Effects of Sulfur Dioxide on
Plants and Animals plant because of legal restrictions CARL SETTERSTROM ucts of the combustion Of imposed in Part as the result B~~~~Thompson Institute for plant Research, I ~ ~ , , of apprehensions of residents coal and of other indusYonkers, N. Y. of the vicinity regarding the trial oDerations. sulfur dioxide is harmful effects of sulfur dioxdischarged into the atmosphere ide on health (42). I n this country extensive research on of industrial centers in large quantities. Pincus and Stern (20) methods for the removal of sulfur compounds from flue gases estimate that, exclusive of the discharge of internal combustion also receives some stimulus from considerations of supposed engines, the amount of sulfur dioxide released into the atmoseffects of these compounds on human health. phere of ?Jew York City during 1934 averaged close to 2000 For the past three years the Boyce Thompson Institute has tons per day. Recent studies by the Air Hygiene Foundation been conducting a series of experiments testing the effects on (16),the National Research Council of Canada (IO),the United plants and animals of exposure to low concentrations of sulfur States Department of Agriculture (37),the Boyce Thompson dioxide. The medical, botanical, and entomological findings Institute (22, 24), and others reveal that measurable conhave been or will be presented in some detail before other procentrations of sulfur dioxide prevail over large areas surroundfessional groups; the present paper will be concerned more ing industrial centers. particularly with the industrial and engineering aspects of The effects of sulfur dioxide on vegetation and on animal the work. The apparatus first developed in this study was and human health are, therefore, of importance to agriculture, described by Setterstrom and Zimmerman (2S), but we shall to industry, and to the general population. briefly recapitulate and consider some recent improvements The injurious effects of sulfur dioxide on plants have been and developments. the source of investigation, extended litigation, and discusKO attempt has been made to evaluate the possible nuision over a period dating back to the work of Stockhardt (97) sance qualities of sulfur dioxide aside from its direct effects as in 1848. Investigators are in general agreement that condetermined by plant and animal experimentation. Psychocentrations of the gas on the order of 1 part per million parts logical factors involved in determining “an annoying, unof air by volume (p. p. m.) will cause typical foliar markings pleasant, or obnoxious” odor were considered to be outside on more sensitive species in a few hours, under favorable conthe scope of the present studies. ditions, and that higher concentrations may cause complete defoliation and death. Apparatus Investigators have not agreed, however, on the effects of I n the study of the effects of long exposure of plants or long exposure to low concentrations of the gas which do not animals to low concentrations of a particular gas, precise conproduce visible markings-i. e., concentrations such as prevail over the larger part of the areas subjected to fumes of trol of the gas concentration, and a t least partial control of sulfur dioxide. other important factors such as temperature and humidity, Proponents (6, 9, 28, 41) of the “invisible injury” theory are essential requirements. maintain that the gas is harmful to plants in all concentrations Apparatus to meet such requirements has evolved largely from studies of the effects of sulfur dioxide on plants. I n and under all circumstances, that it always has an adverse ef1915 the Selby Smelter Commission (8) described a method of fect on yield. Some opponents (7, 29) of this theory believe that the gas does not reduce yield unless it causes markings. fumigating plants which was a great advance over methods of Other opponents (18) maintain that exposure to low nonprevious investigators who had merely added a measured marking concentrations stimulates growth. amount of sulfur dioxide to a known volume of air inside a The implications of the “invisible injury’, theory are of conglass case which contained the plants. Wells of the Selby siderable importance to industrial as well as to agricultural Commission showed that the sulfur dioxide was rapidly abinterests. As Swain (g9)has emphasized, if this theory be sorbed by the glass walls, by the plant, and by the soil with correct, then any industrial operation which contributes sulconsequent decrease in concentration. Therefore, he devised fur dioxide to the atmosphere is not merely a potential but an a method of blowing air to which