- Email: [email protected]
Toxicity of polydimethylsiloxanes in certain environmental systems
ENVIRONMENTAL
RESEARCH
10.
397-406
(1975)
Toxicity of Polydimethylsiloxanes in Certain Environmental Systems E. J. HOBBS DONS Corning
Corporutiotz,
M. L. KEPLINGER
Received
Midlrrnd.
Michigrtn
48640
AND J. C. CALANDRA
February
24. 1975
Selected polydimethylsiloxane. (PDMS) fluids and formulations were studied in certain biological systems to evaluate the possible environmental impact of these materials. These siloxanes are not detectably degraded by sewage microorganisms as shown in a study with [“Cl PDMS. The very 10~ toxicity of these materials to daphnia, fresh water fish, marine species, mallard ducks. bobwhite quail, and domestic chickens; and their nonaccumulation in the flesh and eggs of chickens and in the flesh of fish minimizes concern regarding their potential to cause environmental damage.
INTRODUCTION
The polydimethylsiloxanes
(PDMS)
are represented
by the generic formula
CK CH,---Si-OCH, wherein x may range from 0 to > 10,000. The compounds of this class remain liquid over a large range of molecular weights and viscosities and are characterized by great thermal and chemical stability, low surface tension, water repellency and low toxicity (Rowe et al., 1948; Carson et al., 1966; Cutler et al., 1974). These properties have led to their extensive use in a variety of industrial applications, and it is anticipated that these uses will increase as alternatives are sought in replacement of more hazardous chemicals in applications where the properties of the siloxanes might be appropriate. Some of the known uses of the siloxanes suggest that they may be released into the environment, but no references to environmental contamination resulting from these uses are available. The commercial polysiloxanes are essentially inert at ambient temperatures under neutral conditions, but the polar Si+-0 bond is susceptible to heterolylic cleavage by acids or bases (Noll, 1968), especially at elevated temperature, and structural changes may be induced by irradiation with ultraviolet light (Delmar et al., 1969) or by maintenance at elevated temperatures in air (Scala and Hickam, 1958). These materials appear to be similarly stable in biological systems. The fluids 397 Copyright @ 1975 by Academic Press, Inc. All rights of reproduction in any form reserved.
398
HOBBS,
KEPLINGER
AND
CALANDRA
were nontoxic to a variety of bacteria (Bennett, 1973) which failed to grow without exogenous nutrients. The molecular identity of the fluid components was not altered during growth of these organisms in an adequate medium. Little is known about persistence or accumulation of the siloxanes in the environment because of the scarcity of monitoring data. Methods exist for detection of silicones in foods and biological materials (Horner et al., 1960; Jankowiak and Levier, 1971; Sinclair and Hallan, 1971; Neal et al., 1969); and a method has been developed for determining low levels of silicones in various materials, including soils and water, using optical emission spectroscopy (Smith, 1974), but these methods have not been extensively applied for environmental monitoring. It is the objective of this report to define the effects of some Dow Corning polydimethylsiloxanes in selected environmental systems in order to assess the possible environmental impact of these materials. MATERIALS
AND
METHODS
The materials investigated* were: PDMS. Dow Corning 200 fluid 100 cs; PDMS, Dow Corning 200 fluid 300 cs, 35% emulsion; W-Dow Corning 200 fluid 300 cs (280 yclg), 15% emulsion. Dow Corning Antifoam C emulsion-a 30% emulsion of Dow Corning Antifoam A compound. Dow Corning Antifoam A compound is a PDMS/350 cs fluid containing approximately 12% low molecular weight cyclic PDMS units and 4% silica aerogel. Biodegr-adability
of a PDMS
Emulsiotz
by Sewuge Microorgunisms
The material investigated was a ‘“C-Dow Corning 200 fluid 300 cs emulsion containing 15% PDMS. Five gallon Pyrex carboys, painted black to exclude light and equipped with Teflon-coated stirring bars, were employed as reactors. Each of four carboys was charged through inlet tubes, terminating 2-3 in above the base, with 16,110 ml of deionized water, 1800 ml of settled sewage2, 18 ml of sterile yeast extract solution (50 mg/ml), 72 ml of BOD salt solution and 0.25 ml of benzene. To each of two test reactors was added 180 mg of [‘“Cl PDMS (50.4 PC) as the emulsion and to each of two control reactors was added 300 pg (25 PC) of n-octadecane-I-‘“C in 0.25 ml of benzene, and a quantity of emulsifiers identical to that of the PDMS emulsion. Compressed air at 1.5 psi was passed through the reactors from a manifold surge tank preceded by a train consisting of a dry mechanical filter, activated carbon, ascarite, 25% NaOH solution, and a weak NaOH solution containing phenolphthalein to indicate any carbon dioxide leakage through the train. Downstream from each reactor was a series of traps, one charged with carbon tetrachloride, three with 0.3 N barium hydroxide, and one with a weak NaOH solution and phenolphthalein. The experiment was run continuously for 70 days under ambient room conditions (20-25”C, mean 23”). Each reactor was stirred daily for 5 minutes, and, on each of the first 32 days, 10 ml samples were taken through a sampling port during the mixing period. Reactor samples were taken less frequently during the ’ Supplied ’ Collected
by Dow Corning Corporation, 2111172 from Northwestern
Midland, University
Michigan. Sanitary Engineering
Labinterceptor
sewer
line.
TOXlCITY
OF
POLYDIMETHYLSILOXANES
399
later stages of the study. The pH and scintillation counts were determined for all reactor samples, and bacterial analyses were conducted periodically. Absorbents were renewed as required, daily at the outset and less frequently thereafter. The lqC-activity of all absorbents was determined by scintillation counting. Each reactor was reseeded with fresh sewage in BOD water on Day 61. At termination of the study, each reactor was agitated for 30 minutes and ‘V counts were determined for reactor samples, filtrates of reactor samples passing a 0.45 micron membrane filter, solids retained on the filter and cotton used to swab the interiors of the rinsed and drained reactors. Standard techniques were employed for preparation of samples and counting. Detection of three counts above background could be achieved with extended counting times (100 minutes). This represents five disintegrations per minute and corresponds to the ‘-‘C-activity of 804 ng of PDMS.
