A new non-destructive method for chemical analysis of particulate matter filters: the case of manganese air pollution in Vallecamonica (Italy)

Abstract

Total Reflection X-ray Fluorescence (TXRF) is a well-established technique for chemical analysis, but it is mainly employed for quality control in the electronics semiconductor industry. The capability to analyze liquid and uniformly thin solid samples makes this technique suitable for other applications, and especially in the very critical field of environmental analysis. Comparison with standard methods like inductively coupled plasma (ICP) and atomic absorption spectroscopy (AAS) shows that TXRF is a practical, accurate, and reliable technique in occupational settings. Due to the greater sensitivity necessary in trace heavy metal detection, TXRF is also suitable for environmental chemical analysis. In this paper we show that based on appropriate standards, TXRF can be considered for non-destructive routine quantitative analysis of environmental matrices such as air filters. This work has been developed in the frame of the EU-FP6 PHIME (Public Health Impact of long-term, low-level Mixed element Exposure in susceptible population strata) Integrated Project (www.phime.org). The aim of this work was to investigate Mn air pollution in the area of Vallecamonica (Italy).

Figure 1

Map of all Brescia province. The red points indicate Breno (the most polluted municipal district for Mn presence) and surrounding valley sampling locations (area 1). Blue points represent locations where samples were collected in the Garda Lake reference area (area 2). Black points show the location of the Fe-alloy plants.

Figure 2

TXRF spectra collected on standard filter sample by NIST, treated in accordance with PCT/IT2008/000458. The presence of Si, S, Pb, Sr, Ba, Br, As, Se, Zn, Ni, Cu, Fe, Mn, Cr, Ti, Ca, K, and Cl is evident.

Figure 3

Direct comparison of spectra collected on the NIST standard filter (gray) with that collected on sample 22 (taken in Breno) (dark gray), showing concentrations of many metals about 1.5–2 times higher on sampled filter, with respect to the standard one (see for example Fe, and Zn peaks). Other elements (Cu, Ni and Cr) are comparable in intensities (Mn shows an integrated area larger by 4–5 times in relationship to the standard concentration (see magnification).

Figure 4

Mn mass concentration in the air, calculated considering the pump flowrate and sampling time of 24 h. The samples are divided in two groups: Area 1 which includes the samples collected in the municipal districts of Vallecamonica shown in alphabetical order and Area 2 which involves the samples of Garda lake area taken as reference.