Screening of toxicological properties of 4-methylbenzoic acid by oral administration to rats

Temperature-regulated and starvation-induced refractory para-toluic acid anaerobic biotransformation

Little research was focused on the anerobic degradation of refractory para-toluic acid at present. Thus, temperature-regulated anaerobic system of para-toluic acid fed as sole substrate was built and investigated via microbiota, metabolism intermediates, and function prediction in this study. Results showed that low methane yield was produced in para-toluic acid anaerobic system at alkaline condition. And the causes were owing to anaerobic methane oxidation and potentially H2S production at 37 °C, N2 production by denitrification before starvation and propionic acid occurrence after starvation at 27 °C, and production of N2 and free ammonia, and accumulation of acetic acid at 52 °C. Simultaneously, hydrogenotrophic methanogenesis dependent on syntrophic acetate oxidation (SAO) was predominant, facilitating the removal of para-toluic acid at 52 °C. Moreover, the key intermediate changed from phthalic acid of 37 °C and 27 °C before starvation to terephthalic acid of 52 °C. Starvation promoted removal of para-toluic acid through benzoyl-CoA pathway by Syntrophorhabdus, enrichment of syntrophic propionate degraders of Bacteroidetes and Ignavibacteriaceae, and increase of methylotrophic methanogens.

High expression of ring-hydroxylating dioxygenase genes ensure efficient degradation of p-toluate, phthalate, and terephthalate by Comamonas testosteroni strain 3a2

Para-toluic acid, a major pollutant in industrial wastewater, is hazardous to human health. It has been demonstrated that Gram-negative bacteria are among the most effective degraders of para-toluic acid. In this study, the ability of Comamonas testosteroni strain 3a2, isolated from a petrochemical industry wastewater, to degrade para-toluic acid was investigated. The effect of different carbon (glucose and ethylene glycol) and nitrogen sources (urea, yeast extract, peptone, NaNO₃, NH₄NO₃) on the biodegradation of para-toluic acid by the isolate 3a2 was evaluated. Furthermore, ring hydroxylating dioxygenase genes were amplified by PCR and their expression was evaluated during the biodegradation of para-toluic acid. The results indicated that strain 3a2 was able to degrade up to 1000 mg/L of para-toluic acid after 14 h. The highest degradation yield was recorded in the presence of yeast extract as nitrogen source. However, the formation of terephthalic acid and phthalic acid was noted during para-toluic acid degradation by the isolate 3a2. Toluate 1,2-dioxygenase, terephthalate 1,2 dioxygenase, and phthalate 4,5 dioxygenase genes were detected in the genomic DNA of 3a2. The induction of ring hydroxylating dioxygenase genes was proportional to the concentration of each hydrocarbon. This study showed that the isolate 3a2 can produce terephthalate and phthalate during the para-toluic acid biodegradation, which were also degraded after 24 h.

Experimental and modeling study of pure terephthalic acid (PTA) wastewater transport in the vadose zone

PTA wastewater discharged from a factory was selected as the research object in this project and CODcr was selected as the characteristic pollution factor. Static adsorption and soil column leaching experiments of silty clay and clayey soil were carried out to study the adsorption, bio-degradation and dispersion coefficient of CODcr in PTA wastewater. Hydrus-1D was used to build the convection-diffusion model to demonstrate the migration of PTA wastewater in the vadose zone. The results indicate that silty clay and clayey soil in the vadose zone can adsorb, degrade and impede the contaminants in PTA wastewater; however, the coefficient of adsorption and degradation were very low, they were down to 0.0002 L g(-1), 0.0003 L g(-1) and 0.0097 d(-1), 0.0077 d(-1) for silty clay and clayey soil, respectively. Under the virtual condition that, wastewater in the sewage pool is 5 m deep, CODcr concentration is 4000 mg L(-1), vadose zone is 21 m, PTA wastewater will reach the phreatic surface after 20.87 years. When wastewater in the sewage pool is 7 m with other conditions unchanged, after 17.18 years PTA wastewater will reach groundwater. The results show that there is a higher pollution risk for groundwater if we do not take any anti-seepage measures.

Single and repeated oral dose toxicity study of fucoxanthin (FX), a marine carotenoid, in mice

Fucoxanthin (FX), a xanthophyll derivative, is an orange-colored pigment present in edible brown algae. As a part of safety evaluation, single and repeated oral dose toxicity study of FX was conducted. In a single dose study, FX purified from seaweed was orally administered to male and female ICR mice at doses of 1,000 and 2,000 mg/kg. In a repeated doses study, FX at doses of 500 and 1,000 mg/kg was orally administered for 30 days. In both studies, no mortality and no abnormalities in gross appearance were observed. In the repeated doses study, histological observation revealed no abnormal changes in liver, kidney, spleen and gonadal tissues of any of the FX-treated groups. However, significantly increased total cholesterol concentrations were shown by plasma biochemical analyses in all FX-treated groups. Although total bilirubin concentrations were increased by FX, it was established that presence of fucoxanthinol, a major metabolite of FX, interfered with bilirubin determination in plasma. To further ascertain the safety of FX, the mechanism by which FX induces hypercholesterolemia in mice and species differences in the induction of hypercholesterolemia should be elucidated.