Bioaccumulation of heavy metals using Parmelia sulcata and Parmelia caperata for air pollution studies

k(0)-Standardized INAA was applied to the determination of heavy elements in two lichen varieties of the species Parmelia: caperata and sulcata. The aim was to find out differentiations between the two varieties concerning the accumulation of elements from the air. The samples were collected at about 70 locations randomly chosen in the whole country (Portugal). It was found a similar local variation for both species, between 20-25%. From the comparison it was observed that Parmelia sulcata accumulates larger amounts of most of the elements determined than Parmelia caperata; only Ca is more accumulated by the caperata and Hg are similarly absorbed by both varieties. Therefore, it was concluded that Parmelia sulcata should be preferred as bioaccumulator when both varieties are present. Some pollution sources were identified, but the sampling net was too short to obtain an exhaustive identification. The quality control was made using NIST and IAEA reference materials: an accuracy of +/-10% was found. The precision has also been estimated: it is better than 11% except for Hg (15%), Sr (13%), Ti (19%) and Mg (32%).