1,2-dichlorobenzene

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: acceptable, well-documented publication which meets basic scientific principles (For tissue distribution and biliary excretion, only instead of two dose levels administered)

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1996

Materials and methods

Test guideline

Test guideline 1

Qualifier:

equivalent or similar to guideline

Guideline:

EU Method B.36 (Toxicokinetics)

Deviations:

yes

Remarks:

; For "tissue distribution" and "excretion in bile" only one instead of two dose levels were determined.

Test guideline 2

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

yes

Remarks:

; For "tissue distribution" and "excretion in bile" only one instead of two dose levels were determined.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

1,2-dichlorobenzene

EC Number:

202-425-9

EC Name:

1,2-dichlorobenzene

Cas Number:

95-50-1

Molecular formula:

C6H4Cl2

IUPAC Name:

1,2-dichlorobenzene

Details on test material:

- Radiochemical purity (if radiolabelling): > 98 %
- Specific activity (if radiolabelling): 326 Mbq/mmol
- Locations of the label (if radiolabelling): uniformly distributed [U-14C]
- obtained from: Sigma Chemicals Co., St. Louis, MO, USA

Radiolabelling:

yes

Remarks:

1,2-dichloro[U-14C]benzene

Test animals

Species:

rat

Strain:

other: Wistar, Crl:(WI)WUBR

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Wiga GmbH, Sulzfeld, Germany
- Age at study initiation: 9-11 weeks
- Weight at study initiation: 250 g-300 g
- Individual metabolism cages: yes
- Diet (e.g. ad libitum): ad libidum
- Water (e.g. ad libitum): ad libidum

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

maize oil

Details on exposure:

VEHICLE
- Concentration in vehicle:
- Blood kinetic: 5, 50, 250 mg/kg bw (0.74 MBg/kg bw)
- Excretion in urine and feces: 5, 50, 250 mg/kg bw (0.74 MBq/kg bw)
- Tissue distribution: 10 mg/kg bw (1.48 MBq/kg bw)
- Excretion in bile: 10 mg/kg bw (2.78 MBq/kg bw)
- Amount of vehicle (if gavage): 4 mL/kg bw

Duration and frequency of treatment / exposure:

single dose for each investigation

Doses / concentrations

Remarks:

Doses / Concentrations:
refer to "Details on exposure"
For "excretion in urine and faeces" an additional group was pretreated with 0,1% (w/v) phenobarbital in drinking water for 4 days prior to administration of 5, 50 or 250 mg/kg bw (0.74 MBq/kg) of 1,2-dichlorobenzene (dissolved in maize oil (4 mL/kg bw))

No. of animals per sex per dose / concentration:

- blood kinetics: 3 groups of 3 male rats
- tissue distribution: 4 groups of 3 male rats
- excretion in urine and faeces: 3 groups of 3 rats; in addition, three groups of three rats pretreated with phenobarbital
- excretion in bile: 2 recovered male rats, each with cannulated bile duct

Control animals:

no

Positive control reference chemical:

no data

Details on study design:

- Dose selection rationale: 10 mg/kg bw as a non-toxic dose level and 5, 50 and 250 mg/kg bw as a low-, mid- and high-dose level

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
Blood kinetics:
- Tissues and body fluids sampled: 150 µl blood (plasma, serum) from the tail vain
- Time and frequency of sampling: at 1, 2, 3, 4, 6, 8, 12, 24, 48, 72 and 96 h

Tissue distribution:
- Tissues and body fluids sampled: urine, faeces, blood (plasma, serum) liver, kidneys, spleen, pancreas, lungs, heart, brain, skin, femur bone, skeletal muscle, perirenal fat, testis, urinary bladder, stomach, small intestine, cecum, colon, content of gastrointestinal tract, cage washes, residual carcass
- Time and frequency of sampling: groups sacrificed 6, 15, 30 or 75 h after dosing

Excretion in urine and faeces:
- Tissues and body fluids sampled: urine, faeces
- Time and frequency of sampling: 0-8 h, 8-24 h, then every 24 h up to 6 days

Excretion in bile:
- Tissues and body fluids sampled: bile, urine, faeces,
- Time and frequency of sampling: bile collected immediately after dosing every 15 min up to 2 h, at 2.5, 3, 4, 5, 6, 7, 8 h, from 8 to 24 h and from 24 to 48 h, faeces and urine collected 0-8 h and 8 - 24 h.


