Toxicity of Volcanic-Ash Leachate to a Blue-Green Alga. Results of a Preliminary Bioassay Experiment Diane M. McKnight," Gerald L. Feder, and Eric A. Stiles
U S . Geological Survey, P.O. Box 25046, Mail Stop 413, Denver Federal Center, Denver, Colorado 80225
To assess the possible effects of volcanic ash from the May 18,1980, eruption of Mt. St. Helens, Washington, on aquatic ecosystems, we conducted a bioassay experiment with a blue-green alga, Anabaena flos-aquae. Results showed that leachate (obtained by leaching 151 g of ash with 130 mL of simulated freshwater) was lethal to Anabaena flos-aquae cultures when diluted as much as 1:lOO with culture medium. Cultures exposed to a 1500 dilution grew, but a toxic effect was indicated by abnormalities in the Anabaena filaments. This study indicates that ash from the Mt. St. Helens volcano could have an effect on aquatic ecosystems in the areas of significant ashfall. Further study is needed to determine the toxic chemical constituents in the ash and also its possible effects on other aquatic organisms.
Introduction The possible effect on water quality is one of many concerns raised by the deposition of up to 80 mm of volcanic ash from the May 18,1980, Mt. St. Helens, Washington, eruption over large areas of Washington, Idaho, and Montana. Data on the chemical composition of leachates from four volcanic-ash samples (from Richland and Spokane, WA, and Kalispell and Helena, MT) showed that high, potentially toxic concentrations of several trace metals (manganese, zinc, copper, and cadmium) were present in the initial leachate volume ( 1 ) .High concentrations of dissolved organic carbon, 200-100 mgC/L, were also found in three of the four leachates. The organic compounds identified in the leachate were predominantly breakdown products from the pine forest destroyed in the eruption and included some that may be toxic (phenanthrenes and pentachlorobiphenyl) and others that may form complexes with trace metals and reduce their toxicity (dicarboxylic acids) (2). The leachates also had significant concentrations of nitrate, which could enhance algal growth. The experiment described here was designed to obtain preliminary data indicating whether volcanic-ash leachate has a toxic or beneficial effect on algal growth. In the years following the March 30, 1956, eruption of Mt. Besymjanny, USSR, Kurenkov ( 3 ) observed large increases in diatom populations (from lo4 to lo6 cells/L) in Lake Asabatchye, USSR, where a large quantity of volcanic ash had been deposited, Anabaena flos-aquae, a common blue-green alga, was chosen for the experiment because previous copper-toxicity experiments had shown this species to be sensitive to copper at concentrations greater then M, which might be expected from dilution of the volanic-ash leachate. Experimental Methods To obtain a solution of the chemical constituents likely to be leached by lake and stream waters in contact with volcanic ash, we packed a column with 151 g of volcanic ash from Richland, WA, and saturated it with a simulated lake water ( 4 ) for 9 hr. Then, 130 mL of leachate was eluted from the column, while new simulated lake water was added. A Millipore-type HA 0.45-pm filter, which had been leached in simulated lake water, was placed at the bottom of the column to prevent particulate material from eluting with the leachate. An analysis of the volcanic-ash leachate and simulated lake water used in the leaching procedure is shown in Table I. 382 Environmental Science & Technology
