several orders of magnitude faster than the OrO reaction. About 75 of the SOzremoved precipitated in the form of sulfuric acid mist o n the wall of the reactor. Studies of the precipitated droplets indicate a mean size of 6.36 p before deposition. Deposition patterns were consistent for the entire length of the reactor suggesting that aerosol movement was almost exclusively in the radial direction. Oxides of nitrogen at 50 ppm showed no measurable effect on the sulfur dioxide reaction rate.
I N
O.OP’1 0.0
0.1
’
0.2
’
0.3
1
0.4
0.5
’
0.6
’
0.7
’
0.8
‘ J
0.9
Figure 10. Fraction of sulfur dioxide removed vs. moles of ozone generated during the same residence time Solid line represents A(S0,) = ( 0 3 )dashed ; line is least-squares fit. Residence times = 2.5 min, A ; 1.92 min, 0;1.25 min, A ; 0.63 min, 5 ; 0.42 min, 0 ;0.32 min,
The nucleation process was not studied in this work, but since air humidified by a bubbling process contains water nuclei and since the metal wire cathode is continuously ejecting metal particles, the presence of condensation nuclei may enhance the overall rate of droplet formation and ultimate size of the deposited droplets. This is not expected to be a ratelimiting step, however, since SOa is strongly self-nucleating in the presence of water vapor, and proceeds at rates far greater than the SO, oxidation step. Conclusions
The rate of oxidation of sulfur dioxide in humid air in the presence of a corona discharge is zero order with respect to SO, in the range 500-3000 ppm. The reaction was strongly dependent o n oxygen and the oxidation rate diminished for O2 concentrations below 1 4 z . By measuring the rate of ozone formation in the absence and presence of SO?, it appears that the rate-controlling mechanism for the SO2oxidation lies in the breakdown of the oxygen molecule by the corona discharge to form atomic oxygen. Apparently the S 0 2 - 0 reaction is
Literature Cited American Society for Testing and Materials, “ASTM Standards, Part 23. Industrial Waters ; Atmospheric Analysis,” p p 824-6, March 1964. Browne, W. R., Stone, E. E., “Sulfur Dioxide Conversion Under Corona Discharge Catalysis,” U.S. Dept. HEW Contract PH 86-65-2, March 5,1965. Dunham, S. B., Nature, 51-2 (1960). Filippov, Yu. V., Emel’yanov, Yu. M., Russ. J . Phys. Cliem., 35,196-200 (1961). Filippov, Yu. V., Vendillo, V. P., ibid., 35, 303-6 (1961). Gerhard, E. R., Johnstone, H. F., lnd. Eng. Chem., 47, 972-6 (1955). Horstman, S. W., Jr., Wagman, J., Amer. Ind. H y g . Ass. J., 523-30 (November-December 1967). Miklos, A,, Takacs, P., Szucs, Z . , Magy. Kem. Lapja, 2,96-100 (1966). Morrow, P. E., Mercer, T. T., Amer. Ind. Hyg. Ass. J . , 8-14 (January-February 1964). Moyes, A. J., Smith, C. R., Trans. Inst. Chem. Eng. (London), 190, C E 163-6 (1965). Mulcahv. M. F. R.. Stevens. J. R.. Ward, J. C.. J . Phys. Clzern., 71,2i24-31(1967). Palumbo, F. J., Fraas, F., J . Air Pollut. Contr. Ass., 21, 143-4 (1971). Powers,’J. W., Cadle, R. D., Photochem. Photobiol., 4, 919 (1965). Reese, J. T., Greco, J., Mech. Eng., 90, 34-7 (1968). Renzetti, N . A,, Doyle, G. J., Int. J . Air Pollut., 2, 327-45 ( 19 60). Wilson, W. E., Jr., Levy, A,, Wimmer, D. B., presented a t 63rd Annual Meeting Air Pollution Control Association, St. Louis, Mo., June 10-14, 1970. Receiced fbr reciew December 13, 1971. Accepted May 22, 1972. This ttvrk wus supported b y NSF Grant No. GK-5531, and waspresented in parr ur the National AICIiE Meering, St. Louis, Mo., May 20-24, 1972.
Mercury Levels in Muscle Tissues of Preserved Museum Fish Ronald J. Evans and Jack D. Bails Fish Division, Michigan Department of Natural Resources, Lansing, Mich. 48926
Frank M. D’Itril Institute of Water Research and Department of Fisheries and Wildlife, Michigan State University, East Lansing, Mich. 48823
T
he recent discovery of mercury contamination in the fish populations of the Lake St. Clair-Western Lske Erie area of the Great Lakes has caused some speculation as to the prior duration and extent of this contamination. Knowledge of this aspect of the present mercury pollution problem in this area would give some insight into the length of time
To whom correspondence should be addressed.
