Captan

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Study period:

14 March 1991

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

GLP; The experiments were done according to ICI Group Environmental Laboratory standard operating procedure B168 version 03 in rooms 007,038 and 156. The method is based on that originally described by Bringman and Kuhn (Bringman G and Kuhn R (1980). Comparison of the toxicity thresholds of water pollutants to bacteria, algae and protozoa in the cell multiplication inhibition test. Water Research 14, 231-241, which has been modified by Slabbert (Slabbert J. L. (1986). Improved bacterial growth test for rapid water toxicity screening. Bulletin of Environmental Contamination and Toxicology 37, 565-569.).

Qualifier:

no guideline followed

Principles of method if other than guideline:

The experiments were performed according to IC Group Environmental Laboratory standard operating procedure B168 version 03 in rooms 007,038 and 156. The method is based on that originally described by Bringman and Kuhn (Bringman G and Kuhn R (1980). Comparison of the toxicity thresholds of water pollutants to bacteria, algae and protozoa in the cell multiplication inhibition test. Water Research 14, 231-241.) which has been modified by Slabbert (Slabbert J L (1986). Improved bacterial growth test for rapid water toxicity screening. Bulletin of Environmental Contamination and Toxicology 37, 565-569.). This procedure measures the degree of inhibition of growth of a pure culture of Pseudomonas putida during a six hour period when the cells are in logarithmic growth phase.

GLP compliance:

yes

Specific details on test material used for the study:

- Physical state: white powder
- Analytical purity: 90.0 % (w/w)
- Batch number: sample leference RS 309/H, order number ERH 5167, test substance reference number T505
- Date of arrival: 8 June 1990

Analytical monitoring:

yes

Vehicle:

yes

Remarks:

methanol

Test organisms (inoculum):

other: Pseudomonas putida, strain NCIB9494

Total exposure duration:

6 h

Test temperature:

25°C

Nominal and measured concentrations:

Captan, dissolved in methanol, at 0.056, 0.10, 0.18, 0.32, 0.56 and 1.0 mg/L in comparison with a growth medium only control, a solvent only (0.1% v/v methanol) control

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol (DCP): 18 mg/L

Key result

Duration:

6 h

Dose descriptor:

EC50

Effect conc.:

0.22 other: mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Growth inhibition

Key result

Duration:

6 h

Dose descriptor:

EC10

Effect conc.:

0.07 other: mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Growth inhibition

Results with reference substance (positive control):

Growth inhibition: 98%

The degree of inhibition of growth compared with that of the controls was calculated as follows:

 

% inhibition = {1 - [ mean optical density of test flask - chemical control value* ] } x 100 / [ mean optical density of control flask - blank control value ]

 

Percentage inhibition was plotted against log₁₀concentrations and the EC10 and EC50 values were read directly from the graph. These were the concentrations of captan technical which covered 10% and 50% inhibition of growth respectively. The EC10 and EC50 values were:

 

EC10 = 0.07 mg/L nominal

EC50 = 0.22 mg/L nominal

 

Table 6.3.4-2 Summary of effects of captan on Pseudomonas putida

 

Captan concentration (mg/L)^1	Mean optical density minus value for uninoculated solution	Growth inhibition (%)
Control^2	0.6293	-
Solvent only	0.6958	0
0.056	0.6362	0
0.1	0.4792	24
0.18	0.3765	40
0.32	0.2122	66
0.56	0.0912	86
1.0	0.0589	91
3,5-DCP	0.0131	98

¹Nominal concentrations

²Growth medium only

Validity criteria fulfilled:

not specified

Remarks:

The experiments were done according to ICI Group Environmental Laboratory standard. The method is based on that originally described by Bringman and Kuhn (Bringman G and Kuhn R (1980).

Conclusions:

The EC50 of captan to Pseudomonas putida is 0.22 mg/L. The EC10 was 0.07 mg/L. Based on the functional endpoints of soil microbial activity exposed via the soil matrix, no significant effects on the process mediated by soil micro-organisms would be expected.

Executive summary:

The toxicity of captan technical to Pseudomonas putida was determined. The test doses were: blank, control, solvent control, nominal concentrations of 0.056, 0.10 , 0.18, 0.32, 0.56 and 1.0 mg/1 and a reference concentration of 3,5-dichlorophenol (18 mg/L), 6 hours shaken.

The test species was Pseudomonas putida, strain NCIB9494. Percentage inhibition was plotted against log₁₀concentrations and the EC10 and EC50 values were read directly from the graph. These were the concentrations of captan technical which covered 10% and 50% inhibition of growth respectively. The EC10 and EC50 values were:

EC10 = 0.07 mg/L nominal

EC50 = 0.22 mg/L nominal

Description of key information

Toxicity to soil microorganisms ( Pseudomonas putida): The EC50 of captan to Pseudomonas putida is 0.22 mg/L carried out in aqueous solution. No significant effects on the process mediated by soil micro-organisms would be expected.

Additional information

The EC50 and EC10 of captan to Pseudomonas putida, a commonly occurring soil and water bacterium, was 0.22 and 0.07 mg/L, respectively. The P. putida test was carried out in the water phase, assuming exposure is higher relative to bacteria in soil. Based on the functional endpoints of soil microbial activity exposed via the soil matrix, no significant effects on the process mediated by soil micro-organisms would be expected following the recommended use of captan.