Anabaena flos-aquae UTEX 1444 was cultured at 25 "C in a water bath under continuous light. The culture medium was simulated lake water with trace metals as in Aquil medium (5) and with 2 mg/L of aquatic fulvic acid added. Sterile technique was used throughout the experiment. The cultures were grown in 500-mL acid-washed polycarbonate flasks containing a total volume of 250 mL of autoclaved WC medium and filter-sterilized volcanic-ash leachate. The dilutions of volcanic-ash leachate were l : l O , 1:25,1:50,1:100, and 1:500, with duplicate cultures for each dilution and for the control cultures with no leachate addition. The larger dilutions used in the experiment approximate the concentrations of chemical constituents leached from ash in surface waters in the ashfall area; for example, the 1500 dilution corresponds to 10 mm of ash falling into a lake with a mixing depth of 5 m and being leached by the volume of water in the mixed layer. Following addition of the leachate, the cultures were inoculated with 10 mL of a Anabaena flos-aquae culture. The initial cell count was 4 X lo5 cells/mL. Increases in chlorophyll concentrations were monitored daily by filtering 5-10 mL of culture through 2.5-cm Whatman GFC glass-fiber filters. The filters were stored in a freezer at 5 OC and analyzed within 7 days by grinding the filters, extracting in 90%acetone, and measuring chlorophyll a by spectrofluorescence using an Aminco-Bowman 34-8961 spectrofluorometer (6). Cell counts were made every other day to monitor growth and physiological effects of the leachate. Results The only Anabaena flos-aquae cultures that grew were the controls and cultures exposed to a 1500 dilution of the volcanic-ash leachate (Figure 1).The cultures with the M O O dilution had a lag phase 1 day longer than the control cultures and then increased in chlorophyll a concentration more rapidly than the control cultures. Growth rates, based on the chlorophyll data, computed from day 3 to day 6 were 0.74 d a y 1 in cultures exposed to the volcanic-ash leachate and 0.48 days-l in the control cultures. Cell concentrations in the control cultures were much higher than in the 1:500 dilution cultures (5 x IO6 vs. 7 X lo5 cells/mL on day 5); comparison of this data with the chlorophyll data shows that the chlorophyll concentration per cell was 6 times greater in the 1500 dilution cultures. Further evidence of morphological differences is seen in the photomicrographs taken on day 6 (Figure 2). The Anabaena cells exposed to the leachate are much larger, with the long axis perpendicular to the filament. These filaments are short (10-15 cells per filament) and aggregated in irregular clumps. In contrast, the filaments in the control cultures are long (more than 50 cells per filament); the long axis of the cells is parallel to the filament, and the filaments are representative of healthy Anabaena flos-aquae cultures. Although the culture exposed to the 1500 dilution of volcanic-ash leachate had a growth rate somewhat faster than the control culture, a toxic effect is indicated by abnormalities in the Anabaena filaments. The significance of these cellular abnormalities for the growth of Anabaena in aquatic environments requires further study. The lethal effects of higher concentrations of volcanic-ash leachate (1:lO to 1:lOO dilutions) are clearly seen in Figure 1. Along with the concentrations of chlorophyll a , the concen-
This article not subject to U.S. Copyright. Published 1981 American Chemical Society
A
Table 1. Composition ofVolcanic-Ash Leachate from Richland, WA, and of Culture Medium slrnulalsd lake water and EUIIYT~ mgiL
leachate
major cat1ms.~mglL
calcium, 188.6 magnesium. 31.7 sodium. 120.5 strontium, 0.86 trace metals. pg/L iron, 44 copper. 115 cadmlum. 20 manganese, 4450 zinc. 739 cobalt, 40
12.6 4.9 30.4 0.005 56 0.06 C
1.3 2.6 0.15
lithium. 158 nmlyWenum. 11
C
0.14
lead, 12 dissolved organic carbon. 100.5 mgClL
1
pH 6.4
8.0
B
C
‘Trace metals and lulvic acid were not added lo simulated lake water fw
leading of volcanic ash. Analyzed by using inductive ~ w p l e dplasma atomic emission spectroscopy. Not detected.
Flpure 2. Photomkrographs showing morphological differences between Anabaena flos-aquse cultures exposed to 1:500 dllutlm of volcanlc-ash leachate in WC medium (A) and control cultures (E) with a magnification of 2100X (enlargementsof photomlcrograPhS taken of unpreserved cultures with light microscope.)
