Arch. Environ. Contam. Toxicol. 29, 149-158 (1995)

A R C H I V E S

OF

Environmental Contamination a n d Toxicology © 1995Springer-VerlagNew York Inc.

Toxicity of Alum Sludge Extracts to a Freshwater Alga, Protozoan, Fish, and Marine Bacterium D. B. George, S. G. Berk, V. D. Adams, R. S. Ting, R. O. Roberts, L. H. Parks, R. C. Lott Center for the Management, Utilization, and Protection of Water Resources, Tennessee Technological University, Box 5033, Cookeville, Tennessee 38505. USA Received: 31 January 1994/Revised: 24 January 1995

Abstract. Alum sludges from ten water treatment plants throughout North America were subjected to a battery of toxicity tests which included the S. capricornutum growth test, the fathead minnow survival and growth test, a protozoan mortality test, and the Microtox ® test. S. capricornutum was more sensitive than any other test species to sludge extracts. Algal growth inhibition was observed in extracts obtained at pH 5 but generally not in circumneutral solutions. Alum sludge extracts prepared with natural receiving waters were toxic to S. capricornutum at all extract pH levels tested if receiving water hardness was less than 35 mg CaCO3/L. These results indicate that water-soluble constituents from alum sludges discharged into receiving waters may affect algal growth.

Hutchinson 1982). The aluminum species causing toxicity is dependent on water chemistry, the organism, and the effect monitored. The effects of alum sludges on several trophic levels of aquatic organisms are presented. Both acute and chronic toxicity of alum sludge extracts obtained from ten water treatment plants in North America were determined, using four aquatic test organisms. Acute toxicity was determined using the bacterium Photobacterium phosphorem and the protozoan Tetrahymena pyriformis. Selenastrum capricornutum and the fathead minnow were organisms tested for chronic toxicity.

Participating Utilities

Management of water treatment residues has long been a problem for utilities. Public health concerns and potential adverse environmental effects have caused utilities and federal and state regulators to reassess water treatment sludge management practices; discharge of chemical sludges to surface waters has been a major sludge disposal method. In 1984, at least 548,820 metric tons of sludge, mostly aluminum sludges, were discharged into surface waters in the United States (AWWA 1986). Historically, these residues have little environmental significance, and regulators have been hesitant to control their discharge (Burrows 1977; Novak 1979; Vicory and Weaver 1984). Research by the Ohio River Valley Water Sanitation Commission (ORSANCO) indicated that waste discharged from drinking water treatment processes of coagulation, sedimentation, and filtration contributed little or no additional load to the Ohio River (Vicory and Weaver 1984; ORSANCO 1981). These results would be expected for a high flow, turbid river. When aluminum is mobilized in lakes and streams, however, it may be toxic to aquatic life (Burrows 1977; Schofield and Trojnar 1980; Freeman and Everhart 1971; Havas 1985; Witters et al. 1984; Baker and Schofield 1979; Havas and

Correspondence to: D. B. George

Ten water utilities throughout North America participated in the study. Each water treatment plant used alum as the primary coagulant and discharged waste sludge from sedimentation basins and backwash water to receiving surfce waters. Three of the plants (Cincinnati, OH; Paducah, KY; Evansville, IN) discharged into the Ohio River. The Pasco, Washington water treatment plant discharged into a reservoir on the Columbia River, and Center Hill Reservoir received the waste from the Cookeville, Tennessee water treatment plant. The Concord, California water treatment plant also discharged its waste solids into a reservoir. The Missouri River transported the sludge discharged by the Omaha, Nebraska water treatment plant, and the Elbow River in Alberta, Canada, received sludge from a water treatment plant in Calgary. Two plants (Griffin, Georgia and Mobile, Alabama) sent their alum sludge to small urban creeks. Nine of the ten water treatment systems were conventional coagulation/flocculation/sedimentation facilities followed by filtration and disinfection. Omaha's Florence plant is a lime softening plant. Backwash water was directly wasted to receiving water. The frequency of sludge wasting from sedimentation basins varied from once a year to continuously. Total suspended solids in the discharged sludge samples ranged from approximately 115 mg/L (Paducah) to 50,500 mg/L (Calgary) (Table 1) based on the water treatment processes employed, the frequency of wasting solids, and the amount of backwash water in the plant's waste stream. Total

D.B. George et al.