The 48-hour toxicity of Dow Corning 200 fluid 100 cs was determined in daphnia (Dnphnia magna) under static conditions. Gravid daphnia were introduced into 1 gallon glass jars containing double filtered (charcoal) municipal water which had aged for 7 days. The young of these animals, when 1 to 48 hours old (first instar) were used as test organisms. The animals were fed with a suspension of 10 g of Purina trout chow and 0.5 g of Cerophyll powder blended in 300 ml of water. After a preliminary range finding study to determine the approximately TL50, five concentrations of the test material were selected for bioassay using 20 animals at each concentration. The test material was added without solvent, and the animals were observed by means of a dissecting microscope during a period of 48 hours. Mortalities were recorded and the tolerance limits. TLl, TL50. and TL99, were calculated according to Litchfield and Wilcoxon (1949). The pH and dissolved oxygen concentration were determined at 0 and 48 hours. The 48-hour toxicity of Dow Corning Antifoam C emulsion was determined in analogous animals under dynamic conditions. The water used in the bioassay was double charcoal filtered city water contained in a continuously aerated 100 gallon reservoir and maintained at 18°C. After a preliminary static range finding study to determine the approximate TL50, five concentrations of test material were selected for the dynamic bioassay. The test apparatus consisted of a modified proportional diluter (Mount and Brungs, 1967). Modifications included control of diluent water and vacuum supplies with a time clock and the addition of a mixing chamber between the diluter and the bioassay vessels. Four 3-l polyethylene bioassay vessels, each containing five daphnia, were used for each test concentration and for the untreated control. Overflow pipes maintained a constant level, and the turnover time in each vessel was 1.5 hours. Following introduction of test material, the daphnia were observed during a period of 48 hours and mortalities were recorded. The pH dissolved oxygen, concentration, hardness, specific conductance, and alkalinity were monitored during the study. At the end of 48 hours, the TLI . TLSO, and TL99 of the formulation and of the active ingredient were calculated.
400 Four-Duy
HOBBS,
Toxicity
of a PDMS
KEPLINGER
AND
Fotwmlation
CALANDRA
in Fresh
Water Fish
Four-day TLSOs of Dow Corning Antifoam C emulsion in bluegill sunfish and rainbow trout were determined under static conditions. Healthy young fish (35-75 mm) were used as test animals. All fish were held for observation for not less than 10 days prior to experimental use in large aerated stock tanks, and were maintained on appropriate diets until 3 days prior to testing. The trout were maintained at 13°C and the bluegills at 24°C. All stock tanks and assay vessels contained reconstituted deionized water to which were added, on a per liter basis, 30 mg calcium sulfate, 30 mg magnesium sulfate, 48 mg sodium biocarbonate, and 2 mg potassium chloride. Preliminary screening was conducted to determine the general level of toxicity of the test material and three to five concentrations of each test material were selected for bioassay. Bioassay vessels lined with disposable polyethylene bags were filled with 12.5 1 of well aerated reconstituted water, and ten fish were tested at each concentration. Following the introduction of the test material, the fish were observed for 96 hours and mortalities and reactions were noted. The concentration of dissolved oxygen was determined for all test solutions in which mortalities occurred.3 Concentrations of dissolved oxygen of 4 ppm for warm water fish (bluegills) and 5 ppm for cold water fish (trout) are considered to be minimal for valid testing. The pH of each solution in which mortalities occurred was also determined. As a quality check, each lot of fish was challenged with a reference pesticide, toxaphene, which was added to the bioassay vessels as 0.01% (w/v) solution in acetone. At the end of the 4-day observation period, the median tolerance limits (TLSOs) for Dow Corning Antifoam C emulsion were calculated according to Litchfield and Wilcoxon (1949). Residue
Study
qf a PDMS Emulsion in Bluegill Sunjish
The material investigated was a Dow Corning 200 fluid 300 cs emulsion containing 2 g of [‘“Cl PDMS in 13.33 ml of emulsion and having a ‘“C-activity of 280 j&g of PDMS. Sixty young bluegill sunfish were used to form two groups of 30 each. One group was exposed in a 30-l tank to water containing 1 ppm of the [‘“Cl PDMS emulsion (1.26 PC of Y-activity). The second group was similarly exposed to 10 ppm of the emulsion (12.6 PC of ‘V-activity). Each tank was sampled three times weekly for radioassays, and additional emulsion was added as required to maintain proper tank concentrations. Two fish from each group were sacrificed on Days 0 (no exposure) 1, 3, 5, 7. 14, 21, and 30. Body weights were recorded, the fish were rinsed and scaled, and flesh samples were collected from each flank of each fish. The collected tissues were weighed, and duplicate samples from each fish, one from each flank, were placed in dialysis bags, dried in forced air. and compressed with shredded filter paper into pellets which were burned and radioassayed using conventional techniques. 3 Hach
0X-2-P
Dissolved
Oxygen
Test
Kit,
Hach
Chemical
Company,
Ames.
Iowa.
TOXICITY
OF
Residue data, translating ‘“C-activity into equivalents ported in terms of mean values for each pair of fish. Four-Day
Toxicity
of a PDMS
401
POLYDIMETHYLSILOXANES
Formulation
of [‘“Cl PDMS.
are re-
in Salt Water Species
The 4-day TLSOs of Dow Corning Antifoam C emulsion in cockles (Prothaca mummichogs (Fundrtlus heteroclitus), shore crabs (Pachygrapsus and brown shrimp (Penaerts oxtecus) were determined under static conditions. The animals employed were of appropriate size for testing: valve length of 4W5 mm for cockles: a length of 50-8C mm for mummichogs; carapace width of 30-6 mm for shore crabs; and rostrum length of S-12 mm for brown shrimp. All species were held in stock tanks at 21°C for 4 to 5 days prior to testing, and were fed an appropriate diet until 1 day prior to testing. All stock tanks and assay vessels contained aged seawater” having a density of 1.020 and a calculated salinity of 27.2 O/O0 (2.72%). Assays were run at concentrations of 1, 10, 100, and 1000 ppm using 20 cockles, and ten of each other species at each test level. Dissolved oxygen and pH were monitored throughout the studies. The animals were observed for reactions and mortalities during a 48-hour period, after which time median tolerance limits (4-day TLSOs) were determined.
