Chronic exposures to monomethyl phthalate in Western clawed frogs

An indigenous tubular ceramic membrane integrated bioreactor system for biodegradation of phthalates mixture from contaminated wastewater

Endocrine-disrupting phthalates (EDPs) are widely used as plasticizers for the manufacture of different plastics and polyvinyl chloride by providing flexibility and mechanical strength. On the other hand, they are categorized under priority pollutants list due to their threat to human health and the environment. This study examined biodegradation of a mixture of dimethyl, diethyl, dibutyl, benzyl butyl, di-2-ethylhexyl, and di-n-octyl phthalates using a CSTB (continuous stirred tank bioreactor) operated under batch, fed-batch, continuous, and continuous with biomass recycle operation modes. For operating the CSTB under biomass recycle mode, microfiltration using an indigenous tubular ceramic membrane was employed. Ecotoxicity assessment of the treated water was carried out to evaluate the toxicity removal efficiency by the integrated bioreactor system. From the batch experiments, the EDPs cumulative degradation values were 90 and 75% at 1250 and 1500 mg/L total initial concentration of the mixture, respectively, whereas complete degradation was achieved at 750 mg/L. In the fed-batch study, 93% degradation was achieved at 1500 mg/L total initial concentration of the mixture. In continuous operation mode, 94 and 85% degradation efficiency values were achieved at 43.72 and 52.08 mg/L⋅h inlet loading rate of phthalate mixture. However, continuous feeding with 100% biomass recycle revealed complete degradation at 41.67 mg/L⋅h inlet loading rate within the 84 h operation period. High seed germination index and low mortality percentage of brine shrimps observed with phthalate degraded water from the integrated bioreactor system revealed its excellent potential in the treatment and toxicity removal of phthalates contaminated environment.

Complete genome of Mycolicibacterium phocaicum RL-HY01, a PAEs-degrading marine bacterial strain isolated from Zhanjiang Bay, China

Mycolicibacterium phocaicum RL-HY01, a marine bacterial strain with the capability to degrade phthalic acid esters (PAEs), was isolated from Zhanjiang Bay, China. Here, the complete genome sequence of strain RL-HY01 was presented. The genome of strain RL-HY01 contains one circular chromosome of 6,064,759 bp with a G + C content of 66.93 mol%. The genome contains 5681 predicted protein-encoding genes, 57 tRNA genes, and 6 rRNA genes. Genes and gene clusters potentially involved in the metabolism of PAEs were further identified. The genome Mycolicibacterium phocaicum RL-HY01 will be helpful for advancing our understanding of the fate of PAEs in marine ecosystem.

Alterations in the conformation and function of human serum albumin induced by the binding of methyl hydrogen phthalate

Phthalate esters (PAEs) are widely used as plasticizer components in production. Methyl hydrogen phthalate (MHP) is a metabolite of dimethyl phthalate (DMP, a kind of PAEs), and its toxic residues accumulate in the nature and can enter the human body. Here, the interaction between MHP and human serum albumin (HSA) was probed by using multi-spectral, computer simulations, and biochemical techniques. The results showed that MHP was spontaneously embedded in site I of HSA to form a complex by H-bonds and van der Waals forces (ΔH < 0, ΔS < 0). The binding constant (K_a) of the HSA-MHP system was 1.136 ± 0.026 × 10⁴ M^-1 (298 K). The combination of MHP produced conformational variations of HSA, as shown by the 3D fluorescence spectrum, CD spectra, and molecular dynamics simulation. Additionally, molecular docking indicated that MHP was surrounded by multiple residues, such as Lys199, Leu203, Phe206, and Trp214. Specifically, Lys199 and Trp214 exerted a crucial effect on the interaction of HSA and MHP. The residues with important energy contribution were mostly located in site I. The ASA values of the aromatic amino acids of HSA changed after combining with MHP. The R_g and SASA values of HSA increased after adding MHP, suggesting that the structure of HSA was less compact. Moreover, the esterase-like activity of HSA increased after adding MHP to HSA, indicating that MHP may disturb the normal physiological activities in the human body. This study was helpful to understand the biological function of MHP and provided some insights for its side effect in the human body.

