Determination of three cresol isomers in sewage sludge by solid-liquid extraction with low temperature purification and gas chromatography-mass spectrometry.

Cresols are chemical contaminants derivative from phenol which can be found in sewage sludge. However, little attention has been given to monitoring these compounds in environmental matrices in the literature. Thus, the objective of this study was to develop a simple method based on solid-liquid extraction with low temperature purification for determining three cresol isomers in sludge. The quantification of these compounds was performed by gas chromatography coupled to mass spectrometry with a previous derivatization step. After a detailed study, the cresol recovery was higher than 91%, with relative standard deviation lower than 12% and a limit of quantification of 20 µg kg-1. Linearity was achieved between 10 and 90 µg L-1 (R2 > 0.98) with the standard solutions prepared in matrix extracts due to the trouble caused by the matrix effect. The proposed method was applied with success for monitoring cresols in sewage sludge samples coming from six different wastewater treatment plants. All samples showed contamination by cresols, mainly p-cresol with values between 32.3 and 516.9 µg kg-1. The majority of the analyzed samples showed a total sum of the isomers higher than the maximum residue limit established by Brazilian legislation (160 µg kg-1).

Bacterial community structure within an activated sludge reactor added with phenolic compounds.

Biodegradation of phenolic compounds in bioreactors is well documented, but the changes in the bacterial populations dynamics during degradation were not that often. A glass bubble column used as reactor was inoculated with activated sludge, spiked with 2-chlorophenol, phenol and m-cresol after 28 days and maintained for an additional 56 days, while the 16S rRNA gene from metagenomic DNA was monitored. Proteobacteria (68.1%) dominated the inoculum, but the bacterial composition changed rapidly. The relative abundance of Bacteroidetes and Firmicutes decreased from 4.8 and 9.4 to <0.1 and 0.2% respectively, while that of Actinobacteria and TM7 increased from 4.8 and 2.0 to 19.2 and 16.1% respectively. Phenol application increased the relative abundance of Proteobacteria to 94.2% (mostly Brevundimonas 17.6%), while that of Bacteroidetes remained low (1.2%) until day 42. It then increased to 47.3% (mostly Leadbetterella 46.9%) at day 84. It was found that addition of phenolic compounds did not affect the relative abundance of the Alphaproteobacteria initially, but it decreased slowly while that of the Bacteroidetes increased towards the end.

Respirometric response and microbial succession of nitrifying sludge to m-cresol pulses in a sequencing batch reactor.

A nitrifying consortium was kinetically, stoichiometrically and molecularly characterized via the in situ pulse respirometric method and pyrosequencing analysis before and after the addition of m-cresol (25 mg C L-1) in a sequencing batch reactor (SBR). Five important kinetic and stoichiometric parameters were determined: the maximum oxygen uptake rate, the maximum nitrification rate, the oxidation yield, the biomass growth yield, and the substrate affinity constant. An inhibitory effect was observed in the nitrification process with a recovery of this by up to eight SBR cycles after m-cresol was added to the system. However, full recovery of the nitrification process was not observed, as the maximum oxygen uptake rate was 25% lower than that of the previous operation without m-cresol addition. Furthermore, the pyrosequencing analyses of the nitrifying consortium after the addition of only two pulses of 25 mg C L-1 m-cresol showed an important microbial community change represented by a decrease in the nitrifying populations and an increase in the populations degrading phenolic compounds.

What is the optimum concentration of m-cresol in antivenoms?

Antivenoms against snake and scorpion envenomations are usually equine in nature and composed mostly of F(ab')2; additionally, phenol and m-cresol are mainly employed for their preservation. Although there is no study on this subject, m-cresol is utilized by most manufacturers in a concentration that ranges from 0.15 to 0.35 g percent. Decreasing the concentration of m-cresol to its minimal effective level may protect victims from its toxic effects and keep the antivenom stable during its shelf life without forming any aggregates. In the present work, different concentrations of m-cresol, ranging from 0.1 to 0.35 g percent, were used with some selected batches of snake and scorpion antivenoms. A low concentration of 0.15 g percent showed an acceptable preserving result that complies perfectly with antimicrobial specifications stated by the British Pharmacopoeia. Tested antivenoms (in 12 batches), when kept in a cold room for 39 months (more than their shelf life), retained their physical, chemical and microbiological activities according to the specifications of pharmacopeias. The present data demonstrated that reduction of m-cresol concentration to 0.15 g percent in case of equine F(ab')2 antivenoms will improve safety of such preparations and preserve their stability during their shelf life.(AU)

What is the optimum concentration of m-cresol in antivenoms?

Antivenoms against snake and scorpion envenomations are usually equine in nature and composed mostly of F(ab')2; additionally, phenol and m-cresol are mainly employed for their preservation. Although there is no study on this subject, m-cresol is utilized by most manufacturers in a concentration that ranges from 0.15 to 0.35 g percent. Decreasing the concentration of m-cresol to its minimal effective level may protect victims from its toxic effects and keep the antivenom stable during its shelf life without forming any aggregates. In the present work, different concentrations of m-cresol, ranging from 0.1 to 0.35 g percent, were used with some selected batches of snake and scorpion antivenoms. A low concentration of 0.15 g percent showed an acceptable preserving result that complies perfectly with antimicrobial specifications stated by the British Pharmacopoeia. Tested antivenoms (in 12 batches), when kept in a cold room for 39 months (more than their shelf life), retained their physical, chemical and microbiological activities according to the specifications of pharmacopeias. The present data demonstrated that reduction of m-cresol concentration to 0.15 g percent in case of equine F(ab')2 antivenoms will improve safety of such preparations and preserve their stability during their shelf life.(AU)