Table 1. Comparison of a 48 h and 72 h recovery period for the micronucleus assay following treatment of three dimensional spheroids of MCF-7 cells with increasing doses of benzo[a]pyrene (BaP).

Concentration of BaP	Number of micronuclei per 1000 cells
	48 h recovery	72 h recovery
DMSO	3.5	17.8
10–10 M	11.2	18.5
10–9 M	10.5	17.8
10–8 M	13.0	17.8
10–7 M	16.3	16.0
10–6 M	19.7	23.5
10–5 M	26.0	31.3