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Toxicity to soil microorganisms

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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
Analytical monitoring:
yes
Vehicle:
yes
Remarks:
methanol
Test organisms (inoculum):
other: Pseudomonas putida, strain NCIB9494
Total exposure duration:
6 h
Test temperature:
25°C
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

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

(%)

Control2

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.
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

The EC50 of captan to Pseudomonas putida is 0.22 mg/L carried out in aqueous solution.

Key value for chemical safety assessment

Short-term EC50 for soil microorganisms:
0.22 µg/kg soil dw

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.