30
NUMBER of O M S
Figure 1. Effect of dlfferent dilutions of volmlc-ash leachate on Ihe go& of Anebaena . ( F a c!arlty Ihe averege cah?mWalionS are plotted, and on days 3 and 5 the range of the duplicates also is shown. Aner day 3, data from only one of the 1:lOO dilution cultures are presented.)
tration of intact cells decreased during the first 5 days of the experiment from 4 X lo5to an average of 1.5 X lo5cells/mL. Observed in these cultures were cellular debris and short (5-10 cells per filament), clumped-together filaments of enlarged Anabaena cells, similar to those observed in the k500 dilution culture (Figure 2). In three of the cultures (both 1:50 and one 1:100 leachate dilution), a coccoid green alga was observed near the end of the experiment, indicating that the Anabaena
flos-aquae inoculum was not entirely unialgal. Chlorophyll a data, for the period in which green-algal contamination was observed, are not included in Figure 1. From this preliminary data, it is not possible to determine which of the chemical constituents in the leachate are responsible for the toxic effect on Anabaena flos-aquae. Of the four trace metals with high concentrations in the volcanic-ash leachate, copper is generally more toxic to algae than cadmium, zinc, and manganese. Comparison of these results with those from a previous copper toxicity experiment with this alga (7) shows that toxicity occurred at lower copper concentrations with ash leachate additions (between 2 X lO-? and 4 X 10-9 M copper) than with additions of copper nitrate solutions (between 10-5 and lo-? M copper). This comparison indicates that growth inhibition was caused by a metal other than copper, by a synergistic effect of elevated concentrations of several trace metals, or by toxic organic compounds in the leachate. Conclusions Leachate of volcanic ash from the May 18, 1980, Mt. St. Helens eruption is lethal to the blue-green alga Anabaena flos-aquae at dilutions of as much as 1:100. At a dilution of 1:500, a toxic effect is indicated by abnormalities in Anabaena filaments. I t can be concluded from this experiment with Anabaena flos-aqune that chemical mnstituents leached from volcanic ash and entering lakes and streams may have an efVolume 15, Number 3. March 1981 363
fect on algal populations. A die-off of blue-green algal populations was observed in Liberty Lake in eastern Washington following the ashfall ( 8 ) , whereas no significant changes in blue-green algal populations have been observed in Lake Lenore and Moses Lake in the center of the ashfall area in central Washington (9).
(4) Guillard, R. R. L. “Culture of Marine Invertebrate Animals”; Smith, W. L., Chanley, M. H., Eds.; Plenum Press: New York, 1975. (5) Morel, F. M. M.; Rugter, J.G: Jr.; Anderson, D. M.; Guillard, R. R. J . Phycol. 1979,15, 135. (6) Strickland, J. D.; Parsons, T. R. “A Practical Handbook of Seawater Analysis”; Bull., Fish. Res. Board Can. 1972,167, 311. ( 7 ) McKnight, D. M.; Morel, F. M. M. Limnol. Oceanogr. 1980,25, 62. (8) Funk, W. H., Washington State University, personal communication, 1980. (9) Edmondson, W. T., University of Washington, personal communications, 1980.
Literature Cited (1) Taylor, H. E.; Lichte, F. E. Geophys. Res. Lett., in press. (2) Pereira, W. E.; Rostad, C. E.; Taylor, H. E. Geophys. Res. Lett., in press. (3) Kurenkov, I. I. Limnol. Oceanogr. 1966,II, 426.
Received for review August 4,1980. Accepted November 20,1980.