150

Table 1. Characteristics of alum sludges and receiving waters obtained from water treatment Parameters Water treatment utility Calgary, AB, Canada Cincinnati, OH Concord Water District, CA Cookeville, TN Evansville Water & Sewer Utility, IN Griffin, GA Mobile, AL Omaha, NE Paducah, KY Pasco, WA

Source a

Aluminum (rag/L)

S R S R S R S R S R S R S R S R S R S R

2,900 <0.02 16.5 <0.02 1,126 0.58 1,610 <0.02 43.7 0.07 1,891 0.48 292 0.1 12.0 <0.02 108 0.28 74 0.30

Hardness (rag CaCOJL) 174 135 136 68 130 35 22 143 97 66

Alkalinity (mg CaCO3/L )

pH

2,694 135 410 58 280 82 965 67 70 70 341 37 338 16 4,193 169 66 67 56 57

7.3 8.0 7.2 7.5 7.1 8.0 7.1 8.2 7.9 7.6 6.9 6.9 7.1 7.0 10.2 8.4 7.8 7.4 7.2 7.5

aS = Wasted alum sludge; R = Receiving water

a l u m i n u m in the waste streams sampled ranged from 12 mg/L (Omaha) to 2,900 m g / L (Calgary).

Methods and Materials Personnel at each of the participating water treatment plants collected 8 to 12 L of wasted sludge at the point of discharge and 16 L of receiving water upstream from the point of discharge. The samples were placed in coolers with ice packs and received within 24 h after collection. Once the samples were received, they were prepared for a series of toxicity tests. The fathead minnow survival and growth test was conducted on samples from only four water treatment plants.

Water and Sludge Preparation

were pressure-filtered with nitrogen gas through 0.45 tzm membrane filters. The pH of the filtrate samples was adjusted to their corresponding extraction pH.

Fathead Minnow Toxicity Tests: Fathead minnow toxicity tests were conducted using alum sludges and corresponding receiving water samples obtained from Cincinnati's water treatment plant, Concord's water treatment plant, Cookeville's water filtration plant, and the Pasco water treatment plant. Filtrates were prepared as described above and stored at 4°C. Each day, aliquots of the filtrate were diluted with 20% Perrier water to obtain filtrate concentrations of 12.5, 25, 50, and 100%. The Perrier was purchased at a local grocery store and aerated overnight prior to making the dilutions. Two controls consisted of 20% Perrier made with Type I water (EPA 1979), and filtered receiving water without sludge extracts. During the chronic toxicity tests, the liquid in each test chamber was replaced daily with the appropriate extract concentration. The receiving water was filtered and stored in the same manner as the sludge extracts.

Microtox ®, Protozoan and Algal Tests: Both sludge and receiving water samples arrived at Tennessee Technological University within 24 h after collection. Receiving water from each water treatment plant was filtered through a 0.45 Ixm membrane filter, and the ambient pH was determined. The receiving water sample was divided into three parts. The pH of one part was adjusted to 5 with 6N hydrochloric acid (HC1). Sodium hydroxide (0.2 N) was used to adjust the pH of another aliquot to one pH unit above the ambient pH. The pH of the third aliquot remained at ambient. The receiving water aliquots were used to make dilutions of the sludge filtrates in the algal and protozoan assays and as a control. The sludge samples from the treatment plants were divided into three aliquots, and the pH of each aliquot was adjusted to correspond to the pH of each of the three receiving water aliquots as described previously. Each sludge aliquot was poured into two separate I L Erlenmeyer flasks and mixed on a shaker table at 200 rpm for 24 h. During the extraction period, the aliquot pH increased. Therefore, the pH levels were manually adjusted with 6N HCL every 2 h during the first 12 h and every 4 h for the last 12 h. After 24 h, the sludge samples

Toxicity Test Procedures Microtox ® Assay." Toxicity of the alum sludges to Photobacterium phosphoreum was determined by the Microtox ® test (Beckman Instruments, Inc. 1982). A 20% ethanol solution in reagent grade water was used as the reference toxicant. The extract concentration causing a 50% decrease in light output (ECso) was determined. Alum sludge filtrate samples at each pH level were tested at of 6.25, 12.5, 25, and 50% of the original filtrate concentration. The 15 min ECso was used as the end point for the toxicity assessment. The Microtox ® computer program (Microbics Corp. 1989) was used to determine ECso values.

Protozoan Toxicity Test: The ciliate T. pyriformis was grown axenically at 23°C in a medium containing per L: 2 g proteose peptone, 1 g yeast extract, 0.5 mL of 0.4 M MgSO 4 - 7H20, 1.5 mL of 2 M

