Hydrocarbons, C6-C7, n-alkanes, isoalkanes, cyclics, <5% n-hexane

Endpoint summary

Description of key information

Inhalation
NOAEC (systemic): 8117 mg/m³

Additional information

Inhalation

Male rats were exposed to 305, 915 or 3050 ppm Cypar 7 (hydrocarbons, C6-C7, n-alkanes, isoalkanes, cyclics, <5% n-hexane) for 8 hours/day for 3 consecutive days and checked for health, viability and clinical signs (Lammers, 2001). One animal from the 305 ppm dose group kept its head bent with the left side directed towards the ground. At the high dose level, slightly decreased body weights were observed after the 3-day exposure period. In addition, body temperature was decreased in the high dosed animals after both the first and the third exposure. Under the test conditions, short-term high-level exposure to hydrocarbons, C6-C7, n-alkanes, isoalkanes, cyclics, <5% n-hexane did not induce effects related to general toxicity. The NOAEC was determined to be > 14000 mg/m3 corresponding to 3050 ppm.

Since only basic data were given in this study and the study was limited to 3 days, additional experimental data were used to evaluate repeated dose toxicity via inhalation.

There are reliable data available for the structurally related substance light alkylate naphtha distillate. Thus, read-across was conducted based on a structural analogue.

A 13-week inhalation toxicity study was conducted using wholly vaporized light alkylate naphtha distillate (LAND-2) generated in nitrogen (Schreiner et al., 1998). Male and female rats were exposed by inhalation in whole-body exposure cages 6 hours/day, 5 days/week for 13 weeks at analytical concentrations of 0, 668, 2220, and 6646 ppm. All animals survived the treatment period and were sacrificed according to study design at the end of week 13 or 18 (recovery group). No test-related observations were noted in the exposure chambers during any exposure period for any treatment groups or during non-exposure periods. From weekly clinical observations, the only apparent treatment-related finding was an increased incidence of red facial staining in both male and female rats in the high dose group. At week 13, there were statistically significant dose-related increases in absolute and relative kidney weights in males of all 3 treatment groups. The kidney weights of high-dose males remained elevated after the recovery period. These increases correlated with microscopic observations of hyaline droplet formation in the proximal convoluted tubules considered to contain an alpha2-microglobulin-hydrocarbon complex as well as an increase in incidence and severity of nephropathy and dilated tubules at the corticomedullary junction. These microscopic finding are characteristic of ‘light hydrocarbon nephropathy” also known as hyaline droplet nephropathy and are male rat specific. Therefore these effects are not considered to be relevant to humans. Statistically significant increases in absolute and relative liver weights were observed in high-dose male and female rats after week 13. Differences were not present after the recovery period and had no microscopic correlate. Thus, the NOAEC for systemic toxicity was 8117 mg/m³ corresponding to 2200 ppm.

Comparing both studies, the inhalation study of Schreiner et al. (1998) with light alkylate naphtha distillate revealed the more sensitive endpoint and was conducted for a longer and so more reliable exposure period. Therefore, the NOAEC of 8117 mg/m³ was taken forward to evaluate the risk potential of hydrocarbons, C6-C7, n-alkanes, isoalkanes, cyclics, <5% n-hexane.

Justification for classification or non-classification

The available data on the repeated dose toxicity of hydrocarbons, C6-C7, n-alkanes, isoalkanes, cyclics, <5% n-hexane and structurally related substances are conclusive but not sufficient for classification.