had been added a n approxiactual agent of injury, and the subject of injunctive relief as a mately known amount of sulfur dioxide into long low cabinets nuisance in the eyes of the law. which were placed over the plants t o be fumigated. The effects of sulfur dioxide on men and on animals have This type of cabinet, however, had several disadvantages. been the subject of considerable controversial discussion, but It was not possible to maintain the same concentrations a t inthey have been the source of meager experimental data despite let and a t the far end of the cabinet, and it was difficult to the prevalence of sulfur dioxide as an atmospheric and induscontrol temperature and humidity. trial contaminant, and despite the implications of responsible O’Gara (18) improved the Selby Commission apparatus scientists and echoings of the popular press regarding its considerably. He metered the sulfur dioxide through em“harmful effects on human health”. pirically calibrated flowmeters and measured the volume of The lack of experimental data is the more surprising beair going into the cabinets with a Pitot tube. His cabinets cause here, too, the problem is of peculiar importance to inwere 6 feet square with a height varying upward from 4 feet, dustrial and engineering interests even aside from the immedepending on the material being treated. The air-gas mixture was blown in a t the top of the cabinet and distributed diate question of effect on health of industrial workers. For example, elaborate sulfur dioxide removal equipment was inuniformly by means of radial baffles. As no exit was prostalled in the London Power Company’s Battersea power vided, air leaked out around the bottom of the cabinet. Sul-
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ment, a variablespeed exhauster blower and an orifice meter for precise c o n t r o l of t h e volume of air passing into the cabinet, scrubbers attached to the intake of the blowers to rid the air of sulfur dioxide and other impurities before allowing it to enter the system and tions. The cabinets to effect -a partial FIGURE 1. GREENHOUSE CONTAINING APPARATUS FOR STUDYING THE were made more control of the temEFFECTS OF GASESON PLAXTS ASD APr'IivALs nearly gastight, and perature and hua n exit was provided midity in t h e for the gas mixture. The volume of air entering and leaving cabinet, a Thomas autometer and a conductivity recorder, the cabinets was measured by means of anemometers inand a humidigraph for recording temperature and humidit,y serted in the inlet and outlet pipes. Apparatus for metering in the cabinet. the sulfur dioxide was enclosed and thermostated. HuGM-AIR MIXTURE. In working with concentrations approximidity control was effected by blowing an atomized spray of mating 0.10 p. p. m. unless the volume of air used is greater than water, augmented with steam when necessary, into the intake 350 cubic feet per minute (c. f. m.), the volume of gas metered pipe. into the system is less than 1 cc. per minute. Accurate control of the gas flow is facilitated by using a mixture of 10 or 5 per cent The most important contribution to this problem in recent of the gas and 90 or 95 per cent air and thereby increasing the years has been the development by Thomas and his assovolume of gas metered ten or twenty times with consequent ciates (31, $3, 34) of automatic apparatus (autometers) for greater precision. Commercial mixtures of numerous gases with continuously analyzing air containing low concentrations of air are available on the market. When concentrations greater than 1.00 p. p. m. are used, it is sulfur dioxide. This apparatus automatically draws a given possible to obtain precise control with the undiluted gas. volume of the air-sulfur dioxide mixture through a known METERING OF THE GAS. Delicate control of the gas flow is made volume of absorbing solution in a given length of time. The possible by means of a diaphragm reducing regulator and a sensiabsorbing solution, a slightly acidulated solution of hydrogen tive needle valve. The reducing regulator, equipped with a highpressure gage which measures the pressure within the cylinder and peroxide, oxidizes the sulfurous acid to sulfuric acid, and the a low-pressure gage which registers the pressure on the upstream change in conductivity of the absorbent is recorded on a Miside of the needle valve, enables the maintenance of a constant cromax conductivity recorder. pressure on the needle valve despite fluctuations in tank pressure. By changing the absorbing solution and making minor alCALIBRATION OF CAPILLARY FLOWMETERS. The gas is measured by passing it through a calibrated capillary