Effects of Alum Sludges on Aquatic Organisms

glucose, and 10 mL of a solution of 0.25 M Na2HPO 4 and 0.25 M KH2PO4 at pH of 6.9. The glucose and phosphate mixtures were autoclaved separately and added aseptically. Fifty mL stock cultures were grown in 150 mL flasks without shaking at pH levels of 6.5 to 6.7. Stationary-phase cells (3-days old, 150,000 cells/mL) were washed and collected by centrifugation at 100 × g for 3 min. Cells were rinsed three times with the respective receiving water at each of the three pH levels tested. After washing, the cells were allowed to adjust for 5 h to the new medium prior to exposure to the alum sludge filtrates. This allowed time for any further cell division to occur. A modified procedure developed by Carter and Cameron (1973) was used for testing the toxicity of sludge extracts to the protozoa. The major procedural difference was that the cells were washed and suspended in a buffered saline solution (Roberts and Berk 1990), and then tested in natural receiving water rather than in a nutrient-rich medium. The population density of the cell suspensions at each respective pH was determined by staining a 25 p,L sample with Lugol's iodine and enumerating microscopically. The densities were adjusted to match the density at each respective pH sample (approximately 1,800 to 2,200 cells/mL). One mL of suspension was added to 19 mL of various sludge extract concentrations to yield the same cell density at each desired extract concentration. For each pH value tested, five filtrate concentrations (5, 20, 50, 70, and 95%) and a control of receiving water alone were tested. Triplicate samples were checked at the initial time and at 24 and 48 h to determine the percent mortality. Percent mortality was determined from differences between the controls and the cells exposed to the extracts since cells were not dividing (reproducing). To determine whether protozoan populations were consistent with respect to sensitivity, a reference toxicant, CdC12, was used.

Algal Assay: The freshwater green alga (S. capricornutum) growth test was conducted according to the U.S. Environmental Protection Agency's (EPA) algal assay (EPA 1985). The tests were run in triplicate. At each of the three pH levels tested, the sludge extract was diluted with filtered receiving water at the same pH to produce extract concentrations of 12.5, 25, 50, and 100%. Two controls consisted of receiving water and algal growth medium without sludge extract. The algal growth media control was used as a reference control to ascertain that the culture and nutrient stock solutions were adequate. All data comparisons were made between the receiving water controls and sludge extract treatments. All test solutions of extracts in receiving waters were amended with stock nutrient solutions to yield at least the same nutrient concentrations as in the algal growth media. Algae were cultured for seven days under banks of fluorescent lights at fluxes of 120 p~Es-lm -2, measured with an LI 190 SA Li-Cor quantum sensor (Li-Cor, Lincoln, NE) connected to a Grant 1201 data longer (Science/Electronics, Dayton, OH) which read in millivolts. The readings were converted to microeinsteins per second per square meter in the photosynthetically active radiation range (400 to 700 nm). At the termination of the test, algal cell density in each flask was determined microscopically using a haemocytometer. Analysis of variance (ANOVA) tests followed by Dunnett's test was applied to the data. These tests were performed according to the Toxstat program (Gulley et al. 1988). Any data sets that did not pass for normality and homogeneity were transformed prior to ANOVA tests. This occurred for only a few cases, several of which showed a high toxicity at the highest extract concentration. In these cases, the numbers of cells were so low (e.g., 5 or 7) that the variance was very low compared with the variance of other concentrations. All significant differences (a = 0.05) were determined by comparing the cell densities of the controls and the extract-exposed cells for the same initial pH treatment. ECs0 values were determined graphically using log-probit paper for data sets which showed differences in toxicity for more than two extract concentrations.

Fathead Minnow Toxicity Test: The fathead minnow toxicity test developed by EPA, EPA Method 1002.0 (EPA 1985), was conducted

151

on filtrates prepared from sludges received from four water treatment plants. For the fathead minnow toxicity test, silicon-coated glass beakers were used as test chambers. Eggs were shipped overnight from EPA's Environmental Monitoring Support Laboratory, Cincinnati. Larvae 24 to 48 h old were used. Two replicates of each sludge extract concentration (12.5, 25, 30, and 100%) made in 20% Perrier water (80% Type I water) were used. Controls consisted of 20% Perrier with no sludge extract, and receiving water with no sludge extract. Test solutions were renewed daily. The larvae were fed with newly hatched brine shrimp twice a day and exposed daily to 16 h of light at 4,000 lux. The number of fish surviving was determined daily. At termination of the test, the solution was siphoned out of each beaker, and crushed ice was added to immobilize the larve for transfer wih wide bore pasteur pipet to tared weighing pans for drying and gravimetric analysis. Dunnett's test (SAS 1988) was used to determine significant differences from Pettier controls. Controls were used to check for toxic effects of receiving water compared with Perrier water in order to rule out the effect of receiving water present in the sludge extracts.

Aluminum Speciation The method used for aluminum speciation analysis was developed by Dougan and Wilson (1974) and Goenaga and Williams (1988). The method was modified by the addition of varying amounts of hexamine solution to compensate for the relatively high pH range of the samples analyzed without interfering with the color development in the analysis. The species measured were total filterable aluminum (FT-A1), monomeric aluminum (M-A1), cation exchangeable aluminum (E-A1), and nonexchangeable aluminum (N-A1) (Figure 1). The FT-A1, M-A1, and N-A1 species were measured by the pyrocatechol violet spectrophotometric method (PCV) (Dougan and Wilson 1974). The E-A1 species was calculated as the difference between the M-A1 and N-AI.

