In vitro biotransformation and evaluation of potential transformation products of chlorinated paraffins by high resolution accurate mass spectrometry

Polychlorinated alkanes in indoor environment: A review of levels, sources, exposure, and health implications for chlorinated paraffin mixtures

Polychlorinated n-alkanes (PCAs) are the main components of chlorinated paraffins (CPs) mixtures, that have been commonly grouped into short-chain (SCCPs, C10-13), medium-chain (MCCPs, C14-17), and long-chain (LCCPs, C18-30) CPs. PCAs pose a significant risk to human health as they are broadly present in indoor environments and are potentially persistent, bioaccumulative, and toxic. The lack of specific terminology and harmonization in analytical methodologies for PCA analysis complicates direct comparisons between studies. The present work summarizes the different methodologies applied for the analysis of PCAs in indoor dust, air, and organic films. The large variability between the reviewed studies points to the difficulties to assess PCA contamination in these matrices and to mitigate risks associated with indoor exposure. Based on our review of physicochemical properties of PCAs and previously reported sum of measurable S/M/LCCPs levels, the homologue groups PCAs-C10-13 are found to be mostly present in the gas phase, PCAs-C14-17 in particulate matter and organic films, and PCAs-C≥18 in settled dust. However, we emphasized that mapping PCA sources and distribution in the indoors is highly dependent on the individual homologues. To further comprehend indoor PCA distribution, we described the uses of PCA in building materials and household products to apportion important indoor sources of emissions and pathways for human exposure. The greatest risk for indoor PCAs were estimated to arise from dermal absorption and ingestion through contact with dust and CP containing products. In addition, there are several factors affecting indoor PCA levels and exposure in different regions, including legislation, presence of specific products, cleaning routines, and ventilation frequency. This review provides comprehensive analysis of available indoor PCA data, the physicochemical properties, applied analytical methods, possible interior sources, variables affecting the levels, human exposure to PCAs, as well as need for more information, thereby providing perspectives for future research studies.

Medium-Chain Chlorinated Paraffins Trigger Thyroid Hormone Synthesis and Interfere with Mitochondrial Function in the Thyroid Gland

Medium-chain chlorinated paraffins (MCCPs, C14-C17) are frequently detected in diverse environmental media. It has been proposed to be listed in Annex A of the Convention on Persistent Organic Pollutants in 2023. Although MCCPs are a crucial health concern, their toxicity remains unclear. This study investigated the toxic effects of MCCPs (0.1-50 mg/kg body weight/day) on the thyroid gland of female Sprague-Dawley rats and characterized the potential toxic pathways via transcriptomics and metabolomics approaches. MCCPs exposure caused histopathological changes to the endoplasmic reticula and mitochondria in thyroid follicular cells at a dose of 50 mg/kg bw/d and increased serum thyrotropin-releasing hormone, thyroid-stimulating hormones, and thyroxine when exposed to a higher dose of MCCPs. Transcriptomic analysis indicated the excessive expression of key genes related to thyroid hormone synthesis induced by MCCPs. Integrating the dual-omics analysis revealed mitochondrial dysfunction of the thyroid by mediating fatty acid oxidation, Kreb's cycle, and oxidative phosphorylation. Significant metabolic toxicity on the thyroid might be linked to the characteristics of the chlorine content of MCCPs. This study revealed the toxicity of MCCPs to the thyroid gland via triggering thyroid hormone synthesis and interfering with mitochondrial function, which can provide new insights into the modes of action and mechanism-based risk assessment of MCCPs.

Metabolic disturbance of short- and medium-chain chlorinated paraffins to zebrafish larva

Chlorinated paraffins (CPs) are widely produced chemicals. Short-chain CPs (SCCPs) and medium-chain CPs (MCCPs) were listed as Persistent Organic Pollutants (POPs) and candidate POPs under the Stockholm Convention, respectively. The present study explored the developmental toxicity and metabolic disruption caused by SCCPs and MCCPs in zebrafish (Danio rerio) larvae. CPs exposure at environmentally relevant levels caused no obvious phenotypic changes with zebrafish larvae except that the body length shortening was observed after exposure to CPs at 1-200 μg/L for 7 day post fertilization. A further metabolomic approach was conducted to explore the early biological responses of developmental toxicity induced by CPs at low dose (1, 5, and 10 μg/L). The results of metabolic disorder, pathway analysis and chronic values indicated that, compared with SCCPs, MCCPs exhibited more risks to zebrafish larvae at low doses. Lipid metabolism was markedly affected in SCCPs exposure group, whereas MCCPs primarily disturbed lipid metabolism, amino acid, and nucleotide metabolisms. Compare with SCCPs, the relatively higher lipid solubility, protein affinity and metabolic rate of MCCPs can probably explain why MCCP-mediated metabolic disruption was significantly higher than that of SCCP. Notably, SCCPs and MCCPs have the same potential to cause cancer, but no evidence indicates the mutagenicity. In summary, our study provides insight into the potential adverse outcome for SCCP and MCCP at low doses.

