Effects of Sulfuric Acid Mist on Plant Canopies James B. Wedding* and Michael Ligotke Civil Engineering Department, Colorado State University, Fort Collins, Colo. 80523
F. Dana Hess Department of Botany and Plant Pathology, Purdue University, W. Lafayette, Ind. 74907
Soybean plants 4-6 weeks old were exposed to sulfuric acid mist droplets. The plants were grown under greenhouse conditions. Initially, gross effects of unquantified topically applied sulfuric acid mist were obtained by spraying plants with a dosage of 1 and 10% acid (by volume with water) with a polydisperse atomizer (-5 pm mean diameter, geometric standard deviation -2.5). The 10%solution produced severe necrotic lesions and large chlorotic regions on the acropetal leaves. A heavy application of the 1%solution produced similar effects but with a reduced number of necrotic lesions. A light application had no visual effect on the plants after 24 h. Subsequent detailed quantitative studies were performed using a flow-through exposure chamber equipped with a vibrating orifice aerosol generator and fluorescent lamps. Plants were exposed to 1.7-prn aerodynamic diameter 18 M sulfuric acid. Exposure times were up to 10 h a day extending to 14 consecutive days total fumigation period. Loading up to lo7 particlesheaf was achieved after the full 140 h. Background humidity was -40% and temperature for all tests was 25 “C. No visible toxicity symptoms of damage resulted to the plants from the tests. Scanning electron microscope observations of the 140-h treated plants showed no apparent damage due to the sulfuric acid treatment. The goal of the study was to assess both qualitatively and quantitatively the effects of pure sulfuric acid mist on 4-6 week old soybean plants. The investigation was performed qualitatively using a hand held polydisperse atomizer and plants were lightly and heavily sprayed with both 1 and 10% (by volume with water) solutions. Quantitative results were obtained with a glass exposure chamber equipped with growth lamps. Sulfuric acid droplets (1.7 pm) were generated using a vibrating orifice type atomizer ( 1 1 ) and exposure periods were up to 10 h a day extending to 14 continuous days of exposure. Background
In the early 1970’s it was reported that the installation of an oxidation catalyst in automobile exhaust systems increased the amount of particulate matter emitted ( 1 , Z ) . The chemical nature of the particulate emission was published by Pierson et al. in 1974 (3).They found that “at a 60 mph road load a monolithic oxidation catalyst converts almost half of the SO2 into SO:3, the bulk of which is emitted from the tailpipe as sulfuric acid”. Forty percent of the particle mass was found to be sulfuric acid. The rest of the particulate matter was determined to be water that was associated with the sulfuric acid, a substance known to be hygroscopic especially a t elevated humidities. If the catalyst was removed from the exhaust system, the amount of sulfuric acid was reduced by 98%. There have been no in-depth quantitative measurements of environmental influence of sulfuric acid emitted from automobiles equipped with a catalytic exhaust system. There have, however, been studies of the effects of sulfuric acid originating from other forms of pollution. Scientists in Europe have reported that over the past several years rain a t some locations in Europe has increased acidity (acid rain). One of the strong acids that is causing this decrease in the p H of rain 0013-936X/79/0913-0875$01.00/0
@ 1979 American Chemical Society
is sulfuric acid ( 4 ) .The impact on the ecosystem is unknown; however, such things as increases in leaching of nutrients from plants and soils, and changes in metabolism in plants and other organisms ( 4 ) ,have been proposed. Recently, the effect of simulated acid rain on greenhouse and field grown herbaceous vegetation was investigated ( 4 ) .Dilute sulfuric acid (pH range, 2.2-3.4) was applied for durations of from 1 min to 9 h. The application was repeated daily for up to 4 days. Foliar injury to plants occurred after the 1-min treatment if the p H of the treatment solution was below 2.6. For the 9-h treatment, injury occurred if the pH was 3.4 or below. The most common type of injury observed in this study was necrotic lesions on the foliage of treated plants, which is sometimes called leaf spotting (6).Other symptoms of sulfuric acid injury have also been reported. Tomiya et al. ( 7 ) treated plants with dilute sulfuric acid and found that the sulfur content of the plant tissue significantly increased, the chlorophyll content and number of chloroplasts decreased, and the water content of leaf tissue decreased as the sulfuric acid concentration increased. At concentrations of 0.1% sulfuric acid, there was a disruption of tissue in the spongy mesophyll and palisade layers of the leaf. The purpose of the research being reported is t6 determine if simulated sulfuric acid particle emissions from catalystequipped exhaust systems are capable of inducing damage to the important agronomic crops of corn and soybeans. The significance of this study is that, to date, no comprehensive qualitative or quantitative data have been collected with regard to the overall potential environmental impact of the sulfuric acid particles emitted from automobiles equipped with catalytic exhaust systems. E x p e r i m e n t a l Procedure
