng/g) in house dust (Table 1), constituting an average of


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19% of the total concentrations of all detected OPEs and even comparable with PBDEs

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concentrations previously reported in South China house dust (median: 820 ng/g; range: 215 –

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27,950 ng/g).21 Our data indicate broad applications of these novel OPEs in Chinese household

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products and subsequent releases to home environments in considerable amounts.

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Dust data remain limited for these six novel OPEs (i.e., BPA-BDPP, BPDPP, CDP,

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IDDPP, RDP, and V6). The concentrations and relative abundances of individual novel OPEs

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varied greatly between studies (Table S5).5,6,36,37 BPA-BDPP dominated over other novel OPEs

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in South China house dust, where its concentrations were generally one order of magnitude

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higher than those reported elsewhere (Table S5). By contrast, IDDPP was more abundant than

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other novel OPEs in Norwegian and United Kingdom (UK) house dust. The median

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concentrations of BPA-BDPP, RDP, IDDPP, and V6 were determined to be 35.4, 25 ºC vs. ≤ 25 ºC) was

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inversely associated with Σ8OPEs in both children’s and adults’ hand wipes (10β = 0.49; 95% CI:

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0.29, 0.83 and 10β = 0.43; 95% CI: 0.26, 0.70, respectively), whereas indoor humidity did not

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affect (Table S6). The influence of indoor temperature on hand wipe Σ8OPEs levels was even

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more significant for adults than children (p = 0.002 vs. p = 0.01). Indoor temperature was also

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inversely associated with the levels of TNBP, TEHP, and EHDPHP in adults’ hand wipes and

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TCIPP and TEHP levels in children’s hand wipes. These associations may be due to overall

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greater dust concentrations of OPEs in lower versus higher temperature environment,


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consequently leading to greater levels on hands under lower temperatures. Although our data did

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not reveal an association of lower temperatures with higher dust concentrations (p = 0.20), Cao

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et al. reported seasonal variations of OPEs in indoor dust (i.e., greater concentrations in late

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winter and early spring versus summer).47 Therefore, our results imply that exposure from hand-

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to-mouth contact may be more significant under cooler indoor environments. It is noteworthy

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that two recent studies have shown increased urinary metabolite concentrations of selected OPEs

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(e.g., TDCIPP and TPHP) in the summer compared to winter months, likely suggesting increased

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exposure with temperature.48,49 The underlying factors resulting in these different findings

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remain unknown, but it may suggest that increased exposure via pathways other than hand-to-

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mouth contact or dust ingestion likely occur during warmer periods. For example, seasonal

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fluctuations in outdoor urban air concentrations have been reported for TCEP, TCIPP, TDCIPP,

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TPHP, and TNBP, with increased concentrations during the warmer periods.50 Inhalation in

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outdoor or other microenvironments may constitute an important contribution to internal

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exposure during warm periods.50 Therefore, the prevalent exposure pathways driving OPE

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exposure may be season- or temperature-dependent, which merits future investigations.

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None of the other considered demographic or environmental factors, including age, sex,

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hours/day spent in homes, dwelling size, and the number of electronic equipment, was associated

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with hand wipe Σ8OPEs levels (Tables S6 and S7). The age influence on children’s hand-to-

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mouth behavior is not well studied. A meta-analysis of children’s hand-to-mouth behavioral data

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suggested that both indoor and outdoor hand-to-mouth frequencies decrease as age increases

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from 3 months to

Novel and Traditional Organophosphate Esters in House Dust from

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