Formaldehyde

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

publication

Title:

The determination of exogenous formaldehyde in blood of rats during and after inhalation exposure

Author:

Kleinnijenhuis A.J., Staal Y.C.M., Duistermaat E., Engel R., Woutersen R.A.

Year:

2013

Bibliographic source:

Food and Chemical Toxicology 52 (2013) 105–112

Materials and methods

Objective of study:

absorption

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD Guideline 403 (2009)

Principles of method if other than guideline:

Blood concentrations of FA during and after single 6-h exposure by inhalation were determined. In order to differentiate between exogenous and endogenous FA the rats were exposed to stable isotope (13C) labeled FA by inhalation. During and after exposure of the rats to 13C–FA their blood was analyzed to determine the ratio between labeled and natural FA in blood and the total blood concentration of FA.

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Formaldehyde

EC Number:

200-001-8

EC Name:

Formaldehyde

Cas Number:

50-00-0

Molecular formula:

CH2O

IUPAC Name:

formaldehyde

Details on test material:

- Name of test material (as cited in study report): formaldehyde

Specific details on test material used for the study:

- Name of test material (as cited in study report): formaldehyde–13C solution
- Composition of test material, percentage of components: 19.3% in aqueous solution (99.4 atom% 13C)

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories
- Age at study initiation: about twelve weeks old
- Diet: The animals received a cereal-based (closed formula) rodent diet (Rat & Mouse No. 3 Breeding Diet, RM3; pelleted) from a commercial supplier (SDS Special Diets Services, Witham, England), ad libitum
- Water: ad libitum

Administration / exposure

Route of administration:

inhalation: vapour

Vehicle:

other: pressurized air

Details on exposure:

TYPE OF INHALATION EXPOSURE: nose only
GENERATION OF TEST ATMOSPHERE / CHAMPER DESCRIPTION
To generate the test atmosphere, a volume of test substance diluted in water (0.1276% m/m), controlled by a motordriven syringe pump (WPI Type SP220i, World Precision Instruments, Sarasota FL, USA), was allowed to evaporate in a heated glass evaporator and mixed with a mass flow controlled (Bronkhorst Hi Tec, Ruurlo, The Netherlands) amount of pressurized air. The resulting test atmosphere was led to the noses of the animals. During the generation of the test atmosphere, the readings of the mass flow controller were recorded at regular intervals (approximately each 30 min). The airflow through the exposure chamber measured with a mass flow controller was 15 L/min. The animals were placed in the exposure unit after stabilization of the test atmosphere. The actual FA air concentration was determined by leading test atmosphere through 2,4-DNPH-cartridges and subsequent HPLC–UV analysis, as is described in more detail below.

The animals were exposed to the test atmosphere in a nose-only inhalation chamber, a modification of the design of the chamber manufactured by ADG Developments Ltd., Codicote, Hitchin, Herts SG4 8UB, United Kingdom. The animals were secured in plastic animal holders (Battelle), connected via ports to the inhalation unit. The total air flow through the unit was monitored about every 30 min and was at least 1 L/min for each rat. The air entering the unit was controlled at a temperature of 20–24°C and a relative humidity between 30 and 70%.

FA quantification in air:
The test set for the validation of the quantification method of FA in air contained 5 2,4-DNPH-cartridges fortified at approximately 6 lg FA with a formaldehyde solution in milliQ water, 5 samples fortified at approximately 18 lg FA and 2 unfortified control samples. Air (ambient temperature and relative humidity, 1 L/min) was led through the 2,4-DNPH-cartridges (Waters XpoSure Aldehyde 2,4-DNPH cartridges, lot number 002830309E) for approximately 10 min.

Duration and frequency of treatment / exposure:

6 hr and 3 min. One animal was found dead during exposure and this animal was replaced with another animal, which was exposed for 5 h.

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

10 ppm

Doses / concentrations 2

Dose / conc.:

9.65 ppm

Remarks:

Analytical concentration

No. of animals per sex per dose / concentration:

10

Details on dosing and sampling:

- The animals were observed for clinical signs just before exposure and five times during exposure (about once per hour, starting about 1 h after initiation of treatment).
- Blood samples were taken from each rat prior to exposure (t = 0), at t = 3 h during exposure, at t = 6 h (end of exposure), at t = 6 h and 10 min and at t = 6 h and 30 min (10 and 30 min after exposure).
- FA was determined in blood using High Performance Liquid Chromatography–Tandem Mass Spectrometry (HPLC–MS/MS). The test set for the validation of the quantification method of analysis of FA in blood contained 6 unfortified control samples (from 6 different rats => variation between rats), 5 samples fortified at 2 mg/L and 5 samples fortified at 6 mg/L (in total two and four times the expected endogenous FA concentration of approximately 2 mg/L). The endogenous FA blood concentration was subtracted from the blood concentration found in fortified samples to calculate the recovery. Additionally, unfortified blood samples from 1 rat were prepared and analyzed in fivefold to determine the repeatability in FA blood concentration analysis (analytical variation). Fortified blood samples were prepared using non-derivatized natural FA, which is chemically identical to 13C–FA. Because we determined the fraction of exogenous formaldehyde in blood using the isotopic distribution, the natural formaldehyde signal, for which the isotopic distribution is known, acts as an internal standard for the exogenous formaldehyde signal.

Results and discussion

Metabolite characterisation studies

Metabolites identified:

not measured

Details on metabolites:

- The observed Relative Standard Deviations (RSDs) in FA concentration determined in unfortified blood control samples and the observed RSDs in the recoveries for blood samples fortified at 2 and 6 mg FA/L were lower than 10%. These results demonstrate that FA concentrations can be determined with good repeatability in (un)fortified blood and that fortified FA is recovered from blood under the experimental conditions.
- The FA blood concentrations determined were in the 1.9–5.4 mg/L range.
- The FA concentration in blood did not increase during exposure.
- The applied method would have allowed the detection of exogenous 13C–FA in blood at a concentration approximately 1.5% of the endogenous FA blood concentration. The overall conclusion is that the inhalation of 13C–FA at 9.65 ppm (target concentration 10 ppm) had no effect on the FA concentration in blood. Exogenous 13C–FA was not detected in the blood of rats exposed to 9.65 ppm FA during or after (up to 30 min) inhalation for 6 h and 3 min using the experimental conditions of this study.