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The effects of polydimethylsiloxane (PDMS) in sediment on the polychaete worm Nereis diversicolor
Chemosphere, Vol.21, No.6, pp 751-759, 1990 Printed in Great Britain
0045-6535/90 $3.OO + .00 Pergamon Press plc
THE EFFECTS OF POLYDIMETHYLSILOXANE (PDMS) IN SEDIMENT ON THE POLYCHAETE WORM Nereis diversicolor
N.C.D. CRAIG* and J.E. CAUNTER ICI Group Environment Laboratory, Freshwater Quarry, Overgang, Brixham, Devonshire, TQ5 8BA, UK
ABSTRACT The short and medium term toxicity of polydimethylsiloxane fluids in sediment has been examined in laboratory tests on the polychaete Nereis diversicolor. Exposure to 10,000 mg/kg of PDMS caused no deaths in 96 hours, and exposure to 1,000 mg/kg resulted in no deaths over 28 days.
Introduction The effects of organosilicon compounds on marine and freshwater biota have been reported by several workers (Maggi and Alzieu 1977, Watanabe et al 1984, Aubert et al 1985, Frye 1988), and a comprehensive review of available data has been published by GESAMP (1986). Most data refer to the toxicity of organosilicons in solution or suspension in water. The polydimethylsiloxane fluids are generally less dense than water and only sparingly soluble. Consequently if PDMS fluids are spilled or discharged into estuaries they can form a discrete layer on the water surface. Such a layer would be broken up by wave action in coastal waters, but in sheltered areas and estuaries a layer of PDMS could be deposited on intertidal sediments. The present study was undertaken to assess the effects of PDMS in sediment on an intertidal invertebrate over short (96 hour) and medium (28 day) exposure periods.
The test species The polychaete worm Nereis diversicolor was the selected test species. This species is common in temperate estuaries and is capable of tolerating a wide range of salinity (Stopford 1951, Smith 1956). N. diversicolor has been shown to feed by three different methods, dependent on conditions (Harley 1953, Goerke 1966, 1971). Earlier development work had shown that a population of Nereis could be maintained in good condition in laboratory tanks for periods exceeding 60 days.
751
752
The test c o m p o u n d
The compound tested was the organosilicon fluid DC561, 100% polydimethylsiloxane (PDMS) of 50 centistokes viscosity. The test material was supplied by Dow Corning Ltd, Barry, United Kingdom.
Experimental procedures
The experiments were conducted in glass vessels of overall dimensions 23 x 10 x 26 cm, divided internally into two sections (Fig 1). One section (16 x 10 x 15 cm) was used to retain a layer of sediment, whilst the other section formed an overflow and trap area to reduce sediment loss and to prevent animals escaping. Each test vessel was fitted with an overhanging glass lid. A continuous water flow was maintained through each test vessel via a peristaltic pump providing a flow of 100 ml/minute. maintained a temperature of 11 ° + I°C.
All of the test vessels stood in a water bath that
Throughout both experiments, the water flow rate, pH, dissolved oxygen
and temperature were monitored in each test vessel. WATER INFLOW
O~PING
LID
WATIgR OUTIgLOW
1
]
n~-t-x.!.murm¢l' SPACg
I S~D~
Fig. 1 Diagram of test vess~,
The sediment used was collected from Tor Bay, Devon, UK; a clean sediment consisting of 80% very fine sand with some silt. After collection the sediment was washed first in tap water, then in 2 Normal Hydrochloric Acid before being thoroughly rinsed in distilled water. Finally the sediment was dried at 105°C for 72 hours.
