Decomposition of phenolic endocrine disrupting chemicals by potassium permanganate and γ-ray irradiation

Article abstract of DOI:10.1246/bcsj.76.1681

The decomposition of phenolic endocrine disrupting chemicals (P-EDCs), such as phenol, 4-t-butylphenol (BuP), and bisphenol A (BPA), in aqueous solutions by potassium permanganate (KMnO₄) was studied, and its efficiency was compared with that of hydroxyl radicals (OH^?) generated by ⁶⁰Co γ-ray irradiation. Various organic acids and inorganic carbon were formed in the decomposition of P-EDCs due to either KMnO₄ or OH^?. They were formed via direct aromatic ring cleavage in the case of KMnO₄ and via OH^? addition-substitution reactions, followed by aromatic ring cleavage, in the case of OH^?. Comparing the decrease in the P-EDCs based on the number of electrons, the amount of KMnO₄ spent to completely eliminate BuP and BPA was comparable to that of OH^?. Although three-times more KMnO₄ was needed for phenol decomposition than OH^?, the complete conversion of phenol into organic acids and inorganic carbon was achieved with 720 μM of electrons in both cases.

Full text of DOI:10.1246/bcsj.76.1681

ꢀ 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 1681–1685 (2003) 1681
Decomposition of Phenolic Endocrine Disrupting Chemicals
by Potassium Permanganate and ꢀ-Ray Irradiation
ꢀ
Yasuhiro Abe, Machiko Takigami,y Kouji Sugino,y Mitsumasa Taguchi,y Takuji Kojima,y
Tomonari Umemura,yy and Kin-ichi Tsunodayy
Research & Development Division, Nippon Chemical Industrial Co., Ltd.,
9-11-1, Kameido, Koto-ku, Tokyo 136-8515
yResearch Group for Environmental Conservation Processing, Department of Material Development,
Takasaki Radiation Chemistry Research Establishment, Japan Atomic Energy Research Institute,
1233, Watanuki-cho, Takasaki-shi, Gunma 370-1292
yyDepartment of Chemistry, Faculty of Engineering, Gunma University, 1-5-1, Tenjin-cho, Kiryu-shi, Gunma 376-8515
(Received November 7, 2002)
The decomposition of phenolic endocrine disrupting chemicals (P-EDCs), such as phenol, 4-t-butylphenol (BuP),
and bisphenol A (BPA), in aqueous solutions by potassium permanganate (KMnO4) was studied, and its efficiency was
compared with that of hydroxyl radicals (OHꢁ) generated by 60Co ꢀ-ray irradiation. Various organic acids and inorganic
carbon were formed in the decomposition of P-EDCs due to either KMnO4 or OHꢁ. They were formed via direct aro-
matic ring cleavage in the case of KMnO4 and via OHꢁ addition-substitution reactions, followed by aromatic ring cleav-
age, in the case of OHꢁ. Comparing the decrease in the P-EDCs based on the number of electrons, the amount of
KMnO4 spent to completely eliminate BuP and BPA was comparable to that of OHꢁ. Although three-times more
KMnO4 was needed for phenol decomposition than OHꢁ, the complete conversion of phenol into organic acids and in-
organic carbon was achieved with 720 mM of electrons in both cases.
Low concentrations of phenol and substituted phenols are
found widely in water in nature. Some of these compounds
have detrimental effects on water quality and are toxic to
aquatic organisms. Petrochemical processes and industrial fer-
mentation produce wastewater containing high concentrations
of phenols. Some phenolic compounds, including nonylphe-
nol, bisphenol A, and 2,4-dichlorophenol, have hormonal ac-
tivity, and are known as phenolic endocrine disrupting
chemicals. Bisphenol A and alkylphenols have been detected
at high mM levels (M = mol dmꢂ3) in exudates from waste dis-
posal sites.1,2 Effective methods are required to decompose
these compounds into low or non-toxic substances, such as or-
ganic acids and inorganic carbon.
KMnO4 decomposes phenol into organic acids or inorganic
carbon efficiently.3 In addition, KMnO4 has various advan-
tages for use in water treatment, such as low cost, ready avail-
ability commercially, and ease of handling. In the USA,
KMnO4 is used to remove or decompose phenol in industrial
wastewater treatment plants.4 A preliminary study examined
the use of KMnO4 in decomposing phenolic endocrine disrupt-
ing chemicals in aqueous solutions by analyzing the decrease
in the ratio of these compounds after the addition of KMnO4,
using solid-phase micro-extraction/gas chromatography
(SPME-GC).5 KMnO4 completely decomposed phenolic en-
docrine disrupting chemicals, and the rate constants of these
were higher than that of phenol, although the decomposition
products of these and the comparison of the decomposition ef-
ficiency with other oxidants were not investigated.
The hydroxyl radical (OHꢁ) is a very strong oxidizer, and is
considered to be the most effective method to remove/decom-
pose phenol in water. Advanced oxidation processes, such as
combinations of ozone,6–9 hydrogen peroxide,8,9 and ultravio-
let radiation,6–9 and ionizing (X-ray and ꢀ-ray) radiation10–12
are commonly used to generate OHꢁ, which can decompose
phenol in water effectively. Of these methods, ꢀ-ray irradia-
tion can be used to evaluate the ability of OHꢁ to decompose
phenol in water, because this method can produce uniform
amounts of OHꢁ in water, and the amount of OHꢁ can be easily
estimated from the G-value (moles/100 eV).13
This study investigated the efficiency with which KMnO4
decomposes phenolic endocrine disrupting chemicals, 4-t-bu-
tylphenol, bisphenol A, and phenol to low/non-toxic sub-
stances, such as organic acids and inorganic carbon, and com-
pared it with OHꢁ generated by 60Co ꢀ-ray irradiation.
Experimental
Preparation of Solutions Containing Phenolic Endocrine
Disrupting Chemicals. Phenol, 4-t-butylphenol (BuP), and bi-
sphenol A (BPA) of 99% purity (GL Science, Inc.) were used in
this study without further purification. Here, these three com-
pounds are collectively abbreviated as P-EDCs. They were dis-
solved homogeneously in ultra-pure water (Millipore Milli-Q
PLUS, pH 6.5, electric conductivity 18.2 Mꢀ cmꢂ1) by sonication
for 1 h. The concentration of each substance was 50 mM. A 1.5
dm3 aqueous solution was poured into a 2.0 dm3 glass vessel and
aerated by air bubbling for 15 min. 50 cm3 aliquots were placed
Published on the web August 15, 2003; DOI 10.1246/bcsj.76.1681

