Water Chemistry of Toxaphene-Role
of Lake Sediments
Gilman D. Veith and G. Fred Lee Water Chemistry Laboratory, University of Wisconsin, Madison, Wis. 53706
The role of lake sediments in the detoxification of lakes which were treated with toxaphene was evaluated under environmental and laboratory conditions. The extent of toxaphene accumulation in sediments of three Wisconsin lakes was determined by electron capture gas chromatographic analysis of core sections and Ekman dredge samples. The toxaphene concentration in the 0 to 5-cm level of the sediment increased for 190 days following the treatment of the lakes and then began decreasing by a factor of 2 every 120 days. Toxaphene was transported vertically to the 5 to 10-cm and the 10 to 15-cm level of the sediment at rates varying from 0.4 to 1.1 cm per day in the three lakes. Toxaphene was not detected below the 20-cm level of the sediments. Toxaphene which was sorbed onto the sediment in the lake could not be leached from the sediment by lake water under laboratory conditions.
T
he difficulty of working with a system containing toxaphene originates from the complexity of the toxaphene mixture. Toxaphene is a mixture of chlorinated terpenes and (or) rearrangement products of the bicyclic hydrocarbon chlorination which have unknown chemical structures. When introduced into a lake, the toxicity of the system to fish may be due to a small number or to a combination of the components of toxaphene. The relative concentrations of these individual components may change with time as a result of preferential sorption, chemical reaction, or microbial degradation. Considerable controversy and confusion exists regarding the factors which control the rate of detoxification of lakes which have been treated with toxaphene. In part, the confusion is the result of a tendency by some investigators to give importance to a wide range of parameters because of a lack of data showing the relative importance among these parameters. For example, Fukano and Hooper (1958) and Mayhew (1959) suggested that the persistence of toxaphene in treated lakes was dependent upon such characteristics as the area of the lake, pH, alkalinity, temperature, sunlight, and the dissolved oxygen concentration. More recently, Johnson et al. (1966) showed that little relationship exists between sunlight, pH, temperature, dissolved oxygen concentration, alkalinity, hardness, and the persistence of toxaphene in natural waters. Hughes and Lee (1968) demonstrated that toxaphene disappeared rapidly from lake water and that suspended solids have a great sorption capacity for toxaphene, suggesting that sorption phenomena may be the more significant process leading to the removal of toxaphene from natural waters. 230 Environmental Science & Technology
The role of lake sediments in the detoxification of treated lakes has not been evaluated. Toxaphene has been detected in isolated samples of lake sediments (Terriere et al., 1966; Johnson, 1966). However, while these data locate toxaphene residues in the lake system, the data do not provide information concerning the dynamics of the accumulation and detoxification of toxaphene in the sediment. This paper presents an evaluation of the interaction toxaphene with lake sediments with regard to the accumulation of toxaphene in sediments, the transport within the sediment, and the possibility of the leaching of sorbed toxaphene from sediments. Experimental
Characteristics of Study Lakes. Toxaphene in lake sediments was studied at Fox Lake, Dodge County, Wis., and Ottman Lake and Silver Lake (Scandinavia), located in Waupaca County, Wis. The three lakes were treated with toxaphene to eliminate rough fish. Fox Lake received three treatments at calculated concentrations of 0.10-0.1 5 mg/liter for each treatment. Treatment dates were July 21 and 22, August 3 and 9, 1966. In addition, this lake received a partial treatment in shallow areas on August 30, 1966. Ottman Lake received a dose of 0.1 mg/liter on September 26, 1967, and Silver Lake received a dose of 0.1 mg/liter on September 27, 1967. The physical and typical chemical characteristics of the lakes are summarized in Table I. A