Probabilistic exposure assessment of DEEDMAC using measured effluent and sludge concentrations from 41 wastewater treatment plants across the United States.

The cationic surfactant diethyldialkylester dimethyl ammonium chloride (DEEDMAC) is an active ingredient in liquid fabric softeners and, as such, is disposed of down the drain after consumer use. A monitoring program was conducted across the continental United States to measure the concentration of DEEDMAC in the effluent and sludge from 41 wastewater treatment plants (WWTPs). The concentration in the effluent ranged from 32.4 to 2660ng/L, with a mean and standard deviation of 232±450ng/L. The concentration in the sludge ranged from 0.707 to 314mg/kg dw, with a mean and standard deviation of 29.2±50mg/kg dw. The distribution of measured effluent concentrations was combined with a distribution of mixing zone dilutions factors to predict the distribution of DEEDMAC concentrations in mixing zones and sediments under mean flow and 10-year, 7 consecutive day lowest flow (7Q10 low flow) conditions. Additionally, the distribution of measured sludge concentrations was combined with a distribution of land applied sludge volumes and US tilling practices to obtain a predicted distribution of DEEDMAC concentrations in sludge amended soils. The 90th percentile concentrations of DEEDMAC in mixing zones and sediments under mean flow conditions was 10.3ng/L and 451ng/kg, respectively. The 90th percentile concentration in sludge amended soils was 1.92mg/kg. These predicted exposure concentrations were compared to published eco-toxicity data and showed that DEEDMAC has a wide margin of safety and poses negligible ecologic risk to aquatic, sediment, or terrestrial compartments.