Biological effects of new-generation dialkyl phosphinate flame retardants and their hydrolysates in BALB/C mice

Comparative Assessment of the Toxicity of Brominated and Halogen-Free Flame Retardants to Zebrafish in Terms of Tail Coiling Activity, Biomarkers, and Locomotor Activity

BDE-47, a flame retardant that is frequently detected in environmental compartments and human tissues, has been associated with various toxic effects. In turn, information about the effects of aluminum diethyl-phosphinate (ALPI), a halogen-free flame retardant from a newer generation, is limited. This study aims to assess and compare the toxicity of BDE-47 and ALPI to zebrafish by analyzing the tail coiling, locomotor, acetylcholinesterase activities, and oxidative stress biomarkers. At 3000 µg/L BDE-47, the coiling frequency increased at 26-27 h post-fertilization (hpf), but the burst activity (%) and mean burst duration (s) did not change significantly. Here, we considered that the increased coiling frequency is a slight neurotoxic effect because locomotor activity was impaired at 144 hpf and 300 µg/L BDE-47. Moreover, we hypothesized that oxidative stress could be involved in the BDE-47 toxicity mechanisms. In contrast, only at 30,000 µg/L did ALPI increase the catalase activity, while the motor behavior during different developmental stages remained unaffected. On the basis of these findings, BDE-47 is more toxic than ALPI.

Flame Retardants-Mediated Interferon Signaling in the Pathogenesis of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a growing concern worldwide, affecting 25% of the global population. NAFLD is a multifactorial disease with a broad spectrum of pathology includes steatosis, which gradually progresses to a more severe condition such as nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and eventually leads to hepatic cancer. Several risk factors, including exposure to environmental toxicants, are involved in the development and progression of NAFLD. Environmental factors may promote the development and progression of NAFLD by various biological alterations, including mitochondrial dysfunction, reactive oxygen species production, nuclear receptors dysregulation, and interference in inflammatory and immune-mediated signaling. Moreover, environmental contaminants can influence immune responses by impairing the immune system’s components and, ultimately, disease susceptibility. Flame retardants (FRs) are anthropogenic chemicals or mixtures that are being used to inhibit or delay the spread of fire. FRs have been employed in several household and outdoor products; therefore, human exposure is unavoidable. In this review, we summarized the potential mechanisms of FRs-associated immune and inflammatory signaling and their possible contribution to the development and progression of NAFLD, with an emphasis on FRs-mediated interferon signaling. Knowledge gaps are identified, and emerging pharmacotherapeutic molecules targeting the immune and inflammatory signaling for NAFLD are also discussed.

A comparison of developmental toxicity of brominated and halogen-free flame retardant on zebrafish

Brominated diphenyl ethers (BDEs) are halogenated flame retardants. Several concerns related to persistence and toxicity of BDEs have been resulted in a growing need of BDEs replacement. The use of halogen-free flame retardants (HFFR) has increased as a safer alternative, but little information is available on their toxic potential for environmental health and for developing organisms. Therefore, the aim of this study was to evaluate and compare the toxicity of three congeners of BDEs (BDE-47, BDE-99 and BDE-154) with an HFFR (aluminum diethylphosphinate, ALPI) on zebrafish (Danio rerio) by assessing endpoints of lethality, sub-lethality and teratogenicity at the earlier stages of development. The highest tested concentration of BDE-47 (12.1 mg/L) induced pericardium and yolk sac edemas that first appeared at 48 h post-fertilization (hpf) and then were mostly reabsorbed until 144 hpf. BDE-47 also showed a slight but non-significant tendency to affect swim bladder inflation. The rate of edemas increased in a concentration-dependent manner after exposure to BDE-99, but there were no significant differences. In addition, the congener BDE-99 also presented a slight and non-significant effect on swim bladder inflation, but only at the highest concentration tested. Regarding BDE-154 exposure, the rate of edemas and swim bladder inflation were not affected. Finally, in all ALPI exposure concentrations (0.003 up to 30 mg/L), no sub-lethal or teratogenic effects were observed on developing organisms until 96 hpf. Although further studies are needed, our results demonstrate that when comparing the developmental toxicity induced by flame retardants in zebrafish, the HFFR ALPI may be considered a more suitable alternative to BDE-47.