Characterization and genomic analysis of an efficient dibutyl phthalate degrading bacterium Microbacterium sp. USTB-Y

A promising bacterial strain for biodegrading dibutyl phthalate (DBP) was successfully isolated from activated sludge and characterized as a potential novel Microbacterium sp. USTB-Y based on 16S rRNA sequence analysis and whole genome average nucleotide identity (ANI). Initial DBP of 50 mg/L could be completely biodegraded by USTB-Y both in mineral salt medium and in DBP artificially contaminated soil within 12 h at the optimal culture conditions of pH 7.5 and 30 ℃, which indicates that USTB-Y has a strong ability in DBP biodegradation. Phthalic acid (PA) was identified as the end-product of DBP biodegraded by USTB-Y using GC/MS. The draft genome of USTB-Y was sequenced by Illumina NovaSeq and 29 and 188 genes encoding for putative esterase/carboxylesterase and hydrolase/alpha/beta hydrolase were annotated based on NR (non redundant protein sequence database) analysis, respectively. Gene3781 and gene3780 from strain USTB-Y showed 100% identity with dpeH and mpeH from Microbacterium sp. PAE-1. But no phthalate catabolic gene (pht) cluster was found in the genome of strain USTB-Y. The results in the present study are valuable for obtaining a more holistic understanding on diverse genetic mechanisms of PAEs biodegrading Microbacterium sp. strains.

Chronic Exposure to Two Gestagens Differentially Alters Morphology and Gene Expression in Silurana tropicalis

Gestagens are active ingredients in human and veterinary drugs with progestogenic activity. Two gestagens-progesterone (P4), and the synthetic P4 analogue, melengestrol acetate (MGA)-are approved for use in beef cattle agriculture in North America. Both P4 and MGA have been measured in surface water receiving runoff from animal agricultural operations. This project aimed to assess the morphometric and molecular consequences of chronic exposures to P4, MGA, and their mixture during Western clawed frog metamorphosis. Chronic exposure (from embryo to metamorphosis) to MGA (1.7 µg/L) or P4 + MGA (0.22 µg/L P4 + 1.5 µg/L MGA) caused a considerable dysregulation of metamorphic timing, as evidenced by an inhibition of growth, narrower head, and lack of forelimb emergence in all animals. Molecular analysis revealed that chronic exposure to the mixture induced an additive upregulation of neurosteroid-related (GABA_A receptor subunit α6 (gabra6) and steroid 5-alpha reductase 1 (srd5α1) gene expression in brain tissue. Chronic P4 exposure (0.26 µg/L P4) induced a significant upregulation of the expression hypothalamic-pituitary-gonadal (HPG)-related genes (ipgr, erα) in the gonadal mesonephros complex (GMC). Our data suggest that exposure to P4, MGA, and their mixture induces multiple endocrine responses and adverse effects in larval Western clawed frogs. This study helps to better our understanding of the consequences of chronic gestagen exposure and suggests that the implications and risk of high gestagen use in beef cattle feeding operations may extend to the aquatic environment.

Characterization of phthalate exposure in relation to serum thyroid and growth hormones, and estimated daily intake levels in children exposed to phthalate-tainted products: A longitudinal cohort study

BACKGROUND

No information is available on the long-term effects on thyroid and growth hormones of children exposed to phthalate-tainted products, despite the infamous 2011 Taiwan phthalate episode. We investigated estimated daily intake levels and their long-term effects on serum thyroid and growth hormone levels in children.

METHODS

We recruited 166 children (2-18 years old) in three visits who provided specimens and filled out a questionnaire from the Risk Assessment of Phthalate Incident in Taiwan (RAPIT) project study from 2012 to 2016. Morning spot urine samples were analyzed for nine phthalate metabolites. Serum thyroid (triiodothyronine [T₃], thyroxine [T₄], and free T₄) and growth hormone (insulin-like growth factor-1 [IGF-1] and its binding protein 3 [IGF-BP3]) levels were measured. A generalized estimating equation model was used to evaluate associations between phthalate metabolite levels and children's thyroid and growth hormone levels.

