Lead in particulate matter source apportioning by HR-MC-ICPMS stable isotope ratio measurements

During the last decades great attention was paid to Particulate Matter (PM) due to the correlation between fine PM exposure and adverse health effects.

  Among the airborne pollutants, Lead (Pb) is one of the most widespread and toxicologically important. Metallic Pb and inorganic Pb compounds are classified as possible carcinogenic for humans. Pb can bioaccumulate in the human body system, causing damage to human nervous system, cardiovascular diseases, reproductive impairments, and catalyzing cells oxidative stress.

  In Italy, Legislative Decree no. 155 of 13/08/2010 (implementation of European Directive 2008/50/EC) defines the atmospheric PM10, PM2.5 and airborne pollutants threshold concentration values. These threshold values are applied for anthropogenic particulates, so, the Pb source apportioning in PM can offer the key to manage the problem.

   Pb has four stable isotopes, i.e. ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb. The isotopic ratios of Pb act as “fingerprint” that allows to identify the PM emission sources in the environment (crustal, vehicular traffic, municipal solid waste incinerator, etc …).

  The PM 2.5 and PM10 sampling will be carried out by ARPAC monitoring network, using high-volume samplers placed in Campania (Italy) environmental interest points (urban centers, busy roads…). The sampling flow is 2.36 m³/h, single sampling time is 24 hours and the use of quartz fiber filters Ø = 47mm is provided (according to the technical standard UNI EN 12341:2014).

  Precise and accurate measurement of Pb and relative isotope ratios requires a multi-step process for analysis of solid samples:

• Microwave-assisted treatment of filters with strong acid to solubilize all the metallic species (EPA 3051 A 2007);
• A First qualitative and quantitative measurement by Inducted Coupled Plasma Optical Emission Spectroscopy (ICP-OES) to estimate the total Pb concentration (moreover, the quali-quantitative determination of other metals is an important information for environmental purposes);
• Lead Extraction and purification from matrix and interfering elements by ionic resins in ISO 4 clean room;
• Mass spectrometry measurement for lead isotope analysis by High Resolution Multi-Collector Inducted Coupled Plasma Mass Spectrometry (HR-MC-ICPMS).
• Improvement of data interpretation accuracy comparing experimental data to isotopic lead ratio values in research databases (i.e. IBERLID: lead isotope database and tool for metal provenance and ore deposits research).

  However, the identification of anthropogenic Pb sources enables to establish the origin of a portion of collected PM. So, when an overcoming of PM threshold concentration is observed, thanks to the isotopic analysis information, competent authorities can act in an efficient and successful way.