UDC 614.718

M. T. Dmitriev, S. A. Volkov, E. G. Rastyannikov, E. E. Sotnikov

Investigation of the Composition of Thermal Degradation Products of Biologically Active Compounds as Atmospheric Pollutants

A. N. Sysin Institute of General and Municipal Hygiene, Academy of Medical Sciences of the USSR, Moscow

The most promising method for removing biologically active compounds (microorganisms, antibiotics, food and other household waste) from industrial exhaust gases is their destruction by thermal degradation, including incineration. It must be recognized, however, that during the sterilization and destruction of waste, thermal degradation products are released into the atmosphere alongside carbon dioxide and water vapor; these products may have adverse effects on the population. The composition of toxic products formed by the degradation of biological substances has been scarcely studied, and data are available only for individual industries. Thus, aldehydes and ketones (crotonaldehyde, adipaldehyde, acetone), alcohols (propanol, butanol), amines (ethanolamine, aminodimethylbenzene), unsaturated hydrocarbons (ethylene, butadiene), and aromatic hydrocarbons (benzene, mesitylene) have been detected by mass spectrometry in exhaust gases from antibiotic production (M. T. Dmitriev et al.; Yu. V. Novikov et al.).

In the present work, the products of thermal degradation of biologically active substances were identified during their pyrolysis at 700 °C for 2 min in the presence of air. Proteins and amino acids were selected as the principal constituents. Bovine albumin and protein–vitamin concentrate (BVK) were selected as representative proteins, and DL-β-phenyl-β-alanine and DL-β-alanine as representative amino acids. Pyrolysis was carried out in a U-shaped quartz tube with a nichrome coil wound around its outer surface. The tube was connected to a four-way valve. After pyrolysis, the products were swept into the chromatograph or sampled with a syringe through a rubber cap for direct injection of the gaseous products onto the chromatographic column. The pyrolysis products were analyzed by gas chromatography–mass spectrometry and by gas chromatography using a dual-flame thermionic detector. Most substances were identified using a computer-equipped LKB-2091 gas chromatograph–mass spectrometer. The components of the gas mixture were separated on a 25 m glass capillary column coated with SF-30. The injection system allowed splitless introduction of the sample into the capillary column. The syringe-sampled pyrolysis products were injected through a rubber cap into a heated glass tube connected to the instrument’s gas line. A capillary loop cooled with liquid nitrogen was placed between the glass tube and the capillary column, where the analytes were trapped by freezing. Two to three minutes after sample injection, the liquid nitrogen vessel was removed and the loop heater switched on, whereupon the substances entered the capillary column. The injected sample volume was 0.5–1 mL. For the first 4 min, the column temperature was maintained at 30 °C; it was then raised to 150 °C at 20 °C/min. Helium was used as the carrier gas. The identified thermal degradation products are presented in the table.

To determine highly volatile hydrocarbons and identify nitrogen-containing compounds, gas chromatography with temperature programming and selective detection of nitrogen-containing compounds was used. A dual-flame thermionic detector installed on a Tsvet-104 gas chromatograph served as the selective detector. The lower cell of this detector acts as a conventional flame ionization detector and detects both hydrocarbons and nitrogen-containing compounds, whereas the upper cell detects only the latter. Comparison of chromatograms recorded from the signals of the two cells permits group identification: the absence of a peak in the chromatogram recorded from the upper-cell signal indicates that it belongs to a hydrocarbon; a sharp increase in intensity compared with the signal from the lower—

Concentrations of thermal degradation products of biologically active compounds (%)

Note. (0)—not detected.

…of the lower cell indicated that it belonged to the nitrogen-containing compounds. When the peak from the upper cell was noticeably higher than that from the lower cell, but the latter was also sufficiently intense, it could be assumed that the peak was composite, resulting from the superposition of a hydrocarbon peak and a nitrogen-containing compound peak. After determining the group to which the peak belonged, identification was carried out using retention indices.