In vitro assessment of potential endocrine disrupting activities of chlorinated paraffins of various chain lengths

The production of chlorinated paraffins (CPs) has risen in the past two decades due to their versatile industrial applications. Consequently, CPs are now widely detected in human food sources, the environment, and in human matrices such as serum, the placenta and breast milk. This raises concern about prenatal and postnatal exposure. While some studies suggest that certain short-chained CPs (SCCPs) may have endocrine disrupting properties, knowledge about potential endocrine disrupting potential of medium- (MCCP) and long-chained CPs (LCCPs) remains relativity sparse. Here, we used a panel of in vitro assays to investigate seven pure CPs and two technical mixtures of CPs. These varied in chain length and, chlorination degree. The in vitro panel covered androgen, estrogen, and retinoic acid receptor activities, transthyretin displacement, and steroidogenesis. One of the SCCPs inhibited androgen receptor (AR) activity. All SCCPs induced estrogen receptor (ER) activity. Some SCCPs and MCCPs increased 17β-estradiol levels in the steroidogenesis assay, though not consistently across all substances in these groups. SCCPs exhibited the most pronounced effects in multiple in vitro assays, while the tested LCCPs showed no effects. Based on our results, some CPs can have endocrine disrupting potential in vitro. These findings warrant further examinations to ensure that CPs do not cause issues in intact organisms, including humans.

Identification of Sulfur-Containing Chlorinated Paraffin Structural Analogues in Human Serum: Origination from Biotransformation or Bioaccumulation?

Chlorinated paraffins (CPs) are manufactured and used in high quantities and have diverse structural analogues. It is generally recognized that sulfur-containing structural analogues of CPs are mainly derived from sulfate-conjugated phase II metabolism. In this study, we non-targeted identified three classes of sulfur-containing CP structural analogues (CPs-S) in human serum, including 44 CP sulfates (CPs-SO4H/CPs-SO4H-OH), 14 chlorinated benzene sulfates (CBs-SO4H), and 19 CP sulfite esters (CPs-SO3/CPs-S2O6), which were generated during the production of commercial mixtures of CPs and, thus, bioaccumulated via environmental exposures. We first wrote a program to screen CPs-S, which were baseline-separated from CPs according to their polar functional groups. Then, mass spectral analyses of alkalization-acidification liquid-liquid extracts of serum samples and Orbitrap mass spectrometry analyses in the presence and absence of tetraphenylphosphonium chloride (Ph4PCl), respectively, were performed to determine the ionization forms ([M + Cl]- or [M - H]-) of CPs-S. The presence of fragment ions (SO4H-, SO3-, SO2Cl-, and HSO3-) revealed the structures of CPs-S, which were validated by their detections in commercial mixtures of CPs. The estimated total concentrations of CPs-S in the human serum samples were higher than the concentrations of medium- and long-chain CPs. The profiles of CPs-S in human serum were similar to those detected in CP commercial mixtures and rats exposed to the commercial mixtures, but CPs-S were not detected in human liver S9 fractions or rat tissues after exposure to CP standards. These results, together with the knowledge of the processes used to chemically synthesize CPs, demonstrate that CPs-S in humans originates from environmental bioaccumulation.

Toxic effects and toxicological mechanisms of chlorinated paraffins: A review for insight into species sensitivity and toxicity difference

Chlorinated paraffins (CPs), a group of chlorinated alkane mixtures, are frequently detected in various environmental matrices and human bodies. Recently, CPs have garnered considerable attention owing to their potential to induce health hazards in wildlife and human. Several reviews have discussed short-chain CPs (SCCPs) induced ecological risk; however, a comprehensive understanding of the underlying toxic mechanisms and a comparison among SCCPs, medium-, and long-chain CPs (MCCPs and LCCPs, respectively) are yet to be established. This review summarizes the latest research progress on the toxic effects and the underlying molecular mechanisms of CPs. The main toxicity mechanisms of CPs include activation of several receptors, oxidative stress, disturbance of energy metabolism, and inhibition of gap junction-mediated communication. The sensitivity of different species to CP-mediated toxicities varies markedly, with aquatic organisms exhibiting the highest sensitivity to CP-induced toxicity. The toxicity comparison analysis indicated that MCCPs may be unsafe as potential substitutes for SCCPs.

