Radiological risk induced by road paving and building materials in the city of Naples, south Italy

Natural radioactivity basically depends on the presence of primordial radionuclides (which have been present on Earth since its origin) which spontaneously decay and transform to achieve a stable nuclear conformation. These transformations involve the emission of particles whose energy can have harmful effects on biological material even at low-dose (with stochastic effects). The three main elements responsible for most of the natural radioactivity in the earth’s crust are radioactive potassium (40K), uranium (and mainly 232U isotope) and thorium (232Th). These isotopes are present in minerals and rocks (and in their alteration products) that man has always used as raw materials. The city of Naples is located between two volcanic districts: the Phlegrean Fields, on the west, and Somma-Vesuvio volcanic area, on the east. In the area, rocks generated by volcanic activities have been quarried to be used as both construction materials and road paving since the Greek and Roman times. In fact, the streets of Napoli downtown (the most ancient part of the city) are mostly paved with: (1) Vesuvian effusive rocks constituted by leucotephrites and leucobasanites; and, subordunately, with: (2) Volcanic rocks from Latium volcanoes (mostly leucitites) (Penta, 1930) 3) intrusive rocks (mostly acidic) from northern Italy and Sardinia; (4) effusive basic rocks from Mount Etna in Sicily (which has recently been utilized to substitute Vesuvian materials in some roads); (5) non-geologic materials (NGMs) such as asphalt and other bituminous surface treatments. The paving, except for NGMs, is usually in the shape of rectangular ashlars, roughly chiseled to reduce slippery, (the so-called “Basolato”) or cobblestones (known as “Sampietrini”). Due to the variable activity concentration of 40K, 238U and 232Th in igneous rocks a detailed radiological survey was carried out to assess the radiological risk proceeding from road paving and building materials in the downtown of Naples where about 1 million people are potentially exposed to low-dose ionizing radiations. Specifically, 13 paving materials samples were randomly collected from the city roads and analysed by means of a high purity germanium detector (HPGe) with the energy resolution of 1.8 keV FWHM (for the 1332 keV gamma-ray energy line from 60Co), coupled to a DSA-1000 multichannel analyzer(CANBERRA) at Radioecology Department of Center for Ecological-Noosphere (CENS) in Armenia. In addition, a total of 2548 measurements of ambient dose equivalent rate (µSv/h) were made in open air at heights of 0.2 m (ADER0.2) and 1 m (ADER1) above the ground, respectively, using a handheld gamma-ray spectrometer (ATOMTEX AT6102). In general, the results showed a sensible activity, mostly due to naturally occurring radionuclides (238U, 232Th and 40K), in all the samples, except for NGMs. Further, field measurements showed that ADER1 values strongly depends on ADER0.2 where the streets are paved with geologic materials, while the relationship is not significant in the areas covered with the NGMs where the ambient dose equivalent rate does not change considerably changing the measuring height. Based on the ADER1 data, a Monte Carlo simulation was carried out to calculate the stochastic distribution of the outdoor excess lifetime cancer risk (ELCRoutdoor) for the entire study area and for each city district included in the area. To have a comprehensive assessment of the risk proceeding from gamma radiations for residents, in one of the city districts with the highest ELCRoutdoor, additional ADER1 measurements were conducted in living rooms of 51 private houses to assess the stochastic distribution of indoor ELCR. Finally, the total excess lifetime cancer risk (ELCRtotal) was estimated jointly using the ELCRoutdoor and the ELCRindoor. The results showed that the average ELCRoutdoor values are relatively high. In all districts the average value obtained from the probability distributions generated by Monte Carlo simulations exceeded the world average reference value (2.9E-04) proposed by UNSCEAR 2000, 2010. The ELCRindoor calculated for Pendino distrect as well as the ELCRtotal showed relatively high (1.16E-03 and 1.45E-03 respectively) that exceeded the average values proposed in other works. This study revealed that low-dose gamma radiations, emitted by the geological materials of volcanic origin used as paving or building materials in old cities in Europe and around the world, can pose a radiological risk to health of residents.