UDC 696.43:620.197.7]:628.1.03

Yu. V. Novikov, Doctor of Medical Sciences;
K. O. Lastochkina, Candidate of Biological Sciences;
T. K. Parkhomchuk and A. N. Sergeev, Candidates of Medical Sciences;
D. A. Yakovlev and L. G. Gorokhova

Hygienic Assessment of the AG-4 Anticorrosion Sealant Used in Hot Water Supply Systems

F. F. Erisman Moscow Research Institute of Hygiene; All-Union Research Institute of Petroleum Machinery, Moscow

The development of district heating systems in large cities and industrial centers is based predominantly on open water-withdrawal systems. After mechanical and chemical treatment, the water is degassed in deaerators and supplied to the process system or collected in reservoirs (storage tanks) with capacities of 10–10,000 m³. Maintaining the necessary water reserves makes it possible to meet industrial process and utility needs without interruption, regardless of peak hot water demand.

A serious drawback of open water withdrawal is the extensive corrosion of reservoir and thermal power equipment, caused by the renewed saturation of water with atmospheric gases in reservoirs exposed to air. The kinetics of corrosion are governed by oxygen depolarization, which results from the unimpeded passage of oxygen from the air through the water to the metal surface. Consequently, the reservoirs, which are the most metal-intensive equipment and difficult to repair, bear the first “corrosion shock.” The solution to the problem of corrosion protection was seen in developing a method to prevent water from becoming saturated with oxygen by eliminating its contact with the atmosphere. Such methods included the creation of “air-

Diagram of the application of AG-4 sealant in a storage tank to protect deaerated water.

1 — overflow pipe; 2 — storage tank; 3 — maximum level of water with sealant; 4 — safety device; 5 — minimum level of water with sealant; 6 — anticorrosion protective film of sealant on the tank wall; 7 — deaerated water.

…cushions,” pontoons, floating balls, etc. However, they did not provide an airtight seal. The domestic chemical industry developed liquid sealants of the PG-2, AG-3A, and SVS types, which provided high gas impermeability but lacked durability in contact with hot water (70–95°). AG-4 sealant makes it possible to prevent metal corrosion almost completely. Owing to its viscous, mobile properties, the sealing liquid forms a permanently floating protective barrier 2.5–6 cm thick on the evaporating surface. AG-4 sealant is poured onto the bottom of the tank, after which water is supplied through a manifold installed in its lower part. The AG-4 sealant rises to the surface, forming a protective barrier and, at the same time, a continuous protective film on the inner surface of the tank (see figure) that “self-heals” as the water level is repeatedly lowered and raised.

AG-4 is an anti-aeration sealing liquid which, when applied to the evaporating surface of water (or a hydrophilic liquid), provides improved physicochemical stability and gas impermeability and retains its elasticity and protective, anti-aeration, and anticorrosion properties under operating conditions over a wide temperature range (from −37 to 130°) in contact with neutral, mildly alkaline, and acidic waters used for drinking and industrial and domestic purposes. The sealing liquid is prepared from highly refined mineral oil and synthetic ethylene-propylene rubber, with medical-grade paraffin added. The liquid contains P-200 polyisobutylene, SKEP-40 rubber, medical-grade paraffin, and perfume oil. The polyisobutylene in AG-4 sealant is physiologically harmless and free of monomers and other substances that adversely affect human organs (A. A. Berlin and S. M. Barkan; N. V. Lazarev). Polyisobutylene is approved for use in the food industry in the form of the SPI-200 blend (a paraffin–polyisobutylene composition) and in packaging materials based on it. The official list of new materials and reagents approved by the Main Sanitary and Epidemiological Directorate of the USSR Ministry of Health for use in domestic and drinking-water practice…

Table 1

Results of organoleptic and physicochemical examinations of water

Note. Here and in Table 2, K denotes the control experiment; Г denotes water beneath the AG-4 sealant.

…water supply, polyisobutylene 118-155-200 (TU 1755-54) is approved for lining the interiors of large-diameter reinforced-concrete pipes and, in the form of polyisobutylene lacquer, for coating the inner surfaces of tanks and cisterns for cold drinking water.