carbon analysis of the sediments from the three lakes with use of the Leco dry combustion method is presented in Table 11. It is important to point out that sediment samples from different areas of a lake as large as Fox Lake vary in composition. Fox Lake sediments include areas of black muck, peat, gravel, marl, and sand. Consequently, sediment analysis from Fox Lake is representative of the sampling site only. In Fox Lake, the primary sampling site was the Hilsenhoff buoy, which was located at the deepest point of the west bay of the lake. Ottman and Silver Lakes are much smaller than Fox Lake, but have extremely flocculent sediments. The sampling sites in these two lakes were also in the deepest areas and were marked by buoys. Analytical Procedures. When toxaphene residues are determined by gas-liquid chromatography (GLC),the mixture produces a band of partially superimposed peaks which are sometimes recognized as the toxaphene “fingerprint.” Because toxaphene is not a discrete molecule, determinations must be quantitatively defined by comparing the area under a fingerprint, which may not reflect a relative increase or decrease of one or more components to the area of a chosen standard composition of toxaphene. At the same time, since GLC determinations do not confirm the presence of a chemical, the
Table I. Physicala and Chemicals Characteristics of the Study Lakes at the Time of Treatment Ottman Characteristic Fox Lake Lake Silver Lake Surface area, acres Volume, acre ft Maximum depth, m PI* Condition, pmhos/cm 20°C Turbidity, mgiliter Si02 Alkalinity, mg/liter C a C 0 3 Suspended solids, mg/liter Sodium, mg/liter Magnesium, mg/liter Calcium, mg/liter Chloride, mg/liter Sulfate, mg/liter
2625 19300 5.7 8.6 400 50 170 25 5.8 30.0 36.0 13.7 64.0
13 51 4.5 8.3 230 17 104 2 2.1 17.2 21.0 2.4 14.9
30 136 5.1 7.0 120 33 55 ... 2.8 6.1 10.5 3.5 7.9
Furnished by Wisconsin Conservation Division. Determined in Water Chemistry Laboratory, University of Wisconsin, Madison, Wis. b
Table 11. Organic Carbona and Carbonate Carbonb in Sediment Cores Core Fox Lake” Ottman Lake Silver Lake section, Orgcor coxC C03-C Org-C C Org-C C cm mg/g ~
0-5 5-10 10-15 30-35
47 38 ... 27
127 130 ... 125
134 146 177 168
41 40 38 26
... ... 138 134
... . 28 34
a Org-C = total-C - carbonate-C. b Samples were acidified with 0.5N HCl, boiled gently, to remove COa, filtered, and titrated to phenolphthalein endpoint wlth 0.25N K O H percent Cox-, as CaC03 = [(meq HC1 - meq KOH)/(sample weight,
g)]
x
(50/100) x 100.
Fox Lake core at Hilsenhoff buoy.
toxaphene determination must be qualitatively defined in terms of a colorimetric reaction specific for toxaphene. Since determinations of absolute concentrations of toxaphene components are not feasible at this time, relative concentrations obtained under the above definitions and beginning with pretreatment samples are certainly meaningful. Environmental samples for this study consisted of dredge samples and cores from three Wisconsin lakes. Dredge samples were obtained with an Ekman dredge. One-meter cores were obtained with hand-driven, gravity-type piston corers as described by Wentz (1967). All samples were frozen until analyzed. Toxaphene was removed from the sediment by a 30-hr extraction with the azeotrope of hexane and acetone in an all-glass Soxhlet extractor. The acetone was removed during concentration, and cleanup was achieved by successive chemical treatment and chromatography of the extract on fuming H2SO4-Celiteand florid columns, respectively. Gas chromatographic analyses were conducted on an Aerograph 1520-B gas chromatograph equipped with the concentric tube electron capture detector. The chosen toxaphene “standard” was prepared by Hercules Powder Co. (Wilmington, Del.), eluted 0.5 to 8.5 min on the DC-200 column (2.5%), and provided a standard curve of 0.3 to 2.5 ng for a 1-111injection. With the above procedures, recoveries from “spiked” pretreatment sediments from the study lakes were 88.3 f 2.9%. The above procedures, including the reproducibility of coring, sediment “spiking” techniques, and confirmatory procedures, have been discussed in detail (Hughes et af.,1969). Results