Plant Growth and Care. Five corn ( Z e a m a y s L.) or soybean (Glycine m a x L. Merr.) seeds were planted in 5-in. diameter Styrofoam pots (Tufflite Plastics Inc., Ballston Spa, N.Y. 12020) using a stream sterilized mixture of loam soil, peat, and sand (1:l:l). All plants were grown to 4-6 weeks of age under greenhouse conditions with average day-night temperatures of 25 and 20 “C, respectively. Supplemental lighting was provided by fluorescent lamps (cool-white) in order to obtain a 16-h photoperiod. While growing, the plants received twice weekly applications of Hoagland’s solution (8). After emergence from the soil, the plants were thinned to one uniform plant per pot. After the test plants were subjected to the acid fumigation, they were returned to the greenhouse along with the control plants. All plants were watered an equal amount on a daily basis. Exposure of Plants to Sulfuric Acid. The qualitative, gross effects of sulfuric acid on the plants were determined by a light spraying (one broad sweeping pass) and heavy spraying (leaves were thoroughly inundated) of the foliage of soybean plants with a hand-held polydisperse atomizer. Solutions used were 1 and 10%volumetric concentrations of sulfuric acid mist and water. These percentages were selected after experimental trials with other concentrations in an attempt to utilize dosages that produced severe injury to virtually no injury to the plant. The sulfuric acid used was concentrated (18 M) and -95% pure, diluted to the desired level with distilled, deionVolume 13, Number 7, July 1979
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V i b r a t i n g O r i f i c e Aerosol Genera tor
Figure 1. Plant exposure chamber equipped with growth lamps constructed of glass
ized water. The atomizer produced a mass mean aerodynamic diameter of 5 pm with a geometric standard deviation of 2.1. No attempt was made to quantify the application. Overall, 60 plants were exposed-10 plants per exposure for each of the 1 and 10%solutions with 3 replicAtes of each test. Scrutiny of the leaf surface for damage was performed a t 0, 10,60,and 120 min after application and after 24 h. Detailed quantitative tests were performed with the aid of the glass-walled chamber equipped with fluorescent lamps (cool white) as shown in Figure 1.Six plants were exposed simultaneously in the chamber for varying periods of time. The purpose of this supplemental lighting was to maintain phytochrome in the Pf, state for 16 h/day-not to stimulate growth or simulate daylight. Freshly generated aerosol produced by the vibrating orifice atomizer shown was injected into the chamber with flow continuity achieved by the four exhaust ports. Deposition of the small particles (1.7 pm) was induced by Brownian motion in the near quiescent flow regime (injection rate 12.75 m3/h). The fluid mechanics were designed purposely to induce slow deposition rates, thereby ensuring light particle loading over long periods of time. These conditions were felt to be more representative of an actual atmo876
Environmental Science 8 Technology
spheric environment than excessively large doses over short periods of time. Exposure periods were from 4 to 10 h a day consecutively for up to 14 days. Dosage rates were established according to rates calculated from depositions velocities as determined by Wedding (9) in full-scale wind tunnel tests on 4-6-week old soybean plants. Relative humidity was constant a t 50% for all tests, and temperature was 25 "C. Quantitative assessments of the particles on 1 cm2 of leaf surface area realized in the tests were determined by first calibrating the chamber using 1.9-wm particles of sodium fluorescein equivalent in aerodynamic diameter to the 1.7-pm sulfuric acid droplets. Sections of leaf with known area exposed for various time periods in the chamber were taken from plants and placed into wash water. Subsequent analysis of the solution with the aid of a calibrated Turner Model I11 fluorometer yielded the deposited mass. Careful consideration was given to blanks of unexposed leaves to ensure zeroing out of any residual background fluorescence. Particle size and quality were affirmed by optical microscopy study of the droplets deposited on glass slides placed a t numerous locations within the test chamber. The absence of moisture on the droplets when they arrived a t the plants was affirmed by scrutiny of the stain diameters left on Kromekote cards placed a t random locations throughout the chamber. A steady-state concentration of acid droplets was created in the test chamber before plants were inserted. This was achieved by running the generator into an empty chamber for a period of 70 min prior to the initiation of each test. During exposure periods there were 6 plants placed simultaneously in the chamber as shown in Figure 1. Exposure periods for each set of 6 plants were 1, 2 , 4 , 8, and 10 h/day for a 1-day exposure extending to a total of 14 consecutive days of exposure. At the end of each exposure period, leaves were examined for damage. Growth was assessed by taking photographs of the test plants and comparing the results t o control plants. If no damage was observed after the exposure period, the test was reinitiated with fresh plants for a longer period of exposure.
