



Application
of multitrial Monte Carlo simulations to the estimation of RISKS TO HUMAN HEALTH associated with the use of wastewaters for unrestricted crop irrigation Unrestricted
irrigation refers to the irrigation of all crops, including vegetables
and salad crops eaten uncooked.
Risks to human health due to wastewaterborne pathogens (such as rotavirus, Campylobacter, Cryptosporidium) are estimated by quantitative microbial risk analysis (QMRA) using the scenario of regular consumption of wastewaterirrigated lettuce, which was first described by Shuval, Lampert and Fattal (1987). Dose–response equations Two 'dose–response' equations are used (as described in reference #2 above):
The above equations are for the ingestion of a single dose of d pathogens. However, the consumption of wastewaterirrigated lettuce (or any other crop eaten raw) occurs many times per year, and we need to be able to estimate the annual risk of infection resulting from ingesting d pathogens on n occasions per year. The equation for this annual risk of infection [P_{I(A)}(d)] is:
ie, it is considered acceptable if one person per 1000 in a community is infected in any 12month period by a waterborne pathogen. For an individual this level of annual risk means that he or she has a chance of becoming infected once every 1000 years – or, as we live much less than this, we have a 70year lifetime infection risk from drinking fully treated drinking water of about 1 in 15. : Email either Professor Duncan Mara or, for questions about the Monte Carlo programs, Dr Andrew Sleigh. 

