Registration Dossier

Toxicological information

Basic toxicokinetics

Currently viewing:

Administrative data

Endpoint:
basic toxicokinetics in vivo
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study well documented, meets generally accepted scientific principles, acceptable for assessment.

Data source

Reference
Reference Type:
publication
Title:
Metabolic fate of inhaled Co aerosols in Beagle dogs
Author:
Kreyling WG, Ferron GA, Haider B
Year:
1986
Bibliographic source:
Health Physics 51(6): 773

Materials and methods

Objective of study:
distribution
excretion
Principles of method if other than guideline:
Lung retention of Cobalt (57) in dogs after the inhalation of physically and chemically uniform particles of Co compounds was determined. Excreta and blood analysis were also performed to examine the clearance patterns. Organ analysis was performed to determine the fate of the long term burden of Co in the lungs and other organs.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Physical state: solid particle
- Analytical purity: not reported
- Radiochemical purity (if radiolabelling): not reported
- Specific activity (if radiolabelling): 0.4 - 4 MBq
- Locations of the label (if radiolabelling): Co
Radiolabelling:
yes
Remarks:
57Co

Test animals

Species:
dog
Strain:
Beagle
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: GSF breeding facility
- Age at study initiation: 10-16 mo
- Water (e.g. ad libitum): ad libitum
- Individual metabolism cages: yes, for a period 10 days post exposure

Administration / exposure

Route of administration:
inhalation: aerosol
Vehicle:
unchanged (no vehicle)
Details on exposure:
TYPE OF INHALATION EXPOSURE: other: endotracheal tube

GENERATION OF TEST ATMOSPHERE / CHAMPER DESCRIPTION
- Exposure apparatus: according to Kreyling et al. (1976)
- Method of holding animals in test chamber: barbiturate anaesthesia, lateral position (right side)
- System of generating particulates/aerosols: modified May spinning top aerosol generator
- Composition of vehicle: phys. saline
- Method of particle size determination: low-angle forward-scattering spectrometer
- Treatment of exhaust air: removed


TEST ATMOSPHERE (if not tabulated)
- MMAD (Mass median aerodynamic diameter) / GSD (Geometric st. dev.): 1.5 µm / <1.2
- Geometric mean diameter: 1.1 µm
Duration and frequency of treatment / exposure:
30 to 60 min, single exposure
Doses / concentrations
Remarks:
Doses / Concentrations:
1 to 1000 µg (not further specified)
No. of animals per sex per dose:
2 males
Control animals:
no
Details on dosing and sampling:
PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine (initially daily extraction using catheter, then four nights per week: 16 h urine), faeces, blood, blood cells, serum, lungs, bones, muscles, skin, stomach/intestine, liver, kidneys, spleen, trachea, tracheobronchial lymph nodes, trachea, upper 3-4 generations of bronchi
- Time and frequency of sampling: start immediately after inhalation, at time intervals increasing from daily to once every month and up to 600 days, for various periods, depending on the parameter investigated, for more than 4 years

Retention analysis of deposited Co and its spatial distribution in the lungs:
Measurement was performed using a γ camera. measurements began immediately after inhalation of the aerosols and was performed dorsally, from right and left side of each dog for 15 minutes in each position. Measurements were initially performed on a daily basis, then once every moth for up to a period of 4 years. Occasionally head, larynx or peritoneum were measured. The background radioactivity was subtracted from each picture, thoracic attenuation of retained Co activity was determined at each measurement. In order to correct lung retention for interference from Co retained in the thoracic walls and surrounding organs, thorax activity of the carcass of the dog without lungs was measured at the time of death.

Clearance analysis:
Clearance from bronchial tree and pulmonary region: determination began directly after the exposure. Quantitative collection of excreta during the first 10 days in metabolic cages. Daily extraction of urine by a urinary catheter before the retention measurements. During the next 6 months housing in separate kennels for quantitative faeces collection, during 4 nights/week urine samples of 16 hours were taken inside metabolic cages. After 6 months, excreta were taken for periods of 4 weeks at intervals up to 600 days after exposure. Daily faecal excretion of Co and urinary excretion rates of the first 10 days were determined. Later daily urinary excretion was estimated from measured concentration of Co and an assumed constant daily urinary volume. Blood samples were taken during the first 5-8 months after exposure, blood serum was separated and activity of both samples was determined.

Metabolic studies:
Transfer of Co from the circulatory system into the gastrointestinal (GI) tract and vice versa was studied by additional experiments. Transfer of endogenous Co from the blood was determined after intravenous injection into a leg vein and intramuscular injection into a rear leg muscle, absorption from the GI tract was measured after ingestion of the radiolabeled test compound by other dogs. Retention and excretion measurements were carried out up to 2 months. Liver retention was calculated from the measured abdominal retention by allowing for deposits in other tissues in the field of view of the γ camera as described above for the lungs.

Organ analysis:
At the end of the retention measurements dogs were anesthetized and sacrificed by exsanguinations. All major organs and samples of skin, muscles, lymph nodes, and bones were taken. The tracheobronchial lymph nodes (TBLN), the trachea, and the upper 3-4 generations of bronchi were separated from the rest of the lungs. Background radiation was measured and detector sensitivity was determined using aqueous radiolabeled Co sources.

