Comparative effectiveness of Tillandsia usneoides L. and Parmotrema praesorediosum (Nyl.) Hale as bio-indicators of atmospheric pollution in Louisiana (U.S.A.)

Samples of the epiphytic bromeliad Tillandsia usneoides L. (Bromeliaceae) and the lichen Parmotrema praesorediosum (Nyl.) Hale, growing on bald cypress trees in southern Louisiana, were chemically examined by means of X-ray micro-probe analysis to determine their comparative elemental content. The plants were found to effectively bio-accumulate heavy metals and sulfur from the atmosphere; the accumulatory capacities and implications are discussed. Partitioning occurs within the plants of T. usneoides and consequently any analytical procedure should standardise on precisely which parts are to be analysed. The bio-accumulation of certain heavy metals such as manganese, nickel and cadmium increases with age of the T. usneoides.