Concentrations and homologue patterns of SCCPs and MCCPs in the serum of the general population of adults in Hangzhou, China

Due to their ubiquitous presence in the environment and humans, chlorinated paraffins (CPs) are a major environmental and public health concern. CPs are known to persist, bioaccumulate and potentially threaten human health, but reports on their internal exposure in the adult general population are still scarce. In this study, serum samples collected from adults living in Hangzhou, China, were quantified for SCCPs and MCCPs using GC-NCI-MS methods. A total of 150 samples were collected and subjected to analysis. ∑SCCPs were detected in 98% of the samples with a median concentration of 721 ng/g lw. MCCPs were found in all serum samples with a median concentration of 2210 ng/g lw, indicating that MCCPs were the dominant homologous group. For SCCPs and MCCPs, ∑C₁₀ and ∑C₁₄ were found to be the dominant carbon chain length homologues. Our results showed that age, BMI and lifestyle were not found to be significantly associated with internal exposure to CPs for the samples in this study. Based on PCA analysis, an age-specific distribution of CP homologues was observed. This suggests that internal exposure to CPs in the general population is related to exposure scenarios and history. The results of this study may contribute to a better understanding of the internal exposure to CPs in the general population and may provide a direction for the investigation of the source of exposure to CPs in the environment and daily life.

Identification and yield of metabolites of chlorinated paraffins incubated with chicken liver microsomes: Assessment of their potential to convert into metabolites

Chlorinated paraffins (CPs) are emerging environmental pollutants. Although metabolism has been shown to affect the differential accumulation of short-chain (SCCPs), medium-chain (MCCPs) and long-chain (LCCPs) CPs in birds, CP metabolites have rarely been reported and the extent to which they are formed is still unclear. In this study, single and mixed CP standards were incubated with chicken liver microsomes in vitro to study the generation of CP metabolites. Putative aldehyde/ketone and carboxylic acid metabolites identified by mass spectroscopy data were shown to be false positive results. Phase I metabolism of CPs first formed monohydroxylated ([M-Cl+OH]) and then dihydroxylated ([M-2Cl+2OH]) products. The yields of monohydroxylated metabolites of CPs decreased with increasing carbon chain length and chlorine content at the initial stage of reaction. Notably, the yield of monohydroxylated metabolites of SCCPs with 51.5% Cl content reached 21%, and that of 1,2,5,6,9,10-hexachlorodecane (C₁₀H₁₆Cl₆) was as high as 71%. Thus, monohydroxy metabolites of CPs in birds should not be ignored, especially those of SCCPs. This study provides important data that could support improvements to the ecological/health risk assessment of CPs.

The potential health risks of short-chain chlorinated paraffin: A mini-review from a toxicological perspective

Short-chain chlorinated paraffins (SCCPs) are ubiquitously distributed in various environmental matrics due to their wide production and consumption globally in the past and ongoing production and use in some developing countries. SCCPs have been detected in various human samples including serum, milk, placenta, nail, and hair, and internal SCCP levels were found to be positively correlated with biomarkers of some diseases. While the environmental occurrence has been reported in a lot of studies, the toxicity and underlying molecular mechanisms of SCCPs remain largely unknown. The current tolerable daily intakes (TDIs) recommended by the world health organization/international programme on chemical safety (WHO/IPCS, 100 μg/kg bw/d) and the UK Committee on Toxicity (COT, 30 μg/kg bw/d) were obtained based on a no observed adverse effect level (NOAEL) of SCCP from the repeated-dose study (90 d exposure) in rodents performed nearly 40 years ago. Importantly, the health risks assessment of SCCPs in a variety of studies has shown that the estimated daily intakes (EDIs) may approach and even over the established TDI by UK COT. Furthermore, recent studies revealed that lower doses of SCCPs could also result in damage to multiple organs including the liver, kidney, and thyroid. Long-term effects of SCCPs at environmental-related doses are warranted.

