Organophosphate esters in the Australian environment: sources, fate, and human exposure

Abstract

There is growing concern regarding the use of organophosphate esters (OPEs) due to their suspected reproductive toxicity, carcinogenicity and neurotoxicity. OPEs are used as flame retardants and plasticizers, and due to their extensive application in consumer products, are found globally in the environment. The exposure pathways however, are mostly limited to dermal contact with dust, with little available data on intake via inhalation and diet. This study aims to assess the sources, fate and exposure to OPEs in the Australian population by analyzing the levels of OPEs (and their metabolites) in dust, air, food, and human urine samples.The production and associated use of OPEs have increased in the last two decades, mainly for use as an alternative to some of the brominated flame retardants that have been regulated and phased out, such as polybrominated diphenyl ethers (PBDEs). To investigate the levels of OPEs in the environment, the first task in this study was to develop a method to analyze OPEs and PBDEs in indoor dust, as dermal contact with dust is considered an important pathway for these chemicals. In Chapter 2, we develop a multi-residue method using a two-step SPE sample purification. This enabled us to effectively limit co-extracted matrix/interferences, and therefore simultaneously analyse OPEs and PBDEs in indoor dust.Based on the established method, in Chapter 3 we measured the concentrations of nine OPEs and eight PBDEs in samples of indoor dust and air from Australian houses, offices, hotels and transportation vehicles (bus, train and aircraft). All target compounds were detected in indoor dust and air samples. Median ∑9OPEs concentrations were 40 µg/g in dust and 44 ng/m3 in indoor air, while median ∑8PBDEs concentrations were 2.1 µg/g and 0.049 ng/m3. Concentrations of OPEs and PBDEs were higher in rooms that contained carpet, air conditioners and various electronic items. Daily intakes in adults were estimated to be 14000 pg/kg body weight/day and 330 pg/kg body weight/day for ∑9OPEs and ∑8PBDEs, respectively. Our results suggest that for the volatile FRs such as tris(2-chloroethyl) phosphate (TCEP) and tris (2-chloroisopropyl) phosphate (TCIPP), inhalation is the more important intake pathway compared to dust ingestion and dermal contact.Chapter 4 and 5 focus on internal exposure of OPEs in children in Australia using urinary concentrations of OPE metabolites. The age trends and potential contribution from breastfeeding were investigated in Chapter 4. Concentrations of TCEP, bis(2-chloroethyl) phosphate (BCEP), tris(2-ethylhexyl) phosphate (TEHP), and dibutyl phosphate (DBP) decreased with age, while bis(methylphenyl) phosphate (BMPP) increased with age. The estimated daily intakes via breastfeeding, were 4.6, 26 and 76 ng/kg/day for TCEP, TBP, and TEHP, respectively, and were higher than that via air and dust.We further assessed the influence of personal behavioral and environmental risk factors to urinary concentrations of OPEs and OPE metabolites in Chapter 5, where individual urine samples were collected from 51 children in Australia, aged 3 to 29 months. In multivariable modeling, age was positively associated with concentrations of bis(2-butoxyethyl) phosphate (BBOEP) and negatively associated with concentrations of bis(1-chloroisopropyl) phosphate (BCIPP) and 1-hydroxy-2-propyl bis(1-chloro-2-propyl) phosphate (BCIPHIPP). Other non-age related factors, including vacuuming frequency, hand-washing frequency and presence and numbers of some electrical appliances in the home were also associated with concentrations of OPE metabolites.In Chapter 6, levels of OPEs and their metabolites were measured in food samples purchased in Australian supermarkets. Four parent OPEs and eight metabolites were detected in > 50% of samples. The highest concentrations were found in cereal products. Based on the levels of OPEs in food, air and dust, the estimated daily intake of the Australian population was 32 ng/kg body weight. Diet was the dominant pathway for TBP, TCEP, and TCIPP, while dermal absorption provided the highest contribution of the other OPEs (TDCIPP, TPhP, EHDPP, TMPP, TBOEP, and TEHP). Furthermore, our results suggested that the direct intake of OPE metabolites from food was an important pathway for OPE exposure. For all target chemicals, except for BCEP/TCEP, the average concentration of OPE metabolites was higher than that of their parents across all categories.