of multi-trial 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 wastewater-borne pathogens (such as rotavirus, Campylobacter, Cryptosporidium) are estimated by quantitative microbial risk analysis (QMRA) using the scenario of regular consumption of wastewater-irrigated lettuce, which was first described by Shuval, Lampert and Fattal (1987).
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 wastewater-irrigated 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 [PI(A)(d)] is:
ie, it is considered acceptable if one person per 1000 in a community is infected in any 12-month 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 70-year lifetime infection risk from drinking fully treated drinking water of about 1 in 15.