Journal of Water and Health Vol 5 No 1 pp 39–50 © IWA Publishing 2007 doi:10.2166/wh.2006.055
Health risks in wastewater irrigation: Comparing estimates from quantitative microbial risk analyses and epidemiological studies
D. D. Mara, P. A. Sleigh, U. J. Blumenthal and R. M. Carr
School of Civil Engineering, University of Leeds, Leeds, LS2 9JT, UK Tel.: +44 113 343 2276 Fax: +44 113 343 2243 d.d.mara@leeds.ac.uk; p.a.sleigh@leeds.ac.uk
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel St London, WC1E 7HT, UK Tel.: +44 20 7927 2087 Fax: +44 20 7636 7843 ursula.blumenthal@lshtm.ac.uk
Water, Sanitation and Health, World Health Organization, Avenue Appia 20, 1211 Geneva 27Switzerland Tel.: +41 22 791 3518 Fax: +41 22 791 4159 carrr@who.int
ABSTRACT
The combination of standard quantitative microbial risk analysis (QMRA) techniques and 10,000-trial Monte Carlo risk simulations was used to estimate the human health risks associated with the use of wastewater for unrestricted and restricted crop irrigation. A risk of rotavirus infection of 10-2 per person per year (pppy) was used as the reference level of acceptable risk. Using the model scenario of involuntary soil ingestion for restricted irrigation, the risk of rotavirus infection is ~10-2 pppy when the wastewater contains  106 Escherichia coli per 100 ml and when local agricultural practices are highly mechanised. For labour-intensive agriculture the risk of rotavirus infection is ~10-2 pppy when the wastewater contains 105 E. coli per 100 ml; however, the wastewater quality should be 104 E. coli per 100 ml when children under 15 are exposed. With the model scenario of lettuce consumption for unrestricted irrigation, the use of wastewaters containing 104E. coli per 100 ml results in a rotavirus infection risk of ~10-2 pppy; however, again based on epidemiological evidence from Mexico, the current WHO guideline level of 1,000 E. coli per 100 ml should be retained for root crops eaten raw.
Keywords: epidemiology; health; irrigation; risk analysis; rotavirus; wastewater
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