Natural Radionuclides, Rare Earths and Heavy Metals Transferred to the Wild Vegetation Covering a Phosphogypsum Stockpile at Barreiro, Portugal

Abstract

In Portugal, the industrial production of phosphate fertilizers, has been dealing with a specific raw material—north African phosphate rock—with a high content of trace metals and natural radioactive elements mainly from the ²³⁸U decay series. A disabled phosphate plant located in the vicinity of the river Tejo estuary has produced phosphoric acid for several decades (1950–1989) and dumped tons of phosphogypsum (PG) on retention lagoons, formerly decanted and deposited into a stockpile. This paper deals with the assessment of radionuclides, rare earth elements (REEs) and heavy metals transfer to plants (fam. Plantaginaceae, Plantago sp.) and mosses (fam. Bryaceae, Bryum sp.) growing naturally on the PG pile. In Plantago sp., the concentration ratio (CR, plant tissue/PG) was 0.187 for ²²⁶Ra and 0.293 for ²¹⁰Pb. The translocation factor (TF, aerial parts/roots) was 0.781 for ²²⁶Ra and 0.361 for ²¹⁰Pb. In contradiction to the high CR, the leachability of ²²⁶Ra from PG was low, lower than 2%. The results confirmed the role of mosses as biomonitors. A high quantity of contaminants collected in its biomass confirmed the hypothesis of their significant transport by air and rain water. High concentrations of heavy metals (As, Cd, Zn, W) in samples collected on the stockpile are an evidence of their transport from former industrial zones in the surroundings and present even more important risk for public health and environment than natural radionuclides and REEs from the PG stockpile.

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