Chromatographic separation was performed on packed columns of various lengths (1–2 m), filled with Polysorb-1, Porapak N, or Hexasorb AW containing SF-30 and Carbowax 20 M, with the temperature programmed from 50 to 175 °C at a rate of 40 °C/min. The pyrolysis products were introduced into the chromatographic column directly from a U-shaped quartz tube through a four-way valve.

Typical chromatograms of the pyrolysis products of DL-β-alanine and bovine albumin were obtained on columns packed with Porapak N and Polysorb-1, using a two-flame thermionic detector. The columns with polymeric sorbents enabled the separation of highly volatile hydrocarbons and nitrogen-containing compounds. The combination of gas chromatography with a selective thermionic detector and gas chromatography–mass spectrometry made it possible to separate and identify compounds of different classes in complex mixtures.

Since the total concentration of organic substances in industrial exhaust gases depends on operating conditions (production capacity, the composition of the biologically active substances being removed, the quantity of air used, etc.), it is expedient to express the concentrations of individual constituents as mass percentages of the total organic matter content (M. T. Dmitriev and N. A. Kitrosskii). Ammonia is also included by convention in the total content, making it possible to account for its emission as well. First, the thermal degradation products should be noted for their multicomponent composition: more than 40 specific compounds were identified. Thus, no dominant component was found for the proteins: for both bovine albumin and BVK, four substances are present at approximately equal concentrations. For amino acids, the dominant substances vary; they may be benzene or ethylene cyanide. The toxic substances identified included paraffinic hydrocarbons (ethane, isobutane, isopentane) and unsaturated hydrocarbons (ethylene, acetylene, propylene, butylene, butadiene, pentene, hexene, octene), including cycloolefins (methylcyclopropene, cyclopentene, cyclohexene), dienes (isoprene, hexadiene), and cyclic dienes (cyclopentadiene, cyclohexadiene, methylcyclopentadiene). Aromatic hydrocarbons were also detected (toluene, ethylbenzene, styrene, phenylacetylene). The nitrogen-containing compounds identified included imines (ethylenimine, methylethylenimine), nitriles (acetonitrile, propionitrile), amines (trimethylamine), cyanides (methyl isocyanide, ethylene cyanide), and heterocyclic nitrogen-containing compounds (methylpyrrole, methylpyrazole, methyl- and ethylpyrazines). No substantial difference was found between the thermal degradation products of proteins and amino acids. Most substances released by proteins are also formed during the thermal degradation of amino acids (pentene, benzene, toluene, methylethylenimine, acetonitrile, ethane, ethylene). The combined data therefore also make it possible to determine the average composition of the thermal degradation products of biologically active compounds (see table).

The identified thermal decomposition products were also found in the exhaust gases of industrial plants. Unsaturated and aromatic hydrocarbons, as well as amines, were detected in the largest quantities in the samples. Many of the substances identified can not only have toxic effects but also cause strong unpleasant odors (for example, the odor thresholds for pyrazoles and pyrazines can be as low as 0.01 µg/m³). Thus, a study of unpleasant odors from refuse chutes (G. I. Sidorenko et al.) identified substances such as ammonia, dimethylamine, methylpyrrole, and cyclopentadiene. These same substances are also products of the thermal decomposition of biological substances.

Thus, the studies revealed toxic substances that pollute the ambient air during the removal of biologically active compounds from exhaust gases.

References

Dmitriev, M. T., and Kitrosskii, N. A. Gig. i san., 1968, no. 11, p. 48.

Dmitriev, M. T., Novikov, Yu. V., and Khrustaleva, V. A. In: Proceedings of the 16th All-Union Congress of Hygienists and Sanitary Physicians. Moscow, 1972, p. 171.

Novikov, Yu. V., Dmitriev, M. T., and Khrustaleva, V. A. Gig. i san., 1973, no. 6, p. 70.

Sidorenko, G. I., Gubernskii, Yu. D., and Dmitriev, M. T. Ibid., 1978, no. 5, p. 10.

Received July 2, 1980.