To prepare the individual test concentrations, PDMS fluid was dissolved in AR acetone to provide the required concentration. For each test vessel, 1 kg of prepared sediment was stirred into the acetone/PDMS solution to
753
evenly distribute the test material over the particles. The resultant mixture was spread in a layer approximately 0.5 cm thick on a sheet of "Benchkote" and the acetone evaporated off in a fume cupboard held at ambient temperature for 72 hours. A sample of each prepared sediment was analysed to determine actual PDMS content (Tables I and 2) before the remainder was placed in a test vessel. 800 ml of seawater was then stirred in to the sediment and the whole allowed to resettle before water flow commenced and test animals were introduced. TABLE 1 Analysis of test medium (sediment) for PDMS Exposure time (hours)
96 96 96 96 96 96 96 96 96 96 96 96
Nominal concentration mg/kg
Measured concentration mg/kg
0 (Solvent) 0 (Control) 100 100 560 560 1,000 1,000 5,600 5,600 10,000 10,000
12 12 88 100 480 484 792 816 4,720 5,040 10,480 9,920
0 0 100 100 560 560 1,000 1,000 5,600 5,600 10,000 10,000
<12 <12 80 84 500 460 804 864 5,080 5,400 9,680 9,440
Mean concentration mg/kg 12 94 482 804 4,880 10,200
<12 82 480 834 5,240 9,560
The test specimens were selected from a population collected from the estuary of the River Dart, Devonshire. The animals were acclirnatised to the pretreated Tor Bay sediment, salinity and water temperature conditions used for the test over a period of 96 hours before transfer to the test vessels.
In both tests, ten specimens of Nereis diversicolor were used in each concentration, the wet weight of each animal being determined before it was placed in the test vessel. After worms were added, careful observation of their burrowing activity was kept up for the first three hours.
Subsequently the test vessels were examined for the
presence of animals at the surface at least three times per day.
754
The worms were not fed during the 96 hour test. However, to maintain condition over the 28 day test the animals were fed three times per week with a suspension of yeast ceils in water. To prevent premature food loss, the water flow was interrupted for 60 minutes after the yeast suspension had been added. TABLE 2 Concentrations of PDMS in sediment (all values in mg/kg) Tank number
Nominal exposure concentration
Mean measured concentration Day 0
Mean measured concentration Day 28
1 2 3
Control Control Control
<4 <4 <4
<5 <5 <5
4
Solvent control
<4
<5
100 100 100
96 100 92
61 63 53
1,000 1,000 1,000
872 880 850
598 634 630
<4
<5
96 (92-100)
59 (53-63)
867 (850-880)
621 (598-634)
8 9 10 Mean levels and ranges Control/solvent control 100 mg/kg 1,000 mg/kg Test concentrations
For the 96 hour test five nominal concentrations of PDMS in sediment were used: 100, 560, 1,1300, 5,600 and 10,000 mg/kg. In addition three controls were provided, one of untreated sediment, one of dried sediment rewetted and one of sediment dried and acetone-treated. In the 28 day study two concentrations of PDMS, 100 mg/kg and 1,000 mg/kg and an untreated sediment, were run in triplicate, together with a single acetone-treated sediment.
The analytical determination of PDMS was undertaken on a Perkin-Elmer Model 2380 atomic absorption spectrophotometer (with background correction). The organosilicon was extracted into a h l mixture of methyl isobutyl ketone (MIBK) and pentan-l-ol for analysis.
Results and Discussion (a) 96 hour test There were no mortalities recorded in any concentration of PDMS during the 96 hour period of exposure,
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indicating that concentrations of up to 10,000 mg/kg of PDMS fluid on sediment do not have an acutely toxic effect on Nereis diversicolor.
One specimen was missing from the solvent control tank after 96 hours. It was
presumed to have escaped via the tank overflow.
Observations during the course of the test showed that the burrowing activity of N. diversicolor appeared to be affected by treated sediments. All of the animals placed on the untreated control sediment (Tank 1) had burrowed fully into the substrate within one hour of the start of the test, whereas in other sediments (Tanks 2-8) the worms took up to 24 hours to completely bury themselves. A summary of burrowing activity is given in Table 3. It is possible that the physical pretreatment given to the sediment used in Tanks 2-8 caused some change in the sediment structure that inhibited burrowing.
(b) 28 day test Since the initial 96 hour test showed no acute toxic effect, a further study was undertaken to ascertain whether toxic effects resulted from longer term exposure to PDMS fluids. However, no mortalities were recorded in a population of Nereis diversicolor exposed to 1,000 mg/kg of PDMS for 28 days. Table 4 summarises the survival data and the changes in weights recorded. It will be seen that some specimens were missing from the 100 mg/kg exposures. found.
