TRANSFER FACTOR OF RARE EARTH ELEMENTS FROM PHOSPHOGYPSUM AMENDED BRAZILIAN TROPICAL SOILS TO LETTUCE, CORN AND SOYBEAN

摘要

About 170 million tons of phosphogypsum (PG), a by-product of phosphoric acid factories, are annually produced worldwide and agricultural use approximately 15% of this product. In Brazil, this material has been used for several decades, mainly in cerrado region (Brazilian low vegetation ecosystem). Nevertheless, such material may contain several toxic elements as radionu-clides and rare earth elements (REE) which can be transferred to soil, plants and water sources. This work studied the REE transfer factor (TF) from the PG amended soil to lettuce, corn and soybean. The determination of REE concentration in all samples has been conducted by neutron activation analysis. The main REE present in PG samples was Ce (1730 mg.kg~(-1)), followed by La (973 mg.kg~(-1)). The main REE in clayey soil was Ce (148 mg.kg~(-1)), followed by La (62 mg.kg~(-1)). Sandy soil showed Ce (21 mg.kg~(-1)), followed by Sc (6.6 mg.kg~(-1)). REE TF from clayey soil to soybean was 0.0005 of La and 0.001 of Sc when sandy soil was used. TF from soil to lettuce was 0.003-1.1 of La and 0.001-0.01 of Sc. This paper aims to help the authorities to regulate PG use in tropical agriculture.