13
The Stability of Pentachlorophenol and Chlorinated Dioxins to Sunlight, Heat, and Combustion
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R. H . S T E H L , R. R. PAPENFUSS, R. A. B R E D E W E G , and R. W . ROBERTS Analytical Laboratories, The Dow Chemical Co., Midland, Mich. 48640
Pentachlorophenol
in field-use conditions
is subjected
environmental factors leading to its degradation, theoretically
in
chlorinated
dibenzo-p-dioxin
to
resulting formation.
Analysis of combustion products of wood and paper treated with pentachlorophenol
indicated no increase and possibly
a decrease in octachlorodibenzo-p-dioxin paper treated with sodium
slightly in octachlorodibenzo-p-dioxin combustion.
concentration while
pentachlorophenate
increased
concentration
Photolysis of sodium pentachlorophenate
different sources of artificial sunlight and natural resulted in severe degradation with
only
formed.
trace amounts
2,7-Dichloro-
of the
of
and
after under
daylight
pentachlorophenate
octachlorodibenzo-p-dioxin
2,3,7,8-tetrachlorodibenzo-p-di-
oxins are subject to rapid photolytic decomposition
under
artificial sunlight while octachlorodibenzo-p-dioxin
shows
considerably
more stability.
2,3,7,8-Tetrachlorodibenzo-p-
-dioxin is somewhat stable to 700°C complete at
while decomposition
is
800°C.
/^\ver the past several years concern over the contamination of our environment has increased.
This interest has caused industry to
examine more closely the effects its products might have on our surroundings. N o t only are the possible effects of the products themselves being considered, but it is becoming increasingly necessary to include the effects of impurities contained i n these materials, as well as the effects of the degradation products formed b y environmental forces such as heat, fire, and sunlight. 119
Blair; Chlorodioxins—Origin and Fate Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
120
CHLORODIOXINS
ORIGIN A N D F A T E
This paper discusses the effects of the pyrolysis of wood and paper treated with pentachlorophenol or sodium pentachlorophenate along with the exposure of sodium pentachlorophenate to ultraviolet light. The effect of heat, light, and air with respect to some of the chlorinated dibenzo-p-dioxins w i l l be considered.
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Methods Pyrolysis of Wood or Paper Treated with Pentachlorophenol or Sodium Pentachlorophenate. The treated sample was combusted in a modified 250-ml Erlenmeyer flask that had been fitted with a glass grate. The volatile combustion products were captured in cold traps immersed in an ice bath, dry ice, and liquid nitrogen (connected i n series). Combustion residues, including ashes, were dissolved i n benzene. The benzene solution containing the combustion products was washed with I N sodium hydroxide solution, sulfuric acid, and sulfuric acid containing a small amount of water. Finally, the washed solution was passed through a silica gel column using 20% benzene-hexane (v/v) solution as the eluant. Octachlorodibenzo-p-dioxin in the fraction was determined by gas chromatography using a Varian 1200 gas chromatograph fitted with a 7-foot 1/8 inch 5 % Q F 1 on 60/80 mesh Gas Chrom Q column equipped with either electron capture or flame ionization detectors. Heat Stability of 2,3,7,8-Tetrachlorodibenzo-f-dioxin. A sample boat containing 1-3 mg of 2,3,7,8-tetrachlorodibenzo-p-dioxin was placed in a Sargent Tube Heater ( M o d e l J-807 ) which contained a 1/2 inch i.d. quartz tube. A i r was aspirated through the tube at a velocity of 0.02 ft/sec. This velocity gave a residence time of 21 sec. (Residence time was extended by connecting a second heater in series with the first.) Decomposition products were captured in two traps immersed in dry ice followed by a third trap containing 5 m l of benzene. After 1 hour, the boat, tube, and traps were rinsed with benzene. The benzene solution was analyzed by gas chromatography using an electron capture detector to determine the concentration of unreacted 2,3,7,8-tetrachlorodibenzo-p-dioxin. Light Stability of Sodium Pentachlorophenate. Pentachlorophenol was dissolved i n a high capacity p H 8 phosphate buffer such that the final concentration of sodium pentachlorophenate was 500 ppm. The pentachlorophenate solutions were placed in quartz vessels fitted with ground, quartz stoppers and exposed to various sources of ultraviolet light as well as daylight. T w o 20-watt fluorescent black lights were placed 2 inches from the liquid's surface. A General Electric R.S. sunlamp and a high intensity mineral light emitting at 254 nm were placed 11 inches from the surface of their respective solutions. The flask exposed to daylight was suspended 20 inches above the laboratory roof. Unreacted sodium pentachlorophenate was determined by ultraviolet spectroscopy. Octachlorodibenzo-p-dioxin was separated by extraction with three successive 50-ml portions of benzene. The combined benzene layers were washed with 0.1N sodium hydroxide solution, 0.1N hydrochloric acid solution, and deionized water. Octachlorodibenzo-p-dioxin was determined by gas chromatography using an electron capture detector.
Blair; Chlorodioxins—Origin and Fate Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
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13.
STEHL E T A L .
121
Sunlight, Heat, and Combustion
Light Stability of Chlorinated Dibenzo-£-dioxins. A known concentration of chlorinated dibenzo-p-dioxin was placed i n a quartz 1-cm path length cell. A General Electric R.S. sunlamp was placed either 0.5 or 1.0 meters from the face of the cell. The stability of the chlorinated dibenzo-p-dioxin was monitored using ultraviolet spectroscopy. Stability of 2,3,7,8-Tetrachlorodibenzo-^-dioxin Towards Air Oxidation Under Simulated Conditions. A i r was bubbled through two borosilicate glass gas absorption bottles equipped with fritted glass bubblers. The first bottle contained 1-octanol for presaturation of the air, and the second bottle contained 1-octanol solutions of the dioxin treated as follows: (1) octanol only, (2) octanol mixed with 74-105/* glass beads to increase the surface area, and (3) octanol mixed with magnesium oxide to simulate a basic soil. The original solution and the sample solutions were scanned with a U V spectrophotometer at various time intervals for 4 days to determine the stability of 2,3,7,8-tetrachlorodibenzop-dioxin. Table I. Octachlorodibenzo-^-dioxin Concentration before and after Burning Paper and Wood Treated with Pentachlorophenol and Sodium Pentachlorophenate
Sample Wood Wood Wood Paper Paper Paper Paper Paper
+ Penta + Pure P e n t a + + + +
6
Penta Pure Penta N a Penta Pure N a Pentad
Pentachlorophenol in Unburned Sample, %
Octachlorodibenzodioxin,
ppm
In Sample
In Combustion Products
0.048, 0.050 1.0, 1.0 6.0, 6.0
