Fig. 1

Levels and frequency of cobalt in CHDs and control groups. a Frequency of cobalt in maternal hair. b Boxplots of cobalt levels (Napierian logarithm transformed) of hair samples. c Frequency of cobalt in fetus placental tissues. d Boxplots of cobalt levels (Napierian logarithm transformed) in fetus placental tissues. The line inside the box = medians; the box length = interquartile range (IQR); the upper and lower ends = 95 and 5% value. One-sample Kolmogorov-Smirnov test was used to verify the distributions of cobalt. The distributions of cobalt did not conform to normal distribution. ***P < 0.001, cases compared to the control group