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:
Retention:
Lung burden dropped rapidly by 89 % during the first few days with a biological half-life time (BHLT) of 0.8 days, another 8 % were eliminated with a BHLT of 27 days, and the remaining 3% of the initial burden were retained in the lungs with a BHLT of 400 days.
Details on distribution in tissues:
Tissue distribution:
After inhalation of the aerosol, most of the radioactive Co was found in the lungs, followed by muscle, bone and skin. The amounts of Co in muscle, bone and skin were estimated, assuming 40 % of the dog's body mass for muscle and 10 % each for bone and skin (according to: Anderson AC (1970). The Beagle as an Experimental dog. Ames, IA: Iowa University Press). The organs involved in the digestive process retained small amounts of Co in the range of 1 %. No significant amount of Co was found in the exsanguinations blood sample at the time of death (less than 0.01 % due to detection limit). Negligible amounts of Co were observed in the various lymph nodes outside the lungs or in thymus, thyroids and tonsils. Brain, heart and pancreas retained small amounts, which together constituted only about 1 % of the total body burden.

Cobalt distribution inside the lungs:
The dogs showed considerably increased Co concentrations in the pharynx, trachea and first 3 -4 generations of bronchi at times corresponding to predominant long-term retention. Moreover, concentrations in these fractions increased with extending time before sacrifice.
Details on excretion:
Clearance pathways:
Comparison of lung retention with daily faecal and urinary excretion showed that by a few days after exposure, urinary excretion was the predominant pathway from the body. The fecal excretion rate was about one order of magnitude less and its curve proceeded parallel to the former. No significant activity was observed outside the lungs, indicating that almost all the Co cleared from the lungs was excreted and there was little storage in other organs. The clearance rate of Co from the lungs was very similar to the sum of the faecal and urinary excretion rates. The concentration in blood proceeded parallel to the urinary excretion rate, as long as it was determined, usually 150-200 days after exposure.

Excretion of cobalt after ingestion of cobalt nitrate:
About 95 % of the administered Co was excreted during the first week, about 25 % were absorbed and excreted via urine, 70 % were excreted in faeces. The remaining 5 % were retained and well distributed in the body, there was no significant accumulation in any organ at that time point.

Excretion of cobalt after i.v. and i.m. injection of cobalt nitrate:
Masses of 1 ng and 1 mg of Co administered i.v. did not show a mass dependent clearance effect. 90 % of the administered mass were excreted within the first week, 85 % via urine and 5 % in faeces. Co was homogeneously distributed within the body. The liver was the only organ accumulating sufficient amounts of Co to be distinguishable during the first week. After this time no particular organ accumulation was detectable (see table 3). The long-term retained fraction was estimated to be about 10 % by balance calculations involving excretion measurements during the next 5 weeks.

Since inhalation was carried out via an endotracheal tube, no particles were deposited outside the lungs. Therefore, 2 major clearance mechanisms were likely: particle dissolution, including subsequent translocation into the blood, and mucociliary particle transport from the lungs after inhalation. There was a small but significant transfer of Co from the circulatory system to the gastrointestinal tract and vice versa. Most of the soluble Co was excreted very rapidly.
When cobalt nitrate particles entered the humid respiratory tract they would dissolve and lose their particle structure. More than 80 % of the initial lung burden were absorbed into the circulatory system during the first day and excreted via urine. Because of the rapid exchange between the blood and the bronchial mucus and fluid, the mucociliary clearance of tracheobronchially deposited Co was assumed to be negligible.
Long-term retained Co was cleared predominantly by translocation into the blood and subsequent excretion via urine.

Metabolite characterisation studies

Metabolites identified:
not measured

Any other information on results incl. tables

Table 1: Tissue distribution of cobalt at the time of death obtained from one dog after inhalation:

  % of total body burden
 Time after exposure (days)  1050  1500
 Lungs 77 81
Bones  10   8
Muscles    8 6
Skin    2   3
 Stomach/Intestine  0.8 0.5 
 Liver 1 0.6
Kidneys  0.7  0.5 
Spleen   0.1 0.1 
Other organs  0.3  0.3 

Table 2: Cobalt distribution inside the lungs:

  % of total lung burden
 Time after exposure (days)  1050  1500
 Lungs 48  29 
 Pharynx, trachea, first 3-4 generations of bronchi 52  71 
Tracheobronchial lymph nodes  0.1  0.1 

Table 3: Rapid excretion during the first week and long-term retention after injection or ingestion:

  Injection  Ingestion
  intravenous  intramuscular  
Co mass (µg) 10e-3 to 10e3  2 x 10e3  2 x 10e3
 No. of dogs  4  2  2
          Rapid excretion (%) during the first week after administration:
 Feces   5  70
 Urine 85  85  25 
          Long-term retention (%):
 Liver/Spleen
Soft tissues, Bones, etc.  10   10  5

Applicant's summary and conclusion