RESULTS

The median metabolite levels of monomethyl phthalate (MMP), Σdibutyl phthalate (DBP), and Σdi-(2-ethylhexyl) phthalate (DEHP) at visits 1, 2, and 3 were 6.59, 10.5, and 21.0 ng/mL, 0.15, 0.24, and 0.20 nmol/mL, and 0.15, 0.17, and 0.12 nmol/mL, respectively. After adjusting for potential confounding factors, we found that levels of urinary MMP were negatively associated with T₃ (β = -0.013, p = 0.047), T₄ (β = -0.016, p = 0.006), free T₄ (β = -0.012, p = 0.002), and IGF-BP3 (β = -0.025, p = 0.003). Urinary mono-ethyl phthalate (MEP) was negatively associated with IGF-1 (β = -0.027, p = 0.029) and IGF-BP3 (β = -0.016, p = 0.018). In addition, serum free T₄ was positively associated with urinary mono-2-ethyl-5-hydroxy hexyl phthalate (MEHHP) (β = 0.016, p = 0.043), mono-2-ethyl-5-oxohexyl phthalate (MEOHP) (β = 0.015, p = 0.024), and ΣDEHPm (β = 0.019, p = 0.020).

CONCLUSIONS

Our findings support the hypothesis that specific phthalates disturb the hemostasis of thyroid and growth hormone levels in children exposed to phthalate-tainted products.

Bioremediation of di-(2-ethylhexyl) phthalate contaminated red soil by Gordonia terrae RL-JC02: Characterization, metabolic pathway and kinetics

Di-(2-ethylhexyl) phthalate (DEHP) is the most widely used plasticizer and a representative endocrine disrupting chemical. The toxicological effects of DEHP on environmental and human health have been widely investigated. In this study, the DEHP-degrading bacterial strain RL-JC02 was isolated from red soil with long-term usage of plastic mulch, and it was identified as Gordonia terrae by 16S rRNA gene analysis coupled with physiological and biochemical characterization. The biodegrading capacity of different phthalic acid esters and related intermediates was investigated as well as the performance of strain RL-JC02 under different environmental conditions, such as temperature, pH, salinity and DEHP concentration. Specifically, strain RL-JC02 showed good tolerance to low pH, with 86.6% of DEHP degraded under the initial pH of 5.0 within 72 h. The metabolic pathway of DEHP was examined by metabolic intermediate identification via a high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS) analysis in which DEHP was hydrolyzed into phthalic acid (PA) and 2-ethylhexanol (2-EH) via mono (2-ethylhexyl) phthalate (MEHP). PA and 2-EH were further utilized through the protocatechuic acid metabolic pathway and β-oxidation via protocatechuic acid and 2-ethylhexanoic acid, respectively. The application potential of strain RL-JC02 was confirmed through the bioremediation of artificial DEHP-contaminated red soil showing 91.8% DEHP degradation by strain RL-JC02 within 30 d. The kinetics analysis of DEHP degradation by strain RL-JC02 in soil demonstrated that the process followed the modified Gompertz model. Meanwhile, the cell concentration monitoring of strain RL-JC02 in soil with absolute quantification polymerase chain reaction (qPCR) suggested that strain RL-JC02 survived well during bioremediation. This study provides sufficient evidence of a robust degrader for the bioremediation of PAE-contaminated red soil.

Identification and characterization of a novel phthalate-degrading hydrolase from a soil metagenomic library

Phthalate esters have raised public concerns owing to their effects on the environment and human health. We identified a novel phthalate-degrading hydrolase, EstJ6, from a metagenomic library using function-driven screening. Phylogenetic analysis indicated that EstJ6 is a member of family IV esterases. EstJ6 hydrolyzed various dialkyl and monoalkyl phthalate esters, and exhibited high hydrolytic activity (128 U/mg) toward dibutyl phthalate at 40 °C and pH 7.5. EstJ6 hydrolyzed not only common phthalate esters with simple side chains but also diethylhexyl phthalate and monoethylhexyl phthalate, which have complex and long side chains. Site-directed mutagenesis indicated that the catalytic triad residues of EstJ6 consists of Ser146, Glu240, and His270. EstJ6 is therefore a promising biodegradation enzyme, and our study illustrates the advantages of a metagenomic approach in identifying enzyme-coding genes for agricultural, food, and biotechnological applications.

