Radiological risk proceeding from road paving and building materials in the downtown of Naples (Italy)

Using a radionuclide identification device (RID), the handheld gamma-ray spectrometer ATOMTEX AT6102, 2548 measurements of ambient equivalent dose rate (ADER) were made in air at a distance of 0.2 m (ADER0.2m) and 1 m (ADER1m), respectively, from the ground along the street network of the downtown old sector of the city of Naples, in Italy. Data were sorted and grouped according to the nature of the road paving at each measurement station to determine if a primary influence is exerted on local ADER by the materials used. At a first glace, paving made by natural volcanic rocks (lavas) proceeding from quarries located in the surrounding of the Mt. Somma-Vesuvius volcano show a markedly high ADER values compared to other natural rocks used and non geological materials (i.e. asphalt and concrete). The influence of vesuvian materials on ADER variability is also confirmed by the comparison of its values acquired at different distances from the road paving in the same location (at 0.2 and 1 m from the paved surface) since they show a costant increase as moving close to the ground. ADER data were mapped trough both discrete and interpolated methods. Interpolation of the data was performed by means of the Empirical Bayesian Kriging (EBK) in ArcGIS software. To assess, in a deterministic way, the health risks proceeding from the low-dose ionizing radiation exposure originating from the paving materials, four indexes (i.e.: the Radium equivalent [Re], the dose rate in the air [D], the Annual Effective Dose Equivalent [AEDE] and the Excess Lifetime Cancer Risk [ELCR]) were used in this study in accordance with the European Commission (1999) and UNSCEAR (2000). In addition, the Montecarlo simulation method was applied to assess ELCR including the uncertainty. The ADER1m data (1273 measurements) spatially separated on the basis of the urban districts falling in the study area were used as an input of the stochastic model. The percentage of certainty, that ELCR could exceeds the world average value of 0.00029 proposed by UNSCEAR (2000) was calculated for each involved district showing a critical condition for almost all the downtown territory. The situation is even more complicated if the stochastic ELCR is assessed including also the exposure proceeding from indoor sources since the dwellings of the Naples downtown have been generally built using Neapolitan Yellow Tuff (NYT) which is characterized by a high emission rate of natural gamma radiation.