Bioavailability of classical and novel flame retardants: Effect of fullerene presence

Effects of novel halogen-free flame-retardant binary additives on thermal stability, degradation kinetics and flame retardancy of cotton cellulose biomacromolecule

The principal component of cotton fibers is the cellulose biological macromolecule. However, its highly flammable nature has significantly constrained its utilization in fields where flame retardancy is essential. Herein, in this work, a highly effective binary composite flame retardant coating (APP/MEL-SWCNHs) with ammonium polyphosphate and modified single-walled carbon nanohorns (MEL-SWCNHs) was chemically attached to cotton fabric. With the add-on of 11.3 %, the treated cotton fabric (APP/MEL-SWCNHs)4 exhibited remarkable flame-retardant and self-extinguishing properties. Its LOI value increased to 23.7 ± 0.1 %, and the damage length was significantly reduced from 30.0 ± 0.1 % cm to 7.9 ± 0.1 % cm compared to the pristine cotton fabric. Despite partial carbonization, (APP/MEL-SWCNHs)4 preserved its original structure. Importantly, in the cone calorimeter test, both the pHRR and THR of (APP/MEL-SWCNHs)4 were drastically decreased by 71.8 % and 35.8 %, respectively. The APP/MEL-SWCNHs coating functioned as a flame retardant by inhibiting the emission of flammable volatiles, releasing non-flammable gases, and encouraging the formation of char layer during combustion. Significantly, thermal degradation kinetic analysis revealed that the third-order kinetic equation (O3) was found to have the strongest correlation with (APP/MEL-SWCNHs)4 in both air and N2 atmospheres. The higher activation energy (E) for (APP/MEL-SWCNHs)4 confirmed that incorporating MEL-SWCNHs improved the thermal stability of the char layer.

Evaluation of the oral bioaccessibility of legacy and emerging brominated flame retardants in indoor dust

Indoor dust is the main source of human exposure to brominated flame retardants (BFRs). In this study, in vitro colon-extended physiologically-based extraction test (CE-PBET) with Tenax as a sorptive sink was applied to evaluate the oral bioaccessibility of twenty-two polybrominated diphenyl ethers (PBDEs) and seven novel BFRs (NBFRs) via indoor dust ingestion. The mean bioaccessibilities of two NBFRs pentabromotoluene (PBT) and 1,2-Bis(2,4,6-tribromophenoxy) ethane (BTBPE) were first proposed, reaching 36.0% and 26.7%, respectively. In order to maintain homeostasis of the gastrointestinal tract, 0.4 g Tenax was added in CE-PEBT, which increased BFRs bioaccessibility by up to a factor of 1.4-1.9. The highest bioaccessibility of legacy PBDEs was tri-BDEs (73.3%), while 2-ethylhexyl-tetrabromo-benzoate (EHTBB), one of penta-BDE alternatives, showed the highest (62.2%) among NBFRs. The influence of food nutrients, liquid to solid (L/S) ratio, and octanol-water partition coefficient (Kow) on bioaccessibility was assessed. The oral bioaccessibility of BFRs increased with existence of protein or carbohydrate while lipid did the opposite. The bioaccessibilities of PBDEs and NBFRs were relatively higher with 200:1 L/S ratio. PBDEs bioaccessibility generally decreased with increasing LogKow. No significant correlation was observed between NBFRs bioaccessibility and LogKow. This study comprehensively evaluated the bioaccessibilities of legacy and emerging BFRs via dust ingestion using Tenax-assisted CE-PBET, and highlighted the significance to fully consider potential influencing factors on BFRs bioaccessibility in further human exposure estimation.

Bioconcentration and bioaccumulation of C60 fullerene and C60 epoxide in biofilms and freshwater snails (Radix sp.)

Fullerenes are carbon nanomaterials that have awaken a strong interest due to their adsorption properties and potential applications in many fields. However, there are some gaps of information about their effects and bioconcentration potential in the aquatic biota. In the present work, freshwater biofilms and snails (Radix sp.) were exposed to fullerene C₆₀ aggregates, at concentrations in the low μg/L order, in mesocosms specifically designed to mimic the conditions of a natural stream. The bioconcentration factors of C₆₀ fullerene and its main transformation product, [6,6]C₆₀O epoxide, were studied to the mentioned organisms employing analyses by liquid chromatography coupled to high-resolution mass spectrometry. Our results show that C₆₀ fullerene and its [6,6]C₆₀O present a low bioconcentration factor (BCF) to biofilms: BCF_C60 = 1.34 ± 0.95 L/kg_dw and BCF_C60O = 1.43 ± 0.72 L/kg_dw. This suggests that the sorption of these aggregates to biota may be less favoured than it would be suggested by its hydrophobic character. According to our model, the surface of fullerene aggregates is saturated with [6,6]C₆₀O molecules, which exposes the polar epoxide moieties in the surface of the aggregates and decreases their affinity to biofilms. In contrast, freshwater snails showed a moderate capacity to actively retain C₆₀ fullerenes in their organism (BAF_C60 = 2670 ± 3070 L/kg_dw; BAF_C60O = 1330 ± 1680 L/kg_dw), probably through ingestion. Our results indicate that the bioaccumulation of these carbon nanomaterials can be hardly estimated using their respective octanol-water partition coefficients, and that their colloidal properties, as well as the feeding strategies of the tested organism, play fundamental roles.

Antagonistic Interactions between Benzo[a]pyrene and Fullerene (C60) in Toxicological Response of Marine Mussels

This study aimed to assess the ecotoxicological effects of the interaction of fullerene (C60) and benzo[a]pyrene (B[a]P) on the marine mussel, Mytilus galloprovincialis. The uptake of nC60, B[a]P and mixtures of nC60 and B[a]P into tissues was confirmed by Gas Chromatography-Mass Spectrometry (GC-MS), Liquid Chromatography-High Resolution Mass Spectrometry (LC-HRMS) and Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Biomarkers of DNA damage as well as proteomics analysis were applied to unravel the interactive effect of B[a]P and C60. Antagonistic responses were observed at the genotoxic and proteomic level. Differentially expressed proteins (DEPs) were only identified in the B[a]P single exposure and the B[a]P mixture exposure groups containing 1 mg/L of C60, the majority of which were downregulated (~52%). No DEPs were identified at any of the concentrations of nC60 (p < 0.05, 1% FDR). Using DEPs identified at a threshold of (p < 0.05; B[a]P and B[a]P mixture with nC60), gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis indicated that these proteins were enriched with a broad spectrum of biological processes and pathways, including those broadly associated with protein processing, cellular processes and environmental information processing. Among those significantly enriched pathways, the ribosome was consistently the top enriched term irrespective of treatment or concentration and plays an important role as the site of biological protein synthesis and translation. Our results demonstrate the complex multi-modal response to environmental stressors in M. galloprovincialis.