Ekman dredge samples were obtained from the sampling sites of Fox Lake at about one-week intervals for several months following the multiple treatment of this lake. Results of the toxaphene analysis of these samples are shown in Table 111. Toxaphene accumulated to maximum concentrations (in dredge samples) ranging from 2.1 to 11.9 pg/g about 50 days after treatment. The maximum concentration did not persist,
Table 111. Toxaphene Concentration in Ekman Dredge Samples from Fox Lake Sediments Toxaphene concentration, pg/g dry wt Days after first Date sampled treatment Hilsenhoff Buoy West Bay, north end West Bay, south end a a a 7/30/1969 9 a 8/4/1966 14 0.6 . . .b 8/13/1966 . . .b 23 1.9 1.4 8/20/1966 30 . . .b . . .b 2.1 8/26/1966 36 . . .b 11.9 4.3 b 9/10/1966 51 6.2 7.9 lO/l6/1966 87 2.7 4.5 3.8 11/17/1966 119 . . .b 3.7 2.7 East Bay, north end East Bay, south end East Bay, mid-lake a 7/30/1966 9 ... . . .b (3 , ,)a,, b 8/4/1966 14 0.6 8/13/1966 23 (14.9)“+ 3 . 2 (59.5>” 1.7 8/20/1966 30 . . .b 3.7 2.3 b 8/26/1966 36 2.1 2.1 b 9/10/1966 51 . . .b 9.7 10/16/1966 87 4.3 7.3 4.5 11/17/1966 119 7.6 2.0 19.2 a
Below the detectable limit of 0.5 pg/g dry weight. No analysis made. Concentration determined from 0 to 5 cm section of corresponding core.
Volume 5, Number 3, March 1971 231
and in all but two areas of the lake, the toxaphene concentration decreased from maximum. Table 111also shows the toxaphene concentrations determined from the 0 to 5-cm sections of corresponding cores which were obtained in an effort to evaluate the reliability of dredge sampling. In all cases, the toxaphene concentration in the 0 to 5-cm level of the cores was higher than those determined from dredge samples. The results of the analysis of the core sections from the Hilsenhoff buoy (primary sampling site) in Fox Lake are presented in Figure 1. The toxaphene concentration in the 0 to 5-cm layer increased to 90.0 pg/g after about 50 days, and then decreased to 7.1 pg/g after two years. Toxaphene was vertically transported to the 5 to 10-cm and 10 t o 15-cm levels and maximum concentrations of 9.8 pg/g and 2.0 ,ug/g, respectively, were found, The results of the analysis of the core sections from Ottman and Silver Lakes are presented in Table IV. Maximum toxaphene concentrations in the 0 to 5-cm level were 15.8 pg/g in Ottman sediments and 4.8 pglg in Silver sediments. Toxaphene was found in the 5 to 10-cm and the 10 to 15-cm levels of Ottman sediments at maximum concentrations of 2.6 pg/g and 0.8 pg/g, respectively. The toxaphene concentration in the 5 t o 10-cm and 10 to 15-cm levels of Silver sediments was about 1 p g f g during the 280-day study of this lake. The three cores from Ottman Lake on June 28, 1969, were obtained to evaluate the coring procedures. It can be seen from these data that three replicate cores taken from approximately the same site yielded the same concentration of toxaphene in the sediments. Desorption Studies. Laboratory studies consisted of an examination of the reversibility of the sorption of toxaphene on Ottman Lake sediments. Ottman Lake sediments containing 2.0 pg of toxaphene per gram (dry weight) were added to flasks containing filtered Ottman Lake water to give duplicate flasks containing 100, 200, 400, and 600 ml of sediment (2% solids, air dried) per 1500 ml water. The flasks were mixed thoroughly four times daily for 10 days, and kept a t 23' to 27OC. After the equilibration period, the samples were filtered (glass-fiber) and the water and sediment were analyzed separately. ' The results of the laboratory desorption experiment indicated that the toxaphene concentration in the sediment was essentially the same before and after leaching. For example, the initial sediment concentration was determined to be 2.0 pg/g (dry weight), and the final toxaphene concentrations ranged from 1.8 to 2.1 pg/g. Toxaphene remained below the detectable limit of 1 pg/liter in the water, even though sediment/water ratios varied from 1.3 to 8.0 g (dry weight)/liter. The calculated ratios for the upper 20 cm of sediment (depth of maximum observed mixing) to water volume in Fox, Ottman, and Silver Lakes were 1.8, 3.4, and 2.9 g/liter, respectively.
