Stability and Microbial Toxicity of Silver Nanoparticles under Denitrifying Conditions.

While the antibacterial effect of silver nanoparticles (AgNPs) on environmentally beneficial microbes has drawn considerable attention, the stability and microbial toxicity of AgNPs in a system where nitrate reduction is the dominant terminal electron-accepting process remain understudied. Here, we explore the impact of citrate-coated AgNPs (cit-AgNPs) on the growth and metabolism of two metal-sensitive and one nonsensitive bacterial strains under denitrifying conditions. Dose-response analysis revealed that in contrast to the bacteriostatic effect exhibited at 1 ppm, 5 ppm cit-AgNPs were bactericidal to the metal-sensitive strains. It was observed that the growth of the cells initiated Ag(I) formation, and the supplement of chloride (2.7 mM) to the cultures substantially mitigated the bactericidal capacity of cit-AgNPs, indicating that AgNP dissolution to ionic Ag(I) played a key role in AgNP toxicity. Abiotic experiments confirmed that nitrite, not nitrate, had the capacity to oxidize cit-AgNPs. Transcriptomic analysis revealed that (i) the gene encoding for membrane stress was upregulated proportionally to cit-AgNP concentrations; (ii) cit-AgNPs and Ag(I) at higher levels upregulated genes involved in oxidative stress and iron-sulfur clusters, whereas expressions of the genes responsible for electron transport, ATP synthesis, and denitrification were substantially repressed; (iii) the addition of chloride significantly altered the level of transcriptional profiles of all of the genes. These results not only provide evidence of abiotic AgNP oxidation by metabolic intermediate nitrogen species but also suggest that AgNPs and Ag(I) may induce differential toxicity modes to prokaryotes. Our findings reinforce the importance of evaluating the potential ecological toxicity and risks associated with the transformation of nanomaterials.

Phthalates exposure and attention-deficit/hyperactivity disorder in children: a systematic review of epidemiological literature.

Epidemiological studies have proven that children mental health can be affected by environmental pollutants which are believed to be visible in the form of psychological disorder later in their childhood. Moreover, the effects of children mental health are evidently clear in the case of phthalates which have been observed to increase psychological disorder, specifically attention-deficit hyperactivity disorder (ADHD). Hence, the present study aims to conduct a systematic review and provide an overview of the existing literature on the association between urinary phthalate metabolite concentrations and ADHD symptoms among children by emphasizing the confounding factors and limitations. Additionally, this review addressed the possible phthalate mechanism insights in human body including its impact on ADHD symptoms. In this case, 16 epidemiological studies (five cross-sectional, nine cohort and two case control studies) that met all the inclusion criteria were selected out of the total of 427 papers screened to show varying quantitative associations between phthalate exposure and ADHD symptoms among children with confounding factors and limitations in the existing studies in regard to the exposure and outcomes. This review also attempted to present possible explanation on phthalate mechanism in children body and its connection on neurodevelopment and ADHD symptom development which remains unclear in most of the studies. Finally, it is highly recommended for further research to carefully design cohort studies from prenatal to later childhood development with a complete sample size in order to understand phthalate impacts on children health.

Biodegradation of the endocrine disrupter 4-t-octylphenol by the non-ligninolytic fungus Fusarium falciforme RRK20: Process optimization, estrogenicity assessment, metabolite identification and proposed pathways.

4-t-octylphenol (4-t-OP), a well-known endocrine disrupting compound, is frequently found in various environmental compartments at levels that may cause adverse effects to the ecosystem and public health. To date, most of the studies that investigate microbial transformations of 4-t-OP have focused on the process mediated by bacteria, ligninolytic fungi, or microbial consortia. There is no report on the complete degradation mechanism of 4-t-OP by non-ligninolytic fungi. In this study, we conducted laboratory experiments to explore and characterize the non-ligninolytic fungal strain Fusarium falciforme RRK20 to degrade 4-t-OP. Using the response surface methodology, the initial biomass concentration and temperature were the factors identified to be more influential on the efficiency of the biodegradation process as compared with pH. Under the optimized conditions (i.e., 28 °C, pH 6.5 with an initial inoculum density of 0.6 g L-1), 25 mg L-1 4-t-OP served as sole carbon source was completely depleted within a 14-d incubation; addition of low dosage of glucose was shown to significantly accelerate 4-t-OP degradation. The yeast estrogenic screening assay further confirmed the loss of estrogenic activity during the biodegradation process, though a longer incubation period was required for complete removal of estrogenicity. Metabolites identified by LC-MS/MS revealed that strain RRK20 might degrade 4-t-OP as sole energy source via alkyl chain oxidation and aromatic ring hydroxylation pathways. Together, these results not only suggest the potential use of non-ligninolytic fungi like strain RRK20 in remediation of 4-t-OP contaminated environments but may also improve our understanding of the environmental fate of 4-t-OP.