Evaluation of Results from Plant Exposure Gross Qualitative Study. Significant symptoms of toxicity were noted when the plants were exposed to the hydrated sulfuric acid droplets produced by the hand held polydisperse atomizer. A heavy application of the 10% sulfuric acid solution resulted in severe damage within 2.5 h after treatment (Figure 2d). The foliage was twisted and definite lesions were forming around individual sulfuric acid droplets. Another characteristic response was that all leaves of treated plants were flaccid when compared to control soybean plants. Twenty-four hours after the treatment, the plants had regained their turgidity; however, numerous necrotic lesions were present on the leaves. Lesions'were not observed on the stems of treated plants. In this experiment, the lesions did not increase in size as time from application to observation was increased beyond 24 h. This would indicate that toxic concentrations of sulfuric acid were not translocated. This lack of increase in lesion size may have been due to the acidity being neutralized by the buffering capacity of the cytoplasm in individual cells. Another explanation is that tissue in contact with the sulfuric acid produced instantaneous dehydration, thus preventing translocation to other living tissues. A light application of a 10%solution of sulfuric acid applied to soybean plants caused younger leaves (acropetal leaves) to be more affected by the treatment than older leaves (basipetal leaves). As with the heavy application, the plants appeared flaccid 2.5 h after treatment. Twenty-four hours after treatment the turgidity of the plants was regained. The toxic symptoms of this treatment were large chlorotic regions on
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Figure 2. Plants treated with polydisperse mixture of sulfuricacid mist and water. (a) Plants treated with heavy application of 1% solution 2.5 h after treatment. (b) Plants treated with heavy application of 1% solution 24 h aftertreatment. (c)Plants treated with heavy application of 1% solution 30 d a w after treatment. (d) Plants treated with heavv aDi
location had taken place prior to tissue damage. This region was not limited to any one area of the leaf. Small lesions ohserved in the 10% heavv amlication were not observed on hydration) of the tissue, while the light application of sulfuric acid was causing death by a physiological disorder, which may or mav not he related to the n H effect of the sulfuric acid. Whkn the sulfuric acid concentration applied to the soybean plants was reduced with 1%solutions, the effect of a heavy application was similar to the heavy 10%application; however, the number of necrotic lesions per leaf was significantly reduced. Some leaf curling was noted 2.5 h after treatment; however, no lesions were noted (Figure 2a). Twenty-four hours after treatment, the young expanding leaves were curled and many small necrotic lesions were now apparent on the leaves (Figure 2h). These lesions were most abundant near the margins of the leaves. As was observed for the heavy application of the 10%concentration, there did not appear to be any translocation of the sulfuric acid, A light application of 1% sulfuric acid had no visihle effect on the plants a t the 2.5- or 24-h observation period. One month after treatment with a heavy application of 1% sulfuric acid the small lesions were still apparent. In addition, the leaves were chlorotic and appeared to he undergoing a general senescence (Figure 2d). I t is important to note that the plant tissue formed after the sulfuric acid treatment appeared normal. This normal regrowth indicates that the sulfuric acid was not translocated in toxic concentrations, but rather damage was restricted to areas where the chemical came in direct contact with living epidermal tissues of the plant. Quantitative Study, Glass Exposure Chamber. The plant loadings plotted as droplets of sulfuric acid mist/cm2 of leaf surface vs. exposure time (hours) are given in Figure 3. Note that the loadings become large after long exposure periods, hut the deposition rates are low. T o determine if the rates are realistic to expect for plants existing in the atmosphere, one refers to work by Wedding and Montgomery (9). Deposition velocities are published for 4-6 week old corn and soybean plants in a full-scale wind tunnel test. A deposition