Discussion Ekman dredge samples may not reflect a well-defined sampling depth because of variations in sediment characteristics and sampling techniques. Consequently, for a species whose concentration decreases with increasing depth in the sediment, as was determined for toxaphene, the measured concentration of the material in the dredge samples would vary according to the dilution by the more compact underlying sediment layers. While the Ekman dredge samples from Fox Lake (Table 111) and 0 to 5-cm core sections resulted in the same general descriptions of the accumulation of toxaphene in the sediments, the toxaphene concentration in the former were generally much less. For example, the concentration in 232 Environmental Science & Technology
Table IV. Toxaphene Concentration in Cores from Ottman Lake and Silver Lake Taken at Maximum Water Depth, 5 m Toxaphene concn in section, Days after PPIP Date cored Ottman Lake 10/22/1967 1/25/1968 4/5/1968 6/28/1968 I 6/28/1968 I1 6/28/1968 I11 Silver Lake 10/22/1967 1/25/1968 612811968 a
first
0-5
5-10
26 121 191 275 275 275
1.5 7.9 15.8 8.8 9.5 9.3
0.8 2.6 2.0 1.1 0.9 1.1
0.5
25 120 275
2.1 4.1 4.8
0.9 1.2 0.8
1.0 0.6
treatment
cm
cm
10-15 15-20
cm
cm
a
U
0.7 0.8 0.7
a
a
U
a
Below the detectable limit of 0.5 p g / g dry weight.
the sediment at the Hilsenhoff buoy on September 10, 1966, appeared to be 6.2 p g / g in dredge samples, but 90.0 p g / g in the 0 to 5-cm section of the core. It is likely that sediment dilution caused the lower values in the dredge samples. It was assumed that several transport mechanisms may have resulted in the transport of toxaphene from the water to the sediments. The first mechanism is the direct sorption of dissolved toxaphene onto the sediment interface or onto algal growths at the water-sediment interface. It is likely that the significance of this mechanism in removing toxaphene from the water would be dependent upon the degree of water-sediment contact derived from wind mixing and physical characteristics of the lake. This assumption is, therefore, consistent with the observation that treated lakes which are stratified remained toxic to fish longer than well-mixed, shallow lakes (Henderson et al., 1958; Terriere et al., 1966), and with the observation that increased water-sediment contact in streams flowing from toxic lakes promoted rapid detoxification of the water in regard to fish (Stringer and McMynn, 1958). A second transport mechanism is indirect in that it was assumed dissolved toxaphene was sorbed onto plankton and other suspended solids soon after treatment and then codeposited with solids which settle to the sediment surface. It is unlikely that the direct sorption onto sediment could account for the rapid decrease in dissolved toxaphene which has been observed repeatedly (Hughes and Lee, 1968; Kallman et al., 1961; Johnson, 1966; Royer, 1966). Also, Hughes and Lee (1968) demonstrated the significance of sorption of toxaphene on plankton in the rapid removal of the mixture from natural waters. Therefore, a mechanism of sorption and codeposition of toxaphene with suspended solids is consistent with the observations and conclusions of previous studies and provides a n additional explanation for the accumulation of toxaphene in the sediments. Ottman Lake contained very little plankton before and after treatment, suggesting the transport of toxaphene to the sediment by codeposition with plankton was minimal. Table IV shows that toxaphene increased slowly in the 0 to 5-cm level of Ottman Lake sediments (at the 4.5-m water depth) for 200 days after treatment. Since no deposits or growths of algae were visible on top of the Ottman cores, the accumulation of toxaphene in the sediments of this lake was most likely due primarily to direct sorption onto the flocculent sediment particles.
