However,
after 6, 24 or 72 h incubations, the EC50 values (80, 155 and
34 mg L1 respectively) obtained for velocity were much lower
than those for motility (Fig. 2a–d). Gravitaxis (upward swimming
of cells) was strongly impaired by the detergent immediately after
exposure giving an NOEC value of 90 mg L1 and EC50 value
253 mg L1.