spaminea), crassipes)
Subacute
Toxicity
of a PDMS in Mallard
Ducks
and Bobwhite
Quail
The test material employed was Dow Corning 200 fluid 100 cs, and the animals used were 10-15 day old pen-reared mallard ducks and bobwhite quail. The test material was incorporated into a standard laboratory diet5 at levels of 3 12, 625, 1250, 2500. and 5000 ppm. Dieldrin at five graded dose levels for each species was run as a positive control, and five untreated control groups were employed in each study. Each group consisted of ten birds. Test and positive control birds were fed the treated diets for 5 days and were held on standard diet for an additional 3 days for observation. Control birds received untreated ration for the S-day period. All animals were weighed at the beginning of the studies and at the time of death on Day 8. Group food con sumption was recorded for the test period and for the observation period, and daily observations for mortality and signs of toxicity were made. All animals dying during the study and those killed at termination of the observation period were examined for gross pathologic changes. Dietary LCSOs for dieldrin were calculated according to Litchfield and Wilcoxon (1949). and the toxicity of Dow Corning 200 fluid 100 cs was estimated. Toxocity, Reprodrrction Le<~:llor-n Chickens
and Residue
Study nit/l PDMS
in White
Young white Leghorn chickens, 80 hens and 16 roosters, were equally divided into four groups. All groups were maintained on a basal ration” until the birds reached the age of 24 weeks, at which time the three test groups were started on a The seawater was prepared with deionized water and instant ocean sea salts. 5 Purina Gamebird Startena. Ralston Purina Company. St. Louis. Missouri. li Purina Flock Chow, Ralston Purina Company, St. Louis. Missouri.
402
HOBBS,
KEPLINGER
AND
CALANDRA
basal diet supplemented with 200, 1000, and 5000 ppm of Dow Corning 200 fluid 100 cs. Observations were made daily for signs of toxicity. All chickens were individually weighed each week, and group food consumption was determined weekly. As each group began laying, the eggs were collected daily and egg weights were recorded. The eggs were collected for study of the following parameters when the egg weights were consistently between 50 and 60 g, at least 50% of the hens in the group were laying, and the hens were at least 28 weeks old. Egg production, weight and quality. The total number of eggs, the individual weights of eggs collected, and the total number of untracked and unblemished eggs were recorded. Hatchability. Nondefective eggs were randomly selected for hatching. These eggs were turned twice daily during each 7-day collection period and were then placed in an incubator maintained at 99 to 100°F with a wet bulb reading of 85”. This procedure was followed until a minimum of 100 eggs from the control group and each test group had been set for hatching. The following were recorded: a. Number hatched. b. Number unhatched. c. Viability of chicks over a 30-day period, during which time feed and water were permitted ad libitum. d. Examination of unhatched eggs for fertility and stage of development. e. Weight of chicks after Days 1 and 30. f. Gross pathological examination of chicks after Day 30. Residue studies. The total daily egg production from each test group was taken for residue analysis on Days 3, 7, 14, 21, and 28 of the dosing period, and on Days 7 and 28 of the recovery period. The eggs were kept frozen until analysis.7 After hatching results were available, half of the chickens in each group were killed; they were defeathered and individual samples of liver, kidney, fat, and muscle were collected from each chicken for residue analysis. The remainder of the carcasses were retained in the frozen state until residue determinations were completed. The remaining chickens were placed on a 30-day recovery regimen on unsupplemented basal diet. The remaining chickens were killed at the end of the recovery period, and tissues were similarly collected for residue analysis.
RESULTS Biodegradability
of CI PDMS
Emulsion
by Sruuge
Microorganisms
The 14C-Dow Corning 200 fluid 300 cs emulsion was not degraded to any detectable extent to ‘“COZ, and no volatile organic degradation products were detected. No radioactivity was detected in either the carbon tetrachloride or alkali i Ail analyses
were
done
by the Dow
Corning
Corporation,
Midland.
Michigan
TOXICITY
OF
403
POLYDIMETHYLSILOXANES
traps. Octadecane was extensively degraded under analogous conditions, 60 and 40% of the radioactivity being evolved as 14C0, from the two positive control reactors within 30 days. In the case of the PDMS emulsion, 100% of the radioactivity of the terminal mixture was associated with filtered particulate matter while I1 and 13% of the radioactivity occurred in the filtrates of the terminal octadecane mixtures. This indicates conversion of octadecane to polar metabolites, while no such transformation appears to occur with the PDMS. This study does not positively exclude the possibility of transformation and incorporation of PDMS by sewage bacteria, but this seems highly unlikely in view of the total absence of expired ‘“CO,. Toxicity
of PDMS
in Daphnia
The static 48-hour TLSO for Dow Corning 200 fluid 100 cs was determined to be 44.5 ppm, TLl and TL99 being 379.6 and 5.22 ppm, respectively. The test material remained largely on the surface of the water at each test concentration and, at the higher levels, many of the daphnia became entrapped in the test material and died there. In the dynamic test the TLl, TL50, and TL99 were 600, 73.4, and 8.98 ppm, respectively, expressed in terms of PDMS in the 30% emulsion (Dow Corning Antifoam C emulsion). Water quality in terms of dissolved oxygen, pH, hardness, specific conductance, and alkalinity was judged to be appropriate in a]] cases. Four-Day
Toxicity
of a PDMS Formulation
in Fresh
Water Fish
The 96-hour TL50 of Dow Corning Antifoam C emulsion was > 10,000 ppm, for both bluegill sunfish and rainbow trout. No deaths were noted at any level, but hypoactivity was observed in both species at levels of 1,000 and 10,000 ppm. The TLSOs for toxaphene under analogous conditions were 0.037 and 0.044 ppm for trout and bluegills, respectively. Residue
Study with u PDMS
Emulsion
in Bluegill
Sun&h
It was found necessary to add [‘“Cl PDMS on Days 8, 15, and 22 for approximate maintenance of the desired levels of radioactivity in the water. Values for radioactivity, determined three times weekly on water from each tank, ranged from 0.23 to I .26 at the low level, and from 4.60 to Il.84 at the higher level. That the PDMS was being deposited on the walls of the aquaria was confirmed by high counts in swabbings of the walls of each tank taken on tiay 29. The counts for swabbings from the high level tank were approximately 10 times as great as those from the low level tank, but no attempt was made to obtain a material balance. Tissue residue data are presented in Table 1. The levels are very low and highly variable, and there appears to be no relationship between the residue levels and either duration of exposure or level of exposure. The results suggest that 14C-activity detected may be due to surface contamination rather than to cellular uptake of the silicone and provide no evidence for the accumulation of the PDMS in the flesh of fish.
