Slack wax (petroleum), clay-treated

Carcinogenicity

Description of key information

Slack waxes (non-carcinogenic feed-stock) are not carcinogenic.  Slack waxes (carcinogenic or unknown feed-stock) have a weak carcinogenic potential that is likely based on the aromatic content of the wax and not the paraffin.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

5 700 mg/kg bw/day

Study duration:

chronic

Species:

rat

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Study duration:

chronic

Species:

mouse

Justification for classification or non-classification

Under the EU CLP Regulation (EC No. 1272/2008), slack waxes (carcinogenic or unknown feed-stock) are classified as Carcinogenic Category 1B, H350, unless base oil from which it is derived is not carcinogenic. This classification is based on a study with eight crude slack waxes concluded that the slack waxes were weakly carcinogenic. The carcinogenic potential of slack waxes is associated with the aromatic fractions of the corresponding feedstocks. Slack waxes (non-carcinogenic feed-stock) were not found to be carcinogenic and are, therefore, not classified.

Additional information

Slack waxes are waxes with entrained oils. Since paraffin and hydrocarbon waxes are non-hazardous the category hazard profile is determined by the entrained oils. Since the entrained oils are a minor portion of the slack waxes, this is considered to be a worst-case approach.

The carcinogenic potential of slack waxes is expected to be associated with biologically active impurities such as polycyclic aromatic compounds found in the entrained oil of the wax material. Slack waxes (non-carcinogenic feed-stock), produced from feedstock's which contain significantly reduced amount of polycyclic aromatic compounds and other impurities, are not carcinogenic. In contrast, the carcinogenic potential of slack waxes (carcinogenic or unknown feed-stock) may vary depending on the degree of refining severity of feedstock's and the resulting polycyclic aromatic compound content in waxes.

Slack Waxes (Carcinogenic or Unknown Feed-stock)

One key study (Smith et al. 1951) was identified to evaluate the carcinogenic potential of slack waxes (carcinogenic or unknown feed-stock)

Eight crude slack waxes containing 12-29% aromatic mineral oil were tested in a lifetime mouse skin painting study (Smith et al., 1951; Klimisch score = 2). Approximately 15 milligrams of molten slack waxes were applied 3 days per week to the backs of groups of 30 male albino mice. At 250 days, benign tumours were observed in mice treated with 6 of the 8 waxes and of these malignant tumours had developed in 2 groups. At 450 days, benign tumours had developed in all groups, and malignant tumours had developed in 5 of the 8 wax-treated groups. It was concluded that the slack waxes (carcinogenic or unknown feed-stock) were weakly carcinogenic.

Supporting data from dermal carcinogenicity studies conducted in mice (Dietz et al. 1952) and human epidemiological evidence (Hendricks et al. 1959 and Lione et al. 1959) indicate that slack waxes (carcinogenic or unknown feed-stock) have low or marginal carcinogenic potential, which is likely based on the aromatic fraction in the wax.

Slack Waxes (Non-carcinogenic Feed-stock)

One key study (Shubik et al., 1962) was identified to evaluate the oral carcinogenic potential of slack waxes (Non-carcinogenic feed-stock).

A key oral read-across carcinogenicity study (Shubik et al., 1962) was conducted on five paraffin waxes (3 of the waxes were microcrystalline and the other two were unidentified). The paraffin waxes were selected on the basis of aromatic content and represented the range of material available in commerce at the time of the study (~ 1960).  Each of the paraffin waxes was ground into powder and added to the feed in a 1:9 w/w proportion.  Each of the five waxes was fed ad libitum to male and female Sprague-Dawley rats (50 -55/sex) at a dietary concentration of 10% for 2 years.  An additional group of 140 male and 157 female rats were fed a control diet.

The rats were inspected and weighed every second week, and all gross lesions were recorded.  This was continued until all the rats died or were sacrificed moribund, then the animals were submitted to a complete autopsy followed by histological examination of all abnormal tissues. 

Survival rates and growth rates were unaffected by oral exposure to any of the waxes tested.  A number of tumours were found in all groups at necropsy.  The most common tumours were those of the mammary regions (fibrocarcinomas, adenocarcinomas, fibromas, and sarcomas), of the adrenal glands (cortical adenomas with a few carcinomas and pheochromocytomas) and of the pituitary.  The number of tumour-bearing animals and the incidence of tumours of each type were similar across groups.  No other toxic effects were found at histological examination. The authors concluded that the five paraffin waxes were devoid of carcinogenic or other toxic action when fed at a level of 10% in the diet (Shubik et al., 1962). Based on the body weights, this equates to a daily dose of approximately 5700 mg/kg/day.

One key study (Kane et al. 1984) was identified to evaluate the dermal carcinogenic potential of slack waxes (Non-carcinogenic feed-stock).

Carcinogenicity of refined slack wax (CAS# 64742-61-6) was evaluated by Kane et al. (1984; Klimisch score = 2) as part of a series of mouse skin painting bioassays with 46 clearly defined samples of refinery streams associated with lubricant base oil processing. Male C3H mice (more recently C3H/HeJ) 6 to 8 weeks old were allowed to acclimate and were housed individually or in small groups. The animals were shaved biweekly, and the undiluted test material was applied to the shaven interscapular regions. The undiluted test material was painted on the skin of 50 male C3H mice at 25 mg twice weekly for 80 weeks or until a papilloma formed. Positive control groups were treated with solutions of benzo(a)pyrene, and negative control groups included an inactive oil-treated group and a no-treatment group. No tumours developed in any of the mice to which the highly refined slack wax was applied. The study was repeated in 25 animals using the same application dose of 25 mg/application, twice weekly for 80 weeks, and, again, none of the animals developed tumours.

In a supporting read-across lifetime skin painting carcinogenicity study of paraffin waxes in mice and rabbits (Shubik et al., 1962), five paraffin waxes were selected from 36 samples on the basis of their ultraviolet absorptivity, representing the range of aromatic contents.The five waxes tested did not demonstrate any carcinogenic potential via dermal exposure in either sex of mice.

Justification for selection of carcinogenicity via oral route endpoint:

Only oral carcinogenicity study available.

Justification for selection of carcinogenicity via dermal route endpoint:

One of 4 available dermal carcinogenicity studies

Carcinogenicity: via dermal route (target organ): other: skin