The sediment in these tanks was carefully sieved but no evidence of the death of the animals was
It is assumed that they either escaped, were cannibalised or scavenged by other Nereis in the test
population. No losses occurred from the untreated control sediment.
It was again noted that initial burrowing of the animals when introduced on to the sediment was quicker in the untreated control sediments than in the treated material.
The uniform feeding regime adopted permitted study of the change in wet weights of the test animals over 28 days. The weights recorded are shown in Table 4. The results showed that in all but one of the exposures Nereis gained weight over 28 days, the increase varying between 2% and 80%. The exception occurred in one of the 1,000 mg/kg exposures where there was a mean weight loss of 1.8%.
The values in Table 4 show an apparently lower weight gain in the exposed populations relative to the controls: these data were tested statistically to determine their significance. Each replicate for all treatments was tested by analysis of variance to see whether there was any significant difference between replicates of any one treatment. No significant differences were found between replicates.
Analysis of variance was then used to check whether any significant statistical differences existed between the weights of worms exposed to 100 and 1,000 mg/kg of PDMS and the controls. significant difference at either the 1% or 5% significance level.
This analysis showed no
It is therefore concluded that the recorded
differences result from natural variation within the group of experimental animals.
758
Most published data on the effects of silicones (GESAMP, op cit), show toxic levels for marine species to be well above the water solubility maxima for the compounds, eg 48 hr LC50 for PDMS to Penaeus aztecus (shrimp) is 1,000 mg/kg, 96 hr LC50 to Pleuronectes platessa (plaice) is 10,000 mg/kg.
The experiments with Nereis
diversicolor have shown that even where polydimethyl siloxane is maintained in contact with the polychaete, there
are no short or medium term toxic effects on this species.
Acknowledgements The authors would like to thank G.J. Eales for carrying out the analysis of PDMS in sediment, and J.E.Yersin for the provision of experimental animals.
References Aubert M, J. Aubert, H. Augier and C. Guillemaut 1985 Study of the toxicity of some silicone compounds in relation to marine biological chains. Chemosphere 14(1) p127-38
Frye C.L. 1988 The Environmental Fate of Ecological Impact of Organosilicon Materials: A Review.
Science of the Total
Environment 73 p17-22
GESAMP 1986 (IMO/FAO/UNESCO/WMO/WHO/IAEA/UN/UNEP Joint group of experts on the scientific aspects of marine pollution).
Review of Potentially Harmful Substances: Organosilicon Compounds (Silanes and Siloxanes)
Rep.Stud. GESAMP 29
Goerke H. 1966 Filter feeding in Nereis diversicolor O.F.Muller (Nereidae, Polychaeta). Veroeff Inst Meeres Bremerhavn 10 p4958
Goerke H. 1971 The feeding habits of the Nereis species (Polychaeta, Nereidae) of the German coast. Vereoeff Inst Meeres. Bremerhavn 13 pl-50
Harley M.B. 1953 The feeding habits of Nereis diversicolor (O.F.Muller). Brit. J. Anim. Behav., 1 p88
759
Maggi P. and C. Alzieu 1977 Etude de la activit6 d'huiles polydimethylsiloxane a l'egard d'organismes matins. Science Peche Bull. Inst. Peches Maritimes 269 pl-3
Smith R.I. 1965 The ecology of the Tamar estuary 7. Observations on the interstitial salinity of intertidal muds in the estuarine habitat of Nereis diversicolor. Journal of Marine Biological Association 35 p81-104
Stopford S.C. 1951 An ecological survey of the Cheshire foreshore of the Dee estuary. Jo Anim. Ecol. 19-20 p103-22
Watanabe N. et al 1984 Bioconcentration potential of PDMS fluids in fish. Science of Total Environment 38 p167-72 (Received in Germany 12 July 1990; accepted 16 August 1990)
0045-6535/90 $3.OO + .00 Pergamon Press plc
THE EFFECTS OF POLYDIMETHYLSILOXANE (PDMS) IN SEDIMENT ON THE POLYCHAETE WORM Nereis diversicolor
N.C.D. CRAIG* and J.E. CAUNTER ICI Group Environment Laboratory, Freshwater Quarry, Overgang, Brixham, Devonshire, TQ5 8BA, UK
ABSTRACT The short and medium term toxicity of polydimethylsiloxane fluids in sediment has been examined in laboratory tests on the polychaete Nereis diversicolor. Exposure to 10,000 mg/kg of PDMS caused no deaths in 96 hours, and exposure to 1,000 mg/kg resulted in no deaths over 28 days.
