In vitro bioaccessibility of emerging flame retardants present in indoor dust using simulated human fluids

Polybrominated diphenyl ethers (PBDEs) are flame retardants (FRs) used as additives against fire ignition accidents, present in everyday consumer products including carpets, electronic appliances, clothing and textiles, thermal insulation and cable coatings. PBDE continuous and excessive use in consumer products, has raised concerns regarding their potential adverse health effects including endocrine and thyroid disruption and neurodevelopmental disorders in children. Hence, legislative restrictions on the production and use of PBDEs in the global market have been imposed by the competent authorities. However, limited data exist on the fate, environmental levels and potential effects on human health of PBDE alternatives such as emerging halogenated FRs (EHFRs), phthalate esters (PEs), non-halogenated phosphorous FRs (PFRs) and alternative plasticisers. Oral bioaccessibility (i.e. uptake) studies have been widely used as a research tool to determine the potential human exposure to ingested contaminants via solid matrices such as indoor dust. Colon Extended ­ Physiologically Based Extraction Test (CE-PBET) is a well-established bioaccessibility protocol specifically developed for the testing of organic compounds, rich in dietary components which act as a “biological sink” for organic pollutants, enhancing thus the sorption capacity of the system. Also, strong adsorbents such as Tenax TA®, silicone-activated contaminant traps, cyclodextrins and silicone rods have also been proposed as “absorption sink” materials. Taken all together, the aim of the PhD studies presented here is two-fold: a) to assess human exposure to legacy and alternatives FRs via indoor dust ingestion and inhalation and b) to develop a robust and unified oral bioaccessibilty method with the inclusion of Tenax TA® as a non-biologically active “infinite sink” to the previously established CE-PBET model. Regarding the in vitro gut bioaccessibility, a novel physical separation of the incubated dust with the Tenax TA was successful by employing a regenerated cellulose (RC) dialysis membrane method. The newly developed system was optimised for Tenax TA® bead loading (i.e. 0.25, 0.5 or 0.75g) and allowed sorption to be studied in the stomach, small intestine and colon compartments. Our results show that sorption on Tenax TA® in the stomach was 43.7% and 25.6% for BDE28 and BDE47 respectively, unlike in the colon compartment which was nearly 50% for BDE154 and BDE183. With Tenax TA® inclusion, gut bioaccessibility reached 40% for BDE153 and BDE183, with greater increases seen for less hydrophobic FRs such as BDE28 and BDE47 (60.6%). The combination of Tenax TA® as an infinite sink together with the lipid-rich colon compartment of CE-PBET act as a substantial advance towards a cost-effective and more realistic estimates of FR uptake via the gut and can liaise regulators to redefine human exposure estimates. We also investigated the presence of PBDEs and alternative FRs such as emerging halogenated FRs (EHFRs) and organophosphate flame retardants (PFRs) in indoor dust samples from British and Norwegian houses as well as British stores and offices. BDE209 was the most abundant PBDE congener with median concentrations of 4,700 ng g-1 and 3,400 ng g-1 in UK occupational and house dust, respectively, 30 and 20 fold higher than in Norwegian house dust. Monomeric PFRs (m-PFRs), including triphenyl phosphate (TPHP), tris(chloropropyl) phosphate (TCPP) and tris(2-chloroethyl) phosphate (TCEP) dominated all the studied environments. This is the first report of isodecyldiphenyl phosphate (iDPP) and trixylenyl phosphate (TXP) in indoor environments. iDPP was the most abundant oligomeric PFR (o-PFR) in all dust samples, with median concentrations one order of magnitude higher than TXP and bisphenol A bis(diphenyl phosphate (BDP). iDPP and TXP worst-case scenario exposures for British workers during an 8h exposure in the occupational environment were equal to 34 and 1.4 ng kg bw-1 day-1 , respectively considerably below the proposed reference values. With respect to inhalation as an alternative route of exposure, this is the first study assessing the in vitro pulmonary uptake of established PEs including dimethyl phthalate (DMP), diethyl phthalate (DEP) and di-(2-ethylhexyl) phthalate (DEHP) and alternative plasticisers used as phthalate substitutes such as bis(2-ethylhexyl) terephthalate (DEHT) and cyclohexane-1,2- dicarboxylic acid diisononyl ester (DINCH) present in indoor dust. Two artificial lung fluids, mimicking two distinctively different interstitial conditions were used, namely artificial lysosomal fluid (ALF, pH=4.5) representing the fluid that inhaled particles would contact after phagocytosis by alveolar and interstitial macrophages within the lung and Gamble’s solution (GMB, pH=7.4) as a fluid for deep lung deposition of dust within the interstitial fluid of the lung. Our results suggest that low molecular weight (MW) and short-chained phthalates such as DMP and DEP are highly bioaccessible (>75%) in both artificial pulmonary media tested, whereas high MW compounds such as DEHP, DINCH and DEHT were <5% bioaccessible. Such findings confirm the hypothesis of hydrophobicity and water solubility primarily influencing inhalation bioaccessibility of organic pollutants. Finally, human exposure to alternative FRs is expected to increase in the future, hence continuous monitoring is required. The in vitro bioaccessibility methods presented in this thesis can thus form the foundation upon which an integrated and robust testing strategy for chemicals of emerging concern can be built