In Vivo Profiling and Quantification of Chlorinated Paraffin Homologues in Living Fish

Herein, we demonstrate the ability of a dual-purpose periodic mesoporous organosilica (PMO) probe to track the complex chlorinated paraffin (CP) composition in living animals by assembling it as an adsorbent-assisted atmospheric pressure chemical ionization Fourier-transform ion cyclotron resonance mass spectrometry (APCI-FT-ICR-MS) platform and synchronously performing it as the in vivo sampling device. First, synchronous solvent-free ionization and in-source thermal desorption of CP homologues were achieved by the introduction of the PMO adsorbent-assisted APCI module, generating exclusive adduct ions ([M - H]^-) of individual CP homologues (C_nCl_m) with enhanced ionization efficiency. Improved detection limits of short- and medium-chain CPs (0.10-24 and 0.48-5.0 pg/μL) were achieved versus those of the chloride-anion attachment APCI-MS methods. Second, the dual-purpose PMO probe was applied to extract the complex CP compositions in living animals, following APCI-FT-ICR-MS analysis. A modified pattern-deconvolution algorithm coupled with the sampling-rate calibration method was used for the quantification of CPs in living fish. In vivo quantification of a tilapia exposed to technical CPs for 7 days was successfully achieved, with ∑SCCPs and ∑MCCPs of the sampled fish calculated to be 1108 ± 289 and 831 ± 266 μg/kg, respectively. Meanwhile, 58 potential CP metabolites were identified in living fish for the first time during in vivo sampling of CPs, a capacity that could provide an important tool for future study regarding its expected risks to humans and its environmental fate.

Bioaccumulation and Biotransformation of Chlorinated Paraffins

Chlorinated paraffins (CPs), a class of persistent, toxic, and bioaccumulated compounds, have received increasing attention for their environmental occurrence and ecological and human health risks worldwide in the past decades. Understanding the environmental behavior and fate of CPs faces a huge challenge owing to the extremely complex CP congeners. Consequently, the aims of the present study are to summarize and integrate the bioaccumulation and biotransformation of CPs, including the occurrence of CPs in biota, tissue distribution, biomagnification, and trophic transfer, and biotransformation of CPs in plants, invertebrates, and vertebrates in detail. Biota samples collected in China showed higher CP concentrations than other regions, which is consistent with their huge production and usage. The lipid content is the major factor that determines the physical burden of CPs in tissues or organs. Regarding the bioaccumulation of CPs and their influence factors, inconsistent results were obtained. Biotransformation is an important reason for this variable. Some CP congeners are readily biodegradable in plants, animals, and microorganisms. Hydroxylation, dechlorination, chlorine rearrangement, and carbon chain decomposition are potential biotransformation pathways for the CP congeners. Knowledge of the influence of chain length, chlorination degree, constitution, and stereochemistry on the tissue distribution, bioaccumulation, and biotransformation is still scarce.

Comparative in vitro metabolism of short chain chlorinated paraffins (SCCPs) by human and chicken liver microsomes: First insight into heptachlorodecanes

Short chain chlorinated paraffins (SCCPs) are emerging persistent organic pollutants of great concern due to their ubiquitous distribution in the environment. However, little information is available on the biotransformation of SCCPs in organisms. In this study, a chlorinated decane: 1, 2, 5, 5, 6, 9, 10-heptachlorodecanes (HeptaCDs) was subjected to in vitro metabolism by human and chicken liver microsomes at environmentally relevant concentration. Using ultra-performance liquid chromatography-Q-Exactive Orbitrap mass spectrometry, two metabolites: monohydroxylated hexachlorodecane (HO-HexCD) and monohydroxy heptachlorodecane (HO-HeptaCD) were detected in human liver microsomal assays, while only one metabolite (HO-HexCD) was identified in chicken liver microsomal assays. The formation of HO-HexCD was fitted to a Michaelis-Menten model for chicken liver microsomes with a V_max (maximum metabolic rate) value of 4.52 pmol/mg/min. Metabolic kinetic parameters could not be obtained for human liver microsomes as steady state conditions were not reached under our experimental conditions. Notwithstanding this, the observed average biotransformation rate of HeptaCDs was much faster for human liver microsomes than for chicken liver microsomes. Due to the lack of authentic standards for the identified metabolites, the detailed structure of each metabolite could not be confirmed due to the possibility of conformational isomers. This study provides first insights into the biotransformation of SCCPs, providing potential biomarkers and enhancing understanding of bioaccumulation studies.

