Fate of Pharmaceuticals and Hormones in Mounded Septic Drainfields.

A variety of chemical compounds (known as emerging contaminants) are present in household wastewater due to the use and excretion of different products in the toilets, washers, kitchen, and sinks in the households. Many of these compounds are not completely removed by onsite wastewater treatment systems and can potentially contaminate groundwater. Our objective in this USDA-NIFA funded project was to investigate the occurrence, behavior, and leaching of select pharmaceuticals and hormones in septic system drainfields. Each drainfield received 3 L/ft²/day of septic tank effluent (STE; equivalent to maximum allowable rate for Florida’s sandy soils). Further, three small drainfields (1.5 m length x 0.9 m width x 0.9 m height) containing vertically stacked layers of soil (30 cm) and sand (30 cm) were constructed. Then, a drip line was placed and covered with 15-cm depth of sand and turf grass (St. Augustine) was planted to mimic a residential system. Below the drainfields, soil-water samples were collected using suction cup lysimeters and groundwater samples were collected using piezometers. Collected samples (STE, soil-water, groundwater, and leachate) were analyzed for four pharmaceuticals (acetaminophen, carbamazepine, ibuprofen, sulfamethoxazole) and three hormones (17β-estradiol, estrone, ethynylestradiol) by solid-phase extraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS). In STE, ibuprofen, acetaminophen, and estrone were the most frequently (>80%) detected compounds. Among pharmaceuticals, ibuprofen was the most (>70%) frequently detected compound in soil-water and leachate. Concentrations of ibuprofen were highest in the STE (mean: 7,950 ng/L; n = 40), which reduced to <45 ng/L as STE percolated and leached from the drainfields. Concentrations of acetaminophen and estrone were 700 ng/L and 50 ng/L in STE, respectively. 17β-estradiol, was not detected in STE but was present in soil-water (32 ng/L) and leachate (25 ng/L), suggesting potential accumulation due to repeated applications of STE containing small amounts of 17β-estradiol. Ethynylestradiol was not detected in STE, soil-water, leachate, and groundwater samples. Our mass balance data shows that about 5-14% of applied compounds in STE were recovered in leachate (about 60 cm below drainfield), with the remainder (86-95%) either stored and/or degraded in the drainfield. We did not detect any compounds in groundwater (>700 cm below drainfields) after 7-months of STE dispersal. We hypothesize that some of the compounds are potentially mobile in the soil profile but may be further attenuated before STE reaches groundwater. After the drainfields are deconstructed in 2014, we will determine the amount of pharmaceuticals and hormones stored in the soil. Information from this study will be useful in determining the fate and transport of pharmaceuticals and hormones in septic system drainfields and their potential transport to groundwater in long-running septic systems.