METABOLITE CHARACTERISATION STUDIES
- body fluids sampled: urine, bile
- Time and frequency of sampling: no data
- From how many animals: no data
- Method type(s) for identification: Liquid scintillation counting (radioactivity), HPLC (metabolites), FAB-MS (urine metabolites after drying), LC-MS (biliary metabolites), GC-ECD (parent compound in blood)
- Limits of detection and quantification: detection limit of GC: 0.05 µmol/L, no data for the other methods


TREATMENT FOR CLEAVAGE OF CONJUGATES (if applicable):
fractions of the urine or bile samples were treated with beta-glucuronidase (12000 Fisherman units at 37 °C) for determination of glucuronide conjugates or treated with Helix pomatia (6000 Fisherman units beta-glucuronidase and 48000 Roy units arylsulphatase) for determination of sulfate conjugates

Statistics:

no data

Results and discussion

Preliminary studies:

no data

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Blood kinetics:
5 mg/kg: concentration of parent compound only detected during the first 2 h (detection limit of GC: 0.05 µmol/L)
50 mg/kg: concentration of parent compound decreased after 3 h
250 mg/kg: concentration of parent compound decreased after 6 h

Details on distribution in tissues:

In all tissues except cecum and colon, the highest concentrations of radioactivity were reached after 6 h. The tissues with the highest concentration of radioactivity were kidneys, liver, urinary bladder, small intestine and abdominal skin and perirenal fat. The estimated halflife ranges between 8.7 and 19.3 h in all tissues.

Details on excretion:

Excretion was predominantly in the urine (75-84% of dose). Feces contained 16, 12 and 7% of the dose, for the low, mid and high dose level. Total excretion was almost complete after 24 h after dosing with 5 or 50 mg/kg bw. After dosing with 250 mg/kg bw the faecal excretion was maximal within 24-48 h. The residual carcass contained less than 1% of the dose at all dose levels. Enzyme induction with phenobarbital led to enhanced urinary excretion and less differences in the rate of excretion between the dose levels. The excretion in bile after an oral dose of 10 mg/kg bw was maximal after 6 h. 60 % of the dose was excreted in bile and 25% in urine. Nearly all radioactivity was excreted during the first 24 h. The amount excreted in faeces was < 4%.

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

Only minor differences in urine HPLC profiles were observed between different doses. Major metabolites are phenylmercapturic acids (glutathione conjugates with epoxides of 1,2-DCB) (60% ) and sulfate esters of 2,3- and 3,4-dichlorophenol (20%, hydrolysis with Helix pomatia increased amount of phenols). Phenobarbital lead to an increase of respective sulfate-conjugates.

Any other information on results incl. tables

Doses up to 50 mg/kg bw are completely absorbed and metabolized. Highest concentrations of radioactivity were present in the liver, kidneys and fat. Main metabolites in urine are phenylmercapturic acids (60%) and sulfate esters of 2,3- and 3,4-dichlorophenol (20%). The high amount of phenylmercapturic acid metabolites explains the observed depletion of GSH in rats treated with 1,2-DCB. The high reactivity of the metabolites towards GSH indicate their ability to react with biological macromolecules. In consequence depletion of the GSH-pool may contribute to the previously described hepatotoxic effect of 1,2-DCB.

Applicant's summary and conclusion

Conclusions:

Interpretation of results: no bioaccumulation potential based on study results

Executive summary:

Hissink et al., 1996

The toxicokinetics and the metabolism of radiolabelled 1,2-dichlorobenzene (1,2-DCB) was investigated according to EU Method B.36 and OECD Guideline 417. The study was considered as reliable with restrictions. For "tissue distribution" and "excretion in bile", only one instead of two dose levels were determined.