A similar slow accumulation of toxaphene in Fox Lake sediments at the 4.5-m water depth is apparent in the second of the two maxima of Figure 1. This may again be attributed to direct sorption of toxaphene by the sediment rather than codeposition with suspended solids since the suspended solids in Fox Lake increased slightly rather than decreased 50 to 190 days after treatment (Hughes, 1968) and no deposits or growths of algae were visible on top of the cores obtained during this period. However, the earlier and more rapid accumulation of toxaphene in Fox Lake sediments (Figure 1) may be attributed to deposition of toxaphene-ladened algal blooms or to the rapid sorption of toxaphene on algal mats on the sediment surface. This was substantiated by the fact that the suspended solids in Fox Lake contained up to 1718 pg of toxaphene per gram and decreased rapidly after treatment (Hughes, 1968) and by the presence of layers of green algae on the surface of the cores obtained (August 6 and 8,1966) from Fox Lake. Estimates for the maximum mass of toxaphene found in the lake sediments can be made by summing the products of the sediment dry weight and the maximum toxaphene concentration observed for the 0 to 5-cm, 5 to 10-cm, and 10 to 15-cm levels of sediment. The weight of sediment in the 5-cm layers was estimated with assumptions that the surface area of the sediments in these shallow lakes were approximately equal to the lake surface area (Table I), and that the sediment composition at the sampling sites (approximately 2 % solids) were representative of the entire sediment basin. The maximum toxaphene in the sediments of Fox Lake was observed 51 days after the first treatment when 3030 kg or 47.3% of the 6410 kg applied was present. Of the 6.35 kg of toxaphene applied to Ottman Lake, 2.94 kg (46.3%) was calculated to be present in the sediments 191 days after treatment. Likewise, 2.27 kg, or 13.5x of the 16.8 kg of toxaphene applied, was estimated in the sediments of Silver Lake 275 days after treatment. Since the concentrations of toxaphene in the water of the lakes were below the detectable limit of 1 pglliter when the maxima in the sediments were observed (Hughes, 1968), greater than 50% of the toxaphene applied to the lakes may have been lost during application, lost through evaporation and (or) codistillation with water vapor, and degraded by microbial activity. However, the significance of these additional processes cannot be evaluated yet. The results of this study illustrate that the toxaphene concentration did not remain constant in lake sediments, but decreased rapidly from maximum. The toxaphene concentration decreased by a factor of 2 every 20 days after the first maximum in Fox Lake sediments, and decreased by a factor of 2 every 120 days after the second maximum in Fox Lake sediment and in Ottman Lake sediments. This decrease in concentration is more rapid than is commonly attributed to chlorinated hydrocarbons and differs greatly from the reported 11-year “half-life” of toxaphene in sandy loam (Nash and Woolson, 1967). The observed decrease in toxaphene concentration may be attributed to the type of microbial degradation reported by Castro and Belser (1968); however, sufficientdata are not yet available to substantiate this. The environmental data in Figure 1 and Table IV indicate that toxaphene was transported to sediment depths of 10 to 15 cm soon after treatment. The occurrences of toxaphene at these depths support the sediment model of Berger and Heath (1968), which depicts sediments as laminar historical layers covered by a homogeneous, or well-mixed, layer of sediment at the water-sediment interface. The rate of mixing in the homogeneous layer is dependent upon bottom fauna activity and water movements. T o estimate the rate of ob-