Sorption and transport of aluminum dialkyl phosphinate flame retardants and their hydrolysates in soils

Aluminum dialkyl phosphinates (ADPs) are a class of promising phosphorus-containing flame retardants, but their environmental fate is not well understood. Sorption and transport behaviors of ADPs, and their hydrolysates dialkyl phosphinic acids (DPAs) were studied by batch and column experiments. ADPs are less mobile in soil columns with more than half (>52.6%) of ADPs retained in the soil and residues in the topmost 2-cm layer account for more than 57% of total residues. Dissolution and dispersion of fine grain ADPs were responsible for the transport of ADPs. Sorption DPAs (logK_oc) was significantly related to the lipophilicity of DPAs (logD) (p < 0.05). Soil pH and clay content were the dominant factors governing the sorption and transport of DPAs in soils, indicating the importance of electrostatic interactions. The retardation factors (R) of DPAs derived from leaching experiments were pH-dependent with larger R values in the acidic soil (pH = 4.0) where anionic and neutral species of DPAs coexisted. Both physical and chemical non-equilibrium convection-dispersion equations (CDE) yield appropriate modeling for DPAs transport. In most cases, R values estimated from column tests differed from those derived from the batch experiments, which might be attributed to non-equilibrium sorption processes in dynamic conditions.

Preliminary test on the distribution, hydrolyzation and excretion of aluminum dialkyl phosphinate flame retardants in rats

Aluminum dialkyl phosphinates (ADPs) are a promising class of chemicals offering superior flame retardance. However, knowledge on their behavior in vivo is scarce. Hydrolysis has been suggested as one of the major routes of environmental degradation of ADPs. Herein, aluminum methylcyclohexyl phosphinic (AMHP), a kind of ADPs with industrial production in China, and its hydrolysate methyl cyclohexyl phosphinic acid (MHPA) were continuously exposed to Sprague Dawley (SD) rats for 28 days in this study. The same ratio of MHPA in organs to serum and the same daily excretion of MHPA were observed for AMHP exposure group and MHPA exposure group, suggesting the hydrolysis of AMHP in vivo. The hydrolysis of AMHP to MHPA was further confirmed by in vitro simulated human gastric intestinal juice. Therefore, both AMHP and MHPA distributed in liver, kidney and even brain in the form of MHPA. More than 80% of AMHP and MHPA could be excreted by feces and urine. Feces are the main route of excretion of AMHP and MHPA. The denseness of the inflammatory cell in the hepatic portal area and biochemical indexes showed the obvious dose-effect relationship. However, the toxicity of AMHP and MHPA was quite low even with exposure level up to 100 mg/kg dw/day. The low cumulative ability and mild toxicity indicated AMHP as a promising substitute for brominated flame retardant.

Simultaneous determination of the lipophilicity and dissociation constants of dialkyl phosphinic acids by negligible depletion hollow fiber membrane-protected liquid-phase microextraction

Determination of the physicochemical properties, especially the lipophilicity (expressed as the logarithm of distribution coefficient, log D) and dissociation constant (pK_a), is of great importance in the early stage of environmental risk assessment for an ionizable compound without these data. Currently, the log D and pK_a values of dialkyl phosphinic acids (DPAs), the environmental hydrolysates of aluminum dialkyl phosphinates (ADPs) that is one class of emerging phosphorus-containing flame retardants, are not available. In this study, the log D and pK_a values of three DPAs including methylethylphosphinic acid (MEPA), diethylphosphinic acid (DEPA) and methylcyclohexyl phosphinic acid (MHPA), were simultaneously determined by negligible depletion hollow fiber supported liquid phase microextraction (nd-HF-LPME) followed by ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). The pK_a and log D of DPAs were determined by curve-fitting the experimental data with equations derived on the basis of the Henderson-Hasselbalch equation and compared with model calculated data. For MEPA, DEPA and MHPA, the pK_a values were close and around 3, but the log Ds were strongly pH-dependent with values from -5.01 to 1.01. The log K_OW of the neutral form (logK_OW,HA) and ionic form (logK_OW,A) were in the range of -0.67-1.02 and -3.86--1.33, respectively. The experimentally determined pK_a values were highly in good agreement with ACD/pK_a predicted values and the measured log K_OW,HA values were closely related to KOWWIN calculated ones, suggesting ACD/pK_a and KOWWIN are good alternative methods to estimate pK_a and log K_OW of DPAs, respectively. As far as we know, this is the first report on the pK_a and log D data for DPAs, which are fundamental for the product design and evaluating the environmental behavior and effects of DPAs and ADPs.