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Basic toxicokinetics

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basic toxicokinetics
Type of information:
experimental study
Adequacy of study:
key study
Study period:
19.12.1994 - 03.02.1995
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP, comparable to guideline study
Reason / purpose for cross-reference:
reference to other study

Data source

Reference Type:
study report
Report date:

Materials and methods

Objective of study:
Test guideline
equivalent or similar to guideline
OECD Guideline 417 (Toxicokinetics)
Version / remarks:
(The study was designed according to scientifically accepted procedures and according to validated and standardized methods, developed in the testing facility.)
Principles of method if other than guideline:
Determination of the bioavailability of p-(1,1,3,3-tetramethylbutyl)-phenol after single administration in male Wistar rats.
In addition, blood concentration profiles were obtained after oral and intravenous application to assess the potention of the substance to bioaccumulate in the rat.
The substance concentration in the blood samples was determined by a specially developed gas chromatographic method.
GLP compliance:
yes (incl. QA statement)
GLP-Bescheinigung vom Ministerium für Umwelt, Raumordnung und LAndwirtschaft des Landes Nordrhein-Westfalen

Test material

Constituent 1
Chemical structure
Reference substance name:
EC Number:
EC Name:
Cas Number:
Molecular formula:
Details on test material:
- Name of test material (as cited in study report): p-(1,1,3,3-tetramethylbutyl)-phenol (Octylphenol PT, OCT)
- Substance type: pure active substance
- Physical state: solid, white - slight yellowish
- Analytical purity: appr. 98 %
- Impurities (identity and concentrations): no data
- ID-No.: 0637/81611; internal number.: 0125
- Production date of the lot/batch: 24.01.1994; stability > 1 year
- Storage condition of test material: room temperature, darkness
- Density: 0,95 g/cm³ (20 °C)
- Solubility in water: 4 mg/l (20°C)

Test animals

Details on test animals or test system and environmental conditions:
- Source: Fa. Harlan-Winkelmann, D-33167 Borchen
- Age at study initiation: no data
- Weight at study initiation: 180-200 g (up to 250 g for additional animals in groups I and III)
- Fasting period before study: Animals of the p.o. dose groups were retained from food appr. 16 h before dosing
- Housing: Groups of two (untreated) or three (dosage groups and remainder) in Makrolon cages Type IV
- Diet: ad libitum, Ssniff R10 - laboratory standard rat diet (in pellet form), Fa. Ssniff, Spezialfutter GmbH, D-59494 Soest.
- Water: ad libitum, Fa. Gelsenwaser, D-45721 Haltern
- Acclimation period: animals were acclimated under study conditions except administration for a minimum of 5 days

- Temperature (°C): 22 +- 3°C
- Humidity (%): 30-70 %
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): artificial light; 12/12

Administration / exposure

Route of administration:
other: oral gavage and intravenous injection
propylene glycol
Details on exposure:

- Rate of preparation of diet (frequency): preparation freshly on application day
- Storage temperature of food: roomtemperature, dark

- Justification for use and choice of vehicle (if other than water): used in comparable studies
- Concentration in vehicle: 5 mg OCT/ml (for i.v. dosing); 50 mg OCT/ml (for 50 mg/kg dose group, gavage application); 200 mg OCT/ml (for 200 mg/kg dose group, gavage application);

Duration and frequency of treatment / exposure:
single gavage application & single injection intravenous
Doses / concentrations
Doses / Concentrations:
single gavage application: 50 mg/kg resp. 200 mg/kg bw
single injection intravenous: 5 mg/kg bw
control groups received the vehicle only (p.o.)
No. of animals per sex per dose / concentration:
Group I : 6 males : 5 mg/kg i.v.
Group Ic : 2 males vehicle p.o.
Group II : 6 males : 50 mg/kg p.o.
Group IIc: 2 males vehicle p.o.
Group III : 6 males : 200 mg/kg p.o.
Group IIIc: 2 males vehicle p.o.
Control animals:
yes, concurrent vehicle
Positive control reference chemical:
Details on study design:
Various xenobiotics have recently been reported to show estrogenic activity, since in several in vitro- and in vivo-test systems they mimic effects of estradiol. Those substances are suspected to cause health effects, especially negative effects an reproduction and tumor incidences, in
both humans and wildlife through disruption of the endocrine system. One group of chemicals showing estrogenic activity both in vivo and in vitro are p-alkylated phenols (AP). Although the estrogenic activity of those APs is extremely low (about 4-5 magnitudes lower than the physiological estrogen estradiol-17ß), no data regarding possible bioaccumulation of APs in mammals exist. Bioaccumulation studies in aquatic animals revealed bioconcentration factors (defined as ratio of the concentration in the organism to concentration in the water) up to 300. Therefore, although the estrogenic potency of APs is very low, it is discussed that due to bioaccumulation of APs estrogenic efficient blood levels could be reached.

Because of that Wistar rats were chosen for the investigation.
Details on dosing and sampling:
Measurement: Concentration in blood samples
For blood sampling time see table 2 of annexed document
Blood was taken under light ether anaesthesia from the orbitus sinus.
Within every group subgroups of 3 rats each were formed. Within every subgroup blood samples were taken at 7 different time points after application.

Calculation of U (area of variation; defined as interval containing the results with a probability of P=95%
tP=student factor (p=0,05)
Cmean=average concentration
s=standard deviation

Toxicokinetic parameters:
statistical evaluation: average and standard deviation curve fitting determination of the Area under the blood Concentration Time curve (AUC) by integrating the respective curve (see eq. 1 calculation instruction of annexed document) using the PC Software Microcal Origin Vers. 3.5 (Microcal Software Inc.)

