Quantitative Microbial Risk Assessment and Community-Based Risk Perception of Sewage Overflows by Naco Elementary

Abstract

Transboundary sanitary sewage overflows (SSO) have recurrently affected Ambos Nacos, sister border towns, since the late 1970s. Wastewater pollution is a major issue of concern worldwide because of the presence of pathogens and infectious microorganisms in polluted waters. The proximity of the sewage overflows to Naco Elementary School, has raised questions as to the potential health risks to the students. This is a community-inspired research project and a collaborative effort with Cochise Health and Social Services (CHSS) and Naco Elementary School. The purpose of this study was to assess the potential health risks to the students and improve understanding of risk perception and communication preferences among the school community. Following the quantitative microbial risk assessment (QMRA) paradigm, a single school day risk during a SSO event ranging from 5.08E-04 to 1 far exceeding the accepted annual risk of 1E-04. Inputs in the QMRA model included microbial analyses from superficial soil samples, and student behavior data from survey responses from teachers and parents. Qualitative coding found that approximately half of parents are not concerned or are unsure about SSO related concerns, and those who expressed concern pertained to the health and safety of their community and children, and groundwater contamination. Furthermore, 68% of parents and 50% of teachers said they had been aware of SSOs, highlighting the need for improved communication among all stakeholders (county, school, and parents). Results suggest improved communication during the occurrence of SSOs as well as action steps on how to prevent accidental exposure can mitigate a high risk of infection as calculated by the QMRA. Complementing QMRA studies with ethnographic methods to gather site-specific information can improve exposure data and inform future risk communication and management efforts.