Tetrabutyltin

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

April 1992

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

not specified

GLP compliance:

yes

Analytical monitoring:

no

Details on test solutions:

- Controls: 200 mL of pre-culture were filled into 250 mL Erlenmeyer flask. Then 8 mL of the nutrient solution and 42 mL aqua dem. were added.

- Concentration of vehicle in test medium (stock solution and final test solution(s) including control(s)): Compounds in amounts of 2.5, 7.5, 15 mL and aqua dem was filled up to 250 mL

Test organisms (species):

activated sludge, domestic

Details on inoculum:

The activated sewage sludge for the inoculum was collected on the day before the start of the experiment from a well-operated municipal sewage treatment plant (Klaranlage Berlin-Ruhleben), predominantly dealing with domestic sewage (content of solid particles: 3.51 g/L). Upon arrival at the laboratory, the activated sludge was aerated and stirred for approximately 2 hours. Then it was left to settle for approximately 2 hours. 3000 mL were taken from the supernatant and mixed with 3000 mL water and 240 mL nutrient solution. The mixutre was aerated and stirred for approximately 19 hours.
The synthetic sewage feed was made by disolving 16 g peptone, 11 g meat extract, 3 g urea, 0.7 g sodium chloride, 0.4 g calcium chloride dihydrate, 0,2 g magnesium sulfate heptahydrate and 2.8 g dipotassium hydrogen phophate.

Test type:

static

Water media type:

not specified

Limit test:

no

Total exposure duration:

30 min

Remarks on exposure duration:

Test vessels were incubated under stirring and aerating (45 L/h) for 30 minutes at room temperature.

Test temperature:

Room temperature, 22.7 to 24.1 degrees C after incubation

Nominal and measured concentrations:

10, 20, 40, 100 and 1000 mg/L

Details on test conditions:

TEST SYSTEM
- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates): 1
- No. of vessels per vehicle control (replicates): 1

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water:aqua dem

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol (5, 15 and 30 mg/L)

Key result

Remarks on result:

other: the dissolved fraction of the test compound reduced the activiity to approx. 80 - 90 % of the control. Therefore, it can be concluded that Tetra-n-butyltin has some toxicity on the microbial population in sewage sludge.

Results with reference substance (positive control):

EC10 = 3.5 (2.4 - 4.7); EC50 = 12.3 (10.4-14.3), EC90 = 42.5 (33.-61.2)

Table 1: Respiration Inhibition

Test Compound	Nominal Concentration (mg/L)	Respiration Inhibition (%)
3,5-Dichlorophenol	5	17.7
	15	58.4
	30	82.1
Tetrabutyltin	10	14.9
	20	10.5
	40	10.6
	100	8.8
	1000	19.3

In order to calculate the inhibitory effect of a test substance at a particular concentration, the respiration rate was expressed as a percentage of the mean of the three control respiration rates. The formula below was used to calculated the percentage of inhibition:

I = ((Rb - Rt)/Rb) x 100

where:

I = inhibition of respiration rate in per cent.

Rt = respiration rate at tested concentration of the test or reference substance

Rb = respiration rate of the control vessels (mean over three test vessels)

Validity criteria fulfilled:

yes

Conclusions:

The effects observed may be attributed to the dissolved fraction, since they were not concentration related. The differences in respiration rate inhibition between the concenrations of 10 to 100 mg/L are not relvant, since the variation between the duplicates is quite high. Only the highest concentration has a slightly higer inhibition rate. However, the results show that the dissolved fraction of the test compound reduced the activiity to approx. 80 - 90 % of the control. Therefore, it can be concluded that Tetra-n-butyltin has some toxicity on the microbial population in sewage sludge.

Executive summary:

The purpose of this study was to determine the toxicity of the test compound ZK 24.942 (tetra-n-butyltin) on the microorganisms from a municipal sewage treatment plant over a period of 30 minutes. Study was conducted in agreement with OECD Guideline for Testing Chemicals No. 209 (activated sludge, respiration inhibition test). Results indicate a slight inhibitory effect on the activity of microorganisms from a municipal sewage treatment plant at the maximum solubility of the test compound (approx. 10 mg/L). However, the inhibition of respiration did not increase at higher nominal concentrations. It is therefore concluded that the effect can be attributed to the dissolved fraction of the compound.

Description of key information

A dose related response was not seen with values of repeats differing significantly. Therefore no EC50 value could be determined for the key study. The lack of definitive result is likely to be due to the poor solubility of the test substance.

Additional information

Toxicity to microorganisms.001: 30 minute exposure; results indicate a slight inhibitory effect on the activity of microorganisms from a municipal sewage treatment plant at the maximum solubility of the test compound

Toxicity to microorganisms.002: 18 hour EC50 = 1.7 mg/L

Toxicity to microorganisms.003: 30 minute EC50 = 1.1 µg/L

Toxicity to microorganisms.004: The EC50 (at 15 minutes) was 1.6 µmol/L in Vibrio fischeri 

Toxicity to microorganisms.001 was conducted in accordance with GLP following OECD 209. It was therefore selected as the key study. A dose related response was not seen with values of repeats differing significantly. Therefore no EC50 value could be determined for this study.

Values from the supporting studies are wildly different from the key study and from each other. The variability of the results is likely to be due to the poor solubility of the test compound. The use of a vehicle is likely to aid solubility and this may help to explain why the supporting studies saw a dose related inhibitory effect unlike the key study.