Filtered Total Aluminum: Thirty-five mL of filtered sample were acidified using 0.30 mL of 12 N hydrochloric acid (HC1). The acidified sample was tested for aluminum according to the PCV method.

Monomeric Aluminum: A 35 mL, filtered, unacidified sample was analyzed for aluminum using the PCV method. The lack of acidification restricts the binding of PCV molecules to the monomeric-organic and monomeric-inorganic aluminum complexes, which are collectively referred to as mononuclear aluminum complexes (Bloom and Erich 1989).

Nonexchangeable Aluminum: Thirty-five mL of filtered sample were passed through a 2.5 cm by 1 cm diameter Teflon column containing a cation exchange resin, Amberlite®-IR120 resin (manufactured by Rhone-Poulenc). The columns were able to exchange soluble, labile fractions of aluminum. A maximum of 20 samples were eluted through one column (Rogeberg and Henriksen 1985). The columns were rinsed with two column volumes of sample prior to collecting a sample for N-A1 determination by the PCV analysis.

Colorimetric Aluminum Detection: The pyrocatechol violet spectrophotometric (PCV) method of Dougan and Wilson (1974) was followed for the detection of aluminum in aqueous samples because of its low detection limits, speed of measurement of numerous samples, and the capacity to detect various aluminum species. The samples that were analyzed at each time step were tested immediately following speciation. For each time, a total of 28 sample fractions, 2 aluminum standards, and a blank were prepared and analyzed. The PCV has little interference from phosphate (PO43-) and fluoride ( F ) , yields good detection limits, and is easy to use. The detection range of the PCV method was 0.04 to 0.40 mg/L aluminum and was proven linear throughout the experiment. Standards of 0.04, 0.08, 0.16, 0.20, and 0.40 mg/L were made in 0.10 M HC1 in 1-L batches

D.B. George et al.

152

TOTAL REACTIVE ALUMINUM, ACID DIGEST aluminum n-yeasurements

Total

naonon]eric aluminum (no acid digest}

Cation exchange treMed alonomeric aluminum

aluminum fraction

fraction composition

Non-labile

monomeric

Labile monomeric

Acid soluble

aluminum

aluminum

aluminum

ITJO12O1TIe r i e

a l u m i n o - organic complexes

free

alun~inum;

monomeric aluminum fluoride

colloidal polymeric

sulfate; and

hydroxide

aluminum; strong a l u m i n o organic complexes

complexes

several times throughout the experiment. The PCV and the other color development reagents were combined with 35 mL of standard. Reagent grade water was combined with all reagents to constitute a blank and had a range of optical density from 0.014 to 0.086, averaging 0.041. Dougan and Wilson (1974) indicated that solutions were stable for longer than eleven weeks, which was the storage limit for this experiment. The wavelength used in this experiment was 585 nm (Dougan and Wilson 1974). In order to decrease the influence of time from reagent addition to spectrophotometric determination, a 15- to 20-min time limit, specified by Dougan and Wilson (1974), was observed. Samples were first measured at 100% concentrations (no dilution) and were rerun at a diluted concentration if their absorbance was determined to be greater than the highest standard. Dilutions were made using reagent grade water to a volume of 35 mL. Discriminant analysis and linear regression (SAS 1988) were conducted to determine if toxicity data for S. capricornutum was related to aluminum concentration.

Results Of all the test organisms, S. capricornutum appeared to be the most sensitive to the alum sludge extracts. The Microtox ® data showed significant inhibitory effect at only 3 sites. No significant inhibition was observed in the protozoan acute toxicity test or the fathead minnow test.

Microtox ® Test At pH 5, sludge filtrates from both Paducah (15 min EC5o = 81% sludge extract) and Griffin (15 min ECso = 54.8% sludge extract) demonstrated toxicity using the Microtox ® assay. This toxicity refers to the inhibition compared with the control at pH 5. Filtrates obtained from the sludge collected at the Mobile water treatment plant had a 15 rain ECso equal to 85% of the filtered sludge extract at pH 9. The Microtox ® test showed no toxicity from any of the remaining alum sludge extracts.

Protozoan Toxicity Test None of the sludge extracts produced a significant toxic response in the protozoan mortality test at either 24 or 48 h. No

Fig. 1. Aluminum speciation scheme defining chemical composition of fractions from analytical measurements and calculations (Source: Driscoll 1984)

decreases in cell numbers were observed in controls or extractamended treatments over the 48-h period. Sludge extracts from Cookeville and Griffin promoted growth (i.e., cell division) at pH values greater than or equal to 8. These sludge extracts may have contributed nutrients to the cells.

