Bioaccumulation of Cobalt in Parmelia sulcata

Six locations across mainland Portugal were selected for exposing Parmelia sulcata, for a one-year period (8 months for one site), with simultaneous measurement of total (dry + wet) deposition (one-month periods). The exposed lichens and the total (dry + wet) deposition were analysed for cobalt contents by INAA (instrumental neutron activation analysis) and ICP-MS (inductively coupled plasma mass spectroscopy), respectively. The designated “wet” deposition was evaluated through the collected water volume; the designated “dry” deposition was assessed after the (dried) residual mass of the “wet” deposition. An excellent agreement between Co contents in exposed lichens and the cumulative (1) Co contents in the “dry” deposition, (2) “dry” deposition, and (3) “wet” deposition has been found for the locations with alternate drought and precipitation months, high “dry” deposition, and high Co contents in the latter. Continuous rainfall was found to hinder the Co accumulation in the lichen due to its release from the lichen and\or lower Co contents in the “dry” deposition. At three locations, P. sulcata Co contents, after subtraction of the background (before exposure), equalled or exceeded the Co contents in the cumulative “dry” deposition at the end of the exposure time. The optimal exposure period for this species likely depends on the exposure conditions.