The perfume oil contained in the sealing liquid is a product of highly refined petroleum oils. Perfume oil is a mixture of mineral oils and solid paraffinic hydrocarbons. As is known, this oil, obtained from refined paraffins, is used in the perfume industry. Medical-grade paraffin (GOST 784-53) is also used in the perfume and medical industries.

Ethylene-propylene rubber (TU 38 10367-71) is synthesized from the nontoxic principal monomers ethylene and propylene.

In the literature we examined on the toxicological characteristics of the substances comprising AG-4 sealant, we found no data on the toxicity of the sealant components.

Experimental sanitary-chemical studies were conducted to determine the possible effect of the anti-aeration sealant AG-4 on the composition and quality of hot water. The conditions of these studies were established in accordance with the method of application of the sealant. Enamelled vessels, previously rinsed with hot water, were used both to study the sealant film and for the control. Two 10-liter vessels were filled with hot water at a temperature of 98–100°. In one of them, intended for the experiment, a 2.5 cm layer of sealant was poured over the hot water. Under operating conditions, a film of this thickness is intended to form in storage tanks with a capacity of 5,000 m³. In these tanks, the ratio of water to sealant averages 3,000:1; only during periods of the day when water is discharged from the tanks does it change to 1,000:1 and 500:1. Thus, more stringent conditions were created in the laboratory.

Because the small volume of water caused the vessels to cool rapidly in the experiment, they were periodically reheated during the test. Observations were conducted for 18 days, with the water replaced every 24 hours to simulate operating conditions. Since AG-4 sealant is intended for hot-water supply, hot water was sampled from beneath the film by means of a siphon for analysis. We observed the organoleptic properties of the water (odor—

Table 2

Results of sanitary-chemical analyses of water

odor at 60° and 20°, taste, color, clarity, and active reaction (pH). In the water studied, permanganate and dichromate oxidizability, brominatable substances, and the total content of chloroform-soluble organic substances were determined. Bacteriological tests were not performed because water intended for hot-water supply is heated to 102–105°. The results of the organoleptic and physicochemical analyses are presented in Table 1.

Table 1 shows that hot water in contact with the AG-4 antiaeration sealant for exposure periods of 24, 42, and 72 hours did not acquire any extraneous odor. No odor or taste was detected when the water cooled to room temperature. The sealant studied had no effect on the water’s active reaction, clarity, or color. In all observations over 18 days, these parameters remained at control levels.

The results of the sanitary-chemical analyses of water are presented in Table 2. As Table 2 shows, permanganate oxidizability, an indirect indicator of water contamination, remained at the control level during the first 24 hours. Over the following days, oxidizability under the protective layer of sealant decreased and remained below the control level throughout, owing to the protective barrier that prevented contamination of the water from the atmosphere. No organic matter was leached into the water during the study. This is evidenced by the dichromate oxidizability (chemical oxygen demand), which was at the same level in the experimental and control samples.

The presence of polymeric components of the AG-4 sealing liquid in the water was determined by the bromination method. The results (Table 2) showed that the amounts of brominatable substances in the control and experimental samples were approximately the same. No chloroform-soluble substances were detected in either the control or the experimental water samples (see Table 2).

Thus, organoleptic and sanitary-chemical analyses of water that had been in contact with AG-4 sealant showed that its organoleptic properties (odor, taste, clarity, and color) and active reaction (pH) complied with GOST 2874-73, “Drinking Water.” Indirect indicators of contamination revealed no impurities.

Because the literature contained no data on the sanitary-toxicological assessment of AG-4 sealant in a chronic experiment on laboratory animals, standard clinical and pathomorphological examination techniques were used, together with a number of biochemical and physiological methods, including integrative methods. Volatile substances released from plastics can migrate into drinking water. In our experi-

…that the most suitable biological model for the toxicological study of the AG-4 sealant used in water supply systems is the oral administration to animals of aqueous extracts of the sealant under investigation. The experiment lasted 3 months. Male rats were used as experimental animals, with 15 animals per group. They received aqueous extracts of the AG-4 sealant, while the control animals received municipal tap water. The animals’ general condition—appearance, behavior, and amount of food consumed—was recorded daily. They were weighed once a month. Physiological, biochemical, and other indicators of their condition were examined monthly throughout the experiment.