Algal Assay Responses of S. capricornutum to alum sludge filtrate treatments varied depending on sample location and pH values. These were significant differences between alum sludge extract treatments and receiving water controls which contained no alum sludge filtrates (Table 2). In general, the algal density of receiving water controls (1-2 x 106/mL) were lower than the algal growth medium (4-5 x 106/mL) at pH 7-9. In addition, algal densities at pH 5 in growth medium (2- x 106/mL) were lower than densities observed at pH 7-9. This observation was consistent with reported growth data of S. capricornutum under acid conditions (Miller et al. 1978). Selenastrum capricornutum inhibition exhibited an amphoteric-like response to filtrate concentrations obtained from the Calgary sludge (Figure 2). Inhibition of Selenastrum growth occurred at pH 5 and pH 8. No inhibition was measured at pH 7. Sludge extracts collected from Evansville's sludge showed similar trends at higher filtrate concentrations (50 and 100% filtrate). In each pH 5 sludge filtrate solution tested, the growth of S. capricornutum was inhibited and sufficient data was obtained to compute ECso values for the toxicity of Calgary (10% filtrate), Cookeville (13% filtrate), Concord (22.5% filtrate), Pasco (6% filtrate), and Paducah (16% filtrate) alum sludge filtrates (Table 2). Sludge filtrates prepared from the Griffin alum sludge were very toxic at all concentrations at pH 5 (100% inhibition). ECso values could not be determined for many of the tests because many of the tests showed significant responses at only two concentrations, and other tests showed nearly 100% inhibition at all four concentrations. In general, at cireumneutral pH, the alum sludge extracts either had no statistically significant inhibitory effect on S. capricornutum growth, or growth was stimulated. Only Griffin

Effects of Alum Sludges on Aquatic Organisms

153

Table 2. Selenastrumcapricornutum test results on alum sludge filtrate

Sample site pH Calgary, Alberta pH 5

pH 7

pH 8

Cincinnati, OH pH 5 pH 7.4

pH 8

Cookeville, TN pH 5

pH 7.1

pH 8.5

Concord, CA pH 5

pH 7.5

pH 8

Evansville, IN pH 5

pH 8.5

Percent change from controlsa (+ = stimulatory; - = inhibitory; 0 = no effect)

Percent filtrate

Monomeric aluminum concentration (mg M-A1/L)

12.5 25 50 100 12.5 25 50 100 12.5 25 50 100

0.04 0.08 0.15 0.30 <0.04 <0.04 <0.04 <0.06 0.06 0.11 0.22 0.45

-60 -80 -93 -98 +42 +45 + 19 0 -47 -43 -27 -59

50 100 12.5 25 50 100 12.5 25 50 100

0.10 0.20 <0.04 <0.04 0.07 0.14 0.05 0.10 0.19 0.38

-35 -70 0 0 0 0 0 0 +46 0

12.5 25 50 100 12.5 25 50 100 12.5 25 50 100

<0.04 <0.04 <0.04 0.06 <0.04 <0.04 <0.04 <0.04 0.08 0.16 0.31 0.62

-49 -89 -94 -97 + 110 + 153 + 189 + 195 0 0 + 390 +636

12.5 25 50 100 12.5 25 50 100 12.5 25 50 100

<0.04 0.05 0.10 0.20 <0.04 <0.04 0.05 0.09 0.07 0.14 0.27 0.54

-37 -54 -60 - 100 0 0 +43 0 0 0 0 0

12.5 25 50 100 12.5 25 50 100

<0.04 0.05 0.09 0.17 0.07 0.14 0.27 0.54

0 0 -24 -45 0 0 -44 - 100

ECso 10%

13%

22.5%

D. B. George et al.

154 Table 2. Continued. Selenastrum capricornutum test results on alum sludge filtrate

Sample site pH Griffin, GA pH 5

pH 6.9

pH 8

Mobile, AL pH 6.7

pH 8

pH 9

Omaha, NE pH 6

pH 8.3

pH 9

Pasco, WA pH 5

pH 7

pH 8.5

Paducah, KY pH 5

pH 7.4

Percent filtrate

Monomeric aluminum concentration (mg M-A1/L)

Percent change from controlsa (+ = stimulatory; - = inhibitory; 0 = no effect)

