Oxalonitrile

Toxicity to aquatic plants other than algae

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic plants other than algae

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Ethanedinitrile, hydrogen cyanide (HCN), potassium cyanide and sodium cyanide can be considered as a chemical category, along with and acetone cyanohydrin (ACH, also known as 2-hydroxy-2-methylpropanenitrile), based on structural similarity, common breakdown/metabolic products in physical and biological systems, and similar physico-chemical properties. Particular attention is paid to the dissociation constant of HCN. Ethanedinitrile breaks down in aqueous solution into cyanide ion (CN-) and cyanate ion (OCN-) (Cotton and Wilkinson 1980). Ethanedinitrile due to its low log Kow (0.07) and relatively high solubility in water (2.34 g/L) needs to get dissolved in aqueous solutions in lungs to enter the body. The rate of hydrolysis of ethanedinitrile is very fast (Ajwa 2015). Also, in the vast majority of environmental and physiologic conditions, the cyanide salts will dissolve in water to form hydrogen cyanide. The physico-chemical hazards and toxicity therefore result from the activity of HCN. An ECETOC Task Force, in the 2007 ECETOC Joint Assessment of Commodity Chemicals (JACC) Report No. 53, “Cyanides of Hydrogen, Sodium and Potassium, and Acetone Cyanohydrin (CAS No. 74-90-8, 143-33-9, 151-50-8 and 75-86-5)” supports the development of the chemical category inclusive hydrogen cyanide, sodium and potassium cyanides. Hydrogen cyanide (Index No.006-006-00-X) and salts of hydrogen cyanides (Index No.006-007-00-5) are both listed in Annex VI, Table 3.1 of Regulation (EC) No. 1272/2008, entry 006-007-00-5, and are restricted in comparable ways taking into account physical characteristics. Thus, the assignment of ethanedinitrile to a chemical category does not result in a less protective regulatory status.

Qualifier:

according to guideline

Guideline:

OECD Guideline 221 (Lemna sp. Growth Inhibition Test)

GLP compliance:

yes

Test organisms (species):

Lemna gibba

Test type:

semi-static

Water media type:

freshwater

Total exposure duration:

7 d

Nominal and measured concentrations:

The measured concentrations of free cyanide were between 72.8 and 142.5 % of nominal in the four highest test concentrations at the beginning of the exposure periods (mean recovery per treatment 93.8-132 % of nominal). As expected, the concentration of nominal 5.01 μg CN-/L was below the LOQ. The free cyanide concentrations decreased during the 24-hour exposure periods to levels between For each exposure interval, the mean measured concentration was calculated. The arithmetic means of the individual exposure concentrations were used for the evaluation of the test (3.70, 7.40, 14.0, 39.7, 93.6 μg CN-/L).

Details on test conditions:

The test item was dissolved in the test medium. For the determination of the growth of Lemna, three replicates for each concentration and six replicates for the control (test medium only) were exposed to nominal concentrations in terms of cyanide of 5.01, 15.9, 50.1, 158, 500 μg CN-/L (spacing factor 3.16).

Key result

Duration:

7 d

Dose descriptor:

other: ErC50

Remarks:

frond number (CN-)

Effect conc.:

40.4 µg/L

Key result

Duration:

7 d

Dose descriptor:

other: ErC50

Remarks:

frond area (CN-)

Effect conc.:

31.7 µg/L

Key result

Duration:

7 d

Dose descriptor:

other: ErC50

Remarks:

biomass (dry weight) (CN-)

Effect conc.:

63.3 µg/L

Key result

Duration:

7 d

Dose descriptor:

other: ErC10

Remarks:

frond number (CN-)

Effect conc.:

6.16 µg/L

Key result

Duration:

7 d

Dose descriptor:

other: ErC10

Remarks:

frond area (CN-)

Effect conc.:

5.47 µg/L

Key result

Duration:

7 d

Dose descriptor:

other: ErC10

Remarks:

dry weight (CN-)

Effect conc.:

8.99 µg/L

Key result

Duration:

7 d

Dose descriptor:

NOEC

Remarks:

growth rate: frond number, frond area (CN-)

Effect conc.:

3.7 µg/L

Key result

Duration:

7 d

Dose descriptor:

NOEC

Remarks:

growth rate: dry weight (CN-)

Effect conc.:

7.4 µg/L

Key result

Duration:

7 d

Dose descriptor:

other: EYC50

Remarks:

frond number (CN-)

Effect conc.:

14.8 µg/L

Key result

Duration:

7 d

Dose descriptor:

other: EYC50

Remarks:

frond area (CN-)

Effect conc.:

11.6 µg/L

Key result

Duration:

7 d

Dose descriptor:

other: EYC50

Remarks:

dry weight (CN-)

