The analysis also showed no statistical differences between LC50 mean values for C. colpoda and D. granulosa, and for E. aediculatus and H. grandinella in the tests with chromium. No statistical differences were also found between the ciliates D. granulosa and H. grandinella in the tests with lead, which 24-h LC50 mean values ranged from 0.121 to 0.126 mg Pb l1
.