Effects of triphenyl phosphate on ciliate protozoa Tetrahymena thermophila following acute exposure and sub-chronic exposure
Introduction
Over the past decades, polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCDD) were representative brominated flame retardants (BFRs) that were generally added to a variety of consumer products (Van den Eede et al., 2012). In recent years, the use of PBDEs has been gradually banned and restricted according to the Stockholm Convention on persistent organic pollutants (POPs) due to their persistence, bioaccumulation and the toxic potency for human and wildlife (Van den Eede et al., 2011).
In this context, organophosphorus flame retardants (OPFRs) were extensively used as additive flame retardant as replacements to PBDEs, and thus the manufacture and application amount of OPFRs were significantly increased (Van den Eede et al., 2011; Besis and Samara, 2012). As one of the most commonly used OPFRs, triphenyl phosphate (TPHP) was widely applied in electronic equipment, polyvinyl chloride, hydraulic fluids and foundry resins (Van der Veen and de Boer, 2012; Du et al., 2016) and it was produced in large quantities worldwide. For example, the yield and usage of TPHP in Western Europe was 20,000–30,000 tons in 2000. And the yield/usage volume of TPHP in United States in 2006 was 4500–22,700 tons (Van der Veen and de Boer, 2012). Furthermore, like other OPFRs, TPHP was an additive flame retardant that was not chemically bond to substrate materials. During the manufacture, usage, and disposal of these consumer products, TPHP was inevitably released into the environment media (Matsukami et al., 2015; Wei et al., 2015), and thus it might pose a threat to aquatic organisms and even human health.
Previous environmental monitoring demonstrated that the average concentration of TPHP was 386 ng/g in indoor dust samples collected in 71 microenvironments (homes, offices, cars, coffee shops, restaurants and supermarkets) in Assiut, Egypt (Abdallah and Covaci, 2014). By use of targeted and nontargeted screening methods, two recent studies reported that TPHP was one of the ascendant OPFRs with mean concentration of 460 ng/g in indoor dust samples from Nanjing, eastern China (Meng et al., 2020; Zhao et al., 2020). Tan et al. (2016) reported that the concentrations of TPHP in sediments in the Pearl River Delta region of South China were 5.6–253 ng/g dry mass (dm). And the concentration of TPHP in the Ruhr River in Germany reached 40 ng/L (Andresen et al., 2004), while the highest concentration in Danish rivers was 7900 ng/L (Lassen et al., 1999). Li et al. (2014) analyzed 39 tap water samples from eight cities in China and found that TPHP was one of the most common OPFRs with an average concentration of 40 ng/L. Furthermore, TPHP concentration in the muscles of catfish (Claris fuscus) and grass carp (Ctenopharyngodon idellus) in the Pearl River Delta region in southern China was as high as 45.7 ng/g lipid mass (lm) (Ma et al., 2013), and in the fish (13 families, 20 species) from Manila Bay in the Philippines it was 91 ng/g lm (demersal fish)-350 ng/g lm (pelagic fish) (Kim et al., 2011). In this case, the environmental and bio-health risk assessment of TPHP is particularly urgent.
Several previous reports had indicated that TPHP could cause a variety of toxicities in organisms, especially for aquatic organisms. For example, Yuan et al. (2018) reported that treatment with 0.5 mg TPHP/L for 21 days significantly reduced the body length of F0 and F1 generation and affected the reproduction of F0 generation in Daphnia magna (D. magna). In adult male Chinese rare minnows (Gobiocypris rarus), treatment with 0.1 mg TPHP/L for 28 days significantly inhibited the proliferation of neuronal cells, and reduced dendritic arborization in pyramidal neurons in the cerebellum (Hong et al., 2018). After 7 days of exposure to 0.3 mg TPHP/L, zebrafish liver cells showed vacuoles, nuclear shrinkage, fragmentation and even loss (Du et al., 2016). Additionally, the lipid metabolism, carbohydrate metabolism, and DNA damage repair systems were disrupted by TPHP in zebrafish liver (Du et al., 2016). However, knowledge of the environmental risk and health impact assessments of TPHP was still limited, particularly regarding the effects of exposure to TPHP on lower trophic level aquatic organisms.
Protozoa Tetrahymena is a single-celled eukaryote that plays an important role in food webs of hydrophytic ecosystem and is sensitive to toxic substances in the environment (Fu et al., 2005). Ecotoxicology researchers were increasingly applying Tetrahymena as a model to evaluate environmental risk of pollutants due to its convenience for cultivation under laboratory conditions (Gao et al., 2015; Li et al, 2015, 2016; Cheng et al., 2019). In the present study, the T. thermophila was used as a testing organism, and 18 h of acute exposure and 5 days of sub-chronic exposure tests were implemented to assess the toxic effects of TPHP. In addition, transcriptome sequencing technique was used to reveal possible toxicological mechanisms.
