Study On Human Exposure Pathways And Accumulation Characteristics Of Typical Organophosphate Flame Retardants

Flame retardants are additives applied in various materials to promote the flame retardancy or self-extinguishment. The production and consumption of flame retardants all over the world are only less than plasticizers. Flame retardants pollution in the environment is a hotspot of emerging contamination studies. Organophosphate flame retardants (OPFRs), which have both great properties of flame retardation and plasticization, are currently widely used as additive flame retardants. Due to the restriction and phase-out of brominated flame retardants (BFRs), the market demand for OPFRs as excellent alternatives of BFRs has been rapid increasing. China already becomes a main producer of OPFRs in the world. The consumption is also believed to grow rapidly in China.OPFRs can be solwly released into the environment during production and application. Some OPFRs may be persistent in the environment. As a result, OPFRs havebeen detected in various matrices in the environment and were expected to accumulate in the human body through various pathwayssuch as inhalation and ingestion. OPFRs may cause adverse effects to human health as some of them havebeen identified as neurotoxicants, reproductive toxicants and potential carcinogens. However, the occurrence and distributions of OPFRs in the environment in China are seldom studied as well as their exposure pathway for human. The present study investigated the occurrence of OPFRs in various environmental matricesand in human specimens, estimated the exposure status through different pathways and body burdenof OPFRs, and identified the contributions of major exposure pathways. The major results are as follows. (1) OPFRs were detected in a range of 5.0-147.8 ng/m3 in suspended particulate metter from offices. Tris(chloropropyl)phosphate (TCPP) was the most abundant analog followed by tris(2-chloroethyl) phosphate (TCEP) and triphenyl phosphate (TPhP). Chlorinated OPFRs contributed to about 77% of the total OPFRs.Size-specific distributions revealed that TCEP, TCPP, and tri-n-butylphosphate (TnBP) shared a similar distribution pattern with apeak in the fraction 4.7-5.8 μm.A bimodal distribution was observed for tris(1,3-dichloro-2-propyl) phosphate (TDCPP), TPhP, and tributoxyethyl phosphate(TBOEP). The size-specific distributions of OPFRs were found to be positively correlated with their vapor pressures (Vp) (p< 0.01), indicating that OPFRanalogs with low Vp were inclined to adsorb on small size particles. Average daily doses of OPFRs analogs were estimated in a range of <0.01-0.64 ng/kgbw/day, all well below respective reference doses.The total deposition efficiency of OPFRs in human body wasestimated to be 67.2%.OPFRs mainly deposit in the head region of therespiratory tract.(2) The concentrations of OPFRs in the dust from classrooms were in a range of 805.7-3191.6 ng/g. TCEP, TCPP, TPhP and TDCPP with comparable levels were identified as major analogs. No specific accumulation characteristics were found in dust. However, OPFRs analogs with low Vp (e.g. TDCPP and TPhP) were more difficult to migrate to the indoor air. The intake dose of OPFRs via dust ingestion was about 38.1 ng/day, with all analogs well below respective reference doses.(3) The median concentrationsof OPFRs were determined to be 3.99,4.50,27.6, 59.2 and 192 ng/L in the bottled, well, barreled, filtered and tap waters, respectively. Triethyl phosphate (TEP) was the most abundant OPE in the tap water and filtered drinking water with median concentrations of 50.2 and 30.2 ng/L, respectively. Moreover, TCPP and TCEP were identified as major analogs in all drinking water types. The calculated average daily doses of OPEs ranged from 0.14 to 7.07 ng/kg bw/day for peopleconsuming the five different types of drinking water. Among the drinking water, the tap water exhibited the highest exposure doses of OPEs.The risks of OPFRs exposure via drinking water were at very low levels.(4) The concentrations of OPFRs in different food materials were in a range of 1134-9559 pg/g fresh weight (fw). Tris(2-ethylhexyl) phosphate (TEHP) was the most abundant analog in food stuffs with a median of 1286 pg/g fw, followed by TBOEP and TCEP. The dietary intake of OPFRs for urban residents was estimated as 3577.5 ng/day. Cereals consist of 55% of the total exposure and were the largest contributor of dietary intake of OPFRs, followed by vegetables and animal products. The risks of OPFRs exposureof dietary intake were at low level.(5) The concentrations of the 9 most frequently detected OPFRs ranged from 34.4 to 862 ng/g lipid weight (1w) in human placentas, with a median of 301 ng/g lw. TCEP was identifiedas the most abundant analog, with a median concentration of 142 ng/g 1w, followed by TBOEP and TPhP. Statistical analysis showed the concentrations of OPEs and EOPFRs was not positively correlated with the lipid content of the placentas. There were no correlations observed between the OPE concentrations and maternal characteristics except that TPhP and TnBP were significantly higher in mothers from E-waste recycling site adjacent area. Food consumption habits exhibited weak effects on OPE levels in the placentas.(6) Urinary metabolites severd as good biomarkers of internal body burdens of OPFRs and represent a comprehensive exposure status of all routes. It revealed that the OPFRs exposure in school time seemed various but widespread to adolescent students. TDCPP was the most abundant analog of OPFRs internal body burden with a ceratinine adjusted median level of 5.24 ng/mg creatinine, followed by TnBP and TCPP. Dust ingestion, inhalation and dietary intake were identified as three major sources of OPFRs internal body burden with contributions of 42.8%,29.3% and 27.8%, respectively. The neglect of bio-availabilities of OPFRs residuals in different exposure matrices would result in great misestimation in exposure assessment through various pathways.