1682 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Decomposition of Phenolic EDCs
into glass vessels (volume: ꢁ40 ꢃ 75 mm, glass thickness: 1 mm)
with screw caps for the decomposition by KMnO4 and OHꢁ.
Decomposition of P-EDCs. Aqueous solutions of 0.2 wt %
and 2.0 wt % KMnO4 were prepared by dissolving 99% pure
KMnO4 (Kanto Chemical, Ltd.) in ultra-pure water. These solu-
tions were added to the P-EDC solutions to observe oxidation at
room temperature (25 ꢄC). The KMnO4 concentration in the sam-
ples was 10, 20, 40, 80, 120, 180, or 240 mM. The reaction of
KMnO4 with the P-EDC was allowed to proceed to completion
for 24 h.
ꢀ-ray irradiation using a 60Co-ꢀ-source was carried out at 25
ꢄC at JAERI, Takasaki. The absorbed dose in water was 33.3,
66.5, 133, 267, 400, 600, 800, or 2,400 Gy at a dose rate of 200
Gy hꢂ1, which was estimated by alanine/ESR dosimetry (ISO/
ASTM 51607: ‘‘Practice for use of the Alanine-EPR Dosimetry
System’’).
Analysis. A high-performance liquid chromatograph (HPLC:
Agilent 1100 series) with a UV/visible detector was used at a
wavelength of 280 nm for qualitative and quantitative analyses
of P-EDCs and decomposition products with an aromatic ring.
These substances were separated using a column (Shodex, RSpak
DE-613, 2.1 mm i.d. ꢃ 100 mm long) at 40 ꢄC with water–meth-
anol (25:75) as the eluent at a flow rate of 1.0 cm3 minꢂ1. The
identification and quantitative analysis of the substances were
based on comparisons of their retention times and the peak areas
with reference substances.
are used to calculate the concentrations of the formed
species. Of these species, H2O2, Hþ, OHꢂ, and H2 are stable,
while eꢂaq, Hꢁ, and OHꢁ react with organic compounds
rapidly. In the presence of oxygen, eꢂ and Hꢁ are converted
aq
ꢁ
to Oꢁ2ꢂ and HO2 , and make an insignificant contribution to the
degradation of phenols.14,15 Therefore, OHꢁ, which received
one electron, had the most important role in destroying P-
EDCs. From these assumptions, the decomposition of P-EDCs
by KMnO4 and OHꢁ in water can be compared in terms of the
number of electrons received.
The P-EDC samples decomposed using KMnO4 and OHꢁ
were analyzed by HPLC to measure the decomposition prod-
ucts with an aromatic ring. Figure 1 shows HPLC chromato-
grams with 120 mM of electrons of KMnO4 (KMnO4: 40 mM)
and OHꢁ (absorbed dose: 400 Gy). Peaks (e), (m), and (s) are
due to residual phenol, BuP, and BPA, respectively. For
KMnO4 decomposition, peaks (f), (g), and (t) appeared in
the chromatograms of the P-EDCs. Peaks (f) and (g) resulted
from colloidal MnO2 formed by the reaction of KMnO4 with
P-EDCs. No decomposition products with aromatic rings were
observed in the KMnO4 decomposition, except for unidentified
peak (t) in the chromatogram of BPA. This compound might
be formed via a side reaction, because the peak is very small.
Conversely, several aromatic compounds were observed in the
chromatogram of each P-EDC sample decomposed with OHꢁ.
Decomposition products with large peak areas were identified
as catechol (d), hydroquinone (c), and 4-t-butylcatechol
(BuCa, (l)), while the other peaks (a, b, h–k, and n–r) could
not be identified. The very large peak (r) in BPA might be
a hydroxylated BPA compound, since various hydroxylated
compounds were seen in the decomposition of phenol and
An ion chromatograph (IC: Metrohm 761 Compact IC) with an
anion suppressor was used for qualitative and quantitative analy-
ses of organic acids. The anions were separated using a column
(Shodex, IC SI 90-4E, 4.0 mm i.d. ꢃ 250 mm long) at room tem-
ꢄ
perature (25 C) with a mixture of 1.8 mM Na2CO3 and 1.7 mM
NaHCO3 as the eluent at a flow rate of 1.2 cm3 minꢂ1. The organ-
ic acids forming the decomposition products were identified and
quantitatively analyzed by comparing their retention times and
the peak areas with reference substances.
Inorganic carbon was determined by measuring the total organ-
ic carbon (TOC) concentration, where inorganic carbon was cal-
culated by subtracting the TOC from the carbon concentration
of the initial P-EDC sample (Phenol, 300 mM; BuP, 500 mM;
and BPA, 750 mM). The TOC concentration was measured with
a TOC analyzer (Shimadzu TOC Vwp). Potassium phthalate and
an equimolar mixture of NaHCO3/Na2CO3 were used as calibra-
tion standards to evaluate the total carbon and inorganic carbon,
respectively. The complete oxidation of TOC to carbon dioxide
was carried out with sodium peroxodisulfate and exposure to
UV light at 85 ꢄC. The concentration of CO2 formed was mea-
sured with a non-dispersive infrared detector.
Results and Discussion
KMnO4 can receive one, three, or five electrons when oxi-
dized in alkaline, neutral, and acidic solutions, respectively. In
this study, KMnO4 could receive three electrons, because the
decomposition of P-EDCs by KMnO4 was carried out in a neu-
tral solution.
The primary products of water formed by ꢀ-ray irradiation
(neutral pH) were as follows:13
H2O ! eꢂ
;
Hꢁ; OHꢁ; H2O2; Hþ; OHꢂ; H2 ð1Þ
aq
Fig. 1. HPLC chromatograms of P-EDC samples decom-
posed using KMnO4 and OHꢁ with 120 mM of electrons.
ꢂ ¼ 280 nm. Peaks: (c) hydroquinone, (d) catechol, (e)
phenol, (f) and (g) colloidal MnO2, (l) BuCa, (m) BuP,
(s) BPA, (peaks a, b, h–k, n–r, and t) unknown.
ð2:7Þ ð0:55Þ ð2:8Þ ð0:7Þ ð3:2Þ ð0:5Þ ð0:45Þ
The values in parentheses are the numbers of molecules
generated per 100 eV of absorbed energy, the G-value, and

