**1. Introduction**

There is increased evidence of the association of air pollution and deleterious health effects. Particulate matter (PM) has obtained more attention, especially the small size components (PM10, PM2.5, UFP -ultrafine particles-) that carry on their surface different organic and inorganic elements whose composition differ with local and regional variations [1].

PMs might be identified by source, e.g., primary or secondary; combustion products, traffic, or by particle's size (aerodynamic diameter) (PM10, PM2.5, UFP -ultrafine particles-). This former parameter is important because the larger the particle the shorter the time it remains suspended in the air and the lower the risk of it being inhaled. Also the smaller the particles the higher the chances of deleterious health effects [1].

### **1.1. Metals in particulate matter, air pollution and sources**

Particles toxic components are complex mixtures of solids or liquids with different character‐ istics (e.g., mass, number, size, shape, surface area, chemical composition, acidity, solubility). Chemical components may be located on the surface or inside the particle. Considering the source there are natural and anthropogenic emissions. Natural sources include sea salt, volcanic ash, pollens, fungal spores, soil particles, forest fires and wind-blow dust [2]. An‐

thropogenic sources consist of fossil fuel combustion products, industrial process, mining activities, wood stove burning and cigarette smoking. In urban areas the main source of PM are motor vehicles especially those derived from diesel fuel combustion.

One of the components adhered to the small particles are metals that come from impurities derived from fuel additives and brakes and tires attrition. Transition metals are generated by non-exhaust emissions, impurities in fuel additives, or metallurgic process. Iron (Fe), nickel (Ni), vanadium (V), chromium (Cr) copper (Cu) are considered because its potential to produce Reactive Oxygen Species (ROS) in biological systems [1]. Others such as zinc (Zn) may also exert toxic effects by other mechanisms besides ROS production.

Heavy metals such as cadmium, lead and mercury are some of more common air pollutants emitted by industrial activities, combustion, extraction and processing activities. The diagnosis of health effects for heavy metals might be difficult if there is no previous evidence of the exposure source, while acute exposures usually occur in the workplace and are more easily identified; signs and symptoms differ within metals because each one interacts with different targets such as: specific metal-binding proteins (metallothioneins, transferrin, ferritin, cerulo‐ plasmin) in cases such as Cd, Cu, Hg, Ag, Mn Zn, Al, and Be; membrane carrier-proteins (phosphate and sulphate-transporters), divalent cation-transporters, some examples are V, Cr, Mo, Se. Heavy metals share with transition metals the possibility to exert its toxic effects by the production of ROS [2-4].