404
HOBBS,
KEPLINGER
AND
TABLE RESIDUES
OF ‘T-ACTIVITY
IN
BLUEGILL
Tissue
Day of sacrifice
1
SUNFISH
residue”.“,’
Exposure
DATA
FOR
SALT
= 5 DPM
WATER
0 1.0 10.0 100.0 1000.0
shore
95 100 95 100 90 28.8%
Egg production (%/Day) 82 81 76 84
u Mean values. a Defective eggs were
TO Dow
EXPOSED
crabs
of survival
ppm
for
a
CORNING
of
mummichogs
loo 100 100 100 70
TABLE
0 200 1000 5000
= 0.040
brown
100 100 100 100 80
shrimp 95 90 90 85 60
PDMS.
REPRODUCTIVE
Treatment level (wm)
ng PDMS
C EMULSION Percentage
cockles
= 8.04
2
SPECIES
ANTIFOAM
Level of exposure (ppm)”
of
0.000 0.105 0.115 0.069 0.167 0.758 0.242 0.428
TABLE SURVIVAL
EMULSION
at levels 10 mm
0.000 0.132 0.077 0.000 0.376 0.100 0.130 0.195
Calculated as PDMS. Mean values of four samples for two fish. Detection limit of 3 CPM above background mg sample.
D As the emulsion.
TO A [Y]PDMS
EXPOSED
1 rw
0 I 3 5 7 14 21 31 a * c 200
CALANDRA
cracked
PERFORMANCE Dow CORNING
LEGHORN
200 FLUID
Egg weight w
Normal” em (%)
54.7 54.9 55.0 55.7
45.4 54.4 49.8 51.5
or severely
3
OF WHITE
blemished.
Hatchability v@) 92.2 89.6 80.0 87.0
FED
CHICKENS
100 CS” Body Day 39.2 39.1 39.5 40.9
1
Weight Day 256 266 264 267
(g) 30
Chick survival to Day 30 (%) 100 100 94.6 93.0
TOXICITY
Four-Day
Toxicity
of a PDMS
OF
405
POLYDIMETHYLSILOXANES
Formulution
in Suit Water Species
The TL50 values for all species were > 1000 ppm. Survival data are presented in Table 2. Quiescence and surfacing were noted among some mummichogs, and loss of equilibrium was observed among some shrimp at 1000 ppm, but no other reactions were seen. Subucute
Toxicity
of PDMS
in Mallard
Ducks
and Bobwhite
Quail
The LC50 (5day dietary exposure) of Dow Corning 200 fluid 100 cs in each species was > 5000 ppm. One duckling died on the second day at 625 ppm, but no other deaths occurred among test groups, and no signs of toxicity were observed. The LCSOs for dieldrin were 115 and 32 ppm, respectively, for ducks and quail. Signs of toxicity with dieldrin included hyporeactivity and anorexia. Toxicity, Chickens
Reproduction,
and Residue
Study ,t,ith a PDMS
in White Leghorrl
Ingestion of Dow Corning 200 fluid 100 cs had no adverse effect on body weight or food consumption. Five deaths occurred during the study, one in the control group and two each at dietary levels of 200 and 1000 ppm. These deaths were attributed to physical causes (prolonged rectum, adhesive peritonitis). No differences were noted between test and control birds at necropsy. Egg production and quality, hatchability, and body weights and viability of chicks were not affected by treatment. Data regarding these parameters are summarized in Table 3. Residues of silicon in all samples analyzed were below the limit for quantitative determination. Detection limits were 3 ppm for egg yolks and whites; 2 ppm for kidney, liver, and muscle: and 4 ppm for fat. DISCUSSION
All studies conducted indicate a very low order of toxicity for the Dow Corning polydimethylsiloxanes. No evidence has been obtained to suggest accumulation in the flesh of fish or birds, and there appears to be no significant transfer of the material to the eggs of chickens. The nonbiodegradability and chemical and physical inertness of these siloxanes suggest that material released into the environment could persist for considerable periods of time, but their low toxicity and apparent immobilization by binding to particulate matter in aqueous systems should minimize concern regarding their potential to cause environmental damage. REFERENCES Bennett. D. R. (1973). Metabolism of organosilicon compounds. Communication from Dow Corning Corporation. Carson. S.. Weinberg, M. S.. and Oser. B. L. (1966). Safety evaluation of Dow Corning 360 Fluid and Antifoam A. Proc. Sci. Sec. Toilet Goods Assoc~. 45, 8-19. Cutler. M. G., Callings, A. J.. Kiss, I. S.. and Sharratt. M. (1974). A lifetime study of a polydimethylsiloxane in the mouse. Fd. Cosmt~t. Toxri~l. 12, 443-450. Delman. A. D., Landy. M.. and Simms, B. B. (1969). Photodecomposition of polymethylsiloxane. J. Polwm Sci. 7, 375-386.
406
HOBBS.
KEPLINGER
AND
CALANDRA
Horner, H. .I., Weiler, J. E., and Angelotti. N. C. (1960). Visible and infrared spectroscopic determination of trace amounts of silicones in foods and biological materials. Anal. Chem. 32, 858-861. Jankowiak, M. E., and Levier, R. R. (1971). Elimination of phosphorus interference in the colorimetric determination of silicon in biological material. And. Biochem. 44, 4621172. Litchfield, J. T., and Wilcoxon, F. (1949). A simplified method of evaluating dose-effect experiments, J. Pharm. Exp, Ther. 96, 99-l 13. Mount, D. I., and Brungs, W. (1967). A simplified dosing apparatus for fish toxicity studies. Water Res. 1, 21-29. Neat, P., Campbell, A. D., Firestone, D., and Aldridge, M. H. (1969). Low temperature separation of trace amounts of dimethylpolysiloxane from food. J. Amer. Oil. Chem. Sot. 46, 561-562. Nell, W. (1968). ‘Chemistry and Technology of Silicones.” Academic Press, New York. Rowe, V. K., Spencer, H. C., and Bass, S. L. (1948). Toxicological studies on certain commercial silicones. J. Ind. Hyg. 30, 332-352. Scala. L. C., and Hickman, W. M. (1958). Thermal and oxidative degradation of silicones. J. 2nd. Eng. Chern. SO, 1583-1584. Sinclair, A., and Hallam. T. R. (1971). Determination of dimethylpolysiloxane in beer and yeast. Analyst 96, 14%154. Smith, A. Lee (1974). “Analysis of silicones.” Wiley, New York.