Effect of triadimefon and its metabolite on adult amphibians Xenopus laevis

The decrease in the population of amphibians all over the world has raised concerns. Adult X. laevis frogs were exposed to 0, 1 and 10 mg/L triadimefon and triadimenol. After 14 or 28 days exposure, we collected male and female specimens to study swimming activity, lactic dehydrogenase (LDH) and antioxidant enzyme activity in blood samples, histopathology of liver and thyroid tissue, thyroid hormone levels and thyroid hormone-related gene expression levels in brains. Our results showed that triadimefon and triadimenol could affect the swimming activity of frogs and that this was distinct at different levels of triadimenol. Moreover, triadimefon and triadimenol exposure produced a greater effect on superoxide dismutase (SOD) in females than in males, which was reverse to the finding for glutathione S-transferase (GST) and catalase (CAT). After 28 days exposure, triadimefon produced more toxic effects on the liver than observed for triadimenol. Besides this, triadimefon and triadimenol exposure exerted a greater effect on liver histology and thyroid hormone levels in male frogs than in the females. Our results also found that the expression of genes related to thyroid hormone in brains depended on the exposure level and time, as well as the sex of the treated individual. This study shed light on the relationships between the toxicity of metabolite products and their parent compounds and provided further understanding of the risk of pesticide use on amphibians.

Contaminant and Environmental Influences on Thyroid Hormone Action in Amphibian Metamorphosis

Aquatic and terrestrial environments are increasingly contaminated by anthropogenic sources that include pharmaceuticals, personal care products, and industrial and agricultural chemicals (i. e., pesticides). Many of these substances have the potential to disrupt endocrine function, yet their effect on thyroid hormone (TH) action has garnered relatively little attention. Anuran postembryonic metamorphosis is strictly dependent on TH and perturbation of this process can serve as a sensitive barometer for the detection and mechanistic elucidation of TH disrupting activities of chemical contaminants and their complex mixtures. The ecological threats posed by these contaminants are further exacerbated by changing environmental conditions such as temperature, photoperiod, pond drying, food restriction, and ultraviolet radiation. We review the current knowledge of several chemical and environmental factors that disrupt TH-dependent metamorphosis in amphibian tadpoles as assessed by morphological, thyroid histology, behavioral, and molecular endpoints. Although the molecular mechanisms for TH disruption have yet to be determined for many chemical and environmental factors, several affect TH synthesis, transport or metabolism with subsequent downstream effects. As molecular dysfunction typically precedes phenotypic or histological pathologies, sensitive assays that detect changes in transcript, protein, or metabolite abundance are indispensable for the timely detection of TH disruption. The emergence and application of 'omics techniques-genomics, transcriptomics, proteomics, metabolomics, and epigenomics-on metamorphosing tadpoles are powerful emerging assets for the rapid, proxy assessment of toxicant or environmental damage for all vertebrates including humans. Moreover, these highly informative 'omics techniques will complement morphological, behavioral, and histological assessments, thereby providing a comprehensive understanding of how TH-dependent signal disruption is propagated by environmental contaminants and factors.

Human exposure to phthalate esters associated with e-waste dismantling: Exposure levels, sources, and risk assessment

Phthalate esters (PAEs) can be released into the environment during the dismantling of electronic waste (e-waste), but urinary levels of PAE metabolites (mPAEs) in humans living in e-waste sites have not been documented. In this study, 11 mPAEs were determined in urine samples collected from participants living in e-waste dismantling sites and a reference area in Southern China. The total urinary concentrations of the 11 mPAEs (∑mPAEs) in the e-waste sites (range: 11.1 ng/mL to 3380 ng/mL) were dominated by mono-(2-isobutyl) phthalate and mono-n-butyl phthalate. Participants living in the e-waste sites had significantly higher (p < 0.05) urinary concentrations of ∑mPAEs (and 5 individual mPAEs) than those in the reference area. Hence, e-waste dismantling activities contributed to human exposure to PAEs. The exposure doses of di-n-butyl phthalate, di(2-ethylhexyl)phthalate, di-iso-butyl phthalate, dimethyl phthalate, and diethyl phthalate were 3.41, 3.04, 1.37, 0.25, and 0.20 μg/kg bw/day, respectively. Furthermore, the health risk assessment in terms of hazard quotient and hazard index showed that approximately 22% of the participants living in the e-waste sites had HI values exceeding 1; importantly, 68% of them were non-adults (i.e., 0-18 years old). In the e-waste sites, 8 of the 11 mPAEs in urine samples had significantly positively associations (r = 0.185-0.358, p < 0.05) with the urinary concentration of 8-hydroxy-2'-deoxyguanosine, a marker of DNA oxidative stress. Therefore, people living in e-waste dismantling areas may have a potential health risk caused by PAE exposure. To the best of our knowledge, this study is the first to measure urinary mPAE levels in people living in e-waste dismantling areas.

