Monitoring metals in toenail samples of a population living in the vicinity of the solid waste incinerator of Modena, Northern Italy

Introduction: As part of the authorization process for the expansion of the solid waste incinerator (SWI), a cross-sectional biomonitoring study was conducted to identify markers of chronic exposure. Metals were measured in toenails, as a single sample is assumed to represent long-term exposure. Methods: Around 500 subjects aged 18-69 yrs. and living within 4-km from the plant were enrolled between Oct. 2013-May 2014. Sampling method implied stratification by exposure, gender and age-group. Toenails were disintegrated by acid mineralization and analyzed through inductively coupled plasma mass spectrometry for concentrations of Cd, Cr, Mn and Ni. SWI exposure was estimated through fallout maps. Biannual PM10 level prior to sampling was assigned according to subjects’ residence and workplace. Confounders were assessed by questionnaire covering personal and health data, lifestyle, residential and occupational information, traffic exposure and diet. Multivariate regression models were performed. Results: Cd, not detectable in >50% of samples, was not further analyzed. Cr, Mn and Ni were detectable in >95% of samples. Significant positive relations were observed for diet, personal and lifestyle characteristics, as well as for SWI exposure. Conclusions: results appear consistent with literature-known associations, suggesting that toenails can be appropriate in assessing chronic exposures of Ni, Mn and Cr, while Cd is probably poorly accumulated in nails. Relations observed with SWI exposure should be accurately considered.