Twenty-one years after the Chernobyl accident, lichen and moss samples were collected from the Ordu province, which was already chosen for a related study some years ago. It was observed that (CS)-C-137 activity concentration ranged from 31 to 469 Bq kg(-1) in the moss and from 132 to 1508 Bq kg(-1) in the lichen samples. The decrease of the activity concentrations in the present measurements (2007) relative to those in 1997 (over a period of 10 y) indicated ecological half-lives between 1.8 and 10.4 y for the moss and between 2.1 and 13.7 y for the lichen samples. It was observed that (CS)-C-137 was still eminent in the area studied. Moreover, K-40 activity concentrations and K element concentrations were measured and their relationships were discussed. (c) 2009 Elsevier Ltd. All rights reserved.