To assess the functional state of the body, we used indicators reflecting the condition of the organs and systems most susceptible to the toxic effects of various chemicals. The study of nervous system function in animals occupies an important place in sanitary toxicology.

The general condition and behavior of the animals that received aqueous extracts of AG-4 sealant for 3 months did not change. At the end of the third month, the mean weight of the experimental animals was \(314\pm18.3\) g and that of the controls was \(307\pm11.9\) g; the difference was not statistically significant. After a 24-hour fast, the rats in both groups lost 18–19 g. Weight was regained at a similar rate in both groups, and the animals returned to their initial weight on the third day.

The hexenal (thiopental) test was used to detect impairment of the liver’s detoxifying function, since barbiturates are broken down primarily in the liver. A 2% aqueous solution of hexenal was administered intraperitoneally to mice at a dose of 80 mg/kg. Three measures were recorded: the duration of the anesthetic phase (time spent in the lateral position), the duration of the preanesthetic phase (from administration until the onset of the lateral position), and the total time. No differences were found between the experimental and control animals in the course of the anesthetic phases. The slight shortening of anesthetic sleep in the experimental group compared with the control group was not statistically significant (\(P>0.05\)).

Hemoglobin levels and erythrocyte and leukocyte counts in the blood of the experimental and control animals remained virtually unchanged throughout the experiment. At the end of the third month, mean hemoglobin levels were \(14.7\pm0.49\) g% in the experimental animals and \(15.3\pm0.48\) g% in the controls; erythrocyte counts were \(4.3\pm0.09\) and \(4.4\pm0.09\) million per \(1\ \mathrm{mm}^3\), respectively, and leukocyte counts were \(12.4\pm1.60\) and \(9\pm0.84\) thousand per \(1\ \mathrm{mm}^3\).

No statistically significant increase in blood chloride levels was observed in animals given aqueous extracts of AG-4 sealant to drink compared with the control group.

To assess liver function, we studied alanine and aspartate aminotransferase activity in blood serum and liver homogenates. Umbreit’s method, as modified by A. M. Osherovich and B. I. Milner, was used. The results showed some decrease in serum alanine transaminase activity in the experimental animals receiving aqueous extracts of AG-4 sealant in the third month; aspartate transaminase activity was lower than in the control group in the second month of the experiment. Statistical analysis, however, did not confirm the significance of these differences (\(P>0.05\)).

The study of central nervous system function led to the conclusion that prolonged consumption of aqueous extracts of the AG-4 sealant under investigation causes no substantial changes in the central nervous system of the animals.

Among the biogenic amines of warm-blooded organisms, histamine and serotonin are of the greatest quantitative and biological importance. The evidence reported in the literature supports the view that biogenic amines, and histamine in particular, participate in neurotransmitter metabolism and in the neurohumoral regulation of blood vessel tone, organs containing smooth muscle, blood capillary permeability, digestive gland secretion, and other processes. In many pathological conditions, tissue histamine is released; an excess of it in turn leads to the development of allergic processes and sclerosis of internal organs. Histamine has a very strong pharmacological effect. It is formed by the simple decarboxylation of histidine in all tissues of the body. Particularly large amounts of histamine occur in intestinal cells. Relatively large amounts of histamine are produced during inflammation and following injury. Serotonin, like histamine, is also formed during inflammation. Histamine and serotonin are oxidized by decarboxylase, whose prosthetic group is pyridoxal phosphate. Tissue histamine activity is known to change in accordance with changes in the functional state of the organ.

Thus, stimulation of the cardiac or gastric branches of the vagus nerve leads to an increase in histamine content in the atria or gastric juice, respectively.

In experiments on rats, we used the Taybory colorimetric method, modified for animal experiments, to determine biogenic amines (histamine). The reaction is based on the formation of a colored complex of histamine with diazotized p-nitroaniline. Histamine was extracted from tissue (100 mg) in a 5% solution of trichloroacetic acid for 24 hours at 5°. The optical density of the solution was measured with a domestically produced FEK-N-56 photoelectric colorimeter. Histamine levels in rat liver ranged from 0.30 to 0.47 extinction units. No appreciable difference in liver histamine content was observed between animals in the experimental and control groups (\(P > 0.05\)); likewise, no difference in liver aminotransferase activity was found.