Introduction The effects of organosilicon compounds on marine and freshwater biota have been reported by several workers (Maggi and Alzieu 1977, Watanabe et al 1984, Aubert et al 1985, Frye 1988), and a comprehensive review of available data has been published by GESAMP (1986). Most data refer to the toxicity of organosilicons in solution or suspension in water. The polydimethylsiloxane fluids are generally less dense than water and only sparingly soluble. Consequently if PDMS fluids are spilled or discharged into estuaries they can form a discrete layer on the water surface. Such a layer would be broken up by wave action in coastal waters, but in sheltered areas and estuaries a layer of PDMS could be deposited on intertidal sediments. The present study was undertaken to assess the effects of PDMS in sediment on an intertidal invertebrate over short (96 hour) and medium (28 day) exposure periods.
The test species The polychaete worm Nereis diversicolor was the selected test species. This species is common in temperate estuaries and is capable of tolerating a wide range of salinity (Stopford 1951, Smith 1956). N. diversicolor has been shown to feed by three different methods, dependent on conditions (Harley 1953, Goerke 1966, 1971). Earlier development work had shown that a population of Nereis could be maintained in good condition in laboratory tanks for periods exceeding 60 days.
751
752
The test c o m p o u n d
The compound tested was the organosilicon fluid DC561, 100% polydimethylsiloxane (PDMS) of 50 centistokes viscosity. The test material was supplied by Dow Corning Ltd, Barry, United Kingdom.
Experimental procedures
The experiments were conducted in glass vessels of overall dimensions 23 x 10 x 26 cm, divided internally into two sections (Fig 1). One section (16 x 10 x 15 cm) was used to retain a layer of sediment, whilst the other section formed an overflow and trap area to reduce sediment loss and to prevent animals escaping. Each test vessel was fitted with an overhanging glass lid. A continuous water flow was maintained through each test vessel via a peristaltic pump providing a flow of 100 ml/minute. maintained a temperature of 11 ° + I°C.
All of the test vessels stood in a water bath that
Throughout both experiments, the water flow rate, pH, dissolved oxygen
and temperature were monitored in each test vessel. WATER INFLOW
O~PING
LID
WATIgR OUTIgLOW
1
]
n~-t-x.!.murm¢l' SPACg
I S~D~
Fig. 1 Diagram of test vess~,
The sediment used was collected from Tor Bay, Devon, UK; a clean sediment consisting of 80% very fine sand with some silt. After collection the sediment was washed first in tap water, then in 2 Normal Hydrochloric Acid before being thoroughly rinsed in distilled water. Finally the sediment was dried at 105°C for 72 hours.
To prepare the individual test concentrations, PDMS fluid was dissolved in AR acetone to provide the required concentration. For each test vessel, 1 kg of prepared sediment was stirred into the acetone/PDMS solution to
753
evenly distribute the test material over the particles. The resultant mixture was spread in a layer approximately 0.5 cm thick on a sheet of "Benchkote" and the acetone evaporated off in a fume cupboard held at ambient temperature for 72 hours. A sample of each prepared sediment was analysed to determine actual PDMS content (Tables I and 2) before the remainder was placed in a test vessel. 800 ml of seawater was then stirred in to the sediment and the whole allowed to resettle before water flow commenced and test animals were introduced. TABLE 1 Analysis of test medium (sediment) for PDMS Exposure time (hours)
96 96 96 96 96 96 96 96 96 96 96 96
Nominal concentration mg/kg
Measured concentration mg/kg
0 (Solvent) 0 (Control) 100 100 560 560 1,000 1,000 5,600 5,600 10,000 10,000
12 12 88 100 480 484 792 816 4,720 5,040 10,480 9,920
0 0 100 100 560 560 1,000 1,000 5,600 5,600 10,000 10,000
<12 <12 80 84 500 460 804 864 5,080 5,400 9,680 9,440
Mean concentration mg/kg 12 94 482 804 4,880 10,200
<12 82 480 834 5,240 9,560
The test specimens were selected from a population collected from the estuary of the River Dart, Devonshire. The animals were acclirnatised to the pretreated Tor Bay sediment, salinity and water temperature conditions used for the test over a period of 96 hours before transfer to the test vessels.