CORRESPONDENCE
SIR: In their paper, “Determination of Vehicle Emission Rates from Roadways by Mass Balance Techniques” [ES&T 1980,14, 7001, Bullin et al. have attempted to determine the emission rates of pollutants from vehicles by a simple scheme and have compared the results of their “validated” method to the results from the EPA emission models, AP-42 and MOBILE 1 (I, 2 ) . While the authors accurately point out the shortcomings of the methodology used in AP-42 and MOBILE 1, the mass balance scheme is no panacea. It is unfortunate that the authors did not expound on the obvious and not so obvious limitations of this scheme and its applications, which are serious enough to invalidate their conclusions. The following discussion will bring out the major limitations of their methodology. For a continuous source, if the x coordinate is taken along the downwind direction, the equation for a mass balance is
Q=
Jms-~
CU dz dy
(1)
where Q is the emission rate, C is the measured concentration, and U is the wind velocity. The equation used by the authors
Q=
sm 0
CU, dz
(2)
where U , is the crossroad wind speed, is a valid simplification of the general equation if there is no concentration gradient in the direction parallel to the road. Clearly, this simplification is strictly valid for winds exactly perpendicular to the roadway. In practice, however, the method could be valid for situations where the cross-wind dispersion can be ignored. This assumption requires that the line source have no edge effects. As the wind direction deviates from normality to the roadway segment, the use of eq 2 will result in inaccuracies in the emission rate estimation. This equation predicts zero emission rate when the wind blows parallel to the roadway! These considerations also suggest that the relative distance of the monitor from the roadway will be equally important. Before discussing the applicability of this approach to parallel wind-road orientation angles, it is informative to see how the method performs under perpendicular cases. Even though one can expect eq 2 to hold under perpendicular wind-road orientation cases, the modifications of the flow field adjacent to the roadway, due to the moving traffic, make the application of this method subjective. For example, the authors seem to have used the wind speeds at each of the downwind locations where concentrations were measured, although they do not clearly state this in the paper. If it is so, these wind speeds are significantly affected at the lower levels by the moving traffic as shown by Rao et al. ( 3 , 4 )and Sedefian 364
Environmental Science & Technology
et al. ( 5 ) from the New York and GM experiments. Furthermore, if the winds at the nearest roadside tower are used to estimate the emission rate, the wind-road angle becomes a difficult parameter to determine since the above studies also showed a wind direction shift up to 90° to the wind direction recorded upwind. The authors do not even address these problems. How is one to determine whether the plume is entirely “defined” within the heights of observation as required by the proposed method? The observed concentration profile shape changes from an approximately exponential one to an approximately linear one within 10-m distance from tower 1to tower 2 of the GM data. Does one assume 10%of the maximum concentration to indicate an upper bound to the plume? If there are only two measurements within this height, should these two points be connected by a straight line or should a curve fitting be used? The observed plume dimensions can vary in a nonconservative manner (with respect to the proposed mass balance equation) due to the complex turbulent and mean flow structure adjacent to the highway. The above considerations are even more important in situations where a background concentration of a pollutant, such as CO, exists. Even if this background is assumed to be vertically and horizontally uniform on the upwind side (one needs to assume this if only one monitor exists on the upwind side), it can be easily shown that JmCzL1,2 dz - JmCili,i dz Z Jm(Cz - C d U , dz
(3)
where subseripts 1 and 2 refer to the upwind and downwind locations. The above relation is true regardless of which wind speed is used in the integral on the right-hand side. All of the above considerations suggest a tremendous amount of subjectivity in estimating the emission strength from the proposed methodology. We used a few cases of data presented in their Table I to determine the emission rates graphically from eq 2 by making assumptions such as (a) exponential or linear profile of CU,l, (b) upwind or downwind wind speeds at all heights or at the height of plume release, (c) correcting and not correcting for the angle of the tower line with respect to the roadway (since it is assumed in the method that there are no concentration gradients perpendicular to the flow), and (d) certain combinations of the above assumptions. The results indicated a factor of more than 2 a t the extremes of the estimated emission rates. It is clear that their method, even if applicable, is limited to situations where the emissions are uniform along the roadway so that there are no cross-wind gradients of concentration and, thus, the calculated emission rate per unit length of roadway will be meaningful. For example, if the mass bal0013-936X/81/0915-0364$01.25/0
@ 1981 American Chemical Society