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velocity of 0.02 cm/s was determined for an -2-pm particle diameter at a representative average free-stream velocity of 183 cm/s (4 mph) that would be reasonable for atmospheric conditions. Applying published values for ambient cloud concentration of aerosols of 1 mgIm3 (IO) (which is conservative but not unreasonable to anticipate for the concentrations of sulfuric acid mist droplets existing alongside a roadway) one can calculate the predicted loading of a given leaf in a canopy. The resultingflux would then he given as 0.432 X 10W dropletsi(cm2.s). The slope of Figure 3 yields a value of 0.68 droplet/(cm2s). Thus, the chamber deposition rate is -150 times the projected atmospheric rate. Note, however, that the value of 1 mg/m3 could easily he higher for crops existing adjacent to an interstate or downwind of a coal-fired Dower Dlant eauumed . .. with a scrubber. This accelerated deposition rate was established to shorten the time frame for a test to no longer than a 2-week ueriod of time and still realize a sinnificant loadinn level. For the tcIta1 140-h exposure time a n d a n average learsurface of -20 cm2, particleloadings u p to -107 droplets./leaf were realized chnmhrr did
not result in any visihle toxicity symptoms on the test plants. In addition, growth of the treated plants was not different from the control plants. Photographs of treated and control plaints taken a t selected intervals after treatment revealed essemtially. equal growth rates. Scanning electron microscope . . ohservations of treated (10 h per day fo; 2 weeks) and control SOY bean leaf surfaces showed no auvarent damaee due to the SUI1
in plants exposed to the pure sulfuric acid particles. First, the sulfuric acid load may have been helow the threshold amount needed to induce measurable damage to the plant species tested. Secondly, the sulfuric acid particles werePn a dehydrated state upon contacting the leaf surface and remained dehydrated due to the low relative humidity a t the test site. The lack of moisture may have prevented sulfuric acid interaction with the plant surface. Thirdly, the particles of sulfuric acid may have been of the size where most did not directly contact the plant surface, hut rather remained supported on projections of the cuticle. It seems reasonable to anticipate that some of the droplets did in fact penetrate to the leaf surface and some immediate local damage should have occurred.
Conclusions anc1 Recommendations Severe toxi,:symptoms were observed for 4-6 week old soybean plants tnrurru uvll. 1.61.u droplets of 1and 10% solutions of sulfuric acid mlist. No apparent damage was observed for 4- 6-week old
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soybean plants exposed to realistic loadings of 1.7-pm nonhydrated sulfuric acid mist droplets. Further research is needed in this area. Controlled exposure tests where moisture is added as a n experimental parameter are strongly suggested. Increased relative humidity and hydrated droplets to provide an electrolytic pathway for physiological effects to be realized appear to be needed test conditions. Literature Cited Moran, J. B., Manary, 0. J., Fay, R. H., Baldwin, M. J., EPA Air Programs Publication APTD-0949, 1971. (2) Gentel, J. E., Manary, 0. J., L'alenta J. C., EPA Air Programs Publication APTD-1567, 1973.
