Traces of heavy metals in children toenails as a bio-indicator of environmental exposure in Forlì (Northern Italy): an observational study

OBJECTIVES: to assess the concentration of heavy metals in the nails of children aged 6-9 years residing in Forlì (Emilia-Romagna Region, Northern Italy). DESIGN: biomonitoring survey. SETTING AND PARTICIPANTS: in March 2017, a total of 236 toenail samples were collected, 221 of them were eligible; the concentration of 23 metals were measured in these eligible samples. MAIN OUTCOME MEASURES: a spatial analysis was conducted, considering home addresses as grouped in the four macroareas in which the local territory is administratively divided. RESULTS: In the two North-Center and East areas - which include various industrial operations, two waste incinerators and a motorway - the total concentration of all metals resulted 60% higher than in the West and South areas. Given the lack of Italian reference values, comparison tests between areas were performed for aluminum (Al), cadmium (Cd), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn), which concentrations were detectable in over 50% of the subjects. Higher concentrations were observed in the East area compared with the other areas, with statistical significance for Al (vs North-Center), Cu and Zn (vs West), and Al and Mn (vs South). Further comparisons showed significantly higher concentration of Cu in Nord-Center vs West, which in turn had higher concentrations of Zn compared to the Southern area. By applying a Tobit regression to evaluate possible confounding factors, a marginally significant correlation resulted for the nail concentration of Mn among children practicing outdoor sports and eating locally grown vegetables. The consumption of local vegetables was at the limits of significance also for Cd. CONCLUSIONS: the data obtained came from a voluntary and crowdfunded study and suggest a possible relationship between the exposure to air pollutants and subsequent accumulation of metals in the nails. Further and more detailed epidemiological studies are warranted to identify the exposure sources and to yield preventive intervention.