Y. Abe et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1683
Fig. 2. Decrease in BuP and the formation of decomposi-
tion products (BuCa, total organic acids, and inorganic
carbon) for OHꢁ as a function of the number of
electrons. The concentrations of BuP and the products
are expressed in terms of the carbon concentration.
Fig. 3. Decrease in P-EDCs for KMnO4 and OHꢁ as a func-
tion of the number of electrons.
To evaluate the formation of organic acids and inorganic
carbon by KMnO4 and OHꢁ, the conversion ratios (CR) of or-
ganic acids and inorganic carbon to the initial P-EDCs were
defined as follows:
BuP. These results demonstrate that the decomposition of P-
EDCs by KMnO4 and OHꢁ differs, and few aromatic com-
pounds are formed with KMnO4.
CROA ¼ A=T ꢃ 100ð%Þ;
CRIC ¼ B=T ꢃ 100ð%Þ;
CROA+IC ¼ ðA þ BÞ=T ꢃ 100ð%Þ;
ð2Þ
ð3Þ
ð4Þ
Organic acids, such as formic, malic, maleic, acetic, and ox-
alic acid, as well as inorganic carbon were identified in P-EDC
samples decomposed using KMnO4 and OHꢁ. As an example,
Fig. 2 summarizes the decomposition of BuP with OHꢁ. The
figure shows the decrease in BuP and the formation of decom-
position products, i.e., BuCa, total organic acids, and inorganic
carbon for OHꢁ, in terms of the carbon concentration as a func-
tion of the number of electrons. A hydroxylated compound,
BuCa, was formed early in the decomposition; then, the con-
centrations of total organic acids and inorganic carbon in-
creased as BuCa decreased. Similar results were obtained
for phenol and BPA. These results show that the decomposi-
tion of P-EDCs by OHꢁ consists of OHꢁ addition-substitution
where A is the carbon concentration for all the organic acids
(mM), B is the concentration of inorganic carbon (mM), and
T is the initial carbon concentration of the P-EDCs (phenol,
300 mM; BuP, 500 mM; and BPA, 750 mM).
The total conversion ratio, CROA+IC, for KMnO4 and OHꢁ
as a function of the number of electrons, is shown in Figs.
4(a) and (b), respectively. In the decomposition of P-EDCs
by KMnO4, the CROA+IC for phenol increased almost linearly
with the number of electrons, while CROA+IC for BuP and BPA
started to increase after the P-EDCs were completely eliminat-
ed (see Figs. 3 and 4(a)). These results indicate that KMnO4
reacts not only with phenol, but also with the organic decom-
position products simultaneously, while KMnO4 reacts only
with BuP and BPA in the early stage, then with their decom-
position products. In the case of OHꢁ (Fig. 4(b)), the forma-
tion of organic acids and inorganic carbon for each P-EDC
was not observed in the early stage, because OHꢁ is rapidly
used for addition-substitution reactions, as shown in Fig. 2.
The decomposition curves of the P-EDCs are quite similar,
as shown in Fig. 3, suggesting that their substituent groups
do not influence the addition-substitution reactions of OHꢁ
for each P-EDC. In the later stage of decomposition, however,
CROA+IC is in the order: phenol > BuP > BPA. This means
that hydroxylated phenols are decomposed more easily than
reactions
and
a
subsequent
cleavage
of
the
aromatic ring to form organic acids and inorganic carbon.
In contrast, KMnO4 cleaves the aromatic ring directly to form
organic acids and inorganic carbon, since few decomposition
products with an aromatic ring were seen.
Figure 3 shows the decrease in P-EDCs for KMnO4 and
OHꢁ as a function of the number of electrons. There is an ap-
parent difference in the decomposition curves of the P-EDCs
with KMnO4; BuP and BPA were decomposed more rapidly
than phenol with the same number of electrons. In contrast,
the decomposition curves of the P-EDCs with OHꢁ were quite
similar. The amount of KMnO4 required for the complete
elimination of BuP and BPA was comparable to the amount
of OHꢁ, while three-times more KMnO4 than OHꢁ was needed
for phenol.