In both tests, ten specimens of Nereis diversicolor were used in each concentration, the wet weight of each animal being determined before it was placed in the test vessel. After worms were added, careful observation of their burrowing activity was kept up for the first three hours.
Subsequently the test vessels were examined for the
presence of animals at the surface at least three times per day.
754
The worms were not fed during the 96 hour test. However, to maintain condition over the 28 day test the animals were fed three times per week with a suspension of yeast ceils in water. To prevent premature food loss, the water flow was interrupted for 60 minutes after the yeast suspension had been added. TABLE 2 Concentrations of PDMS in sediment (all values in mg/kg) Tank number
Nominal exposure concentration
Mean measured concentration Day 0
Mean measured concentration Day 28
1 2 3
Control Control Control
<4 <4 <4
<5 <5 <5
4
Solvent control
<4
<5
100 100 100
96 100 92
61 63 53
1,000 1,000 1,000
872 880 850
598 634 630
<4
<5
96 (92-100)
59 (53-63)
867 (850-880)
621 (598-634)
8 9 10 Mean levels and ranges Control/solvent control 100 mg/kg 1,000 mg/kg Test concentrations
For the 96 hour test five nominal concentrations of PDMS in sediment were used: 100, 560, 1,1300, 5,600 and 10,000 mg/kg. In addition three controls were provided, one of untreated sediment, one of dried sediment rewetted and one of sediment dried and acetone-treated. In the 28 day study two concentrations of PDMS, 100 mg/kg and 1,000 mg/kg and an untreated sediment, were run in triplicate, together with a single acetone-treated sediment.
The analytical determination of PDMS was undertaken on a Perkin-Elmer Model 2380 atomic absorption spectrophotometer (with background correction). The organosilicon was extracted into a h l mixture of methyl isobutyl ketone (MIBK) and pentan-l-ol for analysis.
Results and Discussion (a) 96 hour test There were no mortalities recorded in any concentration of PDMS during the 96 hour period of exposure,
755
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o o O ,.= ~D
~§ ~
&)
X~
%) uD
..= O
o'%
&)
O
© ~D
5
756
+
"-~ ~
0%
0o
%O
0
+
+
+
+
~ +
•
<5
o
c5
c5
c5
~ c~
o. o
o o
o o
o
~
+
o0
+
• +
0o +
00
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o
o
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o o
o. o
[23
o -~
•
o o
o'3
U~
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E-
C~
757
indicating that concentrations of up to 10,000 mg/kg of PDMS fluid on sediment do not have an acutely toxic effect on Nereis diversicolor.
One specimen was missing from the solvent control tank after 96 hours. It was
presumed to have escaped via the tank overflow.
Observations during the course of the test showed that the burrowing activity of N. diversicolor appeared to be affected by treated sediments. All of the animals placed on the untreated control sediment (Tank 1) had burrowed fully into the substrate within one hour of the start of the test, whereas in other sediments (Tanks 2-8) the worms took up to 24 hours to completely bury themselves. A summary of burrowing activity is given in Table 3. It is possible that the physical pretreatment given to the sediment used in Tanks 2-8 caused some change in the sediment structure that inhibited burrowing.
