Absorption of Excess Selenium and Sulfur by Plants and Animals

Abstract

High concentrations of selenium (Se) and sulfur (S) often occur in overburden soils and underlying shales associated with western coal mining areas. Knowing the role of Se and S in the soil-plant-animal system is important for proper management of mine spoil reclamation. I will discuss recent findings about Se and S forms in soil, their absorption and accumulation by plants, and their subsequent toxicity to grazing animals. Selenium absorbed by the accumulating plants is metabolized to non-protein forms, while that absorbed by the nonaccumulating plants occurs predominantly as selenomethionine which is readily absorbed by animals. In animals, both acute and chronic forms of selenosis are known. Death occurs when a large dose of highly-available Se is ingested. One chronic form "alkali disease", produces symptoms of inappetence, hair loss, hardening and extension of nails and hooves, reduced weight gains, and poor reproductive performance. Rosenfeld and Beath identified "blind staggers" as another form of selenosis, but this disorder; more appropriately called polioencephalomalacia (PEM), occurs only in ruminants. However, the attribution of "blind staggers" (PEM) to excess Se is being questioned. Recent experimental evidence has shown that PEM is likely caused by excess sulfur. Cases of this disorder have been documented in the U.S. and Canada when ruminants have high sulfate intake from herbage and drinking water. Decisions regarding western mine reclamation should consider the potential for not only causing excess Se, but also excess sulfate in water, soil, and plants.