Radium‐226 and Calcium Uptake by Crops Grown in Mixtures of Sand and Clay Tailings from Phosphate Mining

Abstract

AbstractRadium‐226 is a naturally occurring radionuclide found in reclaimed clay and sand tailings from phosphate mining. Field studies were conducted to investigate the effects of sand/clay ratio (SCR), Ca supplement, and organic amendments on the 226Ra concentration in turnip (Brassica rapa L.), banana pepper (Capsicum annum L.), cabbage (Brassica oleracea var. capitata), yellow squash (Cucurbita pepo L.), mustard [Brassica juncea (L.) Czern & Coss.] and alfalfa (Medicago sativa L.). For vegetables, treatment effects included SCR (2:1, 4:1, 6:1, and 8:1), phosphogypsum (PG) (0, 22, and 134 Mg ha−1), and peat (0, 100, 200 Mg ha−1). For alfalfa grown in a 1:1 SCR mixture, treatments included organic amendments (control, peat, sewage sludge, sawdust, composted sewage sludge, composted garbage and humate) applied at 44.8 Mg ha−1 (2.2 Mg ha−1 for humate). Plant 226Ra concentration tended to be higher in the 4:1 than in the 2:1 SCR mix but this depended on the crop and the season. Organic amendments and PG had no effect (p < 0.05) on the 226Ra concentration in vegetables and alfalfa. Mean 226Ra concentration in plant tissues ranged from 3.4 Bq kg−1 in banana pepper fruit to 31.1 Bq kg−1 in turnip leaf. Sand‐clay mixtures contained 289 to 592 Bq 226Ra kg−1. A quadratic relationship based on 631 observations was observed between 226Ra and Ca concentration in plant tissues. The 226Ra/Ca ratio in plant tissues ranged from 0.85 to 2.13 kBq 226Ra kg−1 Ca and decreased with increasing plant 226Ra. Results indicated that wide differences in plant 226Ca concentration were related more to differences in plant Ca levels than to soil factors.