flowmeter. terations in the apparatus, the Thomas autometers can be For use with the gas-air mixture, a series of flowmeters were caliadapted t o record automatically concentrations of many brated with air, and the calibrations corrected for the presence of other gases. Thomas describes a similar apparatus for dethe gas. The calibrations were checked by using a mixture of termining carbon dioxide (32, 35). Walter (39) reports that 5 per cent sulfur dioxide and 95 per cent air; the sulfur dioxide mas absorbed in a weak solution of hydrogen peroxide and tithe following gases have been determined by measuring contrated with standard alkali using methyl red as an indicator. ductivity of absorbing solution: hydrogen sulfide (absorbed BLOWERS.The air is blown into the fumigating cage by means in lead acetate), sulfur dioxide (absorbed in potassium diof a clockwise vertical discharge blower with a wheel 18.25 inches chromate), ammonia (absorbed in pure water or in very diin diameter, handling up to 600 cubic feet per minute. The blower is driven by a motor with an automatic push-button lute sulfuric acid), carbon dioxide (absorbed in sodium starter and speed regulator. hydroxide), oxygen (absorbed in potassium pyrogallate), acetyThe speed regulator and a sealed gas-blast gate which is lolene (absorbed in ammoniacal cuprous chloride), carbon cated on the discharge side of the blower together make possible monoxide (absorbed in cuprous chloride), nitrogen oxides (abprecise regulation of the air flow. ORIFICEMETER. The volume of air entering the fumigating sorbed in ferrous sulfate), chlorine and bromine (absorbed in cabinet is measured by means of an indicating orifice meter. water or in alkaline hydrogen peroxide), and sulfur dichloride The orifice is set in the 4-inch cast-iron pipe, which delivers the (absorbed in potassium hydroxide). Many organic vapors air from blower to fumigating cabinet, between two flanges which can be determined by measuring carbon dioxide liberated on contain the upstream and downstream taps for determining differential pressure. combustion. Two sizes of orifices are used: one for measuring 20 to 100 Further improvements in design of fumigating cabinets c. f. m., the other for measuring 100 to 500 c. f. m. The orifice have been described by Zimmerman and Crocker (43). plates can easily be interchanged. Swain and Johnson (50) washed and humidified the air before F U M I G A T I N G CABINETS.The fumigating cabinets are 46 inches high, 34 inches wide, and 82 inches long with capacities of passing it into their fumigating system. 74.2 cubic feet. They are constructed of single-strength BI n designing the apparatus described in this paper, the quality flat-drawn glass. The bottoms of the cabinets are galwriters were particularly anxious to obtain precise control, vanized iron covered with white enamel. Each cabinet has a removable side door and removable end sections. The cabinets are . with a minimum of care, of gas concentrations approximating convenient for treating animals or potted plants. Measurements 0.10 p. p. m. for fumigations lasting several weeks. in sunlight with a Lange photocell with neutral filters show that The apparatus (Figure 1) consists of duplicate sets and, with light intensity is reduced about 16 per cent on passing through the exception of the conductivity recorders, is housed in a the greenhouse glass and about 15 per cent on passing through the cabinet glass. The total reduction in light intensity on passing small greenhouse provided with automatic temperature conthrough both the greenhouse and the cabinet glass is, therefore, trol. The recorders are installed in a laboratory within the about-29 per cent. institute building. The air passes from the 4-inch pipe through a wrought-iron Figure 2 is a close-up of one of the duplicate sets. It intruncated hollow pyramid, 23 inches long, into a 10 X 27 inch opening at the top of one end of the cage. The air leaves the cludes a cabinet in which the material is placed during experifur dioxide concentrations in the cabinets were checked intermittently by means of the iodine titration method developed by the Selby Smelter Commis-
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and a gght, hinged damper prevent balk draft. Careful dispersion tests indicate thst the air blown into the cabinet is uniformly dispersed throughout. THOMAS AUTOMETERS. The air-gas mixtures are sampled automatically hv means of the Thomas autometers ( S I . 55. 54). Changes in conductivity 08 the absorbing salttion are measwed ductivity reaches a certain point and thusgive warning when the
Ror use with sulfur dioxide, the svst
