Are soft wood based pet beddings harmful?

By Arnold Dijkstra

Wood based bedding material is favoured by many pet owners, breeders and pet retailers due to several beneficial properties. It is inexpensive and easy to handle, has excellent absorbing characteristics, prevents odour and will sometimes exert insecticidal and bactericidal properties.

On the other hand these natural materials can also harbour several chemical substances that may cause illness. Possible dangers are discussed.

Types of pet bedding

A wide range of materials are used for pet beddings. Hard woods (aspen, beech), softwoods (pine and cedar), corn-cob, paper (crinkled strips of kraft paper), recycled newspaper, grasses (wheat, hay, hemp) and other organic materials. Materials are selected for their ability to absorb fluids, to control odour, the comfort for the pet and pet owner, easiness to handle and dust formation. Also more high-grade properties like the ability to prevent the growth of micro- organisms and moulds, fleas, mites and other pests are considered. Wood-based bedding is usually produced from the waste of sawmills and lumber trade. A small personal research in pet stores revealed that packages of most of the commercial wood shavings or chips don't mention the type(s) of wood used, but the colour and smell point to pine.

Controversial properties

The use of soft woods like pine and cedar as pet bedding is however controversial. An extensive amount of sources claim that the bacterial - and insect repellent and odour controlling chemicals may also be harmful for the pets living on or in it and even for the pet owner, breeder and pet retailer. It is a fact that cedar and other aromatic soft woods, such as white and yellow pines, releases nice smelling volatile hydrocarbons (phenols). The most important volatile hydrocarbon in cedar is plicatic acid, which may cause respiratory diseases, like asthma, rhinitis or conjunctivitis in humans and in animals, and the damage can be progressive. Cedar shavings have also been incriminated in increased mortality in rat pups, and various scientists over the years have suggested carcinogenicity. Wood from western red cedar (Thuja plicata) has one of the most potent insecticidal compounds, which accounts for its popularity to repel or kill clothes' moths. In pine (family Pinaceae), the most important irritating compound is abietic acid, the principal sensitizer in rosin (colophony). Abietic acid itself causes relatively weak allergic responses. However a number of compounds formed by air oxidation of abietic acid are potent contact allergens. Other hydrocarbons result in changes in the liver, which may impair its ability to detoxify certain drugs, including various anaesthetic agents. Pine products also include pine resin, used in adhesives, paints and varnishes, inks and in sizing for paper, paperboard and fabrics.

Finally wood-based embedding material produces dust and some studies have found an association between exposure to some wood dusts and oral cancers.

Size of the problem

Recently a veterinarian initiated a study on presence of abietic acid in several brands of pine-based embedding material sold in the Netherlands. A laboratory of the Wageningen University and Research Center investigated several brands of pet embedding material for the presence of abietic acid and the volatility of the acid, using gas chromatography (GC-MS). The results (Klaver DVM, personal communication) showed amounts ranging from 0,2 to 2 mg abietic acid per g of litter. Also several other compounds related to abietic acid were detected. No significant amounts of abietic acid released into the air could be detected, but ¨peaks¨ of other volatile carbohydrates were identified. Direct inhalation of abietic acid is therefore not likely, but the inhalation of saw dust and/or the consumption of embedding material expose the pets indirectly. Very little is known on the toxicity of the observed levels, but it is suggested that the LD50 value (lethal doses for 50% of mice under investigation) is 180 mg/kg (= 0,18 mg/g). This would mean that even small amounts of litter eaten or inhaled could cause diseases. Perhaps of greater concern is chronic exposure to low concentrations, which is usually the case for pet living lifetime on or in abietic acid containing embeddings material.

Alternative wood and wood alternatives

There are many alternatives to wood shavings, most of which are just as absorbent and make excellent bedding. If you however wish to use wood shavings as litter, hardwoods such as aspen and beech are alternatives to pine and cedar. Unlike softwoods, hardwoods do not contain any phenols.
Similarly, softwoods that have had their phenols removed via a heating and drying process, such as is the case with kiln-dried pine, are also safe for use.
A nice wood alternative is produced from paper pulp which is made from non- toxic, untreated cellulose fiber. The pieces are small and soft (not pelleted), and in fact feel very much like shavings. This material is dust-free, controls odour beautifully, and makes a nice nest.
Another option is plain, unprinted newsprint (printed paper will release ink). Most newspapers will either give away or sell for a nominal cost the end of their newsprint rolls, which can then be shredded into comfortable, absorbent bedding and used in sheets on the bottom of the cage.
Finally a rather new natural product is prepared from waste product from local cotton production in West Africa. It consists of processed dark brown peelings (like peanut shells) and small rests of cotton fluff (cellulose fibers) that grows on the seed and yet available in Western Europe.

Evaluation

Although quantities figures on the effects of harmful compounds in softwoods are lacking, the extensive amount of publications suggest at least that something is wrong with pine and cedar as embedding material. Some publications suggest that pine is arguably less dangerous than cedar.

Like with food in European Union, the so called precaution principle should be employed. This means that until the contrary is proven, untreated pine and cedar wood should not be used for the production of pet embedding material. There are plenty of good alternatives that are chemically safe, offer the appropriate absorption, help to prevent odour, are usually not dusty and don't harm the environment when discarded.

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