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Toxicity to microorganisms

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Endpoint:
toxicity to microorganisms, other
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2014
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Although not a standard OECD method the suitability of the method is well documented in peer-reviewed scientific literature (Ma, X.Y., Wang, X.C., Ngo, H.H., Guo, W.S., Wu, M.N., Wang, N., 2014. Bioassay based luminescent bacteria: interferences, improvements, and applications. Sci. Total Environ. 468 – 469, 1 – 11). Thus, the results are considered reliable with restrictions.
Reason / purpose:
reference to same study
Qualifier:
according to
Guideline:
other: Microtox assay system
Principles of method if other than guideline:
The Microtox assay system has been recognized to be one of the most rapid and cost-effective methods, which is based on the measurement of the reduction in light emission of luminescent bacteria exposed to a toxic substance (see Bulich, A.A., 1979. Use of Luminescent Bacteria for Determining Toxicity in Aquatic
Environments. American Society for Testing and Materials, Philadelphia, PA, USA. pp. 98–106)
GLP compliance:
not specified
Remarks:
not indicated in the publication
Analytical monitoring:
not specified
Vehicle:
yes
Details on test solutions:
The assay was carried out by adding 2 mL test medium and 10 µL bacterial suspension to a glass tube. The medium was thoroughly mixed and the light unit was recorded by a DXY-3 biological toxicity detector (Nanjing Kuake, China) after 15 min incubation at 22 ± 1 °C. The concentration gradient of DP is 0.591, 2.95, 14.8, 73.8, 369 µg/L, which were diluted by distilled water from DP stock solution accordingly (with the highest final concentration of DMSO 0.1% in 369 µg/L). Relative luminosities (RL) were used to evaluate the effects of DP.
RL = Lt/Lc * 100%
where Lc is luminescence of bacteria exposed to the blank sample, Lt is luminescence of bacteria exposed to the DP samples.
Test organisms (species):
other: lyophilized T3 luminous bacteria
Details on inoculum:
Bioassay with luminous bacterium
The lyophilized T3 luminous bacterium was purchased from Institute of Soil Science, Chinese Academy of Sciences (Nanjing, China). The suspension was prepared according to the assay procedure of GB/T 15441-1995. Briefly, 0.5 g freeze-dried bacteria was revived in 0.5 mL chilled 2% NaCl at 4 °C for 20 – 30 min before testing.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
15 min
Hardness:
not reported
Test temperature:
22 ±1 °C
pH:
not reported
Dissolved oxygen:
not reported
Salinity:
not reported
Nominal and measured concentrations:
nominal concentrations of 0.591, 2.95, 14.8, 73.8, 369 µg DP/L
Reference substance (positive control):
no
Duration:
15 min
Dose descriptor:
NOEC
Effect conc.:
>= 369 µg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: luminescence
Remarks on result:
other: no effects observed at highest tested concentration
Details on results:
In this assay, the EC 50 values could not be calculated because the luminosities did not decrease with increasing concentrations of DP. Graphical analysis shows the luminosities of luminous bacteria with respect to time following three different treatment protocols (Control, 0.1% DMSO and highest DP concentration used in the experiment, 369 µg/L). The luminosities were relatively stable with respect to time. In addition, the results showed there was no significant difference (p > 0.05) among the different treatment groups. It was seen that the relative light units of luminous bacteria after exposure to different concentrations of DP fluctuate around 100%, suggesting that there is no acute toxicity to luminous bacteria under the studied DP concentrations.
Results with reference substance (positive control):
none applied
Reported statistics and error estimates:
Results were analyzed by SPSS 18.0 software (SPSS Inc.). Statistical differences of biological parameters between DP-treated groups and control group were evaluated using one-way ANOVA test. A probability value < 0.05 (p < 0.05) was accepted as significance.

It is known that the light emission of luminous bacteria is related to cellular metabolism, therefore the light intensity can reflect the metabolic status of the bacteria. When exposed to the toxicant, the luciferase of the bacteria could be inhibited, and the light intensity decreased rapidly (Ma, X.Y., Wang, X.C., Ngo, H.H., Guo, W.S., Wu, M.N., Wang, N., 2014. Bioassay based luminescent bacteria: interferences, improvements, and applications. Sci. Total Environ. 468 – 469, 1 – 11.). This rapid, sensitive and cost-effective assay was used in this study to evaluate the acute toxicity of DP on the environment levels by obtaining the EC 50 values.

Validity criteria fulfilled:
yes
Conclusions:
No acute toxicity to luminuous bacteria up to 369 µg DP/L (highest tested concentration) was observed.
Executive summary:

In this study, luminous bacteria were chosen as testing organisms to investigate the acute toxicity of DP. The concentration gradient of DP used in this study was chosen based on its environmental levels (experiments of luminous bacteria: 0.591, 2.95, 14.8, 73.8, 369 µg/L). For luminous bacteria, the relative luminosities were around 100% in treated groups, which suggested that there is no acute toxicity to luminous bacteria under the studied DP concentrations.

Endpoint:
activated sludge respiration inhibition testing
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is highly insoluble in water, hence indicating that aquatic toxicity is unlikely to occur

Description of key information

The substance is highly insoluble in water and it is not hazardous. No OECD 209 study is available. However, in a bioassay with luminous bacterium, no toxicity was observed up to the highest tested concentration of 369 µg DP/L.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
369 µg/L

Additional information

In a bioassay with luminous bacteria as testing organisms the acute toxicity of DP was investigated. The concentration gradient of DP used in this study was chosen based on its environmental levels (experiments of luminous bacteria: 0.591, 2.95, 14.8, 73.8, 369 µg/L). For luminous bacteria, the relative luminosities were around 100% in treated groups, which suggested that there is no acute toxicity to luminous bacteria under the studied DP concentrations.