(1)
(3) Pierson, W. R., Hammerle, R. H., Kummer J. T., SAE Paper 750095, 1974. (4) Likens, G. E., Borman, F. H., Johnson N. M., Environment, 14, 33-40 (1972) . . ~
(5)>acobson, J. S., Van Leuken, P., Proc. Znt. Clean Air Congr., Tokyo, 4th, 4, 124-7 (1977). (6) Middleton, J. T., Bull. W.H.O., 34,477-80 (1966). (7) Tomiya, K., Tanida, S., Aonuma, K., Takahashi, M., Kawana, A., Doi, M., Proc. Jpn. For. Soc., 86,449-51 (1975). (8) Hoagland,D. R., Arnon, R. I., California Agricultural Experiment Service Circular No. 547, 1950. (9) Wedding, J. B., Montgomery, M. E., Int. J . Enuiron., in press. (10) Stukel, J. J., Solomon, R. L. Hudson, J. L., Atmos. Enuiron. 9, 990-9 (1975). (11) Wedding, J. B., Enuiron. Sci. Technol., 9, 673 (1975). Received for reuiew November 27,1978. Accepted March 26, 1979.
Polynuclear Aromatic Hydrocarbons in Baltimore Canyon Fish Ralph A. Brown and Roy J. Pancirov+ Analytical and Information Division, Exxon Research and Engineering Company, Linden, N.J. 07036
This work provides the beginnings of a base-line study with regard to the present level of polynuclear aromatic hydrocarbons in selected marine tissue of the Baltimore Canyon. In case oil and/or gas production ever occurs in the Baltimore Canyon area, data of this type will be useful in establishing if the fish population has been contaminated by polynuclear aromatic hydrocarbons. This is extremely important because some of these hydrocarbons are potential carcinogens. During the past few years, the American Petroleum Institute has sponsored studies of the occurrence of polynuclear aromatic hydrocarbons (PNAs) in marine animal tissue. One study showed that benzo[a]pyrene (BaP) and other PNA hydrocarbons occur in shell and fin fish a t the low parts per billion level ( I ) . This level is comparable to that in other foodstuffs and would not appear to be a health hazard. With the start of exploration and possible production of oil and/or gas off the east coast of the US., there is a concern that environmental damage may result. Of interest in this paper is a possible future health concern with regard to the level of polynuclear aromatic hydrocarbons in the fish population. To provide a base-line study of the present quality of fish relative to PNA levels, five species of fish and one species of shellfish from the general area of the Baltimore Canyon were analyzed.
Environmental Science & Technology
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Experimental Method of Analysis. The method of analysis is described elsewhere ( I ) . Briefly, 14C-labeledbenz[a]anthracene (BaA) and BaP are employed as internal standards. Known quantities of these compounds are added to the starting sample of approximately 450 g of the edible portion of the fish. After digestion, solvent extraction and column chromatography are employed to prepare a PNA concentrate. An aliquot of this concentrate is then injected into a gas chromatograph where the gas chromatographic peaks are trapped and the ultraviolet absorption spectra of selected trapped peaks are then measured. These spectra provide a quantitative measure of individual PNAs. Quantitation on a total sample basis is calculated from the observed recovery of the 14C-labeled internal standards. Precision and accuracy of the method were evaluated by analyzing known blends of PNAs having individual concen878
trations of 1 and 6 ppb. Individual compounds were measured within 2a limits of 1and 2 ppb, respectively. Sensitivity of the method varies with the type of marine tissue. Concentrations of 0.1 ppb can be observed in shellfish, whereas 1 ppb is generally the limit for fin fish. This is attributed to the quantity of organic residue finally present in the fraction injected into the gas chromatograph. Shellfish fractions contain much less of this residue and thus are purer with regard to PNA content. This higher level of purity provides greater sensitivity. Relatively high "less than" values occur for butterfish and red hake. For the butterfish, this may be attributed to its organic residue, but in the case of red hake the high "less than" values are due to the restrictively small sample of 72 g. Samples. All of the marine tissue samples are varieties which are commonly eaten. They are bottom feeders that are collected using a standard otter/chain sweep a t depths of 39 to 102 m. Samples were taken by the NOAA Fishery Laboratory of Sandy Hook, N.J., and the Virginia Institute of Marine Science, Gloucester Point, Va. Samples analyzed were a composite of several different organisms.
38' 30
38' 30
38'
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37' 30
37. 30
CAPE CHARLES
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75' 30
75'
71' 30
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I 74.
73' 30
14'
Figure 1. Origin of samples in Baltimore Canyon area: ( 0 )some 1978 drilling sites; (shaded areas) approximate location for second oil and gas lease sale. Species can be identified by locations listed in Table I
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1979 American Chemical Society
