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Basic toxicokinetics

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basic toxicokinetics
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well designed study to investigate toxicokinetics, prior to establishment of OECD guideline.

Data source

Reference Type:
Toxicokinetic aspects of chronic cyanide exposure in the rat
Leuschner J, Winkler A and Leuschner F
Bibliographic source:
Toxicology Letters 57: 195-201

Materials and methods

Objective of study:
Test guideline
equivalent or similar to guideline
EU Method B.36 (Toxicokinetics)
GLP compliance:
not specified

Test material

Constituent 1
Chemical structure
Reference substance name:
Potassium cyanide
EC Number:
EC Name:
Potassium cyanide
Cas Number:
Molecular formula:
potassium cyanide
Details on test material:
KCN was purchased from Fluka GmbH, D-7910 Neu-Ulm, purity > 99%.

Test animals

Details on test animals or test system and environmental conditions:
Animals were used with an average age of 35 days and an average weight of 100-117 g. Rats were kept individually in Makrolon cages type III at a room temperature of 21 +/- 1 degrees C and a relative humidity of 55 +/- 5%. A 12-hour light (150 lux at approx 1.5 m room height)/dark cycle was used. Standardized diet for rats was Altromin 1321 (Altomin GmbH, Lage/Lippe).

Administration / exposure

Route of administration:
oral: drinking water
The stability of the KCN in the drinking water was regularly checked for all dose groups. The concentrations administered were stable for at least 4 days after preparation.
Details on exposure:
Each animal received its individual 250-ml drinking water bottle on 7 days per week. The bottles were exchanged twice a week containing freshly prepared test solution or tap water. The amount of KCN administered in the drinking water was adjusted to the body weight and drinking water consumption once per week. The data of the week just completed were used for this calculation. Behaviour and mortality were checked daily. Body weight and food consumption were determined weekly.
Duration and frequency of treatment / exposure:
Daily for 13 weeks. The individual water bottles were exchanged twice a week containing freshly prepared test solution or tap water.
Doses / concentrations
Doses / Concentrations:
0, 40, 80 and 160 mg/kg body weight/24 hours. The high dose group experienced some toxicity, so the dose was lowered to 140 mg/kg bw/day from the beginning of the 12th week until the end of the study.
No. of animals per sex per dose / concentration:
26-40 animals per sex per dose group
Control animals:
other: Two groups of controls: one drinking tap water ad libitum, the other receiving the amount of water consumed by the high-dose group of rats, calculated from the prior week's consumption.
Positive control reference chemical:
Details on study design:
Rats received 0, 40, 80 and 160 mg KCN/kg bw/day in the drinking water for 13 weeks. Cyanide and thiocyanate were quantitated in the blood, urine and plasma over the 13 week time course of the study. A preliminary acute study took place, in which groups of 3 rats were administered KCN by gavage at a dose of 1.0 mg KCN/kg bw in a volume of 10 ml/kg body weight. Tap water was the vehicle. Blood was collected by cardiac puncture at 2,5,15,30, 45 and 60 min following administration.
Details on dosing and sampling:
Cyanide and thiocyanate determinations in whole blood and plasma were carried out in weeks 1, 3, 5, 7, 9, 11 and 13, always using animals 1-5 of each group. Blood was obtained from the retrobulbar plexus. Urine was collected from 5 animals per group (animal numbers 6-10) in test weeks 6 and 13. Urine was collected over 16 h using Urimax-funnels. Urine was also analysed for cyanide and thiocyanate.
For the estimation of the half-life, a first order elimination was assumed. Food consumption and body weight of the test groups were compared using the Dunnett test. The p ≤ 0.01 level was used for significant changes.

Results and discussion

Preliminary studies:
No toxic effects or signs were observed in rats given 1.0 mg KCN/kg bw acutely. A peak blood level of 6.2 nmol CN anion/ml blood was observed 2 min after application. 60 min after administration blood levels had dropped to 0.3 nmol CN-/ml blood (the limit of detection). A blood elimination half-life of 14.1 min was calculated. The correlation coefficient for the regression line was 0.943.

Toxicokinetic / pharmacokinetic studies

Toxicokinetic parameters
Test no.:
Toxicokinetic parameters:
half-life 1st: 14.1 min

Metabolite characterisation studies

Metabolites identified:
Details on metabolites:
Main metabolite is thiocyanate. Plasma levels of thiocyanate ranged from 341 to 877 nmol SCN- per ml. Urinary excretion of thiocyanate ranged from 100 to 500 μmol/kg bw/d.

