3,4-dihydroxybenzonitrile

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics, other

Type of information:

other: Review

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Review of toxicokinetics based on available information (Reliability 2)

Justification for type of information:

All available information on the test substance was used to assess the potential toxicokinetics, based on the REACH Guidance on Toxicokinetics (Reach Guidance 7c).

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2017

Report date:

2018

Materials and methods

Objective of study:

toxicokinetics

Test guideline

Qualifier:

according to guideline

Guideline:

other: R.7.12 Guidance on Toxicokinetics

Test material

Test material information

Constituent 1

Reference substance name:

3,4-dihydroxybenzonitrile

EC Number:

241-367-9

EC Name:

3,4-dihydroxybenzonitrile

Cas Number:

17345-61-8

Molecular formula:

C7H5NO2

IUPAC Name:

3,4-dihydroxybenzonitrile

Test material form:

solid: particulate/powder

Remarks:

white to brownish

Details on test material:

Batch 151222

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on distribution in tissues:

After exposure, a substance can enter the body via the lungs, the gastrointestinal tract, and the skin. Since different parameters are relevant depending on the route of exposure, the three routes will be addressed individually.
After oral administration, in general, a compound needs to be dissolved before it can be taken up from the gastrointestinal tract. CH02906 has a moderate water solubility of 14.1 g/L at 20°C. This implies that the substance will readily dissolve into the gastrointestinal fluids and uptake via passive diffusion (passage of small water-soluble molecules through aqueous pores or carriage across membranes with the bulk passage of water) will take place. The moderate molecular weight (approx. 135 g/mol) will not hamper this process. CH02906 has a moderate partition coefficient (log Pow = 1.3 at pH 5), therefore this substance will dissolve to some extent in lipids and has the ability to cross epithelia by passive diffusion.
The dissociation constants of the acidic groups in the molecular structure of CH02906 were calculated to be 7.87 and 10.99. Therefore it is expected that the substance is present as a free acid (non-ionized) under physiological circumstances in the stomach and most parts of the intestinal tract, as the pH is below 7.5 in the majority of the gastro-intestinal tract. Since it is generally thought that ionized substances do not readily diffuse across biological membranes, the state of the substance in the gastro-intestinal tract is not expected to hamper uptake.
Considering all this data, there are no indications that oral absorption of CH02906 is largely hampered: its water solubility, its moderate molecular size, and its ability to dissolve in lipids will favour systemic uptake. Therefore, for risk assessment purposes oral absorption of CH02906 is set at 100%. The oral toxicity data do not provide reason to deviate from the proposed oral absorption factor.
Once absorbed, distribution of the test substance throughout the body is expected based on its water solubility and moderate molecular weight. Absorbed CH02906 is expected to be excreted mainly via urine3. Based on its moderate partition coefficient, CH02906 is not expected to significantly accumulate in adipose tissue, which is further indicated by its water solubility and moderate molecular size. Therefore bioaccumulation is expected to be low.
CH02906 has a very low vapour pressure (5.9 * 10^-7 Pa at 25ºC), which indicates that exposure to the substance as a vapour is unlikely. CH02906 is a white to brownish powder with an average particle size of 95 µm. The deposition pattern in the lung can be determined based on its distribution, although shape and electrostatic properties can influence this as well. Since particles with aerodynamic diameters below 100 μm have the potential to be inspired, at least half of the test substance is available for inhalation based on their size. In addition, particles with aerodynamic diameters below 50 μm may reach the thoracic region and those below 15 μm the alveolar region of the respiratory tract. It is noted that the substance has a high density, which is expected to limit the exposure of particles via air. Overall it is expected that the exposure via inhalation will be very limited. However, if the substance reaches the lung regions, CH02906 is likely to dissolve in the mucus lining the respiratory tract and to get absorbed. Since CH02906 is able to both dissolve in water and in lipids (based on the log Kow), uptake through respiratory epithelium will take place. Therefore it is concluded that for risk assessment purposes the inhalation absorption of CH02906 should be set at 100%.

As CH02906 is a powder, uptake through the skin is unlikely to occur unless it is dissolved in a body fluid (sweat) or under influence of humidity. The water solubility of CH02906 is moderate, which is indicative for partition from the stratum corneum into the epidermis. Its ability to dissolve in lipids will favour crossing of epidermal barriers. Its moderate molecular size is not expected to hamper uptake through dermal epithelium. According to the guidance on dermal absorption2, a default value of 100% skin absorption is generally used unless molecular mass is above 500 and log Pow is outside the range [-1, 4]. Since the substance has a molecular weight of approx. 135 g/mol and a log Pow of 1.3, it does not meet either criteria and the dermal absorption of CH02906 for risk assessment purposes is set at 100%. The dermal toxicity data do not provide reason to deviate from the proposed dermal absorption factor.

Applicant's summary and conclusion

Conclusions:

A toxicokinetic assessment was performed based on the available data of the substance. Based on the physical/chemical properties of the substance, absorption factors for this substance are derived to be 100% (oral), 100% (inhalation) and 100% (dermal) for risk assessment purposes. The bioaccumulation potential is expected to be low.