Semiquantitative Characterization of Bromo-chloro Paraffins and Olefins in the Australian Environment

A semiquantitative high-resolution mass spectrometry method was developed and applied to assess the occurrence of bromo-/chloro paraffins (BCPs) and olefins (BCOs) in the environment. More than 400 possible BCPs and BCO congener groups were detected in dust, air, and sewage sludge samples collected from Australia. Median chain analytes with the number of halogen atoms <7 (C_nH_mCl_xBr_y, 14 ≤ n ≤ 17, x + y < 7) prevailed in the dust and sludge samples, while short chain analytes (C_nH_mCl_xBr_y, 10 ≤ n ≤ 13, x + y < 7) predominated the air samples. The estimated concentrations of ∑BCPs and ∑BCOs in dust and sludge were approximately 20% that of the chlorinated paraffins (CPs) present, with the median concentrations of 5.4 μg/g (dust) and 0.18 μg/g (sludge) for ∑BCPs and 22 μg/g (in dust) and 0.50 μg/g (sludge) for BCOs. In the air samples, the concentrations of BCPs (0.020 pg/m³) and BCOs (0.032 pg/m³) were 3-4 orders of magnitudes lower than the concentrations of CPs (790 pg/m³). Significant correlations (P < 0.001) were found between the concentration of CPs, BCPs, and BCOs in all the matrices.

Critical review on disposition of chlorinated paraffins in animals and humans

Even though the chlorinated paraffins (CPs) have been on the environmental pollution agenda throughout the last 50 years it is a class of chemicals that only now is discussed in terms of an emerging issue with extensive annual publication rates. Major reviews on CPs have been produced, but a deeper understanding of the chemical fate of CPs, including formation of metabolites in animals and humans, is still missing. Thus, the present review aims to critically compile our present knowledge on the disposition, i.e. Adsorption, Disposition, Metabolism, and Excretion (ADME) of CPs in biota and to identify research needs. We conclude that CPs could be effectively absorbed from the gastro-intestinal tract (GI) tract, and probably also from the lungs, and transported to various organs. A biphasic elimination is suggested, with a rapid initial phase followed by a terminal phase, the latter (e.g., fat tissues) covering half-lives of weeks and months. CPs are metabolized in the liver and excreted mainly via the bile and faeces, and the metabolic rate and type of metabolites are dependent on chlorine content and chain length. Results that strengthen CP metabolism are in vivo findings of phase II metabolites in bile, and CP degradation to carbon fragments in experimental animals. Still the metabolic transformations of CPs are poorly studied, and no metabolic scheme has yet been presented. Further, toxicokinetic mass balance calculations suggest that a large part of a given dose (not found as parent compound) is transformation products of CPs, and in vitro metabolism studies present numerous CP metabolites (e.g., chloroalkenes, chlorinated ketones, aldehydes, and carboxylic acids).

Chlorinated paraffins and tris (1-chloro-2-propyl) phosphate in spray polyurethane foams - A source for indoor exposure?

In this study, we investigated chemical additives present in new and used spray polyurethane foams (SPFs) and assessed the dermal transfer through direct contact. This first study shows that cured do-it-yourself spray one-component SPFs (OCFs) often contain chlorinated paraffins (C₁₄-C₃₇), and tris (1-chloro-2-propyl) phosphate (TCIPP), ranging 0.2-50%, and 0.9-30% w/w, respectively. Six OCFs contained CP levels ranging 22-50% w/w, whereas nine OCFs used for similar applications only contained CP levels ranging 2-17% w/w. It is unclear if the combination CPs/TCIPP is meant to improve the flame retardancy of products, and could suggest an unnecessary use of high CPs/TCIPP concentrations in OCFs. The two-component SPFs (TCFs) contained only TCIPP with levels ranging from 7.0% to 9.0%. The CPs and TCIPP were easily transferred from cured OCFs to the hands. Levels up to 590 µg per hand for CPs and up to 2.7 µg per hand for TCIPP were found. After end-of-life, it is challenging to recycle used SPFs. They may, therefore, end up at landfills where the TCIPP/CPs may leach into the environment. Therefore, further investigation is needed to assess potential exposure risks associated with general and occupational use, and the impact of landfill leaching on the environment.