RESEARCH
10.
397-406
(1975)
Toxicity of Polydimethylsiloxanes in Certain Environmental Systems E. J. HOBBS DONS Corning
Corporutiotz,
M. L. KEPLINGER
Received
Midlrrnd.
Michigrtn
48640
AND J. C. CALANDRA
February
24. 1975
Selected polydimethylsiloxane. (PDMS) fluids and formulations were studied in certain biological systems to evaluate the possible environmental impact of these materials. These siloxanes are not detectably degraded by sewage microorganisms as shown in a study with [“Cl PDMS. The very 10~ toxicity of these materials to daphnia, fresh water fish, marine species, mallard ducks. bobwhite quail, and domestic chickens; and their nonaccumulation in the flesh and eggs of chickens and in the flesh of fish minimizes concern regarding their potential to cause environmental damage.
INTRODUCTION
The polydimethylsiloxanes
(PDMS)
are represented
by the generic formula
CK CH,---Si-OCH, wherein x may range from 0 to > 10,000. The compounds of this class remain liquid over a large range of molecular weights and viscosities and are characterized by great thermal and chemical stability, low surface tension, water repellency and low toxicity (Rowe et al., 1948; Carson et al., 1966; Cutler et al., 1974). These properties have led to their extensive use in a variety of industrial applications, and it is anticipated that these uses will increase as alternatives are sought in replacement of more hazardous chemicals in applications where the properties of the siloxanes might be appropriate. Some of the known uses of the siloxanes suggest that they may be released into the environment, but no references to environmental contamination resulting from these uses are available. The commercial polysiloxanes are essentially inert at ambient temperatures under neutral conditions, but the polar Si+-0 bond is susceptible to heterolylic cleavage by acids or bases (Noll, 1968), especially at elevated temperature, and structural changes may be induced by irradiation with ultraviolet light (Delmar et al., 1969) or by maintenance at elevated temperatures in air (Scala and Hickam, 1958). These materials appear to be similarly stable in biological systems. The fluids 397 Copyright @ 1975 by Academic Press, Inc. All rights of reproduction in any form reserved.
398
HOBBS,
KEPLINGER
AND
CALANDRA
were nontoxic to a variety of bacteria (Bennett, 1973) which failed to grow without exogenous nutrients. The molecular identity of the fluid components was not altered during growth of these organisms in an adequate medium. Little is known about persistence or accumulation of the siloxanes in the environment because of the scarcity of monitoring data. Methods exist for detection of silicones in foods and biological materials (Horner et al., 1960; Jankowiak and Levier, 1971; Sinclair and Hallan, 1971; Neal et al., 1969); and a method has been developed for determining low levels of silicones in various materials, including soils and water, using optical emission spectroscopy (Smith, 1974), but these methods have not been extensively applied for environmental monitoring. It is the objective of this report to define the effects of some Dow Corning polydimethylsiloxanes in selected environmental systems in order to assess the possible environmental impact of these materials. MATERIALS
AND
METHODS
The materials investigated* were: PDMS. Dow Corning 200 fluid 100 cs; PDMS, Dow Corning 200 fluid 300 cs, 35% emulsion; W-Dow Corning 200 fluid 300 cs (280 yclg), 15% emulsion. Dow Corning Antifoam C emulsion-a 30% emulsion of Dow Corning Antifoam A compound. Dow Corning Antifoam A compound is a PDMS/350 cs fluid containing approximately 12% low molecular weight cyclic PDMS units and 4% silica aerogel. Biodegr-adability
of a PDMS
Emulsiotz
by Sewuge Microorgunisms
The material investigated was a ‘“C-Dow Corning 200 fluid 300 cs emulsion containing 15% PDMS. Five gallon Pyrex carboys, painted black to exclude light and equipped with Teflon-coated stirring bars, were employed as reactors. Each of four carboys was charged through inlet tubes, terminating 2-3 in above the base, with 16,110 ml of deionized water, 1800 ml of settled sewage2, 18 ml of sterile yeast extract solution (50 mg/ml), 72 ml of BOD salt solution and 0.25 ml of benzene. To each of two test reactors was added 180 mg of [‘“Cl PDMS (50.4 PC) as the emulsion and to each of two control reactors was added 300 pg (25 PC) of n-octadecane-I-‘“C in 0.25 ml of benzene, and a quantity of emulsifiers identical to that of the PDMS emulsion. Compressed air at 1.5 psi was passed through the reactors from a manifold surge tank preceded by a train consisting of a dry mechanical filter, activated carbon, ascarite, 25% NaOH solution, and a weak NaOH solution containing phenolphthalein to indicate any carbon dioxide leakage through the train. Downstream from each reactor was a series of traps, one charged with carbon tetrachloride, three with 0.3 N barium hydroxide, and one with a weak NaOH solution and phenolphthalein. The experiment was run continuously for 70 days under ambient room conditions (20-25”C, mean 23”). Each reactor was stirred daily for 5 minutes, and, on each of the first 32 days, 10 ml samples were taken through a sampling port during the mixing period. Reactor samples were taken less frequently during the ’ Supplied ’ Collected
by Dow Corning Corporation, 2111172 from Northwestern
Midland, University
Michigan. Sanitary Engineering
Labinterceptor
sewer
line.
TOXlCITY
OF
POLYDIMETHYLSILOXANES
399
later stages of the study. The pH and scintillation counts were determined for all reactor samples, and bacterial analyses were conducted periodically. Absorbents were renewed as required, daily at the outset and less frequently thereafter. The lqC-activity of all absorbents was determined by scintillation counting. Each reactor was reseeded with fresh sewage in BOD water on Day 61. At termination of the study, each reactor was agitated for 30 minutes and ‘V counts were determined for reactor samples, filtrates of reactor samples passing a 0.45 micron membrane filter, solids retained on the filter and cotton used to swab the interiors of the rinsed and drained reactors. Standard techniques were employed for preparation of samples and counting. Detection of three counts above background could be achieved with extended counting times (100 minutes). This represents five disintegrations per minute and corresponds to the ‘-‘C-activity of 804 ng of PDMS.
