Differences in mean levels of metal compounds as well as the
potential influence of predictor variables and potential confounders
(age, gender, residence area, body mass index – BMI, type of
water consumed, physical activity,...) on these levels were
assessed by using the non parametric Mann–Whitney and Kruskal–Wallis
tests. The magnitude of the correlation between metal
concentration in urine and hair samples was assessed by the Spearman
rank correlation test.