Biomonitoring of the population living near the solid waste incinerator plant in Modena, Italy.

Background and aims: As part of the authorization process for the expansion of the municipal solid waste incinerator of Modena, a cross-sectional biomonitoring study on toenail samples was conducted to identify biomarkers of exposure in resident population. Methods: Approximately 500 people were enrolled between October 2013 and May 2014, among residents for at least 3 years within 4 km from the plant. Sampling method implied stratification by exposure, gender and age-group (18-34, 35-49 and 50-69 years). Sampling exposure level was measured through the annual mean PM10 concentration map for 2010. Toenail samples were disintegrated by acid mineralization and tested through inductively coupled plasma mass spectrometry for concentrations of cadmium, chromium, manganese and nickel. Confounders were assessed through a questionnaire covering: personal and biometric data, lifestyle, residential information including traffic exposure, occupational history, health condition and diet. Effective exposure was estimated through fall-out maps from a quasi-gaussian dispersion model. Biannual PM10 concentration prior to the collection date (second semester 2013/first semester 2014) was assigned according to subjects residence and workplace address; exposure values were divided into quartiles. Multivariate regression analyses were performed. Results: Chromium, manganese and nickel were measurable in >95% of samples. Concentrations varied between 0.02-35.11 µg/g for chromium (median 0.52, 5th-95th perc 0.09-4.95), 0.02-7.23 for manganese (median 0.25, 5th-95th perc 0.07-0.97), 0.004-39.28 for nickel (median 0.28, 5th-95th perc 0.03-3.74). Cadmium resulted under the limit of quantification in 74.1% of the samples (range 0.006-0.19 µg/g), and was not included in the analysis. Multivariate regression models showed the following relations: - Chromium: positive relation with incinerator exposure, female gender, education level, hair dye, permanent make-up, woodworking hobby, locally-grown food consumption, orange juice consumption; negative relation with foreign citizenship. - Manganese: positive relation with incinerator exposure, female gender, occupational exposure, sculpture/building hobby, time spent outdoor, presence of prostheses, use of wood as heating system, locally-grown food and red wine consumption; negative relation with age and with all the months of collection except for the last one (May 2014) compared with the first (Oct 2013). - Nickel: positive relation with use of costume jewelry, presence of amalgam fillings, consumption of tomatoes and vegetable pies; negative relation with age. Conclusions: The analysis of heavy metal levels in toenails is a relatively recent technique, therefore reference levels are not available in literature and an analysis on the general distribution of sample levels cannot be performed. However, the presence of some expected associations in multivariate analysis (nickel with use of costume jewelry and tomatoes consumption; manganese with firewood use) suggests that our study method can be appropriate in assessing chronic exposures. Results showed association trends with incinerator exposure for manganese and chromium levels. Findings should be reassessed as soon as more accurate traffic exposure control is available.