Phthalates modulate steroid 5-reductase transcripts in the Western clawed frog embryo

Phthalates are used worldwide in the manufacturing of plastics, added to cosmetic products, personal care products, pharmaceuticals, medical devices, and paints; and are widely detected in soil, surface water, and organism tissues. Phthalate esters have been previously shown to interfere with the endocrine system in vertebrates. However, few studies have investigated the effects of phthalates on testosterone-converting enzymes that affect hormone levels and reproduction. In the present study, we exposed the Western clawed frog (Silurana tropicalis) to 0.1, 1, and 10 μM diethylhexyl phthalate (DEHP), dibutyl phthalate (DBP), and diethyl phthalate (DEP) during early amphibian embryonic development. Additional DBP exposures were conducted ex vivo using mature frog testes. Malformations and mRNA levels of genes associated to reproduction and oxidative stress were evaluated. 0.1 μM DEHP, DBP, and DEP induced an array of malformations, including incomplete gut coiling, edemas, and eye malformations. Moreover, all three phthalates increased the expression of androgen-related genes, such as steroid-5α-reductase 1, 2, 3, steroid-5β-reductase, and androgen receptor at concentrations ranging from 0.1 to 10 μM depending on the phthalate and gene. Data suggest that the phthalate esters tested are teratogens to the amphibian embryo and that these phthalates exhibit an androgenic activity in amphibians.

Comparison of triadimefon and its metabolite on acute toxicity and chronic effects during the early development of Rana nigromaculata tadpoles

Pesticides are one of major causes for amphibian population declines and the behavior of pesticide metabolite products to amphibians has become a rising concern. In this study, the acute toxicity and the chronic effects of triadimefon and triadimenol (the metabolite of triadimefon) on Rana. nigromaculata were investigated. In the acute assay, significant differences were observed in antioxidant enzyme activities and malondialdehyde levels between the triadimefon and triadimenol. The 96 h-acute toxicity of triadimefon (25.97 mg/L) and triadimenol (34.55 mg/L) to tadpoles was low. In 28d-chronic exposure, we studied the relative expression of tadpoles genes related to thyroid hormone-dependent metamorphic development, histological examination of liver and some biological index, including wet weight, snout-to-vent length (SVL) and development stages. The results revealed that the effects of triadimefon and triadimenol on tadpole development are driven by a disruption of the hormonal pathways involved in metamorphosis. Interestingly, triadimefon was more harmful on R. nigromaculata than triadimenol at high dose, whereas the reverse result was observed at low doses. According to the relative expression of thyroid hormone-dependent genes, we also found that the two compounds may have different mechanisms of toxic action on R. nigromaculata. Our study developed a pragmatic approach for use in the risk assessment of pesticide and its metabolite，and increased the information and understanding of the impacts of fungicides and other potential endocrine disrupting environmental contaminants on amphibians.

