Pent-1-ene

Endpoint summary

Description of key information

Based on available data, the target substance is expected to be bioavailable via the oral and the inhalation routes and less bioavailable via the dermal route. Moreover, exposure by dermal route is limited considering the high volatility of the substance.The source substances as all gases, therefore they are expected to be bioavailable mainly via the inhalation route.Target and source substances may cross cellular barriers or may be distributed into tissues as fatty tissues. They are expected to be rapidly and mainly excreted in urine.This is corroborated by the prediction in Class I of Cramer's decision tree, this means that the substances have simple chemical structures and for which efficient modes metabolism exist, suggesting a low order of oral toxicity. Moreover, using iSafeRat v1.0, the mechanism of action (MechoA) predicted for all of the substances is non-polar narcosis for all species including humans (MechoA 1.1).

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

Absorption

The physical chemical characteristics described above suggest that pent-1-ene is of adequate molecular size to participate in endogenous absorption mechanisms by passive diffusion within the mammalian gastrointestinal tract. Several effects were observed in an acute oral gavage toxicity study. Macroscopic-anatomically the internal organs revealed no abnormalities.

However, exposure by oral route is not expected for pent-1-ene based in the described uses for consumers (fuels) and source substances are gaseous substances.

 

Regarding the dermal absorption, the target substance being a liquid with a low molecular weight (< 100 g/mol), moderately lipophilic and water soluble, theses properties are favourable to dermal uptake. However, the rate of penetation of pent-1-ene into the stratum corneum is expected to be very limited based on quick evaporation of the substance following dermal exposure. Moreover, enhanced skin penetration is not expected since pent-1-ene is not a skin irritant or corrosive. Regarding the source substances, dermal absorption is not anticipated as they are gaseous substances.

 

Both the moderate partition coefficient and water solubility of pent-1-ene and source substances are favourable for absorption by inhalation.

However, if absorption occured, no effects was observed following « whole body » inhalation exposure in :

- an acute toxicity study performed on rats with but-2-ene,

- a combined repeated dose toxicity with reproductive/developmental screening test performed on rats with but-1-ene,

- a 14-week repeated dose toxicity study performed on rats and mice with isobutene

All of these substances are analogue substances considered as worst-cases based on higher vapour pressure by comparison with those of pen-1-ene.

Moreover, considering that pent-1-ene is neither skin nor eye irritant, no respiratory irritation is anticipated that could increase inhalation absorption.

 

Distribution

Based on the chemical properties of pent-1-ene and the source substances, it is assumed that there is a distribution of the substances throughout the body via the blood stream. As the substances are hydrophilic , they are likely to distribute into all tissues without bioaccumulation.

In a toxicokinetics study, rats were exposed to 300 ppm of individual 1-alkenes for 12h/d for 3 consecutive days (Eideet al.1995). Concentrations of the substances in blood and tissues were measured. Immediately after exposure, but-1-ene and pent-1-ene were found mainly in fat tissues but the concentrations decreased significantly after 12h elimination (TCEQ, 2015).

 

Metabolism

As for isobutene, it is likely that Pent-1-ene and but-1-ene et but-2-ene are metabolized by the liver in reactive epoxides that possess alkylating capacity towards nucleophilic sites in proteins and DNA. However, epoxides may be rapidly metabolised by epoxide hydrolase (EH) and then, or directly, conjugated to glutathion via glutathione-S-transferase (GST) allowing detoxication.

 

Excretion

Pent-1-ene and the analogue substances having a molecular weight lower than 300 g/mol, they are expected to be mainly excreted in urine following conjugation with glutathion. Following oral ingestion, the low amount of substance that may not be absorbed from the gastro-intestinal tract will be excreted in the faeces.

 

Following dermal exposure, the amount of substance which has been absorbed will be excreted mostly in urine, faeces and gall bladder.

 

As for the oral and dermal route, following an inhalation exposure, the source and target substances are expected to be mostly absorbed and excreted via the urine.

 

 

REFERENCE :

Texas Commission on Environmental Quality (TCEQ). 2015. Development support document Pentene, CAS registry numbers: 1-pentene : 109-67-1, cis-2-pentene : 627-20-3, trans-2-pentene : 646-04-8, Revised September 14, 2015. Toxicology Division, Office of the Executive Director