A risk-based approach for developing standards for irrigation with reclaimed water.

Area of Science:

• Environmental Science
• Public Health
• Risk Assessment

Background:

• Reclaimed water use in irrigation presents potential human health risks from microbial and chemical contaminants.
• Establishing safe reclaimed water quality standards requires robust risk assessment methodologies.

Purpose of the Study:

• To develop a generalized quantitative risk assessment (QRA) model for evaluating human health risks associated with reclaimed water irrigation.
• To determine acceptable concentration levels of hazards in reclaimed water effluent to inform treatment requirements and quality standards.

Main Methods:

• A backward calculation approach was used, starting from acceptable risk levels (10⁻⁴ annual infection risk for pathogens, reference doses for chemicals).
• Fuzzy set theory (possibilistic approach) was applied to handle uncertainties in numerous input parameters.
• Two scenarios (amenity irrigation, food crop irrigation) and six example hazards (norovirus, Cryptosporidium, cadmium, lead, PCB118, naphthalene) were analyzed using UK-specific data.

Main Results:

• Amenity irrigation risks were generally low, but UV disinfection may be needed for norovirus and Cryptosporidium.
• Stricter standards are needed for hazards with strong soil binding or higher toxicity/infectivity.
• For food crop irrigation, pathogen ingestion via crop surface contamination was dominant; organic compounds and heavy metals via plant uptake posed risks.

Conclusions:

• The QRA provides a framework for setting reclaimed water quality standards, highlighting the need for scenario-specific risk management.
• Uncertainty in QRA predictions necessitates careful consideration in standard setting and suggests areas for future data collection to reduce uncertainty.