Uptake of Natural and Synthetic Estrogens by Maize Seedlings

Runoff from manure-fertilized crop fields constitutes a significant source of natural estrogens (e.g., estradiol [17 beta-E2] and estrone [E1]) and synthetic estrogen mimics (e.g., zeranol [alpha-ZAL] and zearalanone [ZAN]) in the environment. However, processes such as sorption to and uptake by plants may inhibit the environmental mobility of hormonally active compounds. Sorption to dried root tissue was assessed in batch sorption tests; and resulting sorption isotherms were nonlinear at aqueous concentrations below 0.1 mu M and linear above that limit. To evaluate the role of crop plants in the environmental fate of such compounds, we exposed hydroponic solutions containing 2 mu M 17 beta-E2, El, alpha-ZAL, or ZAN to maize. seedlings. After 22 days of exposure, alpha-ZAL and ZAN concentrations decreased by more than 96%, and 17 beta-E2 and El were undetectable: The, decrease. in alpha-ZAL and ZAN concentrations in maize-exposed solutions was initially slow, but the observed uptake exceeded that predicted by sorption alone within 3 d. All four estrogens were detected in root tissues at concentrations up to 0.19 mu mol g(-1) with concentrations peaking after 1-3 days of exposure. Only 17 beta-E2 and alpha-ZAL were detected in shoots, and maximum concentrations were measured after 2 days for 17 beta-E2 (0.02 mu mol g(-1)) and 16 days,for a-ZAL (0.8 nmol g(-1)). Concentrations measured in root and shoot tissues were 82% or less than those predicted by a partition-limited uptake model, which is attributed., to transformation and possibly irreversible binding processes.