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Questions and answers

Why is gamma irradiation used?

The Department of Agriculture (the department) applies a range of biosecurity treatments to products of animal origin. The treatments available include heat treatment and gamma irradiation.

Gamma irradiation is a risk management measure that may be offered for certain products of animal origin that do not fully meet Australia’s import requirements, or where the importer is unable to provide the department with sufficient information to complete a risk assessment.

What is the objective of this review?

The main objective of the review is to identify and recommend appropriate doses of irradiation needed to inactivate bacterial, fungal and viral pathogens, and parasites of animal biosecurity concern.

This review will enable the department to take a more flexible approach to the irradiation dose used, and may allow the use of lower levels of irradiation that still protect Australia’s favourable animal health status in cases where the specific pathogens of concern are identified.

How was this review conducted?

The review analysed scientific literature, current scientific evidence, standards and recommendations of international bodies such as the Food and Agriculture Organization of the United Nations (FAO), the International Atomic Energy Agency (IAEA) and the World Health Organization (WHO), and other balanced sources of information and opinion about the radiosensitivity of pathogens.
What are the findings of the review?

The review found that while 50 kGy should remain the current standard, it may be possible to use lower levels of irradiation and still protect Australia’s favourable animal health status in cases where the pathogens of concern are known. However, there may be instances where the department may recommend a higher dose for some high risk products (e.g. infected tissue for research purposes). Gamma irradiation was not found to be a practical treatment to address biosecurity issues with transmissible spongiform encephalopathy (TSE) agents such as bovine spongiform encephalopathy and scrapie.

​What are the effects of irradiation?

Effect on microorganisms

Gamma irradiation causes damage to the microorganism. The potential for lethal damage is influenced by a range of environmental conditions such as oxygen, temperature, and water content.

Effect on product and product safety

It is now well established that irradiation does affect certain vitamins and other nutrients and does produce peroxides and other radiolytic by-products, some of which may be toxic and/or carcinogenic, and that these effects are dose related.

However, the same is true for thermal processing and possibly other food production technologies.

All food, imported or domestically produced, intended for human consumption, must comply with the Australia New Zealand Food Standards Code (the Code). Irradiation is not an option as a biosecurity measure for food imported for human consumption unless supported by the Code.

Can irradiation be used as a biosecuritytreatment for pet food?

Irradiation of pet food for cats presents a unique case and because of detrimental nutritional changes in cat food, irradiation has not been used for this commodity since 2009. To address the risk associated with cats being fed irradiated dog food, the department requires, as a condition on the import permit, that imported irradiated dog food be appropriately labelled as not fit for consumption by cats.

The available scientific evidence supports the use of irradiation as a biosecurity treatment for pet food only in exceptional circumstances. It is not supported for those products likely to be consumed as a significant proportion of an animal’s diet (e.g. kibble).

How is the inactivation of organisms measured?

The D10 value, sometimes referred to as the D value, is a measure of the treatment required to inactivate 90 per cent (i.e. a one log reduction) of the organisms present or to reduce the microbial population to one-tenth its number. For irradiation, the value is measured as the irradiation dose required is to achieve a one log reduction in the titre (i.e. population) of the organism.

What does sterility assurance level mean?

Sterility assurance level (SAL) is a term used in microbiology to describe the acceptable probability of a single organism being viable after it has been subjected to the sterilisation process. Because absolute sterility cannot be ensured, SAL is used as a predetermined limit to the number of viable organisms that would be tolerated in the product following treatment.

SAL is also used to describe the killing efficacy of a sterilisation process: a very effective sterilisation process has a very high SAL. The department has set the SAL at 10-6 for each pathogen of biosecurity concern unless an alternative SAL is established, through a risk analysis, for the specific pathogen or product.

How is the bio-burden in product estimated?

The department generally assumes that tissues used in the manufacture of biological material such as vaccines would be derived from healthy sources. In most cases, the department assumes the bio-burden to be close to zero.

Was the public consulted about the review?

Yes, the draft review was released on 30 January 2013 for a 60-day public consultation period. A total of three submissions were received.

The department considered these stakeholder submissions when finalising the review.