Temperature Effects on Aqueous Selenium Removal By Cattail and Duckweed.

Precipitation over coal fly ash surfaces raises concerns about potential downstream impact of selenium (Se) on aquatic ecosystems. While selenium is an essential dietary mineral for humans, it can be toxic to fish and aquatic wildlife. Cattail (Typha angustifolia L.; CAT) and duckweed (Lemna minor L.; DWD) are aquatic species known to improve the quality of Se-impacted runoff. This research was conducted to evaluate temperature effects on the environmental fate of Se in CAT or DWD-planted systems. Borosilicate glass cylinders (12 L) containing three kg soil were planted to either one CAT, 25 g fresh DWD, or left unplanted (UNP) (control). Planted and UNP cylinders were treated with 3 L of a zero Se control or 35 μg Se L^-1, as sodium selenate (Na₂SeO₄). Cylinders were sealed and arranged in a randomized complete block (n=6) replicated three times within each of two growth chambers. Chambers were maintained at 20 or 30°C under a 12 h photoperiod with an irradiance of 400 μmol m^-2 s^-1. After 20 d, water, plant, soil, and carbon samples were collected and analyzed for total [Se] with inductively coupled plasma-mass spectroscopy (ICP-MS). Data were analyzed with PROC GLM with SAS v9.4 at α=0.05. Results indicate greater aqueous Se removal at 30°C (60%) compared to 20°C (51%) (p<0.0001). At 30°C, in chambers planted to DWD, nearly 75% of the applied Se was removed. Cattail (61%) also demonstrated greater Se removal compared to UNP controls (51%) (p=0.0347). Given their efficacy and abundance in the South, DWD and CAT are likely suitable species for Se removal in constructed wetlands.