produced from the decomposition of plant litter could induce progressively a
transformation of inorganic metal components into more available organic metal
components. In this way, there can be a greater risk of soil-plant metal transfer.
However, there exists comparatively less data about the deposition of metal-PMcontaminated plant litter on soil and its subsequent fate in soil. Further studies are
required to investigate the speciation, bioavailability, and uptake of metals released
from the decomposition of contaminated leaves.
4 Plant Contamination Due to Atmospheric Deposition
of Metal-PM
Besides the deposition on soil, metal-PM also falls on foliar organs of plants (Martin
et al. 2018; Pratte et al. 2018). Urban vegetation is considered an excellent biological
filter as they are efficient in adsorbing and reducing harmful UV rays, noise, and
atmospheric contamination (metal-PM) (Bottalico et al. 2016; Safari et al. 2018).
Dust deposition on a plant’s canopy is a continuous process that is controlled by
wind and gravity, which allows atmospheric dust back to the ground (González et al.
2014; Grantz et al. 2003a). Dust deposition and retention on leaf surface particularly
depend on the roughness of the surface and size of the PM (Fowler 2002; Liu et al.
2018a; Shahid et al. 2017b).
The forest canopy/ecosystem is highly sensitive to atmospheric PM due to the
large interaction surface area (leaf area index ¼ 3–10 m
2 /m
2 ) (Bytnerowicz et al.
2007; Paoletti et al. 2010; Serengil et al. 2011; Sicard et al. 2016; Ulrich et al. 1995).
This interaction between plant canopy and metal-PM includes adsorption of PM,
assimilation, or release of PM by the canopy (Balestrini et al. 1998; Gandois et al.
2010). Several studies have evaluated the composition of atmospheric deposition on
plant canopy as well as the interaction (adsorption, assimilation, etc.) processes
occurring in the phyllosphere (Gandois et al. 2010; Hou et al. 2005). It is reported
that these interaction processes between metal-PM and forest canopy depend on
element-specific dynamics and the morphology of forest canopy. For example, the
speciation, composition, and size of metal-PM govern their environmental pathways, availability, and transport or immobilization in the ecosystem compartments
(Gandois et al. 2010).
Yang et al. (2005) investigated that most of the atmospheric pollutants are
removed by vegetative cover. They estimated that trees remove about 1,261 tons
of pollutants in 2002 from the atmosphere of central part of Beijing, China. In a city
of China, Chen et al. (2015) indicated that vegetation on greenbelts improved
atmospheric quality near footpaths by 7–15% and remarkably removed PM 10 . A
case study in Strasbourg, France, indicated that during 1 year of the study, trees in
the city removed almost 88 tons of total atmospheric pollutants from which 12 tons
of PM 10 and 5 tons of PM 2.5 were removed (Selmi et al. 2016). A study suggested
that trees can trap atmospheric pollutants up to about 7% of total air pollutant
concentration at Marylebone, London (Jeanjean et al. 2017).
80
M. Shahid et al.
transformation of inorganic metal components into more available organic metal
components. In this way, there can be a greater risk of soil-plant metal transfer.
However, there exists comparatively less data about the deposition of metal-PMcontaminated plant litter on soil and its subsequent fate in soil. Further studies are
required to investigate the speciation, bioavailability, and uptake of metals released
from the decomposition of contaminated leaves.
4 Plant Contamination Due to Atmospheric Deposition
of Metal-PM
Besides the deposition on soil, metal-PM also falls on foliar organs of plants (Martin
et al. 2018; Pratte et al. 2018). Urban vegetation is considered an excellent biological
filter as they are efficient in adsorbing and reducing harmful UV rays, noise, and
atmospheric contamination (metal-PM) (Bottalico et al. 2016; Safari et al. 2018).
Dust deposition on a plant’s canopy is a continuous process that is controlled by
wind and gravity, which allows atmospheric dust back to the ground (González et al.
2014; Grantz et al. 2003a). Dust deposition and retention on leaf surface particularly
depend on the roughness of the surface and size of the PM (Fowler 2002; Liu et al.
2018a; Shahid et al. 2017b).
The forest canopy/ecosystem is highly sensitive to atmospheric PM due to the
large interaction surface area (leaf area index ¼ 3–10 m
2 /m
2 ) (Bytnerowicz et al.
2007; Paoletti et al. 2010; Serengil et al. 2011; Sicard et al. 2016; Ulrich et al. 1995).
This interaction between plant canopy and metal-PM includes adsorption of PM,
assimilation, or release of PM by the canopy (Balestrini et al. 1998; Gandois et al.
2010). Several studies have evaluated the composition of atmospheric deposition on
plant canopy as well as the interaction (adsorption, assimilation, etc.) processes
occurring in the phyllosphere (Gandois et al. 2010; Hou et al. 2005). It is reported
that these interaction processes between metal-PM and forest canopy depend on
element-specific dynamics and the morphology of forest canopy. For example, the
speciation, composition, and size of metal-PM govern their environmental pathways, availability, and transport or immobilization in the ecosystem compartments
(Gandois et al. 2010).
Yang et al. (2005) investigated that most of the atmospheric pollutants are
removed by vegetative cover. They estimated that trees remove about 1,261 tons
of pollutants in 2002 from the atmosphere of central part of Beijing, China. In a city
of China, Chen et al. (2015) indicated that vegetation on greenbelts improved
atmospheric quality near footpaths by 7–15% and remarkably removed PM 10 . A
case study in Strasbourg, France, indicated that during 1 year of the study, trees in
the city removed almost 88 tons of total atmospheric pollutants from which 12 tons
of PM 10 and 5 tons of PM 2.5 were removed (Selmi et al. 2016). A study suggested
that trees can trap atmospheric pollutants up to about 7% of total air pollutant
concentration at Marylebone, London (Jeanjean et al. 2017).
80
M. Shahid et al.