Recent updates on phthalate exposure and human health: a special focus on liver toxicity and stem cell regeneration.

Phthalates have been blended in various compositions as plasticizers worldwide for a variety of purposes. Consequently, humans are exposed to a wide spectrum of phthalates that needs to be researched and understood correctly. The goal of this review is to focus on phthalate's internal exposure pathways and possible role of human digestion on liver toxicity. In addition, special focus was made on stem cell therapy in reverting liver toxicity. The known entry of higher molecular weight phthalates is through ingestion while inhalation and dermal pathways are for lower molecular weight phthalates. In human body, certain phthalates are digested through phase 1 (hydrolysis, oxidation) and phase 2 (conjugation) metabolic processes. The phthalates that are made bioavailable through digestion enter the blood stream and reach the liver for further detoxification, and these are excreted via urine and/or feces. Bis(2-ethylhexyl) phthalate (DEHP) is a compound well studied involving human metabolism. Liver plays a pivotal role in humans for detoxification of pollutants. Thus, continuous exposure to phthalates in humans may lead to inhibition of liver detoxifying enzymes and may result in liver dysfunction. The potential of stem cell therapy addressed herewith will revert liver dysfunction and lead to restoration of liver function properly.

Enrichment, isolation, and biodegradation potential of long-branched chain alkylphenol degrading non-ligninolytic fungi from wastewater.

4-t-Octylphenol (4-t-OP) has become a serious environmental concern due to the endocrine disruption in animals and humans. The biodegradation of 4-t-OP by pure cultures has been extensively investigated only in bacteria and wood-decaying fungi. In this study we isolated and identified 14 filamentous fungal strains from wastewater samples in Taiwan using 4-t-OP as a sole carbon and energy source. The isolates were identified based on sequences from different DNA regions. Of 14 fungal isolates, 10 strains grew effectively on solid medium with a wide variety of endocrine disrupting chemicals as the sole carbon and energy source. As revealed by high-performance liquid chromatography analysis, the most effective 4-t-OP degradation (>70%) in liquid medium was observed in Fusarium falciforme after 15days. To our knowledge, this is the first report on the degradation of 4-t-OP as a sole carbon and energy source by non-ligninolytic fungi.

Biodegradation of the endocrine disrupter 4-tert-octylphenol by the yeast strain Candida rugopelliculosa RRKY5 via phenolic ring hydroxylation and alkyl chain oxidation pathways.

4-(1,1,3,3-tetramethylbutane)-phenol (4-tert-OP) is one of the most prevalent endocrine disrupting pollutants. Information about bioremediation of 4-tert-OP remains limited, and no study has been reported on the mechanism of 4-tert-OP degradation by yeasts. The yeast Candida rugopelliculosa RRKY5 was proved to be able to utilize 4-methylphenol, bisphenol A, 4-ethylphenol, 4-tert-butylphenol, 4-tert-OP, 4-tert-nonylphenol, isooctane, and phenol under aerobic conditions. The optimum conditions for 4-tert-OP degradation were 30°C, pH 5.0, and an initial 4-tert-OP concentration of 30mgL-1; the maximum biodegradation rate constant was 0.107d-1, equivalent to a minimum half-life of 9.6d. Scanning electron microscopy revealed formation of arthroconidia when cells were grown in the presence of 4-tert-OP, whereas the cells remained in the budding form without 4-tert-OP. Identification of the 4-tert-OP degradation metabolites using liquid chromatography-hybrid mass spectrometry revealed three different mechanisms via both branched alkyl side chain and aromatic ring cleavage pathways.

Onychomycosis Associated with Exophiala oligosperma in Taiwan.

A fungus was isolated from a nail of a 54-year-old female patient with onychomycosis in Taiwan. Based on ITS rDNA as well as beta tubulin gene sequences and microscopic analyses, this fungus was identified as Exophiala oligosperma. This is the first record of E. oligosperma in Taiwan. Negative keratin azure test indicates that keratin degradation is not involved in cases of E. oligosperma associated with skin and nail diseases.