Results and discussion

Main ADME resultsopen allclose all
other: bioavailability
2% of 50 mg/kg (gavage)
other: bioavailability
10% of 200 mg/kg (gavage)

Toxicokinetic / pharmacokinetic studies

Details on absorption:
100 µl of blood of untreated animals was spiked with three different amounts of OTC in duplicate (50ng, 500 ng and 2 µg).
Recovery rates were estimated to taget concentration:
a) 50 ng/100 ml blood => measured concentration: appr. 25 ng/100 µl
=> recovery rate appr. 50%
b) 500 ng/100 ml blood => measured concentration: appr. 56 ng/100 µl
=> recovery rate appr. 56%
c) 2000 ng/100 ml blood => measured concentration: appr. 75 ng/100 µl
=> recovery rate appr. 75%

overall recovery rate = 60,5 % ,
standard deviation = 11,65 %

However, the results indicate, that the recovery of OCT increases with increasing OTC concentrations in the samples.
Toxicokinetic parametersopen allclose all
Test no.:
Toxicokinetic parameters:
AUC: 0.433 µg*h/ml (group I: 5 mg/kg i.v.)
Test no.:
Toxicokinetic parameters:
AUC: 0.086 µg*h/ml (group II: 50 mg/kg oral gavage)
Test no.:
Toxicokinetic parameters:
AUC: 1.778 µg*h/ml (group III: 200 mg/kg oral gavage)
Test no.:
Toxicokinetic parameters:
Cmax: 40 ng/ml (max blood level) within 20 min after single gavage of 50 mg/kg; 3-7 ng/ml after 4- 6h
Test no.:
Toxicokinetic parameters:
Cmax: highly variable max blood level within up to 480 min after single gavage of 200 mg/kg; OCT not detectible after 32 or 48 h
Test no.:
Toxicokinetic parameters:
half-life 1st: 310 min (elimination half-life by fitted to 3 compartment model)

Metabolite characterisation studies

Metabolites identified:
not measured

Any other information on results incl. tables

For further results see results in annexed document.

From area under the blood concentration-time curve the bioavailability can be calculated using the following equation:

F=(AUCoral x dose i.v.)/(dose oral x AUC i.v.)

Oral bioavailability:

F(50 mg/kg bw oral gavage) = 0,02 = 2%

F(200 mg/kg bw oral gavage) = 0,10 = 10%

=> low bioavailability

One reason might be that OCT is only incompletely resorbed from the gastrointestinal tract after oral application, due to the low solubility of OCT in aqueous media. However, the increasing bioavailability at the high dose is difficult to explain by this assumption. Another reason might be a marked liver first pass effect, i.e. extensive metabolism of OCT in the liver during the first passage through the liver. If this assumption is valid, the increased bioavailability at the high dose may be explained by saturation of elimination processes in the liver, resulting in higher OCT blood concentrations. Both explanations have to be further investigated.

The blood concentration-time curve can be mathematically described using a three-compartment model (see figure 1 in annexed document)

The best fit was achieved using the parameters:

A: 2218.91 alpha: 0.35782

B: 419.10 beta: 0.0335

C: 12.80 gamma: 0.00223


In the model used, the body is assumed to consist of 3 different compartments. These compartments are a central compartment, normally the blood, a shallow peripheral compartment (e.g. richly perfused tissues) and deep peripheral compartment (i.e. slowly perfused tissues. especially fat tissue).

The substance enters the central compartment via resorption from the gastrointestinal tract or via intravenous injection and is rapidly distributed throughout the richly perfused organs, the shallow peripheral compartment. In this phase the blood level rapidly decreases until in a second phase this decrease slows down. The second phase can be described by slow distribution of the substance into the deep peripheral compartment. The third part of the blood concentration-time curve is determined mostly by elimination processes from the body.

Applicant's summary and conclusion

Interpretation of results (migrated information): low bioaccumulation potential based on study results
The bioaccumulation potential of OCT after injection of 5 mg/kg bw seems to be negligible. After oral application of high doses, saturating the detoxification pathways, a bioaccumulation potential of OCT cannot be excluded.
Executive summary:

In a toxicokinetic study p-(1,1,3,3 -tetramethylbutyl)-phenol (98 %) was administered to 3 groups of 6 male Wistar rats either receiving a single gavage application of 50 mg or 200 mg OCT/kg bw or a single intravenous injection of 5 mg/kg bw. Blood concentration profiles were used to assess the potential of OCT to bioaccumulate.

The elimination rate was found to be 0.00223, resulting in a half life for elimination of t1/2 = 310 min. After approximately 24 hours more than 95 % of the substance already has been eliminated. However, after application of higher doses (200 mg/kg oral gavage) OCT was detectable in blood samples of single animals 24 - 48 hours after dosing. Whether these data show a bioaccumulation potential which is relevant for doses expected for human exposure is questionable. The high dose probably resulted in saturation of elimination processes. In addition, the blood levels detected 24 - 48 hours after dosing were found to be very low, i.e. in the range of the detection limit of 1 - 5 ng/ml blood. These data indicate that the bioaccumulation potential of OCT in the blood after intravenous injection of 5 mg/kg bw seems to be negligible, whereas after oral application of high doses, saturating the detoxification pathways, a bioaccumulation potential of OCT cannot be excluded.

This toxicokinetics study in rats is classified acceptable and satisfies essential requirements for a toxicokinetics study (OECD 417) in rats. The study does not cover the total endpoint information, but is only the first part of a series of four supplementary studies.