The 48-hour toxicity of Dow Corning 200 fluid 100 cs was determined in daphnia (Dnphnia magna) under static conditions. Gravid daphnia were introduced into 1 gallon glass jars containing double filtered (charcoal) municipal water which had aged for 7 days. The young of these animals, when 1 to 48 hours old (first instar) were used as test organisms. The animals were fed with a suspension of 10 g of Purina trout chow and 0.5 g of Cerophyll powder blended in 300 ml of water. After a preliminary range finding study to determine the approximately TL50, five concentrations of the test material were selected for bioassay using 20 animals at each concentration. The test material was added without solvent, and the animals were observed by means of a dissecting microscope during a period of 48 hours. Mortalities were recorded and the tolerance limits. TLl, TL50. and TL99, were calculated according to Litchfield and Wilcoxon (1949). The pH and dissolved oxygen concentration were determined at 0 and 48 hours. The 48-hour toxicity of Dow Corning Antifoam C emulsion was determined in analogous animals under dynamic conditions. The water used in the bioassay was double charcoal filtered city water contained in a continuously aerated 100 gallon reservoir and maintained at 18°C. After a preliminary static range finding study to determine the approximate TL50, five concentrations of test material were selected for the dynamic bioassay. The test apparatus consisted of a modified proportional diluter (Mount and Brungs, 1967). Modifications included control of diluent water and vacuum supplies with a time clock and the addition of a mixing chamber between the diluter and the bioassay vessels. Four 3-l polyethylene bioassay vessels, each containing five daphnia, were used for each test concentration and for the untreated control. Overflow pipes maintained a constant level, and the turnover time in each vessel was 1.5 hours. Following introduction of test material, the daphnia were observed during a period of 48 hours and mortalities were recorded. The pH dissolved oxygen, concentration, hardness, specific conductance, and alkalinity were monitored during the study. At the end of 48 hours, the TLI . TLSO, and TL99 of the formulation and of the active ingredient were calculated.
400 Four-Duy
HOBBS,
Toxicity
of a PDMS
KEPLINGER
AND
Fotwmlation
CALANDRA
in Fresh
Water Fish
Four-day TLSOs of Dow Corning Antifoam C emulsion in bluegill sunfish and rainbow trout were determined under static conditions. Healthy young fish (35-75 mm) were used as test animals. All fish were held for observation for not less than 10 days prior to experimental use in large aerated stock tanks, and were maintained on appropriate diets until 3 days prior to testing. The trout were maintained at 13°C and the bluegills at 24°C. All stock tanks and assay vessels contained reconstituted deionized water to which were added, on a per liter basis, 30 mg calcium sulfate, 30 mg magnesium sulfate, 48 mg sodium biocarbonate, and 2 mg potassium chloride. Preliminary screening was conducted to determine the general level of toxicity of the test material and three to five concentrations of each test material were selected for bioassay. Bioassay vessels lined with disposable polyethylene bags were filled with 12.5 1 of well aerated reconstituted water, and ten fish were tested at each concentration. Following the introduction of the test material, the fish were observed for 96 hours and mortalities and reactions were noted. The concentration of dissolved oxygen was determined for all test solutions in which mortalities occurred.3 Concentrations of dissolved oxygen of 4 ppm for warm water fish (bluegills) and 5 ppm for cold water fish (trout) are considered to be minimal for valid testing. The pH of each solution in which mortalities occurred was also determined. As a quality check, each lot of fish was challenged with a reference pesticide, toxaphene, which was added to the bioassay vessels as 0.01% (w/v) solution in acetone. At the end of the 4-day observation period, the median tolerance limits (TLSOs) for Dow Corning Antifoam C emulsion were calculated according to Litchfield and Wilcoxon (1949). Residue
Study
qf a PDMS Emulsion in Bluegill Sunjish
The material investigated was a Dow Corning 200 fluid 300 cs emulsion containing 2 g of [‘“Cl PDMS in 13.33 ml of emulsion and having a ‘“C-activity of 280 j&g of PDMS. Sixty young bluegill sunfish were used to form two groups of 30 each. One group was exposed in a 30-l tank to water containing 1 ppm of the [‘“Cl PDMS emulsion (1.26 PC of Y-activity). The second group was similarly exposed to 10 ppm of the emulsion (12.6 PC of ‘V-activity). Each tank was sampled three times weekly for radioassays, and additional emulsion was added as required to maintain proper tank concentrations. Two fish from each group were sacrificed on Days 0 (no exposure) 1, 3, 5, 7. 14, 21, and 30. Body weights were recorded, the fish were rinsed and scaled, and flesh samples were collected from each flank of each fish. The collected tissues were weighed, and duplicate samples from each fish, one from each flank, were placed in dialysis bags, dried in forced air. and compressed with shredded filter paper into pellets which were burned and radioassayed using conventional techniques. 3 Hach
0X-2-P
Dissolved
Oxygen
Test
Kit,
Hach
Chemical
Company,
Ames.
Iowa.
TOXICITY
OF
Residue data, translating ‘“C-activity into equivalents ported in terms of mean values for each pair of fish. Four-Day
Toxicity
of a PDMS
401
POLYDIMETHYLSILOXANES
Formulation
of [‘“Cl PDMS.
are re-
in Salt Water Species
The 4-day TLSOs of Dow Corning Antifoam C emulsion in cockles (Prothaca mummichogs (Fundrtlus heteroclitus), shore crabs (Pachygrapsus and brown shrimp (Penaerts oxtecus) were determined under static conditions. The animals employed were of appropriate size for testing: valve length of 4W5 mm for cockles: a length of 50-8C mm for mummichogs; carapace width of 30-6 mm for shore crabs; and rostrum length of S-12 mm for brown shrimp. All species were held in stock tanks at 21°C for 4 to 5 days prior to testing, and were fed an appropriate diet until 1 day prior to testing. All stock tanks and assay vessels contained aged seawater” having a density of 1.020 and a calculated salinity of 27.2 O/O0 (2.72%). Assays were run at concentrations of 1, 10, 100, and 1000 ppm using 20 cockles, and ten of each other species at each test level. Dissolved oxygen and pH were monitored throughout the studies. The animals were observed for reactions and mortalities during a 48-hour period, after which time median tolerance limits (4-day TLSOs) were determined.