12.5 25 50 100 12.5 25 50 100 12.5 25 50 100

0.08 0.16 0.31 0.62 <0.04 <0.04 0.06 0.11 0.08 0.16 0.32 0.64

-100 -100 -100 -100 -40 -41 -85 -99 -41 -73 -83 -88

12.5 25 50 100 12.5 25 50 100 12.5 25 50 100

0.04 0.08 0.17 0.34 0.04 0.08 0.17 0.34 1.48 2.95 5.90 11.80

-18 -27 -62 -92 -30 -63 -95 -99 -100 - 100 - 100 100

12.5 25 50 100 12.5 25 50 100 12.5 25 50 100

<0.04 0.07 0.14 0.28 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04

-40 0 -53 -99 0 0 -57 -76 0 0 0 0

12.5 25 50 100 12.5 25 50 100 12.5 25 50 100

<0.04
-75 -81 -85 -99 0 0 0 0 0 0 0 -99

6%

12.5 25 50 100 12.5 25 50 100

<0.04 0.06 0.12 0.25 <0.04 <0.04 0.05 0.10

-35 -90 -94 - 100 0 0 0 -74

16%

1.40

ECso

13.5%

37%

19%

155

Effects of Alum Sludges on Aquatic Organisms Table

2. Continued

Sample site pH pH 8

Percent filtrate

Monomeric aluminum concentration (rag M-A1/L)

Percent change from controlsa (+ = stimulatory; - = inhibitory; 0 = no effect)

12.5 25 50 100

<0.04 0.08 0.15 0.30

0 -50 0 +130

ECso

aPercent inhibition or stimulation of S. capricornutum growth was based on comparison of treatment to growth in receiving water controls

A .J

o=

Fathead Minnow Toxicity Test 0.5 0.4 0.3 0.2

O E

0.1

o

=E

FT

M

N

E

Aluminum Species pH m

5.00

~

7.00

~

Average survivorship of minnows in all extract concentrations was well above the 80% level required for controls; therefore, no significant mortality occurred. A 27% decrease in weight observed for the 100% extract sample from the Concord sludge was significantly greater than the 0% controls. For unexplained reasons, the 25% extract of Cookeville sludge showed significantly less average weight per fish, although there was no effect using 50 and 100% sludges.

8.00

FT-fittered total, M.monomeric, N.nonexchangeable, E-exchangeable

Aluminum Speciation for Acute Toxicity Bioassays

A. Aluminum s p e c i e s in 100% filtrate sample ( C a l g a r y )

In general, sludge filtrates used in the acute toxicity bioassays contained mostly monomeric aluminum (Table 3), which has been implicated as the primary aluminum species that is toxic to aquatic organisms (Burrows 1977; Nelson et al. 1987; EPA 1988). Monomeric aluminum existed primarily as nonexchangeable aluminum (i.e., aluminum associated with organic and anionic aluminum species). An increase in nonexchangeable aluminum in the filtrates occurred at basic pH compared to acidic or circumneutral pH conditions. In basic solutions, aluminate ion [AI(OH)-4] was probably the primary aluminum species. The amphoteric nature of aluminum was evident in five of the sludges tested, with the lowest aluminum species concentration in filtrates obtained from sludge aliquots at circumneutral pH and increased solubility in acidic and basic sludge samples. This phenomenon is illustrated by aluminum speciation data for the Calgary and Griffin sludge filtrates (Figures 2, 3). The highest FT-A1 concentration (12.9 mg/L) and corresponding M-A1 (11.8 mg/L) were contained in a filtrate obtained from an aliquot of the alum sludge collected at Mobile adjusted to pH 9.0. At pH 8 and 6.7, the filtrate M-AI concentrations were both 0.34 mg/L. Inhibition of Selenastrum occurred for each Mobile sludge filtrate tested at each corresponding pH level (Table 2). Similarly, filtrates obtained from alum sludge collected from Griffin inhibited Selenastrum at each pH level. As stated previously, the amount of soluble aluminum was lowest at circumneutral pH (0.43 mg/L), with higher concentrations in acidic (0.67 rag/L) and basic (1.24 mg/L) solutions. Aluminum in Evansville sludge filtrates did not exhibit an amphoteric response to pH, but increased as solution pH at which the filtrates were obtained increased (Table 3). Cincinnati and Pasco sludge filtrates also had small differences in FT-A1 (0.08 mg/L and 0.04 mg/L, respectively), as sludge

= 120 o 100 .o

~ so ~

60

~ ,o g.

2o

5

7 pH Value

8

m

12.5% Filtrate

~ - ~ 25% Filtrate

[~

50% FIIt;'ate

~

100% FiltrBte

B. S e l e n a s t r u m capricornutum inhibition ( C a l g a r y )

Fig. 2. Calgary sludge filtrate aluminum speciation (A) and inhibition of Selenastrum capricornutum (B)

filtrates at pH 6.9 and Mobile filtrates at pH 6.7 were toxic, with ECso values of 28% filtrate and 37% filtrate, respectively (Table 2). As previously mentioned, Evansville and Calgary extracts exhibited inhibition of algal growth in basic solutions (Table 2). In basic solutions, sludge extracts from Griffin and Mobile caused toxicity, with an ECso value of 13.5% filtrate for Griffin and 100% mortality at all dilutions for the Mobile sludge extract. The Mobile sludge extract also contained approximately 12 mg-A1/L at pH 9.