Effect conc.:

13.1 µg/L

Key result

Duration:

7 d

Dose descriptor:

other: EYC10

Remarks:

frond number (CN-)

Effect conc.:

3.81 µg/L

Key result

Duration:

7 d

Dose descriptor:

other: EYC10

Remarks:

frond area - extrapolated (CN-)

Effect conc.:

3.67 µg/L

Key result

Duration:

7 d

Dose descriptor:

other: EYC10

Remarks:

dry weight - extrapolated (CN-)

Effect conc.:

3.58 µg/L

Key result

Duration:

7 d

Dose descriptor:

NOEC

Remarks:

Yield: frond number, frond area, dry weight (CN-)

Effect conc.:

3.7 µg/L

Details on results:

The ErC50 for the test endpoint growth rate of the primary measurement variable frond number was calculated to be 40.4 μg CN-/L, for frond area 31.7 μg CN-/L and for dry weight 63.3 μg CN-/L. The respective ErC10 values were 6.16, 5.47 and 8.99 μg CN-/L. The NOEC values for both frond number and area were 3.70 μg CN-/L and for dry weight 7.40 μg CN-/L. The EYC50 value for frond number was 14.8 μg CN-/L, for frond area 11.6 μg CN-/L and for dry weight 13.1 μg CN-/L. The respective EYC10 values were 3.81 μg CN-/L, 3.67 μg CN-/L and 3.58 μg CN-/L (the two last mentioned values were extrapolated, the lowest test concentration was 3.70 μg/L). The NOEC values for the three parameters were 3.70 μg CN-/L. The 7-day EYC50 for frond area of 11.6 μg CN-/L represented the lowest EC50 value.

Conclusions:

In a growth inhibition test with Lemna gibba exposed to sodium cyanide over 7 days the ErC50 values for growth rate of frond number, frond area and biomass (dry weight) were calculated to be 40.4, 31.7 and 63.3 μg/L, respectively. The 7 day EYC50 values for yield of frond number, frond area and biomass (dry weight) were 14.8, 11.6 and 13.1 μg/L. The most sensitive endpoint was the EC50 for yield of frond area of 11.6 μg CN-/L. The NOEC values for all parameters related to frond number, frond area and of biomass were determined to be 3.70 μg CN-/L, except for growth rate of biomass (7.40 μg CN-/L). For frond area, inhibition of growth rate and yield was only 3.9 and 8.5 %, respectively, at the lowest test concentration. Though the reduced values were statistically significantly different from the control due to the small standard deviations of the replicates, inhibition < 10 % is generally not considered to be ecotoxicologically relevant. Therefore, as NOEC for these parameters 3.70 μg CN-/L was used. The effect values are expressed in terms of mean measured concentrations of free cyanide.
Regarding the effects of CN- towards macrophytes reported in literature only two values were located Gensemer et al. (2005). It is EC50 measured as root weight for Myriophyllum spicatum, which was 22,400 ug CN-/L. Secondly effect on Lemna gibba in decreased potassium uptake was noted at 26,000 ug CN-/L. Therefore data reported in GLP study from Fraunhofer seems to be highly conservative in comparison to effects described in literature.

Executive summary:

Summary

A study was performed at the Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) to determine the toxicity of the test item sodium cyanide on the growth of the aquatic plantLemna gibbaunder semi-static conditions (daily media renewal) over a test period of 7 days according to the OECD guideline 221. The test item was dissolved in the test medium. For the determination of the growth of Lemna, three replicates for each concentration and six replicates for the control (test medium only) were exposed to nominal concentrations in terms of cyanide of 5.01, 15.9, 50.1, 158, 500 μg CN^-/L (spacing factor 3.16). The concentrations of free cyanide in the Lemna test were analysed photometrically (Merck Spectroquant® 14800) at the beginning and the end of each exposure period (LOQ = 7.4 μg CN^-/L).

 

Exposure concentration

The measured concentrations of free cyanide were between 72.8 and 142.5 % of nominal in the four highest test concentrations at the beginning of the exposure periods (mean recovery per treatment 93.8-132 % of nominal). As expected, the concentration of nominal 5.01 μg CN^-/L was below the LOQ. The free cyanide concentrations decreased during the 24-hour exposure periods to levels between <LOQ and 5.99 % of the measured initial concentrations in the two highest treatments. Based on the measured values the mean recovery was 4.81 % of the measured initial values. In the other treatments, the free cyanide concentrations were below LOQ at the end of the 24-hour exposure period. The dissipations of free cyanide in 500 and 50 μg/L solutions were recorded in a separate non-GLP study and 1^storder kinetics could be calculated (r² 0.999). However, the measured concentrations in the test at the end of the test were mostly lower than the calculated values. To avoid an underestimation of toxicity by using the calculated values, the measured values were preferred. For concentrations <LOQ (7.4 μg CN^-/L) the half LOQ (3.7 μg CN^-/L) was used for the calculation of the mean measured concentrations (geometric mean).