spaminea), crassipes)
Subacute
Toxicity
of a PDMS in Mallard
Ducks
and Bobwhite
Quail
The test material employed was Dow Corning 200 fluid 100 cs, and the animals used were 10-15 day old pen-reared mallard ducks and bobwhite quail. The test material was incorporated into a standard laboratory diet5 at levels of 3 12, 625, 1250, 2500. and 5000 ppm. Dieldrin at five graded dose levels for each species was run as a positive control, and five untreated control groups were employed in each study. Each group consisted of ten birds. Test and positive control birds were fed the treated diets for 5 days and were held on standard diet for an additional 3 days for observation. Control birds received untreated ration for the S-day period. All animals were weighed at the beginning of the studies and at the time of death on Day 8. Group food con sumption was recorded for the test period and for the observation period, and daily observations for mortality and signs of toxicity were made. All animals dying during the study and those killed at termination of the observation period were examined for gross pathologic changes. Dietary LCSOs for dieldrin were calculated according to Litchfield and Wilcoxon (1949). and the toxicity of Dow Corning 200 fluid 100 cs was estimated. Toxocity, Reprodrrction Le<~:llor-n Chickens
and Residue
Study nit/l PDMS
in White
Young white Leghorn chickens, 80 hens and 16 roosters, were equally divided into four groups. All groups were maintained on a basal ration” until the birds reached the age of 24 weeks, at which time the three test groups were started on a The seawater was prepared with deionized water and instant ocean sea salts. 5 Purina Gamebird Startena. Ralston Purina Company. St. Louis. Missouri. li Purina Flock Chow, Ralston Purina Company, St. Louis. Missouri.
402
HOBBS,
KEPLINGER
AND
CALANDRA
basal diet supplemented with 200, 1000, and 5000 ppm of Dow Corning 200 fluid 100 cs. Observations were made daily for signs of toxicity. All chickens were individually weighed each week, and group food consumption was determined weekly. As each group began laying, the eggs were collected daily and egg weights were recorded. The eggs were collected for study of the following parameters when the egg weights were consistently between 50 and 60 g, at least 50% of the hens in the group were laying, and the hens were at least 28 weeks old. Egg production, weight and quality. The total number of eggs, the individual weights of eggs collected, and the total number of untracked and unblemished eggs were recorded. Hatchability. Nondefective eggs were randomly selected for hatching. These eggs were turned twice daily during each 7-day collection period and were then placed in an incubator maintained at 99 to 100°F with a wet bulb reading of 85”. This procedure was followed until a minimum of 100 eggs from the control group and each test group had been set for hatching. The following were recorded: a. Number hatched. b. Number unhatched. c. Viability of chicks over a 30-day period, during which time feed and water were permitted ad libitum. d. Examination of unhatched eggs for fertility and stage of development. e. Weight of chicks after Days 1 and 30. f. Gross pathological examination of chicks after Day 30. Residue studies. The total daily egg production from each test group was taken for residue analysis on Days 3, 7, 14, 21, and 28 of the dosing period, and on Days 7 and 28 of the recovery period. The eggs were kept frozen until analysis.7 After hatching results were available, half of the chickens in each group were killed; they were defeathered and individual samples of liver, kidney, fat, and muscle were collected from each chicken for residue analysis. The remainder of the carcasses were retained in the frozen state until residue determinations were completed. The remaining chickens were placed on a 30-day recovery regimen on unsupplemented basal diet. The remaining chickens were killed at the end of the recovery period, and tissues were similarly collected for residue analysis.
RESULTS Biodegradability
of CI PDMS
Emulsion
by Sruuge
Microorganisms
The 14C-Dow Corning 200 fluid 300 cs emulsion was not degraded to any detectable extent to ‘“COZ, and no volatile organic degradation products were detected. No radioactivity was detected in either the carbon tetrachloride or alkali i Ail analyses
were
done
by the Dow
Corning
Corporation,
Midland.
Michigan
TOXICITY
OF
403
POLYDIMETHYLSILOXANES
traps. Octadecane was extensively degraded under analogous conditions, 60 and 40% of the radioactivity being evolved as 14C0, from the two positive control reactors within 30 days. In the case of the PDMS emulsion, 100% of the radioactivity of the terminal mixture was associated with filtered particulate matter while I1 and 13% of the radioactivity occurred in the filtrates of the terminal octadecane mixtures. This indicates conversion of octadecane to polar metabolites, while no such transformation appears to occur with the PDMS. This study does not positively exclude the possibility of transformation and incorporation of PDMS by sewage bacteria, but this seems highly unlikely in view of the total absence of expired ‘“CO,. Toxicity
of PDMS
in Daphnia
The static 48-hour TLSO for Dow Corning 200 fluid 100 cs was determined to be 44.5 ppm, TLl and TL99 being 379.6 and 5.22 ppm, respectively. The test material remained largely on the surface of the water at each test concentration and, at the higher levels, many of the daphnia became entrapped in the test material and died there. In the dynamic test the TLl, TL50, and TL99 were 600, 73.4, and 8.98 ppm, respectively, expressed in terms of PDMS in the 30% emulsion (Dow Corning Antifoam C emulsion). Water quality in terms of dissolved oxygen, pH, hardness, specific conductance, and alkalinity was judged to be appropriate in a]] cases. Four-Day
Toxicity
of a PDMS Formulation
in Fresh
Water Fish
The 96-hour TL50 of Dow Corning Antifoam C emulsion was > 10,000 ppm, for both bluegill sunfish and rainbow trout. No deaths were noted at any level, but hypoactivity was observed in both species at levels of 1,000 and 10,000 ppm. The TLSOs for toxaphene under analogous conditions were 0.037 and 0.044 ppm for trout and bluegills, respectively. Residue
Study with u PDMS
Emulsion
in Bluegill
Sun&h
It was found necessary to add [‘“Cl PDMS on Days 8, 15, and 22 for approximate maintenance of the desired levels of radioactivity in the water. Values for radioactivity, determined three times weekly on water from each tank, ranged from 0.23 to I .26 at the low level, and from 4.60 to Il.84 at the higher level. That the PDMS was being deposited on the walls of the aquaria was confirmed by high counts in swabbings of the walls of each tank taken on tiay 29. The counts for swabbings from the high level tank were approximately 10 times as great as those from the low level tank, but no attempt was made to obtain a material balance. Tissue residue data are presented in Table 1. The levels are very low and highly variable, and there appears to be no relationship between the residue levels and either duration of exposure or level of exposure. The results suggest that 14C-activity detected may be due to surface contamination rather than to cellular uptake of the silicone and provide no evidence for the accumulation of the PDMS in the flesh of fish.