D.B. George et al.

156

Table 3. Aluminum speciation of alum sludges used in the acute toxicity assays Total A1

Aluminum species (mg/L)a

Location

(rag/L)

pH

FT-A1

M-A1

N-A1

E-A1

Calgary, AB

2,900.0

5.0 7.0 8.0 5.0 7.4 8.0 5.0 7.5 8.5 5.0 7.1 8.5 5.0 7.6 8.5 5.0 6.9 8.0 6.7 8.0 9.0 5.0 7.0 8.3 5.0 7.4 8.0 5.0 7.5 8.5

0.47 0.08 0.44 0.20 0.28 0.41 0.26 0.11 0.64 0.09 <0.04 0.70 0.20 0.65 1.59 0.67 0.43 1.24 0.34 0.65 12.90 0.28 <0.04 <0.04 0.31 0.11 0.33 0.10 0.14 1.39

0.22 0.06 0.44 0.20 0.14 0.38 0.20 0.09 0.54 0.06 <0.04 0.62 0.17 0.34 0.54 0.62 0.11 0.64 0.34 0.34 11.80 0.28 <0.04 <0.04 0.25 0.10 0.30 0.09 0.12 1.39

0.22 <0.04 0.40 0.20 0.11 0.31 0.09 0.09 0.47 <0.04 <0.04 0.26 0.10 0.30 0.54 0.45 0.09 0.56 <0.04 0.19 11.80 0.28 <0.04 <0.04 0.14 0.06 0.18 0.04 0.12 1.39

0.0 <0.04 0.04 0.0 0.03 0.07 0.11 0.0 0.07 <0.04 <0.04 0.36 0.07 0.04 0.0 0.17 0.02 0.08 0.32 0.15 0.0 0.0 <0.04 <0.04 0.11 0.04 0.12 0.05 0.0 0.0

Cincinnati, OH

Concord, CA

Cookeville, TN

Evansville, I N

1.69

803.0

1,610.0

2.05

Griffin, GA

1,891.0

Mobile, AL

201.0

Omaha, NB

12.0

Paducah, KY

Pasco, WA

3.35

56.2

aFt-A1 = filtered total aluminum; M-AI = monomeric aluminum; N-A1 = non-cation-exchangeable aluminum; E-A1 = cation-exchangeable aluminum

aliquot pH varied from 5.0 to circumneutral. The sludge sample provided by Cincinnati had a low total aluminum concentration (1.69 rag/L). Omaha provided a sludge containing 12.0 mg/L aluminum. Only 0.28 mg/L of the aluminum was soluble at pH 5. Less than 0.04 mg/L aluminum was detected at pH levels of 7.0 and 8.3. The Omaha water treatment plant was a lime softening facility. Aluminum interactions with calcium may have reduced the solubility of aluminum in circumneutral and basic solutions (Sposito 1989).

Discussion In the series of bioassays, the algal bioassay employing S. capricornutum was the most sensitive to the potential inhibitory effects from soluble ions or constituents extracted from the sludges under various pH conditions. This observation is corroborated by Wong (1989), who reported that three species of algae were more sensitive than fish or daphnids to copper and natural waters. Aluminum concentrations determined to be toxic to the algae in this study were far below those reported to cause lethal toxicity to fish (Boyd 1979; Hall and Hall 1989) and ceriodaphnids (McCauley et al. 1986). Selenastrum capri-

cornutum growth response varied with the chemical composition of the filtrates from each sludge and receiving water mixture. The pH at which the filtrates were obtained also significantly affected growth rate for all the samples tested except those from Calgary, Mobile, and Omaha. Hardness and alkalinity of water can protect aquatic organisms from metal toxicity (Burrows 1977). Sludge extracts from the Mobile and Griffin water treatment plants were diluted with soft receiving waters: 22 mg CaCO3/L and 35 mg CaCO3/L hardness, respectively. Low alkalinity corresponded to the low hardness of the receiving waters. The alkalinity of the receiving water from Mobile averaged 16 mg CaCO3/L, and the alkalinity of the receiving water from the drainage ditch at Griffin was 37 mg CaCO3/L. The low hardness and alkalinity existing in the receiving waters of Mobile and Griffin may have failed to protect S. capricornutum from the toxic effects of the alum sludge at each pH level. Growth inhibition, however, was noted in basic extracts obtained from Calgary's sludge, which were diluted with the receiving water having a 174 mg CaCO3/L (Figure 4). In each of the filtrates obtained from alum sludges at pH 5, the growth of S. capricornutum was inhibited. Since algal growth was compared with growth in receiving water alone at pH 5, this inhibition was not caused by acid stress alone, but by

Effects of Alum Sludges on Aquatic Organisms

157

E 1.4 ._.

