Abstract
Pollution and water quality is a global issue often exacerbated in urban areas if not properly managed. Fecal contamination of waterways is a part of overall water quality, and is of particular concern to human health as exposure to fecal contamination in water comes with risks to various illnesses. Levels of enterococci bacteria are often used as indicators of fecal contamination, and the EPA uses enterococci levels as part of its regional water quality criteria. However, enterococci levels do not determine the host sources of fecal contamination nor where this contamination may be coming from. Microbial source tracking (MST) refers to methods with the purpose of ascertaining the sources of fecal pollution in water. Quantitative polymerase chain reaction (qPCR) is a technique that can be used for microbial source tracking, as it determines presence and quantity of host-specific fecal indicator bacteria from humans, dogs, and other species. This study used enterococci levels and qPCR for source tracking of fecal contamination in the coastal waters, canals and rivers of Miami, Florida, and calculate the potential health risk from this pollution. Source tracking focused on two markers , HF183 human Bacteroides and DogBact canine Bacteroides and potential human health risk was determined using a risk-based threshold (RBT) of 525 copies of HF183 per 100mL based on a quantitative microbial risk assessment study (Boehm and Soller, 2020). Contamination from human and dog sources was found in almost all samples, with consistently high levels of HF183 in Little River and along the coastline and low levels of DogBact everywhere. Only about 18 percent of samples exceeded the RBT for HF183, but the majority were from Little River and the Miami coastline. Most samples were taken during the wet season, so contamination is likely coming from failing septic tank systems and stormwater runoff. This study concluded that prioritizing septic conversion to sewage systems and improving stormwater infrastructure should reduce fecal contamination and continued monitoring of enterococci concentrations using qPCR when possible is critically important to manage the health risk for swimmers and others using the waters for recreation.