For each exposure interval, the mean measured concentration was calculated. The arithmetic means of the individual exposure concentrations were used for the evaluation of the test (3.70, 7.40, 14.0, 39.7, 93.6 μg CN^-/L).

 

Effects on Lemna growth

The ErC₅₀for the test endpoint growth rate of the primary measurement variable frond number was calculated to be 40.4 μg CN^-/L, for frond area 31.7 μg CN^-/L and for dry weight 63.3 μg CN^-/L. The respective ErC₁₀values were 6.16, 5.47 and 8.99 μg CN^-/L. The NOEC values

for both frond number and area were 3.70 μg CN^-/L and for dry weight 7.40 μg CN^-/L. The EYC₅₀value for frond number was 14.8 μg CN^-/L, for frond area 11.6 μg CN^-/L and for dry weight 13.1 μg CN^-/L. The respective EYC₁₀values were 3.81 μg CN^-/L, 3.67 μg CN^-/L and 3.58 μg CN^-/L (the two last mentioned values were extrapolated, the lowest test concentration was 3.70 μg/L). The NOEC values for the three parameters were 3.70 μg CN^-/L. The 7-day EYC₅₀for frond area of 11.6 μg CN^-/L represented the lowest EC₅₀value.

 

Conclusion

In a growth inhibition test withLemna gibbaexposed to sodium cyanide over 7 days the ErC₅₀values for growth rate of frond number, frond area and biomass (dry weight) were calculated to be 40.4, 31.7 and 63.3 μg/L, respectively. The 7 day EYC₅₀values for yield of frond number, frond area and biomass (dry weight) were 14.8, 11.6 and 13.1 μg/L. The most sensitive endpoint was the EC₅₀for yield of frond area of 11.6 μg CN^-/L. The NOEC values for all parameters related to frond number, frond area and of biomass were determined to be 3.70 μg CN^-/L, except for growth rate of biomass (7.40 μg CN^-/L). For frond area, inhibition of growth rate and yield was only 3.9 and 8.5 %, respectively, at the lowest test concentration. Though the reduced values were statistically significantly different from the control due to the small standard deviations of the replicates, inhibition < 10 % is generally not considered to be ecotoxicologically relevant. Therefore, as NOEC for these parameters 3.70 μg CN^-/L was used. The effect values are expressed in terms of mean measured concentrations of free cyanide.

 

Regarding the effects of CN^-towards macrophytes reported in literature only two values were locatedGensemer et al. (2005).It is EC₅₀measured as root weight forMyriophyllum spicatum, which was 22,400 ug CN^-/L. Secondly effect onLemna gibbain decreased potassium uptake was noted at 26,000 ug CN^-/L. Therefore data reported in GLP study from Fraunhofer seems to be highly conservative in comparison to effects described in literature.

Description of key information

 

In a growth inhibition test with Lemna gibba exposed to sodium cyanide over 7 days the ErC₅₀values for growth rate of frond number, frond area and biomass (dry weight) were calculated to be 40.4, 31.7 and 63.3 μg/L, respectively. The 7 day EYC₅₀values for yield of frond number, frond area and biomass (dry weight) were 14.8, 11.6 and 13.1 μg/L. The most sensitive endpoint was the EC₅₀for yield of frond area of 11.6 μg CN^-/L. The NOEC values for all parameters related to frond number, frond area and of biomass were determined to be 3.70 μg CN^-/L, except for growth rate of biomass (7.40 μg CN^-/L). For frond area, inhibition of growth rate and yield was only 3.9 and 8.5 %, respectively, at the lowest test concentration. Though the reduced values were statistically significantly different from the control due to the small standard deviations of the replicates, inhibition < 10 % is generally not considered to be ecotoxicologically relevant. Therefore, as NOEC for these parameters 3.70 μg CN^-/L was used. The effect values are expressed in terms of mean measured concentrations of free cyanide.

 

Regarding the effects of CN^-towards macrophytes reported in literature only two values were locatedGensemer et al. (2005).It is EC₅₀measured as root weight for Myriophyllum spicatum, which was 22,400 ug CN^-/L. Secondly effect on Lemna gibbain decreased potassium uptake was noted at 26,000 ug CN^-/L. Therefore data reported in GLP study from Fraunhofer seems to be highly conservative in comparison to effects described in literature.

Key value for chemical safety assessment

EC10 or NOEC for freshwater plants:

3.7 µg/L