Pyrogallol

Hydrolysis

Administrative data

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Data source

Reference

Reference Type:

review article or handbook

Title:

The Effect of Tannic Compounds on Anaerobic Wastewater Treatment

Author:

J. A. Field

Year:

1989

Bibliographic source:

Field, J. A. (1989) The Effect of Tannic Compounds on Anaerobic Wastewater Treatment. Doctoral Thesis. Wageningen Agricultural University. Wageningen, The Netherlands.

Report date:

1989

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

In thi study was performen a measurement of COD, UV absorbance, color and tannins; the H PLC characterization of phenolic solutions; and the autoxidation method (as described in the "Details on analytical method" field). The tannin determination was based on the COD and UV of the phenolic stock solution which was adsorbed on an insoluble polyamide, polyvinylpyrrolidone (PVP).

In this study, granular sludge was first prefed for one week with 4 g COD L~' of stock VFA solution to adapt the sludge to the VFA substrate. At the end of the prefeeding period, the supernatent was decanted, thereafter phenolic compounds were added together with 4 g COD L~' VFA to initiate the first feeding of the toxicity assay. After two weeks of exposure to the phenolic medium, the supernatant was decanted and replaced with a 4 g COD L~' VFA solution in order to determine the residual activity of the sludge during the second feeding of the toxicity assay in the absence of the phenolic solution. The specific conditions during the assays are reported in Table 1. Two experimentswere conducted. In the first experiment the toxic effects of autoxidizing pyrogallol were examined. The characteristics of the pyrogallol stock solution are reported in Table 1. In the second experiment, the toxicity of purpurogallin was examined at various concentrations. The purpurogallin stock solutions were prepared in demineralized water, as they had lower solubility in tap water (presumably due to the interactions with Ca2+).

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Pyrogallol

EC Number:

201-762-9

EC Name:

Pyrogallol

Cas Number:

87-66-1

Molecular formula:

C6H6O3

IUPAC Name:

benzene-1,2,3-triol

Test material form:

solid

Specific details on test material used for the study:

The phenolic compounds, pyrogallol and purpurogallin were obtained from Jassen Cheica (Tilburg, The Netherlands).

Radiolabelling:

no

Study design

Analytical monitoring:

yes

Buffers:

KHPO4 0.2 M

Results and discussion

Preliminary study:

Not performed

Transformation products:

yes

Identity of transformation products

No.:

#1

Reference

Reference substance name:

Unnamed

IUPAC name:

2,3,4,6-tetrahydroxybenzo[7]annulen-5-one

CAS number:

569-77-7

Molecular formula:

C11H8O5

Molecular weight:

220.18

SMILES notation:

C1=CC2=CC(=C(C(=C2C(=O)C(=C1)O)O)O)O

InChl:

InChI=1S/C11H8O5/c12-6-3-1-2-5-4-7(13)10(15)11(16)8(5)9(6)14/h1-4,13,15-16H,(H,12,14)

Total recovery of test substance (in %)

Remarks on result:

not measured/tested

Dissipation DT50 of parent compound

Remarks on result:

not measured/tested

Any other information on results incl. tables

The data collected at various stages of the pyrogallol autoxidation are summarized in Figure 1. During the initial stages of the autoxidation, the formation of color was

associated with the conversion of pyrogallol to its first autoxidation intermediate, purpurogallin (Figure 1A, 2A and 2B). Associated with the formation of purpurogallin was a precipitate. It was first evident after 10 minutes of autoxidation when the pH of the solution was dropped to 7 by addition of HCl (ie. in order to render the solutions suitable for the bioassays). A purpurogallin standard also had the same poor solubility in water at a neutral or acidic pH. The large decreases in UV and COD of the filtered solutions from 10 minutes to 1 hour of autoxidation are due to the formation of the purpurogallin precipitate rather than oxidative destruction of the phenolic compounds (Figure 1A). Eventually, the precipitate accumulated to up to approximately 50% of the original pyrogallol COD when the oxidation was stopped (pH lowered to 7) at time intervals between 1.5 and 3 hours (data not shown).

When the autoxidation was continued to 6 hours, the precipitate was no longer evident. Most of the purpurogallin was further oxidized to soluble products. These products were present in the HPLC chromatogram as nontannic peak area with a low retention time or as tannic peak area at high retention times (Figure 2C). The estimation of high MW tannins by assuming they occupy the peak area of more than 28 minute retention time, as was the case with catechin, was not applicable for the autoxidation products of pyrogallol. Purpurogallin, a dimer, had a retention time of 31 minutes with the HPLC procedure. Therefore, it is conceivable that other products of the autoxidation with low MW also occupied the peak area at high retention times.

When the autoxidation was continued beyond 6 hours, a destructive effect on the intermediate autoxidation products was evident. A decrease in color, COD and UV215 was observed and most of the HPLC peak area was present at very low retention times (Figure 2D), which indicates polar low MW compounds.

Pyrogallol was not a good tannin since it was only partially (36%) adsorbed by PVP. Its first autoxidation product, purpurogallin was adsorbed by PVP to the same extent. In factduring the first 6 hours of the autoxidation, there was no significant change in the percentage of the phenolic compounds adsorbed by PVP (tannins) (Figure IB). Since between 1 and 6 hours of autoxidation there was a considerable loss in pyrogallol and purpurogallin,the PVP determinable tannins remaining are attributable at least in part to some tannic compounds (with a high percentage adsorbance by PVP) as is evident in the HPLC plots (Figure 2C). During the destructive phase of the autoxidation (beyond 6 hours), the PVP determinable tannin concentration decreased. The tannic compounds formed were eventually destroyed (Figure 2D).

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Executive summary:

Monomeric phenolic compounds are susceptible to oxidative alterations to colored products during short periods of exposure to air. These alterations can potentially affect the methanogenic toxicity of phenolic wastewaters intended for anaerobic treatment. The autoxidation of dihydroxy ring type phenols like catechin, a condensed tannin monomer, causes polymerization. Initially, methanogenic toxic oligomeric tannins are formed, but these are later polymerized further to nontoxic compounds of high MW. The tannin theory is applicable to describing the modifications in the methanogenic toxicity that result from the alterations in MW by polymerization. However with trihydroxy ring phenols, the oxidative reactions are not entirely polymerative, and the resulting products do not necessarily have tannic structures. Nonetheless, these modifications may be of great importance, since rather strong methanogenic toxins were produced by short autoxidation of the hydrolyzable tannin monomer model compound, pyrogallol. The objective of this work was to study the methanogenic toxic products of pyrogallol autoxidation in more detail.