404
HOBBS,
KEPLINGER
AND
TABLE RESIDUES
OF ‘T-ACTIVITY
IN
BLUEGILL
Tissue
Day of sacrifice
1
SUNFISH
residue”.“,’
Exposure
DATA
FOR
SALT
= 5 DPM
WATER
0 1.0 10.0 100.0 1000.0
shore
95 100 95 100 90 28.8%
Egg production (%/Day) 82 81 76 84
u Mean values. a Defective eggs were
TO Dow
EXPOSED
crabs
of survival
ppm
for
a
CORNING
of
mummichogs
loo 100 100 100 70
TABLE
0 200 1000 5000
= 0.040
brown
100 100 100 100 80
shrimp 95 90 90 85 60
PDMS.
REPRODUCTIVE
Treatment level (wm)
ng PDMS
C EMULSION Percentage
cockles
= 8.04
2
SPECIES
ANTIFOAM
Level of exposure (ppm)”
of
0.000 0.105 0.115 0.069 0.167 0.758 0.242 0.428
TABLE SURVIVAL
EMULSION
at levels 10 mm
0.000 0.132 0.077 0.000 0.376 0.100 0.130 0.195
Calculated as PDMS. Mean values of four samples for two fish. Detection limit of 3 CPM above background mg sample.
D As the emulsion.
TO A [Y]PDMS
EXPOSED
1 rw
0 I 3 5 7 14 21 31 a * c 200
CALANDRA
cracked
PERFORMANCE Dow CORNING
LEGHORN
200 FLUID
Egg weight w
Normal” em (%)
54.7 54.9 55.0 55.7
45.4 54.4 49.8 51.5
or severely
3
OF WHITE
blemished.
Hatchability v@) 92.2 89.6 80.0 87.0
FED
CHICKENS
100 CS” Body Day 39.2 39.1 39.5 40.9
1
Weight Day 256 266 264 267
(g) 30
Chick survival to Day 30 (%) 100 100 94.6 93.0
TOXICITY
Four-Day
Toxicity
of a PDMS
OF
405
POLYDIMETHYLSILOXANES
Formulution
in Suit Water Species
The TL50 values for all species were > 1000 ppm. Survival data are presented in Table 2. Quiescence and surfacing were noted among some mummichogs, and loss of equilibrium was observed among some shrimp at 1000 ppm, but no other reactions were seen. Subucute
Toxicity
of PDMS
in Mallard
Ducks
and Bobwhite
Quail
The LC50 (5day dietary exposure) of Dow Corning 200 fluid 100 cs in each species was > 5000 ppm. One duckling died on the second day at 625 ppm, but no other deaths occurred among test groups, and no signs of toxicity were observed. The LCSOs for dieldrin were 115 and 32 ppm, respectively, for ducks and quail. Signs of toxicity with dieldrin included hyporeactivity and anorexia. Toxicity, Chickens
Reproduction,
and Residue
Study ,t,ith a PDMS
in White Leghorrl
Ingestion of Dow Corning 200 fluid 100 cs had no adverse effect on body weight or food consumption. Five deaths occurred during the study, one in the control group and two each at dietary levels of 200 and 1000 ppm. These deaths were attributed to physical causes (prolonged rectum, adhesive peritonitis). No differences were noted between test and control birds at necropsy. Egg production and quality, hatchability, and body weights and viability of chicks were not affected by treatment. Data regarding these parameters are summarized in Table 3. Residues of silicon in all samples analyzed were below the limit for quantitative determination. Detection limits were 3 ppm for egg yolks and whites; 2 ppm for kidney, liver, and muscle: and 4 ppm for fat. DISCUSSION
All studies conducted indicate a very low order of toxicity for the Dow Corning polydimethylsiloxanes. No evidence has been obtained to suggest accumulation in the flesh of fish or birds, and there appears to be no significant transfer of the material to the eggs of chickens. The nonbiodegradability and chemical and physical inertness of these siloxanes suggest that material released into the environment could persist for considerable periods of time, but their low toxicity and apparent immobilization by binding to particulate matter in aqueous systems should minimize concern regarding their potential to cause environmental damage. REFERENCES Bennett. D. R. (1973). Metabolism of organosilicon compounds. Communication from Dow Corning Corporation. Carson. S.. Weinberg, M. S.. and Oser. B. L. (1966). Safety evaluation of Dow Corning 360 Fluid and Antifoam A. Proc. Sci. Sec. Toilet Goods Assoc~. 45, 8-19. Cutler. M. G., Callings, A. J.. Kiss, I. S.. and Sharratt. M. (1974). A lifetime study of a polydimethylsiloxane in the mouse. Fd. Cosmt~t. Toxri~l. 12, 443-450. Delman. A. D., Landy. M.. and Simms, B. B. (1969). Photodecomposition of polymethylsiloxane. J. Polwm Sci. 7, 375-386.
406
HOBBS.
KEPLINGER
AND
CALANDRA
Horner, H. .I., Weiler, J. E., and Angelotti. N. C. (1960). Visible and infrared spectroscopic determination of trace amounts of silicones in foods and biological materials. Anal. Chem. 32, 858-861. Jankowiak, M. E., and Levier, R. R. (1971). Elimination of phosphorus interference in the colorimetric determination of silicon in biological material. And. Biochem. 44, 4621172. Litchfield, J. T., and Wilcoxon, F. (1949). A simplified method of evaluating dose-effect experiments, J. Pharm. Exp, Ther. 96, 99-l 13. Mount, D. I., and Brungs, W. (1967). A simplified dosing apparatus for fish toxicity studies. Water Res. 1, 21-29. Neat, P., Campbell, A. D., Firestone, D., and Aldridge, M. H. (1969). Low temperature separation of trace amounts of dimethylpolysiloxane from food. J. Amer. Oil. Chem. Sot. 46, 561-562. Nell, W. (1968). ‘Chemistry and Technology of Silicones.” Academic Press, New York. Rowe, V. K., Spencer, H. C., and Bass, S. L. (1948). Toxicological studies on certain commercial silicones. J. Ind. Hyg. 30, 332-352. Scala. L. C., and Hickman, W. M. (1958). Thermal and oxidative degradation of silicones. J. 2nd. Eng. Chern. SO, 1583-1584. Sinclair, A., and Hallam. T. R. (1971). Determination of dimethylpolysiloxane in beer and yeast. Analyst 96, 14%154. Smith, A. Lee (1974). “Analysis of silicones.” Wiley, New York.