1.2

c o

1

"~ 0.8

~, 0.6 0.4

E

~ o.e "E o FT

m

M

N

E

Aluminum S p e c i e s pH

m

6.oo

6.90

~

8.00

FT=filtered total, M=monomeric, N=nonexchangeable, E=exchang e a b l e

100

80

o ,m

,.Q t-"

60

40 (9 o

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0.

qltrate iltrate

0 22

Receiving

35

66

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68

97 130 135 136 143 174

ca° Hardness (mg CaCO3/L)

Fig. 4. Inhibition of Selenastrum capricornutum inhibition in basic (pH equal to or greater than 8) alum sludge extract solutions as related to receiving water hardness

the presence of another ion, possibly aluminum, that singularly or in combination with acid stress caused inhibition. This phenomenon has been observed in other toxicity studies conducted at low pH using fish as the test organism (Buckler et al. 1987; Muniz and Leivestad 1980; Wood and McDonald 1987). Except for the sludge samples obtained from Mobile and Griffin, wasted alum sludge existing in circumneutral aquatic environments presented minimal toxic risk to S. capricornutum growth. Growth inhibition did not appear to be directly proportional to alum concentrations in the extract. Acute toxicity was greatest with sludge extracts obtained from Mobile and Griffin which were diluted with their corresponding soft receiving water (hardness less than 35 mg CaCO3/L) (Table 2).

Fig. 3. Aluminum speciation for Griffin sludge filtrate

The growth response of S. capricornutum varied when exposed to filtrates from more basic sludge-receiving water mixtures. As the aluminum concentration in the Calgary filtrate increased, growth inhibition was observed. Only when S. capricornutum was exposed to 50 and 100% filtrate obtained at pH 8.3 from the Omaha sludge was inhibition observed, whereas exposure to pH 9 filtrate showed no inhibition at any filtrate concentration. In basic solutions, sludge extracts from Griffin and Mobile caused toxicity, with an ECso value of 13.5 percent for Griffin and 100 percent at all dilutions for the Mobile sludge extract. The Mobile filtrate contained 12.9 mg/L FT-A1 and approximately 12 mg/L M-A1. Filtrates obtained from alum sludges collected at Calgary showed that the degree of inhibition of S. capricornutum growth rate was significantly affected by the amount of soluble aluminum present. As soluble aluminum in the filtrates from the Calgary sludge exhibited the amphoteric nature of the metal, inhibition of S. capricornutum similarly occurred in filtrates obtained under acidic and basic conditions, and no effect or stimulation of the growth rate was observed under circumneutral conditions (Table 2). Extracts from the Evansville sludge showed similar trends with inhibition only in filtrates obtained under acidic and basic conditions, whereas filtrates from Mobile and Griffin were inhibitory at all pH and aluminum levels. Growth rate inhibition from the Griffin filtrate was affected by aluminum concentration and pH with the greatest inhibition at pH 5, whereas neither pH nor FT-AL significantly affected S. capricornutum growth rate in filtrates from Mobile's sludge. Stimulation of growth is reported for Cookeville extracts, however, this is probably only an "apparent" stimulation, since growth of controls was so low compared with the controls of other sites. The Cookeville receiving water appeared to be inhibitory to the growth of the algae, and addition of filtrate reduced the inhibition, thus resulting in significantly more algal cells in the extract-amended samples. Stimulation reported for Calgary at pH 7 was probably real, since control growth was good.

158

Conclusions Chemical constituents leached from alum sludges of water treatment may adversely impact primary productivity after discharge to freshwater. The alga S. capricornutum was more sensitive to alum sludge extracts than the bacteria of the Microtox ® assay, the protozoan T. pyriformis, or the fathead minnow. S. capricornutum growth inhibition varied depending on the alum sludge tested and the receiving water chemistry. Leachates from sludges in pH 5 receiving water inhibited growth of S. capricornutum. Furthermore, sludge extracts obtained using receiving water, which had a hardness of less than or equal to 35 mg CaCO3, inhibited growth of S. capricornutum at all pH levels (5 to 9). Except for sludge extracts that were inhibitory at all pH levels (Mobile and Griffin), waste alum sludge in circumneutral aquatic environments present minimal toxic risk to S. capricornutum. Six of the eight sludges were non-inhibitory under basic conditions. In general, growth inhibition did not appear to be proportional to aluminum concentrations in the alum sludge extract which was primarily monomeric aluminum.

Acknowledgments. This research project was funded in part by the American Water Works Association Research Foundation and their support was greatly appreciated. The authors want to thank Amy Welch for her significant contribution to this research effort.

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