that a human health hazard has existed. It would also help demonstrate whether changes jn the mercury content of the fish could be correlated with increases in the industrialization and urbanization of the Detroit area. Until recently, the main source of mercury into the environment has been the erosion and leaching of mercurycontaining geological formations by rainfall that also transports the mercury to streams and lakes by groundwater runoff. Since the industrial revolution, however, increasing Volume 6, Number 10, October 1972 901
Flameless atomic absorption spectrophotometry was used t o establish the total mercury levels in 57 preserved fish specimens of various species collected in the Lake St. ClairWestern Lake Erie region of the Great Lakes between the years of 1920-65. Only five fish were found to contain mercury levels in excess of 0.5 ppm-three large muskellunge collected in Lake St. Clair in 1939 (2.38, 1.57, and 1.58 ppm) and two adult sea lampreys collected in the Clinton River tributary to Lake St. Clair in 1938 (0.90 and 1.29 ppm). A trend was established relating the mercury content of selected categories of fishes with the year and location of collection for the fish specimens. The 1970-71 mercury levels in fish from the two study areas were found to average more than those preserved museum specimens in the same categories taken from the same area.
amounts of mercury have been lost to the environment from waste products as a result of manufacturing processes that utilize mercury or from the disposal of industrial and consumer products which contain mercury compounds (D’Itri, 1972). In urban and industrial areas, the sanitary sewer systems serve as a convenient disposal system for mercury-containing consumer products. On the average, the mercury concentration of sewage treatment plant effluents are one order of magnitude greater than the water course that receives it (D’Itri, 1972). Klein and Goldberg (1970) have reported that the mercury concentration in surface sediment samples near municipal sewer ocean outfalls are eight to 10 times higher than similar sediments that are farther from the outfall. Large quantities of mercury are lost to the environment through burning or other utilization of fossil fuels. The very limited data available in the literature indicates that while levels of mercury in coal are highly variable, concentrations in the range of 0.1 to 1 ppm are common (Joensuu, 1971). Therefore, considering a yearly worldwide consumption of approximately 3 billion tons of coal (Young and Gallagher, 1968), 0.6 to 6 million l b of mercury are lost to the environment from this source alone. Another potentially very large environmental mercury contamination source occurs in the recovery or use of raw materials which contain small amounts of mercury. Klein (1971) has identified the smelting of sulfide ores of various metals as a major source of mercury to the atmosphere and has estimated the yearly worldwide contribution from this source to be between 6 and 40 million lb. The accumulative effects of all sources of mercury in the Great Lakes area in the past 70 years has been great. For example, using known rates of sediment accumulation,Thomas (1972) found that the levels of mercury in the lake sediments began t o rise above background levels of 358 ppb about the year 1900. Between 1900 and 1940, a gradual increase in mercury levels was noted until the period between 1940 and 1952 when the levels quadrupled over the mean background level. Since 1950, the mercury levels in the sediments have fluctuated, but they have shown a steady, slow increase to the present time. In Sweden, Berg et al. (1966) analyzed the mercury content of feathers on birds preserved in several Scandinavian university museums. They were able to correlate a sharp increase in the mercury content of the feathers of seed-eating 902
Environmental Science & Technology
birds with the introduction of alkylmercury fungicides as grain seed treatments in the early 1940’s. Moreover, they also demonstrated a slow but significant increase in the amount of mercury found in the feathers of fish-eating birds, beginning around 1900. They speculated that this increase in the mercury levels of fish-eating birds paralleled Sweden’s industrial growth and was the result of the attendant increased losses of mercury in the environment. In this study, attempts were made to test this general method of utilizing preserved museum samples to provide information about historical mercury levels in fish from the study area. To accomplish this, muscle tissue samples were taken from preserved fish specimens originally collected in the St. Clair and Detroit Rivers and Lake St. Clair as well as the western basin of Lake Erie (Figure l), and includes the area most seriously affected by mercury contamination in the United States. Methods and Materials Preserved fish specimens that were originally collected from these waters were obtained primarily from the fish collection at the University of Michigan Museum of Zoology. Additional preserved fish were supplied by the Department of Biology at Wayne State University and the Department of Fisheries and Wildlife at Michigan State University. The tissue sample from each preserved fish specimen was taken from the dorsal muscle, located between the head and dorsal fin. After removing the skin, approximately 2 grams of this preserved muscle tissue were gently pressed between absorbent (mercury-free) tissue paper to remove as much of the preservant solution as possible. This sample was then homogenized with 15 ml of distilled water for two min in a
1
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Figure. 1. Region of the Great Lakes where the preserved museum fish were originally taken