The test substance was dissolved in corn oil and the following doses were administered to groups of adult male Wistar rats for the following investigations:

- Blood kinetic: 5, 50, 250 mg/kg bw (0.74 MBg/kg bw)

- Excretion in urine and feces: 5, 50, 250 mg/kg bw (0.74 MBq/kg bw)

- Tissue distribution: 10 mg/kg bw (1.48 MBq/kg bw)

- Excretion in bile: 10 mg/kg bw (2.78 MBq/kg bw)

For "excretion in urine and faeces" an additional group was pre-treated with 0,1% (w/v) phenobarbital in drinking water for 4 days prior to exposure.

For blood kinetics 150 µL blood (plasma, serum) from the tail vain was sampled at 1, 2, 3, 4, 6, 8, 12, 24, 48, 72 and 96 h after administration. For tissue distribution, radioactivity was determined in urine, faeces, blood (plasma, serum) liver, kidneys, spleen, pancreas, lungs, heart, brain, skin, femur bone, skeletal muscle, perirenal fat, testis, urinary bladder, stomach, small intestine, cecum, colon, content of gastrointestinal tract, cage washes and residual carcass. Therefore, groups of test animals were sacrificed 6, 15, 30 or 75 h after dosing. Excretion in urine and faeces was analysed between 0 and 8 h, 8 and 24 h, and then every 24 h up to 6 days. For biliary excretion experiments, bile was collected immediately after dosing every 15 min up to 2 h, at 2.5, 3, 4, 5, 6, 7, 8 h, from 8 to 24 h and from 24 to 48 h, and faeces and urine were collected between 0 and 8 h and 8 and 24 h.

Metabolites in urine, bile and blood were characterized and/or identified by liquid scintillation counting (radioactivity), HPLC (metabolites), FAB-MS (urine metabolites after drying), LC-MS (biliary metabolites), GC-ECD (parent compound in blood). For conjugate analysis, fractions of the urine or bile samples were treated with beta-glucuronidase for determination of glucuronide conjugates or with Helix pomatia for determination of sulfate conjugates.

In blood, concentration of parent compound could only be detected during the first 2 h (detection limit of GC: 0.05 µmol/L). For the higher dose groups (50 and 250 mg/kg), parent compound decreased after 3h and 6h, respectively. In all tissues except cecum and colon, the highest concentrations of radioactivity were reached after 6 h. The tissues with the highest concentration of radioactivity were kidneys, liver, urinary bladder, small intestine and abdominal skin and perirenal fat. The estimated halflife ranges between 8.7 and 19.3 h in all tissues. Excretion was predominantly in the urine (75-84% of dose). Feces contained 16, 12 and 7% of the dose, for the low, mid and high dose level. Total excretion was almost complete after 24 h after dosing with 5 or 50 mg/kg bw. After dosing with 250 mg/kg bw the faecal excretion was maximal within 24-48 h. The residual carcass contained less than 1% of the dose at all dose levels. Enzyme induction with phenobarbital led to enhanced urinary excretion and less differences in the rate of excretion between the dose levels. The excretion in bile after an oral dose of 10 mg/kg bw was maximal after 6 h. 60 % of the dose was excreted in bile and 25% in urine. Nearly all radioactivity was excreted during the first 24 h. The amount excreted in faeces was < 4%. Only minor differences in urine HPLC profiles were observed between different doses. Major metabolites are phenylmercapturic acids (glutathione conjugates with epoxids of 1,2-DCB) (60% ) and sulfate esters of 2,3- and 3,4-dichlorophenol (20%, hydrolysis with Helix pomatia increased amount of phenols). Phenobarbital lead to an increase of respective sulfate-conjugates. Doses up to 50 mg/kg bw are completely absorbed and metabolized. Highest concentrations of radioactivity were present in the liver, kidneys and fat. Main metabolites in urine are phenylmercapturic acids (60%) and sulfate esters of 2,3- and 3,4-dichlorophenol (20%). The high amount of phenylmercapturic acid metabolites explains the observed depletion of GSH in rats treated with 1,2-DCB. The high reactivity of the metabolites towards GSH indicate their ability to react with biological macromolecules. In consequence depletion of the GSH-pool may contribute to the previously described hepatotoxic effect of 1,2-DCB.