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Risks associated with pathogens in composted biosolids - a discussion paper prepared for the Water Authority of Western Australia

Gibbs, R.A. and Ho, G.E. (1995) Risks associated with pathogens in composted biosolids - a discussion paper prepared for the Water Authority of Western Australia. Institute for Environmental Science, Murdoch University, Perth, Western Australia.



Information available from published epidemiological studies, laboratory studies and field studies was surveyed and it was concluded that there was not sufficient evidence to suggest that the composting process completely removed the risk associated with the unrestricted marketing of biosolids to home gardens. A risk assessment was therefore carried out to develop criteria for acceptable concentrations of pathogens in composted biosolids products. A number of principles were developed for the risk assessment. One of the principles was that the most at risk individuals should be protected and it was decided that these would be young children playing in home gardens. Another principle was that microbial risk assessments should be based on risks of disease, rather than risks of death or risks of infection. The principle adopted for deciding acceptable risk was that the risk of disease transmission through the re-use of composted biosolids products should be less than background transmission rates for that disease from other sources.

The above risk assessment approach was used to develop suggested limits for Salmonella in composted biosolids products. The suggested limit is less than 1 Salmonella in 50 g of biosolids product. A recommendation is that guidelines should also require a maturation period for composted biosolids. Further research on the regrowth potential of Salmonella in composted biosolids products is recommended.

Although there is a high potential risk associated with Giardia and enteric viruses in composted biosolids, it is recommended that guidelines should not require the monitoring of composted biosolids products for Giardia or enteric viruses until methods are further developed.

It is also recommended that an epidemiological study of the effect of the unrestricted marketing of composted biosolids on the spread on enteric disease should be carried out.

Publication Type: Report
Series Name: Environmental Science Report No. 95/6
Publisher: Institute for Environmental Science, Murdoch University
Notes: October 1995
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