Table 1.

Chronic exposure (3 days) to the indicated metals increased proliferation (BrdU incorporation) in human thyrospheres (stem/precursor thyroid cells) but not in mature thyrocytes in primary culture.

Cu       (16 nM)	CuSO4 (nM)	1	10	100	1000
	Thyrospheres	120.3 ± 10.3	136.7 ± 6.9 ***	128.2 ± 7.8 **	111.3 ± 6.1
	Thyrocytes	101.6 ± 8.3	113.9 ± 15.0	103.2 ± 7.1	98.7 ± 7.5
Hg       (0.02 nM)	HgCl2 (nM)	0.001	0.01	0.1	1
	Thyrospheres	108.0 ± 6.7	122.4 ± 7.0 *	137.0 ± 10.16 **	84,94 ± 9.6
	Thyrocytes	102.5 ± 11.44	101.7 ± 7.0	104.3 ± 5.1	98.3 ± 12.45
Pd       (0.03 nM)	PdCl2 (nM)	0.001	0.01	0.1	1
	Thyrospheres	129.7 ± 6.7 **	136.2 ± 7.2 ***	120.9 ± 7.4 *	114.5 ± 7.3
	Thyrocytes	92.8 ± 14.5	90.7 ± 6.0	104.1 ± 8.7	74.8 ± 8
W       (1.1 nM)	Na2WO4 (nM)	1	10	100	1000
	Thyrospheres	129.9 ± 7.5 *	159.5 ± 13.0 **	158.5 ± 18.6 *	109.7 ± 8.8
	Thyrocytes	106.4 ± 8.6	102.5 ± 7.4	97.2 ± 9	99.7 ± 11.3
Zn       (47 nM)	ZnCl2 (nM)	10	100	1000	10,000
	Thyrospheres	130.8 ± 10.8 *	158.8 ± 10.1 ***	162.2 ± 13.3 **	133.4 ± 11.3
	Thyrocytes	100.8 ± 10.5	116.5 ± 10.13	98.8 ± 13.32	97.1 ± 11.26

The data indicate the mean ± standard error of the mean percent change relative to the basal level of unexposed cells (always equal 100) considering four separate experiments. The average metal concentration in the drinking water of the volcanic area in Sicily is also indicated (in parentheses). All metals, used at a very low concentration, caused a biphasic response typical of hormesis. The values in bold indicate the peak value for each metal. * p < 0.05, ** p < 0.01 and *** p < 0.001 relative to the basal value. Represented data are derived from ref. [56].