RIRA: A tool for conducting health risk assessments for irrigation of edible crops with recycled water

Irrigation of food crops with reclaimed water is becoming increasingly common, owing to a combination of agricultural, environmental, social and economic drivers. Despite the benefits of irrigation with recycled water, the practice does nonetheless pose risks to human health, most notably through contamination of produce with human pathogens. Microbiological risks can be characterised through a modelling process known as Quantitative Microbial Risk Assessment (QMRA). The construction of a QMRA model is an essential component of risk management for any recycled water irrigation scheme. This can, however, be a tedious and technically demanding process. Here we present the decision support tool Recycled water Irrigation Risk Analysis (RIRA), which can be used by water resource and public health managers to conduct QMRAs for recycled water irrigation. RIRA is designed to accommodate a wide range of scenarios. Once the user has defined the pathogen of interest and the exposure scenario, RIRA uses pathogen-specific dose–response models to calculate the annual risk of infection. This is the primary end-point of the model, but given adequate information RIRA can also calculate a disease burden metric, the Disability Adjusted Life-Year (DALY), which accounts for the severity and duration of a disease. The generic and flexible structure of RIRA means that it can be used to conduct risk assessments in accordance with the methods recommended in major recycled water guidelines.