Different tests based on yeast cells were developed for determination of mu
tagenic/carcinogenic action; however, they all showed lower sensitivity com
pared to bacterial tests, the main reason for this being the limited permea
bility of yeast cells. We found that general permeability of Saccharomyces
cerevisiae cells can be increased by mutation and on this basis we develope
d a more sensitive test. The aim of this study was to prove the applicabili
ty of our test, called D7ts1, in environmental studies. Soil, water and air
samples were taken during 1998 from regions in Bulgaria with declared low,
average or high pollution levels and investigated for presence of mutageni
c/carcinogenic activities in the bacterial test of Ames, the yeast D7 test
of Zimmermann and our new D7ts1 test. Results obtained evidenced the follow
ing conclusions: (1) the usage of D7ts1 test instead of D7 test permits a c
learer measurement of positive samples and detects mutagenic/carcinogenic a
ctivities undetectable by D7 test; (2) all samples with positive Ames test
were positive in the D7ts1 test; however, some samples, clearly positive in
the D7ts1, were negative in the Ames test; therefore, the simultaneous usa
ge of D7ts1 and Ames tests in environmental studies is advantageous because
it detects dangers for the human health activities to which bacterial cell
s do not respond; and (3) regions in Bulgaria declared clean were found to
be polluted; particularly troubled are the whole-year positive data in the
three tests for air samples from a 'clean' region. (C) 2000 Elsevier Scienc
e Ltd. All rights reserved.