served transport in the lake sediments in this study, the data were examined for the last sampling date after treatment at which toxaphene remained undetected in the lower core sections, and the date at which toxaphene was first observed. It was assumed that the transport rate would be in the range of these observed limits. For example, in Fox Lake at the Hilsenhoff buoy (Figure l), toxaphene was not yet detectable in the sediment nine days after treatment, but was detected in the 0 to 5-cm and 5 to 10-cm core sections on the sampling date 16 days after treatment. Thus, it is likely that the transport rate to the 10-cm level would be greater than 0.6-cm per day but less than 1.1 cm per day. Likewise, estimates of the transport rates for toxaphene at other locations are as follows: in Fox Lake, toxaphene was transported vertically approximately 0.9 to 1.0 cm per day and 0.8 cm per day in the East Bay-South Side and North Side sediments, respectively; in Ottman and Silver Lakes, toxaphene moved approximately 0.4 cm per day into the underlying sediments. These estimates suggest that interactions exist between the lake water and upper sediment layers, which are rapid in comparison to the estimated 1-to-3 mm per year deposition rates for these lakes. Although there is not sufficient environmental data to determine the mechanism(s) which resulted in the observed vertical movement of toxaphene in lake sediments, molecular diffusion of toxaphene and the vertical mixing of the upper sediment layers by benthic organisms and (or) wind-generated currents (Arrhenius, 1963; Emery, 1963; Emiliani and Flint, 1963; Berger and Heath, 1968) may be the more likely considerations. The significance of molecular diffusion of toxaphene in the sediments may be estimated indirectly by comparing the calculated molecular diffusion rate of toxaphene in water to the observed rate of vertical movement in the sediments. If the calculated diffusion rate in water is much less than the
(L
?
5
‘ E
60”-
50-
?
0
2
40-
W
(L
W
50 TIME, DAYS A F T E R FIRST TREATMENT Figure 1. Relationship between extent of toxaphene accumulation and the time after first treatment for Fox Lake sediments at the Hilsenhoff buoy Volume 5, Number 3, March 1971 233
observed rate in the sediments, than molecular diffusion of toxaphene in sediments may be considered insignificant, since diffusion in sediments would be slower than in water due to sorption phenomena. Fick’s law of molecular diffusion can be used to describe the diffusion of a dissolved species. If it is assumed that the mixture of chlorinated bicyclic hydrocarbons, toxaphene, consists of spherical molecules having a lo-A radius, the diffusion coefficient for toxaphene in water at 15OC would be approximately 5.6 x 10-6cm2 sec-1. This estimated diffusion coefficient can be used to approximate the transport of toxaphene in an idealized system. Although the concentration gradient of toxaphene would be expected to change in time and depth, for the purpose of a comparison the system is simplified to a 20-cm column of water (the depth of maximum observed mixing in sediments) containing no toxaphene at the bottom and the saturation concentration of 300 pg/liter (Gunther et a/., 1968) at the top. Under these simplified conditions with a relatively constant gradient in water, molecular diffusion would account for a pg cm-* day-l over transport of approximately 7.2 X the 20-cm distance. It is not likely that this estimated rate could account for the accumulation of pgig quantities of toxaphene in the sediments at the observed rates. Also, since the toxaphene concentration gradient in the pore water of the sediment would be much less due to the high sorptive capacity of the solids for chlorinated hydrocarbons, it was concluded that molecular diffusion of toxaphene in sediments is most likely insignificant. Thus, physical mixing of the upper 10 to 15-cm layers of the sediment with the sediment at the watersediment interface which contained sorbed toxaphene may be the more likely explanation of the vertical movement of toxaphene. The desorption study indicated that the toxaphene concentration in the water and the sediment was essentially