Bioaccessibility of PBDEs present in indoor dust: a novel dialysis membrane method with a Tenax TA® absorption sink

Human uptake of flame retardants (FRs) such as polybrominated diphenyl ethers (PBDEs) via indoor dust ingestion is commonly considered as 100% bioaccessible, leading to potential risk overestimation. Here, we present a novel in vitro colon-extended physiologically-based extraction test (CE-PBET) with Tenax TA® as an absorptive "sink" capable to enhance PBDE gut bioaccessibility. A cellulose-based dialysis membrane (MW cut-off 3.5kDa) with high pH and temperature tolerance was used to encapsulate Tenax TA®, facilitating efficient physical separation between the absorbent and the dust, while minimizing re-absorption of the ingested PBDEs to the dust particles. As a proof of concept, PBDE-spiked indoor dust samples (n=3) were tested under four different conditions; without any Tenax TA® addition (control) and with three different Tenax TA® loadings (i.e. 0.25, 0.5 or 0.75g). Our results show that in order to maintain a constant sorptive gradient for the low MW PBDEs, 0.5g of Tenax TA® are required in CE-PBET. Tenax TA® inclusion (0.5g) resulted in 40% gut bioaccessibility for BDE153 and BDE183, whereas greater bioaccessibility values were seen for less hydrophobic PBDEs such as BDE28 and BDE47 (~60%). When tested using SRM 2585 (n=3), our new Tenax TA® method did not present any statistically significant effect (p>0.05) between non-spiked and PBDE-spiked SRM 2585 treatments. Our study describes an efficient method where due to the sophisticated design, Tenax TA® recovery and subsequent bioaccessibility determination can be simply and reliably achieved

Legacy and alternative flame retardants in Norwegian and UK indoor environment: implications of human exposure via dust ingestion

Indoor dust has been acknowledged as a major source of flame retardants (FRs) and dust ingestion is considered a major route of exposure for humans. In the present study, we investigated the presence of PBDEs and alternative FRs such as emerging halogenated FRs (EHFRs) and organophosphate flame retardants (PFRs) in indoor dust samples from British and Norwegian houses as well as British stores and offices. BDE209 was the most abundant PBDE congener with median concentrations of 4,700 ng g-1 and 3,400 ng g-1 in UK occupational and house dust, respectively, 30 and 20 fold higher than in Norwegian house dust. Monomeric PFRs (m-PFRs), including triphenyl phosphate (TPHP), tris(chloropropyl) phosphate (TCPP) and tris(2-chloroethyl) phosphate (TCEP) dominated all the studied environments. To the best of our knowledge, this is the first report of isodecyldiphenyl phosphate (iDPP) and trixylenyl phosphate (TXP) in indoor environments. iDPP was the most abundant oligomeric PFR (o-PFR) in all dust samples, with median concentrations one order of magnitude higher than TXP and bisphenol A bis(diphenyl phosphate (BDP). iDPP and TXP worst-case scenario exposures for British workers during an 8h exposure in the occupational environment were equal to 34 and 1.4 ng kg bw-1 day-1, respectively. The worst-case scenario for BDE209 estimated exposure for British toddlers (820 ng kg bw-1 day-1) did not exceeded the proposed reference dose (RfD) (7,000 ng kg bw-1 day-1), while exposures for sum of m-PFRs (Σm-PFRs) in British toddlers and adults (17,900 and 785 ng kg bw-1 day-1 respectively) were an order of magnitude higher than for Norwegian toddlers and adults (1,600 and 70 ng kg bw-1 day-1)

