Temporal analysis of pollutant metals in trees of three parks in Mexico City’s Metropolitan Area

High concentrations of atmospheric pollutants, resulting from anthropogenic activities, cause direct precipitation of metals and metalloids on soil and vegetation surfaces. Urban trees can be used as passive monitors of particulate pollutants. This study aimed to evaluate the distribution of heavy metals and metalloids, namely iron (Fe), copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), boron (B), and arsenic (As), in the soil and roots and foliage of Pinus greggii at three parks with different atmospheric pollution levels: San Juan de Aragón (SJA - high pollution level); Sierra de Guadalupe State Park (GUAD - medium level); and Viveros de Coyoacán Park (COY - low level). The highest concentrations of metals and metalloids in the soil were observed at the surface layer (0-10 cm), except for As, which was higher at the 10-20 cm layer. According to Official Mexican Standard NOM-147-SEMARNAT/SSA1-2004, the analyzed soils did not show excessive contamination. However, a super accumulation of metals and metalloids was identified in fine roots of P. greggii; for example, Cd (3.90 ppm) exceeded the limits or requirements for the plant at COY, indicating contamination in roots. The highest foliage concentrations for B, Cu, and Fe were found at SJA, whereas those for As and Pb were at GUAD. A remarkable variation in foliage accumulation of metals and metalloids was recorded throughout the year at all sites, with peak values for external surface concentrations in the spring and for intracellular concentrations in the winter, indicating movement of metals through the soil and tree components. The results confirms that urban trees are useful bio-indicators of pollution accumulation and dynamics in the soil-plant system.

Abstract licence: CC BY-NC

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