Obesogens in the aquatic environment: an evolutionary and toxicological perspective

The rise of obesity in humans is a major health concern of our times, affecting an increasing proportion of the population worldwide. It is now evident that this phenomenon is not only associated with the lack of exercise and a balanced diet, but also due to environmental factors, such as exposure to environmental chemicals that interfere with lipid homeostasis. These chemicals, also known as obesogens, are present in a wide range of products of our daily life, such as cosmetics, paints, plastics, food cans and pesticide-treated food, among others. A growing body of evidences indicates that their action is not limited to mammals. Obesogens also end up in the aquatic environment, potentially affecting its ecosystems. In fact, reports show that some environmental chemicals are able to alter lipid homeostasis, impacting weight, lipid profile, signaling pathways and/or protein activity, of several taxa of aquatic animals. Such perturbations may give rise to physiological disorders and disease. Although largely unexplored from a comparative perspective, the key molecular components implicated in lipid homeostasis have likely appeared early in animal evolution. Therefore, it is not surprising that the obesogen effects are found in other animal groups beyond mammals. Collectively, data indicates that suspected obesogens impact lipid metabolism across phyla that have diverged over 600 million years ago. Thus, a consistent link between environmental chemical exposure and the obesity epidemic has emerged. This review aims to summarize the available information on the effects of putative obesogens in aquatic organisms, considering the similarities and differences of lipid homeostasis pathways among metazoans, thus contributing to a better understanding of the etiology of obesity in human populations. Finally, we identify the knowledge gaps in this field and we set future research priorities.

Urinary concentrations of 25 phthalate metabolites in Brazilian children and their association with oxidative DNA damage

Exposure of humans to phthalates has received considerable attention due to the ubiquitous occurrence and potential adverse health effects of these chemicals. Nevertheless, little is known about the exposure of the Brazilian population to phthalates. In this study, concentrations of 25 phthalate metabolites were determined in urine samples collected from 300 Brazilian children (6-14years old). Further, the association between urinary phthalate concentrations and a biomarker of oxidative stress, 8-hydroxy-2'-deoxyguanosine (8OHDG), was examined. Overall, eleven phthalate metabolites were found in at least 95% of the samples analyzed. The highest median concentrations were found for monoethyl phthalate (mEP; 57.3ngmL^-1), mono-(2-ethyl-5-carboxypentyl) phthalate (mECPP; 52.8ngmL^-1), mono-isobutyl phthalate (mIBP; 43.8ngmL^-1), and mono-n-butyl phthalate (mBP; 42.4ngmL^-1). The secondary metabolites of di(2-ethylhexyl) phthalate (DEHP), and mEP, mIBP, and mBP were the most abundant compounds, accounting for >90% of the total concentrations. On the basis of the measured concentrations of urinary phthalate metabolites, we estimated daily intakes of the parent phthalates, which were 0.3, 1.7, 1.8, 2.1, and 7.2μg/kg-bw/day for dimethyl phthalate, di-n-butyl phthalate, diisobutyl phthalate, diethyl phthalate, and DEHP, respectively. Approximately one-quarter of the Brazilian children had a hazard index of >1 for phthalate exposures. Statistically significant positive associations were found between 8OHDG and the concentration of the sum of phthalate metabolites, sum of DEHP metabolites, mEP, mIBP, mBP, monomethyl phthalate, mono(3-carboxypropyl) phthalate, monobenzyl phthalate, monocarboxyoctyl phthalate, monocarboxynonyl phthalate, monoisopentyl phthalate, and mono-n-propyl phthalate. To the best of our knowledge, this is the first study to report the exposure of a Brazilian population to phthalates.

Influence of Lipophilicity on the Toxicity of Bisphenol A and Phthalates to Aquatic Organisms

Bisphenol A (BPA) and phthalates are among the most popular plasticizers used today and have been reported ubiquitously in surface water, ground water, and sediment. For aquatic organisms, BPA was the most toxic (96 h LC50s) to aquatic invertebrates (0.96-2.70 mg/L) and less toxic to fish (6.8-17.9 mg/L). The toxicity of BPA to amphibians differed among developmental stages, with embryos having an LC50 of 4.6-6.8 mg/L and juveniles 0.50-1.4 mg/L. The toxicity of phthalates is affected by aromatic ring substitution, alkyl chain length, and metabolism. The toxicity (96 h LC50s) of phthalates was similar to aquatic invertebrates (0.46-377 mg/L) and fish (0.48-121 mg/L). In general, the toxicity of phthalates appears to be highest around a log KOW of 6, which corresponds to the highest potential for bioconcentration and bioaccumulation. In conclusion, the lipophilicity of BPA and phthalates influence their toxicity to aquatic species.