# Quantifying Total Phosphorus and Heavy Metals in Residential Septage
## 3 Results and Discussion
### Mass and Watershed Mass of Pollutants from Domestic Septage

Table 5: Individual, median (range), and mean (standard deviation (SD)) concentrations of total phosphorus (TP) and trace metals in septic tanks that had not been pumped in at least 8 years. not limited to the homeowner's maintenance schedule, household wastewater practices, wastewater strength, and volume of wastewater generated. Routinely pumping septic tanks is necessary to maintain the design performance and prevent malfunction [3]. The solid accumulation rate in septic tanks may vary considerably [70], as it is affected by household wastewater practices. Using garbage disposals, plumbing greywater into septic tanks, and flushing household wastes (e.g., tissues, cigarette butts, food waste, oils, grease, or other cooking wastes) are household wastewater practices that can increase the scum and sludge accumulation rate. These practices can also increase mass loads of TP and metals to the septic tank, thereby increasing concentrations of contaminants and requiring additional treatment [3]. The most dominant sources of TP in septic tank septage are typically human feces, household cleaning products and detergents, and food wastes [2,71]. Most of these sources are contributed from toilets and baths, sinks, and appliances [2,3]. Human feces contain nucleic acids and adenosine tri-phosphate, which are organic forms of phosphorus [2]. [PERSON] et al. [71] detected phosphorus in 97% of 156 household products. Food products also contain various sugars, phospholipids, and nucleotides that contribute to organic phosphorus levels in septic tanks. However, these contributions are typically much lower relative to fecal matter and household products. Most forms of phosphorus enter the tank as organics or polyphosphates until anaerobic processes convert these forms of phosphorus into orthophosphate [2,7]. Approximately 70-80% of the TP that enters the septic tank will leave as effluent [29,51,72,73], which is later discharged to subsoils, where adsorption and/or mineralization processes can reduce the TP concentrations further [10]. The remaining 20-30% of TP remains in the septic tank, where TP may settle out and accumulate in the sludge layer [2] or bind with dissolved iron to form vivianite in the tank [74,75]. These studies suggest that sources of TP are common in residential settings, where the generation of wastes from humans, household products, and food sources occurs daily. Sources of heavy metals are more variable. Zinc and copper are essential micronutrients that catalyze enzymatic processes [76,77], thus food can often serve as a source of these metals. Nickel is another essential micronutrient [78] which is also important for growth of cereal crops [79]. Past studies have also quantified trace amounts of lead, nickel, and cadmium in food [80,81]. Older construction homes may have leaded pipe infrastructures and/or lead paints, which may leach into septic tanks. In the United States, lead-based paints were banned in 1978 [82], and the use of pipes, plumbing fixtures, solder, or flux containing lead was banned in 1986 [83]. Most of the residences in the current study were originally built between the 1950s and 1970s [84], thus it is possible that leaded materials were used and, if corroded, may have increased the lead loads to the septic tanks. Two septic tanks contained higher concentrations and masses of lead than others in the study, which could be due to corroded leaded pipes, but more investigation is warranted to confirm this. Corrosion of pipes and taps (i.e., pipe infrastructure constructed from copper alloy or galvanized steel) is also a potential source of copper or zinc [81,85,86]. Another possible source of trace metals is drinking water supplies [81], but metal loads may be highly variable based on the potable water source and surrounding land uses. Household products (e.g., cleaning products, detergents, soaps, sunscreen, deodorant) are common sources of zinc, and traces of lead and nickel can also be detected in many products. Copper and cadmium are typically not found in many household products.