(b) 28 day test Since the initial 96 hour test showed no acute toxic effect, a further study was undertaken to ascertain whether toxic effects resulted from longer term exposure to PDMS fluids. However, no mortalities were recorded in a population of Nereis diversicolor exposed to 1,000 mg/kg of PDMS for 28 days. Table 4 summarises the survival data and the changes in weights recorded. It will be seen that some specimens were missing from the 100 mg/kg exposures. found.
The sediment in these tanks was carefully sieved but no evidence of the death of the animals was
It is assumed that they either escaped, were cannibalised or scavenged by other Nereis in the test
population. No losses occurred from the untreated control sediment.
It was again noted that initial burrowing of the animals when introduced on to the sediment was quicker in the untreated control sediments than in the treated material.
The uniform feeding regime adopted permitted study of the change in wet weights of the test animals over 28 days. The weights recorded are shown in Table 4. The results showed that in all but one of the exposures Nereis gained weight over 28 days, the increase varying between 2% and 80%. The exception occurred in one of the 1,000 mg/kg exposures where there was a mean weight loss of 1.8%.
The values in Table 4 show an apparently lower weight gain in the exposed populations relative to the controls: these data were tested statistically to determine their significance. Each replicate for all treatments was tested by analysis of variance to see whether there was any significant difference between replicates of any one treatment. No significant differences were found between replicates.
Analysis of variance was then used to check whether any significant statistical differences existed between the weights of worms exposed to 100 and 1,000 mg/kg of PDMS and the controls. significant difference at either the 1% or 5% significance level.
This analysis showed no
It is therefore concluded that the recorded
differences result from natural variation within the group of experimental animals.
758
Most published data on the effects of silicones (GESAMP, op cit), show toxic levels for marine species to be well above the water solubility maxima for the compounds, eg 48 hr LC50 for PDMS to Penaeus aztecus (shrimp) is 1,000 mg/kg, 96 hr LC50 to Pleuronectes platessa (plaice) is 10,000 mg/kg.
The experiments with Nereis
diversicolor have shown that even where polydimethyl siloxane is maintained in contact with the polychaete, there
are no short or medium term toxic effects on this species.
Acknowledgements The authors would like to thank G.J. Eales for carrying out the analysis of PDMS in sediment, and J.E.Yersin for the provision of experimental animals.
References Aubert M, J. Aubert, H. Augier and C. Guillemaut 1985 Study of the toxicity of some silicone compounds in relation to marine biological chains. Chemosphere 14(1) p127-38
Frye C.L. 1988 The Environmental Fate of Ecological Impact of Organosilicon Materials: A Review.
Science of the Total
Environment 73 p17-22
GESAMP 1986 (IMO/FAO/UNESCO/WMO/WHO/IAEA/UN/UNEP Joint group of experts on the scientific aspects of marine pollution).
Review of Potentially Harmful Substances: Organosilicon Compounds (Silanes and Siloxanes)
Rep.Stud. GESAMP 29
Goerke H. 1966 Filter feeding in Nereis diversicolor O.F.Muller (Nereidae, Polychaeta). Veroeff Inst Meeres Bremerhavn 10 p4958
Goerke H. 1971 The feeding habits of the Nereis species (Polychaeta, Nereidae) of the German coast. Vereoeff Inst Meeres. Bremerhavn 13 pl-50
Harley M.B. 1953 The feeding habits of Nereis diversicolor (O.F.Muller). Brit. J. Anim. Behav., 1 p88
759
Maggi P. and C. Alzieu 1977 Etude de la activit6 d'huiles polydimethylsiloxane a l'egard d'organismes matins. Science Peche Bull. Inst. Peches Maritimes 269 pl-3
Smith R.I. 1965 The ecology of the Tamar estuary 7. Observations on the interstitial salinity of intertidal muds in the estuarine habitat of Nereis diversicolor. Journal of Marine Biological Association 35 p81-104
Stopford S.C. 1951 An ecological survey of the Cheshire foreshore of the Dee estuary. Jo Anim. Ecol. 19-20 p103-22
Watanabe N. et al 1984 Bioconcentration potential of PDMS fluids in fish. Science of Total Environment 38 p167-72 (Received in Germany 12 July 1990; accepted 16 August 1990)