It is well known that, under many chemical exposures, the decisive link in pathogenesis lies at the molecular level and consists in disruption of the activity or formation of enzymes or active protein groups that serve as functional components of many enzymatic processes. Of all the functional groups of proteins, sulfhydryl (SH) groups are the most reactive. Study of the biological role of protein SH groups helps elucidate the mechanism of complex pathological reactions that arise when the body is exposed to certain physical factors and a substantial group of chemicals. Thus, oxidation of an SH group produces a disulfide bond; acetylation replaces the hydrogen of the thiol group with a hydrocarbon radical; and, finally, replacement of the hydrogen of an SH group by a metal results in the formation of mercaptides. The highest levels of SH groups are observed in liver tissue, where they are apparently formed, and in brain tissue, which has the highest functional reactivity. In our experiments, we used a spectrophotometric method for determining SH groups, the principle of which was developed by Kh. A. Rubina and L. A. Romanchuk. The reaction conditions and procedure for laboratory animals were developed by N. V. Klimkina and S. I. Plitman. We found no statistically significant increase in SH-group content in liver homogenates from animals in the experimental group compared with the control group. The weight coefficients of the liver, kidneys, heart, spleen, and adrenal glands were similar in both groups and fell within the range for intact animals of the same species, sex, and weight.

After chronic exposure to aqueous extracts of AG-4 sealant, the experimental animals were killed by decapitation. They underwent postmortem examination, followed by microscopic examination of the internal organs. Microscopic examination of the liver showed clearly defined lobular and hepatocyte structure in both experimental and control animals. The renal cortex of the experimental and control animals was histologically normal. Hematoxylin and eosin staining of the adrenal glands revealed clearly defined glomerular and fascicular zones in both groups. Thus, microscopic examination of the internal organs revealed no differences between the experimental and control animals.

Taken together, the data obtained in the sanitary-toxicological experiment indicate that, when drinking water is treated with AG-4 sealant, the combined low-molecular-weight compounds migrating from the formulation cause no changes in such relatively labile systems and functions of warm-blooded animals as the liver’s antitoxic and enzymatic activity, histamine and SH-group metabolism, central nervous system function, and internal homeostasis. No systemic effects of the aqueous extracts of the sealant under study were observed, as assessed by the general condition and weight changes of the experimental animals, as well as by the loss and recovery of body weight during a fasting challenge. Functional challenge tests likewise revealed no changes in the animals. No pathomorphological changes were found in the experimental animals.

Conclusions

1. After contact with AG-4 sealant, water meets the requirements of GOST 2874-73, “Drinking Water,” with respect to organoleptic properties—odor, taste, transparency, and color—and pH. Indirect indicators revealed no impurities.
2. In experimental studies of the biological effects of water after contact with AG-4 sealant under chronic exposure conditions, biochemical, physiological, and pathomorphological methods characterizing the activity of the body’s major systems revealed no effects on the experimental animals.
3. The body of research supports recommending AG-4 sealant for use in hot-water supply systems.

References

Berlin A. A., Barkan S. M. Polymers in the Food Industry and Agriculture. Moscow, 1969. — Lazarev N. V. Harmful Substances in Industry. Vol. 1. Leningrad, 1965. — Osherovich A. M., Milner B. I. Laboratory Practice, no. 11, pp. 662–665.

Received May 6, 1976.

Hygienic Assessment of an Anticorrosion Sealant AH-4 Used in Hot-Water Supply Systems

Yu. V. Novikov, K. O. Lastochkina, T. K. Parkhomchuk, A. N. Sergeev, D. A. Yakovlev, L. G. Gorokhova

The authors conducted a series of sanitary-chemical and toxicological investigations of the quality and biological properties of water that had been in contact with AH-4 sealant. After contact with the sealant, the water’s properties—odor, taste, transparency, color, and pH—met the requirements of State Standard 2874-73 for drinking water. No additives were detected in the water. In experimental investigations under chronic exposure conditions, biochemical, physiological, and pathological methods detected no biological effects of the water that had been in contact with AH-4 sealant on experimental animals. On the basis of these investigations, AH-4 sealant may be recommended for use in hot-water supply systems.