In vitro inhalation bioaccessibility of phthalate esters and alternative plasticisers present in indoor dust using artificial lung fluids

Phthalate esters (PEs) are plasticiser additives imparting durability, elasticity and flexibility to consumer products. The low migration stability of PEs along with their ubiquitous character and adverse health effects to humans and especially children has resulted in their classification as major indoor contaminants. This study assesses inhalation exposure to PEs via indoor dust using an in vitro inhalation bioaccessibility test (i.e. uptake) for of dimethyl phthalate (DMP), diethyl phthalate (DEP) and di-(2-ethylhexyl) phthalate (DEHP) and the alternative non phthalate plasticisers bis(2-ethylhexyl) terephthalate (DEHT) and cyclohexane-1,2-dicarboxylic acid diisononyl ester (DINCH), exposure. Using artificial lung fluids, which mimicktwo distinctively different pulmonary environments, namely artificial lysosomal fluid (ALF, pH = 4.5) representing the fluid that inhaled particles would contact after phagocytosis by alveolar and interstitial macrophages within the lung and Gamble’s solution (pH = 7.4), the fluid for deep dust deposition within the pulmonary environment. Low molecular weight (MW) PEs such as DMP and DEP were highly bioaccessible (> 75 %) in both artificial pulmonary media, whereas highly hydrophobic compounds such as DEHP, DINCH and DEHT were < 5 % bioaccessible via the lung. Our findings show that the in vitro pulmonary uptake of PEs is primarily governed by their hydrophobicity and water solubility, highlighting thus the need for the establishment of a unified and biologically relevant inhalation bioaccessibility test format, employed within the risk assessment framework for volatile and semi-volatile organic pollutants

SETAC 2015

<p>Flame retardants (FRs) are man-made chemical compounds widely used in industry during the manufacturing of various commercial products such as computers, plastics, fabrics, textiles and polyurethane foam products in order to minimise or prevent fire. Worldwide phase-out campaigns and legislative restrictions on the use of polybrominated diphenylethers (PBDEs) have resulted in the production of new PBDE-replacement products, also known as emerging FRs (Stapleton et al., 2008).</p> <p>Sampling sites representing three different indoor environments (houses, stores and offices) were selected at the area of Reading (UK) and the area of Oslo (Norway) respectively. N=18 samples of indoor dust were collected from vacuum cleaner bags in houses, stores, offices and libraries in the area of Reading (UK) during August - December 2013. N=10 samples of indoor dust were collected during November 2013-April 2014 from vacuum cleaner bags in houses from the wider area of Oslo (Norway) as a part of a cohort study of N=60 people within the framework of the ‘Advanced Tools for Exposure Assessment and Biomonitoring’ (A-TEAM) project, a Marie Curie Initial Training Network aiming to establish tools for human exposure biomonitoring of emerging FRs.</p> <p>We report levels of emerging FRs in British and Norwegian indoor environments where humans spend eight hours minimum on a daily basis. Preliminary results will be presented on how variability from diverse indoor dust sources such as houses, stores and offices can affect the levels of emerging FRs, as well as to compare the geographical trends of emerging FRs between Norway and the UK.</p

In vitro bioaccessibility of plasticisers present in indoor dust using simulated human lung fluids

SETAC Europe 2016 (Nante, France)<br

Towards a unified approach for the determination of the bioaccessibility of organic pollutants

Bioaccessibility studies have been widely used as a research tool to determine the potential human exposure to ingested contaminants. More recently they have been practically applied for soil borne toxic elements. This paper reviews the application of bioaccessibility tests across a range of organic pollutants and contaminated matrices. Important factors are reported to be: the physiological relevance of the test, the components in the gut media, the size fraction chosen for the test and whether it contains a sorptive sink. The bioaccessibility is also a function of the composition of the matrix (e.g. organic carbon content of soils) and the physico-chemical characteristics of the pollutant under test. Despite the widespread use of these tests, there are a large number of formats used and very few validation studies with animal models. We propose a unified format for a bioaccessibility test for organic pollutants. The robustness of this test should first be confirmed through inter laboratory comparison, then tested in-vivo