1684 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Decomposition of Phenolic EDCs
Fig. 4. Conversion ratio, CROA+IC, for KMnO4 (a) and OHꢁ (b) as a function of the number of electrons. See text for the definition
of the conversion ratio.
sition with KMnO4 causes direct aromatic ring cleavage to
form organic acids and inorganic carbon, while decomposition
Table 1. Conversion Ratios CROA, CRIC, and CROA+IC, for
the Decomposition of P-EDCs with 720 mM of Electrons
with OHꢁ proceeds through two steps: the addition-substitution
of OHꢁ and the subsequent cleavage of the remaining aromatic
rings. The amount of KMnO4 spent to completely eliminate
BuP and BPA was comparable to the amount of OHꢁ based
on the number of electrons. Although three-times more
KMnO4 than OHꢁ was needed to completely eliminate phenol,
the complete conversion of phenol into organic acids and inor-
ganic carbon was achieved with 720 mM of electrons in both
cases. These results demonstrate that KMnO4 is as effective
as OHꢁ generated by ꢀ-ray irradiation for decomposing P-
EDCs into low/non-toxic substances in water.
Using KMnO4 and OHꢁaÞ
KMnO4
OHꢁ
CROA CRIC CROA+IC CROA CRIC CROA+IC
Phenol
BuP
BPA
79
37
17
21
12
8
100
49
25
36
20
18
64
36
13
100
56
31
a) See text for the definitions of the conversion ratios.
hydroxylated BuP or BPA.
The conversion ratios CROA, CRIC, and CROA+IC for 720
mM of electrons of KMnO4 and OHꢁ are summarized in
Table 1. As shown in Table 1, CROA+IC of each P-EDC at
720 mM KMnO4 is comparable to that of OHꢁ. Especially,
the complete conversion of phenol into organic acids and inor-
ganic carbon was achieved in both cases. On the other hand,
the CROA+IC values in BuP and BPA were lower than that of
phenol. Since the carbon number of these molecules is higher
than that of phenol, larger amounts of the oxidants were need-
ed for their complete conversion into organic acids and inor-
ganic carbon. The percentage of inorganic carbon produced
by OHꢁ was higher than that produced by KMnO4. This can
be explained by the fact that OHꢁ has the highest redox poten-
tial.
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