COMPARATIVE EFFECTIVENESS OF TILLANDSIA USNEOIDES L. AND PARMOTREMA PRAESOREDIOSUM (NYL.) HALE AS BIO-INDICATORS OF ATMOSPHERIC POLLUTION IN LOUISIANA (U.S.A.) F. B. PYATT 1* , J.P. GRATTAN 2 , D. LACY 1 , A. J. PYATT 1 and M. R. D. SEAWARD 3 1 Department of Life Sciences, Nottingham Trent University, Nottingham, U.K.; 2 Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, U.K.; 3 Department of Environmental Science, University of Bradford, Bradford, U.K. ( * author for correspondence, e-mail: brian.pyatt@ntu.ac.uk. (Received 28 January 1997; accepted in revised form 1 April 1998) Abstract. 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 ele- mental 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. Keywords: bio-accumulation, heavy metals, Louisiana, Parmotrema praesorediosum, partitioning, sulfur dioxide, Tillandsia usneoides, X-ray micro-probe analysis 1. Introduction Both the bromeliad Tillandsia usneoides L. (also known as Spanish moss) and the lichen Parmotrema praesorediosum (Nyl.) Hale are common in the southern states of the U.S.A., especially in swamplands; this investigation focused on the area of the Audubon Park adjacent to New Orleans in the sub-tropical state of Louisiana. T. usneoides there is an important and prolific epiphyte particularly on trees of Taxodium sp. It is pendulous and hangs 1 m or more from the lateral branches of the trees. The foliose lichen P. praesorediosum is horizontally positioned and covers extensive areas of both branches and trunks of the same trees and is also widespread in the Audubon Park area and the immediate vicinity. This lichen is a pan-tropical species but restricted in the U.S.A. to the south-eastern states; according to Hale (1965) it is apparently a weedy species of areas subjected to human disturbance. The bromeliad is absent from the town of New Orleans which is situated some 10 km from the Audubon Park, this is conceivably a response to the diminished humidity in the city and the enhanced values of some of the atmospherically transported pollutants. The lichen is largely absent from the New Water, Air, and Soil Pollution 111: 317–326, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands.