 Commonwealth of Australia 2002

15.3Health hazards

Limonene is a skin irritant in both experimental animals and humans. It has the potential to cause eye irritation and respiratory irritation, but data on these effects are limited. Changing concentrations of limonene in indoor air have been shown to cause changes in the responsiveness of breathing airways. Acute toxicity of limonene is low.

Studies in guinea pigs revealed that autoxidized d-limonene induced contact allergy. As d- and l- are enantiomers, this could be true for l-limonene and dipentene (the mixture). Limonene is classified as a skin sensitiser and it is believed the effect is due to oxidation products rather than limonene itself. Limited data are available on the potential to cause respiratory sensitisation.

Renal tumours are induced by limonene in male rats and these are thought to be sex and species specific and are not considered relevant to humans. Other than the kidneys, the critical organ in animals is the liver, with effects having been observed in mice, rats and dogs. Exposure affects the amount and activity of liver enzymes, liver weight, cholesterol levels and bile flow. However, no toxic effects on the liver have been reported. The liver effects in animals are thought to be due to physiological adaptation. From the data available, it is not possible to identify a NOAEL for these effects.

In general, limonene could be considered to be a chemical with fairly low toxicity, with exception of its irritative and sensitising properties.

15.4Occupational health and safety

Under the ADG Code, dl-limonene (dipentene) has the specific UN number 2052. The d- and l- isomers are not mentioned specifically under this number. As the physico-chemical properties and flammability of these isomers would be similar to those of the racemic mixture, this UN number could also be used for d- and l- limonene.

Additional information used in transport includes the generic Initial Emergency Response Guides (IERG) produced by Standards Australia / Standards NZ. It is considered that UN 2052 would be more suitably linked to generic Guide 15, rather than Guide 14 as at present, based on flammability.

Autoxidation of limonene occurs readily in the presence of light and air forming a variety of oxygenated monocyclic terpenes. The sensitising properties of limonene are acknowledged to be due to its oxidation products. Risk of skin sensitisation is high in situations where oxidation products of limonene are likely to be formed during use of limonene. However, autoxidation of limonene can be controlled by addition of antioxidant, protection against air, light and elevated temperature, and monitoring shelf life. Inclusion of oxidised limonene in patch testing for allergy would be a useful diagnostic tool.

Information on the total number of workers handling limonene during manufacture, importation, repacking, formulation and use in Australia is not available, but it is expected to be large, especially for end use. Occupational exposure during manufacture, importation, transportation and storage of limonene is limited, except in cases of accidental spills or leaks of the chemicals. Therefore the risk of developing any adverse effects is low. During repacking and formulation, operators are likely to be exposed by skin and eye contact during manual operations and cleaning of equipment. There is also a potential for inhalation exposure, especially when working in a confined space and in places with limited ventilation, heated blending process, high speed mechanical stirring and at worksites with an open mixing process and no exhaust ventilation. The potential for worker exposure during use of limonene or limonene products is high based on the widespread end uses, modes of use and lack of control measures at some worksites.

A number of areas of concern have been identified in this assessment. There is a risk of skin, eyes and respiratory irritation from working in confined spaces and in places with limited ventilation e.g. cleaning of storage tanks, and during end use of limonene and/or products containing high concentrations of limonene. Repeated exposure to these conditions would increase the risk of health effects. Hand cleaners are a product category where dermal contact with limonene is deliberate rather than incidental, suggesting that caution in the use of these products is warranted, and that control of oxidation is critical. “Wash-off” hand cleaners are preferable to “wipe-off” products.

Inadvertent exposures to limonene can be controlled by use of an automated or enclosed system, decontamination of equipment where appropriate, use of local exhaust ventilation and PPE. Where limonene mists/aerosols may be generated, potential inhalation exposure can be also controlled by using anti-mist additives in the formulations. Respiratory protection suitable for normal working conditions may not be suitable for confined spaces. The minimum requirement for working in a confined space is set out in the Australian Standard AS 2865 Safe Working in a Confined Space (Standards Australia, 1995).

Based on the information available during this assessment, and the results of the risk characterisation, establishment of an occupational exposure standard is not warranted.