Section snippets
Chemicals and reagents
Triphenyl phosphate (TPHP, purity ≥ 99.0%) and dimethyl sulfoxide (DMSO) were obtained from Sigma-Aldrich (MO, USA). Reagents for the preparation of super proteose peptone (SPP) medium were purchased from the following sources: Proteose peptone was obtained from BactoDifco (USA); Yeast extract was purchased from Oxioid Ltd (Basingstoke Hampshire, England); D (+) glucose was purchased from Biosharp (USA); Ethylendiaminetetraacetic acid monosodium ferric salt (Fe-EDTA) was obtained from Aladdin
Acute exposure to TPHP caused toxic effects on T. thermophila
The results of the acute toxicity test could provide the preliminary comparison for the contaminant toxicity. The effects of TPHP on the cell proliferation and viability were tested at the concentrations of 2.5–160 mg/L after exposure for 12 and 18 h. As shown in Table 1, using the number of cells to be an indicator, the calculated IC50 were 23.46 mg/L for 12 h and 17.47 mg/L for 18 h, respectively. Moreover, using the cell viability as an indicator, the calculated IC50 were 18.04 mg/L for 12 h
CRediT authorship contribution statement
Hui Hao: Investigation, Data curation, Writing - original draft, Methodology, Software, Formal analysis. Yao Dang: Writing - review & editing, Investigation, Validation, Formal analysis. Sheng Chen: Writing - review & editing, Validation. Qian Sun: Investigation, Methodology, Formal analysis, Project administration. Ren Kong: Investigation, Methodology, Formal analysis. Shiyang Cheng: Methodology, Writing - review & editing. Chunsheng Liu: Resources, Writing - review & editing, Supervision,
Declaration of competing interest
All of the authors declare no competing financial interests.
Acknowledgements
This work was supported by National Key R&D Program of China (2017YFF0211203).
References (35)
- et al.
Organophosphorus flame retardants and plasticisers in surface waters
Sci. Total Environ.
(2004) - et al.
Polybrominated diphenyl ethers (PBDEs) in the indoor and outdoor environments–a review on occurrence and human exposure
Environ. Pollut.
(2012) - et al.
Immunotoxicity of organophosphate flame retardants TPHP and TDCIPP on murine dendritic cells in vitro
Chemosphere
(2017) - et al.
Progression of liver tumor was promoted by tris (1, 3-dichloro-2-propyl) phosphate through the induction of inflammatory responses in krasV12 transgenic zebrafish
Environ. Pollut.
(2019) - et al.
Occurrence of the fungus mycotoxin, ustiloxin A, in surface waters of paddy fields in Enshi, Hubei, China, and toxicity in Tetrahymena thermophila
Environ. Pollut.
(2019) - et al.
Effects of triclosan and triclocarban on the growth inhibition, cell viability, genotoxicity and multixenobiotic resistance responses of Tetrahymena thermophila
Chemosphere
(2015) - et al.
Levels and distribution of organophosphorus flame retardants and plasticizers in fishes from Manila Bay, the Philippines
Environ. Pollut.
(2011) - et al.
Crystal structure of a 70S ribosome-tRNA complex reveals functional interactions and rearrangements
Cell
(2006) - et al.
Growth control and ribosome biogenesis
Curr. Opin. Cell Biol.
(2009) - et al.
Multigenerational effects of tris (1, 3-dichloro-2-propyl) phosphate on the free-living ciliate protozoa Tetrahymena thermophila exposed to environmentally relevant concentrations and after subsequent recovery
Environ. Pollut.
(2016)
Occurrence of organophosphate flame retardants in drinking water from China
Water Res.
Microwave-assisted extraction combined with gel permeation chromatography and silica gel cleanup followed by gas chromatography–mass spectrometry for the determination of organophosphorus flame retardants and plasticizers in biological samples
Anal. Chim. Acta
Acute exposure to triphenyl phosphate (TPhP) disturbs ocular development and muscular organization in zebrafish larvae
Ecotoxicol. Environ. Saf.
Distribution of organophosphorus flame retardants in sediments from the Pearl River Delta in south China
Sci. Total Environ.
Multi-residue method for the determination of brominated and organophosphate flame retardants in indoor dust
Talanta
Analytical developments and preliminary assessment of human exposure to organophosphate flame retardants from indoor dust
Environ. Int.
Phosphorus flame retardants: properties, production, environmental occurrence, toxicity and analysis
Chemosphere
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