the same before and after the study, and that the toxaphene which accumulated under natural conditions in the sediments could not readily be removed from the sediments by lake water. Thus, if leaching of toxaphene was not observed under the vigorous laboratory conditions, the sediments certainly could not be expected to be a significant source of toxaphene for lake waters under natural conditions. These results do not support the suggestions of a number of investigators (Johnson, 1966; Terriere et al., 1966) that desorption of toxaphene from the sediments produced yearly fluctuations of pg/liter in the toxaphene concentration in the water. However, the possibility exists that toxaphene may become accessible to the lake through the migration of toxaphene-ladened bottom fauna from the sediments into the lake (Hughes, 1968). Also, the laboratory study does not rule out lake waters that may contain ng/liter concentrations of toxaphene due to desorption from the sediments. Conclusions
Toxaphene accumulated to concentrations as great as 90.0 pg/g (dry weight) and the transport to the sediments was
attributed to direct sorption onto the sediment and to co-
234 Environmental Science & Technology
deposition with toxaphene-Iadened algal blooms and other particulate matter. Toxaphene concentrations in the sediment decreased from observed maxima by a factor of 2 every four months in the three Wisconsin lakes. Toxaphene was transported vertically in the sediments at rates of 0.4 to 1.1 cm per day to the 10 to ,15-cm level and was attributed to physical mixing of the sediments. Laboratory studies demonstrated that the sorption of toxaphene on sediment was irreversible in aqueous solution and that leaching of appreciable amounts of toxaphene by water is highly improbable. Acknowledgment
The authors acknowledge the assistance of R. A. Hughes of the University of Wisconsin Water Chemistry Program and Vern Hacker and Ronald Poff of the Wisconsin Conservation Division of the Department of Natural Resources. Literature Cited
Arrhenius, G., “The Sea,” Vol. 111, Interscience, New York, 1963, pp 265-718. Berger, W. H., Heath, G. R., J . Mar. Res. 26(2), 134-43 11968). \--
- - I -
Castro, C. E., Belser, N. O., ENVIRON. SCI.TECHNOL. 2(10), 779-83 (1968). Emery, K: O., ’“The Sea,” Vol. 111, Interscience, New York, 1963, pp 776-89. Emiliani, C., Flint, R. F., “The Sea,” Vol. 111, 1963, pp 888-919. Fukano, K. G., Hooper, F. F., Prog. Fish Cult. 20, 189-90 (1958). Gunther, F. A., Westlake, W. E., Jaglan, P. S., Residue Reo. 20,l-148 (1968). Henderson, C., Pickering, Q. H., Tarzwell, C. M., Trans. Ainer. Fish. SOC.88,23-32 (1958). Hughes, R. A., M.S. thesis, University of Wisconsin, Madison, Wis., 1968. Hughes, R. A., Lee, G. F., Report to the Wisconsin Conservation Division, Department of Natural Resources, Mimeo, 1968. Hughes, R. A., Veith, G . D., Lee, G. F., Presented at the Society for Applied Spectroscopy Meeting, Chicago, Ill., May 1969. Johnson, W. C., Ca/$ Fish Game 58(8), 173-9 (1966). Johnson, W. D., Lee, G. Fred, Spyridakis, D., J . Air Water PollUt. 10,555-60 (1966). Kallman, G. J., Cope, 0. B., Navarre, R. J., Trans. Amer. Fish. Soc. 90,14-22 (1961). Mayhew, J., Proc. Iowa Acad. Sci. 66,513-7 (1959). Nash, R. G., Woolson, E. A., Science 157,924-6 (1967). Royer, L. M., J. Fish. Res. Board Can. 23(5), 723-7 (1966). Stringer, G. E., McMynn, R. C., Can. Fish. Cult. 23,143 (1958). Terriere, L. C., Kiigemagi, U., Gerlach, A. R., Borovicka, R. T., J . Agr. FoodChen?.14(1), 66-9 (1966). Wentz, D. A., M.S. Thesis, University of Wisconsin, Madison, Wis., 1967, pp 42-9. Receiced for reciew April I , 1969. Accepted September 18, 1970. This work was supported by the Wisconsin Consercation Dicision of the National Resources Department and by Training grant no. 5T1- WP-184-01 (Federal Water Pohtion Control Administration), by a N D E A Title IV FeUowship, and by the Unicersitj, of Wisconsin Engineering Experiment Station and the Department of Civil Engineering.