Waring Blendor equipped with a mini-container attachment. The dry weight of fish per unit volume of this slurry was determined by drying a 3-ml portion of the homogenate to a constant weight in a vacuum oven a t 50°C with 250 mm pressure for 25 hr. This dried material was then discarded. F o r the mercury analysis, 3 ml of the homogenated preserved flesh was pipetted into a 100-ml volumetric flask. Then 5 ml of concentrated sulfuric acid was added and the sample heated in a n 80°C waterbath for 15-30 min to decompose the homogenate. The flask was cooled in an ice bath before 15 ml of a 6 z wlv potassium permanganate was added to it after which the solution was removed from the ice bath. After the solution reached room temperature it was returned to the 80°C water bath for from 15 to 20 min or until the frothing action ceased. Then it was transferred to a hot plate and heated to its incipient boiling point. After the solution had cooled to room temperature, enough 10% wiv hydroxylamine hydrochloride solution was added to eliminate the excess potassium permanganate and manganese dioxide. Then the solution was made up with distilled water to the calibration mark. The measurement of the total mercury of each sample has been described (Annett et al., 1972). Since storage in formalin, and especially storage in alcohol. causes shrinkage and dehydration of the flesh of the fish, a 75 value for the percentage of water in fish muscle was assumed, and the d r y weight mercury concentrations were divided by a factor of 4 to arrive at the live weight mercury concentrations. Results and Discussion
Preserved flesh samples were obtained from all museum fish samples available to the authors from the study area without regard to species, sizes, collection dates or the specific locations from which the fish were originally taken. The result is a collection of muscle tissue samples taken from 57 individual fish of 26 different species in the study area between 1920 and 1965. The fish varied between 10 and 102 cm in length and between 1 and 8 years in estimated age. The museum specimens were originally collected throughout the Etudy area with: 4 fish from the St. Clair River, 24 from Lake St. Clair. 11 from the Detroit River, and 18 from western Lake Erie. Breaking down the collection data into decades: 9 fish were collected from 1920-29, 20 from the 1930's, 7 from the 1940's, 12 from the 1950's, and 9 from 1960-65. Duplicate analyses were accomplished o n all specimens whenever the size of the fish sample was sufficient, and additional analyses for a given sample were also performed if the original duplicate analyses did not agree well. The complete results of the total mercury analyses of the preserved fish flesh are available from the American Chemical Society Primary Publications Microfilm Depository Service. A summary of these data show the following range of averages after duplicate tests :
areas generally show total mercury levels below 0.20 ppm. The data also show only five preserved fish specimens with mercury levels in excess of the United States Food and Drug Administration interim action level of 0.5 ppm. These fish were three muskellunge taken in the Anchor Bay area of Lake St. Clair in 1939 and two adult migrating sea lampreys collected in 1938 from the Clinton River which empties into Anchor Bay. Significantly these species are also the highestlevel predators in the waters surveyed and the muskellunge at 40+ in., 20f Ib, and approximately 7-8 years in age, clearly the largest and oldest fish in the survey. It is apparent from mercury analyses reported for fish throughout the country that the mercury concentration rates vary between species. Generally, the highest trophic level species like muskellunge and sea lamprey have the highest levels of mercury while the planktivores like smelt and gizzard shad show the lowest levels. During 1970, extensive fish samples were collected from Lake St. Clair by the Michigan Department of Natural Resources. These fish samples were analyzed by various laboratories. The Lake St. Clair fish species collected were placed in four categories given in Table I according to the mean level of mercury found in their muscle tissues (Bails, 1972). Sea lamprey were not sampled from Lake St. Clair during 1970; however, fresh sea lamprey that were obtained and analyzed by the authors from Lake Superior indicated that the mercury content of the predatory sea lamprey averaged three to four times greater than the primary prey species, thereby placing the sea lamprey in Category I. Figure 2 graphically compares the mean mercury levels by category of preserved fish specimens from Lake St. Clair and the St. Clair River to those obtained during the 1970 sampling from the same area. The specimens collected before 1945 show the same low mean levels for all categories except one. Sea lamprey and muskellunge, as mentioned earlier, showed high levels even prior to 1945. The 1965 samples indicate that all specimens except those in Category IV had
LAKE ST. CLAIR FISH 30
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mercury levels mercury levels mercury levels mercury levels mercury levels
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These data show that 70% of the preserved fish contained total mercury levels of less than 0.20 ppm or about the same mercury levels reported in some freshwater fish in 1934, vis 0.03-0.18 ppm (Stock and Cucuel, 1934). Moreover, Great Lakes fish which are currently taken from uncontaminated
CATEGORY Ill
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Figure 2. Comparison of mean mercury levels of preserved museum fish specimens from Lake St. Clair and the St. Clair River to mean mercury levels of fresh fish taken in 1970 from the same area Volume 6, Number 10, October 1972 903
Table I. Scientific Names and 1970 Mean Mercury Levels of Fish Taken From Lake St. Clair and the St. Clair River 1970 Mean mercury Common name Scientific name Category levels, ppm Muskellunge Esox masquinongy I >3.0 Sea lampreya Petromyzon marinus Lake sturgeon Acipenser fuloescens I1 2.0-3.0 Northern pike Esox lucius Sauger Stizostedion canadense Smallmouth bass Micropterus dolomieui Walleye Stizostedion sitreum White crappie Pomoxis annularis Channel catfish Ictalurus punctarus 111 0.5-2.0 Drum (freshwater) Aplodinotus grunniens Longnose gar Lepisosteus osseus Rock bass Ambloplites rupestris White bass Morone Chrysops Yellow perch Perca Jlacescens Black bullhead Ictalurus melas IV