Any other information on results incl. tables

High dose group animals were sedated, had significantly reduced drinking water consumption and body weight gain, and experience several deaths.  The dose level was reduced from 160 to 140 mg/kg bw/d at beginning of week 12.  The mid-dose group (80 mg/kg bw/d) also experienced significantly reduced body weight gain and drinking water intake. There were no decrements in body weight gain in the low dose group (40 mg/kg bw/d), although drinking water consumption was significantly reduced.


Cyanide and thiocyanate levels in blood and plasma displayed a dose relationship. Cyanide levels remained fairly constant during the test weeks. For the high dose group, blood cyanide concentrations ranged from 16.0-25.5 nmol CN-/ml blood, and thiocyanate in the range of 341-877 nmol SCN-/ml plasma. Whereas no endogenous cyanide was detected in control animals, small quantities of thiocyanate were detected in the plasma, ranging from 11.4 to 53.3 nmol/ml. Both cyanide and thiocyanate demonstrated a dose-response relationship in urine.

Body Weight, Food and Water Consumption in the Rat during 13 Weeks Exposure to KCN via Drinking Water


Dose Levels (mg/kg bw/d)










Body Weight (g)





149.9 ± 9.0

149.2 ± 77

149.5 ± 7.2

148.1 ± 9.3


327.6 ± 33.3

320.6 ± 25.0

289.6 ± 26.1*

189.6 ± 27.9)


378.0 ± 36.6

363.5 ± 30.8

321.7 ± 31.5*

218.6 ± 23.8*


Food Consumption (g/kg/d)





112.3 ± 13.4

105.2 ± 7.6

112.1 ± 14.2

107.9 ± 10.5


  77.5 ± 9.1

  77.8 ± 11.7

  80.4 ± 7.6

  96.8 ± 29.7*


  64.7 ± 7.3

  63.1 ± 6.8

  66.3 ± 9.8

  79.0 ± 19.9*


Water Consumption (ml/kg/d)





153.7 ± 22.1

133.1 ± 9.9*

101.5 ± 12.6*

  45.0 ± 14.8*


112.0 ± 30.4

  86.5 ± 9.0*

  85.1 ± 10.3*

  67.0 ± 10.7*


  86.1 ± 20.5

  71.3 ± 7.7*

  68.3 ± 9.2*

  58.5 ± 4.9*





















The elimination half-life was 14.1 min. Continuous 13-week exposure via oral drinking water resulted in a dose-related increase in the blood and urine cyanide and thiocyanate levels.  Cyanide levels ranged from 16.0-25.5 nmol CN-/ml blood, well below the lethal levels reported for the rat of 100 nmol/ml following acute oral administration.  Constant plateau levels of cyanide were reached within 3 weeks of initiation of intake. The major metabolite excreted in urine was thiocyanate;  all dose groups excreted approximately 11% of the administered cyanide per day in urine as this metabolite, from week 6 to 13. These results indicate that chronic cyanide administration does not lead to substrate saturation of cyanide detoxification pathways, and does not influence the mode of cyanide excretion.

Applicant's summary and conclusion

Interpretation of results (migrated information): no bioaccumulation potential based on study results
Subchronic oral administration of KCN in the drinking water of rats, at doses up to the maximally tolerated dose, resulting in fairly constant blood cyanide levels throughout the 13 week test period. Blood cyanide levels in the high dose group (140-160 mg/kg bw/d) were 16.0-25.5 nmol CN-/ml blood, and thiocyanate in the range of 341-877 nmol SCN-/ml plasma. Both blood cyanide and urinary thiocyanate levels demonstrated a dose-response relationship. Rats restricted their water intake when cyanide was present, with the high dose group ingesting only 68% of control volume. Body weight gain in the two highest doses was significantly decreased throughout the second half of the experiment, indicating the onset of chronic toxicity. However, the consistency of thiocyanate excretion in the urine suggests that 13 weeks of cyanide exposure does not lead to saturation of cyanide detoxification pathways.
A review of experimental data on cyanides was undertaken by an ECETOC Task Force, and published as 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)”. The report is a weight of evidence approach to an extensive body of literature by this scientific non-governmental organization (NGO). This group evaluated this study and judged the methods and results to be valid and consistent with other data.

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