Clostridium perfringens testing improves the reliability of detecting non-point source sewage contamination in Hawaiian coastal waters compared to using Enterococci alone.

Non-point sources of sewage-related pollution in tropical marine waters are difficult to ascertain. Enterococci (ENT) are widely used as indicators of human waste but their efficacy in tropical waters is highly debated due to natural presence in tropical soils. Clostridium perfringens (CP) is often used as a secondary indicator of fecal contamination because its presence indicates sewage, and in tropical waters environmental sources are unlikely. We analyzed a 27-year dataset containing over 29,000 samples collected by the State of Hawaii, to determine a proposed CP standard for detecting human sewage, which has applicability throughout tropical marine waters globally. Measured ENT concentrations were highly correlated with turbidity. In three instances, sewage contamination was not detected by ENT samples alone, and impairments from non-point pollution may be highly misinformed in Hawaii. The EPA should examine relationships between CP and human health and implement CP as the primary FIB in tropical marine waters.