The deposition rate of metal-PM varies with the type of metal. For example,
Sharma et al. (2008) reported that the deposition rates of PM S of Cu, Zn, and Cd
were significantly higher during winter and summer seasons, while deposition rate of
Pb was higher in summer and rainy seasons. Pandey et al. (2008) investigated the
deposition of dust, Pb, Cd, Ni, Zn, Mn, and Cu at selected urban and suburban sites
of Varanasi, India, using a dust collector. Average fluxes of 2.88, 0.34, 2.96, 12.22,
22.27, and 2.89 g/h
/ year were measured for Pb, Cd, Cr, Ni, Zn, Mn, and Cu,
respectively. The result showed that the dust load was significantly higher in summer
and winter as compared to rainy season. Rohbock (1982) evaluated mass balances of
dry and wet deposition rates separately at 13 sites in Germany. They reported that
metals bound to large PM are deposited mainly via dry deposition, whereas metals
bound to submicron PM are deposited by wet deposition.
After falling on soil surface, the metal-PMs can have different fates in the soil.
This fate of metal-PM is controlled both by soil physicochemical properties as well
as the type, size, and composition of metal-PM. In most cases, the metal-PM is
sorbed on the upper soil surface. For example, Cecchi et al. (2008b) reported that the
soil in the vicinity of a Pb recycling plant was contaminated by Pb, Cu, As, Zn, Sb,
and Sn in the upper horizons.
Inside the soil, heavy metal(loid)s deposited by atmospheric deposition may
occur in different chemical forms. Speciation of atmospheric deposited metal may
vary with the type of metal and the soil characteristics (Jung 2008; Olaniran et al.
2013; Shahid et al. 2013). Cecchi et al. (2008b) reported that 40–60% Pb was mainly
found in the acid-soluble fraction (carbonates and phosphates) between 0 and 50 cm,
while 20–50% Pb was contained mainly in the form of iron oxides. Similarly,
Clemente et al. (2006) found 42% Pb in the same acid-soluble fraction near a
Pb-Zn mine area. It is reported that the heavy metal(loid) fraction deposited on
soil from the atmosphere is generally present in the soil solution (Shahid et al. 2013).
These metals deposited from atmosphere do not become the structural part of soil
constituents. Therefore, it is believed that the heavy metal(loid) contents introduced
to soil via atmospheric deposition or other human activities are more bioavailable
than those present in parent materials or minerals (Cecchi et al. 2008a). However,
this bioavailable/exchangeable fraction of atmospheric deposited metal may vary
with the type of soil and metal as well as the size of PM.
It is also observed that the size of PM attached to metal affects metal bioavailability in soil. Uzu et al. (2009) carried out a microculture experiment with numerous
calcareous soils spiked with micronic and submicronic PM containing
1,650 Æ 20 mg/kg Pb. They reported a higher soil-plant transfer with the finest
PM. This shows that size and composition of PM emitted from industrial units must
be monitored for their possible environmental pollution and associated health risks.
In addition to direct atmospheric deposition of metal-PM on soil, these metalPMs may get attached on plant canopy and then fall on soil with plant litter. In this
case the speciation and fate of metal may vary greatly compared to direct fall of
metal-PM on soil. A study conducted by Shahid et al. (2013) indicated high metal
contamination of topsoil from the decaying of industrially contaminated popular
leaves (litter containing metal-PM). It was demonstrated that organic matter
Ecotoxicology of Heavy Metal(loid)-Enriched Particulate Matter: Foliar. . .
79
Sharma et al. (2008) reported that the deposition rates of PM S of Cu, Zn, and Cd
were significantly higher during winter and summer seasons, while deposition rate of
Pb was higher in summer and rainy seasons. Pandey et al. (2008) investigated the
deposition of dust, Pb, Cd, Ni, Zn, Mn, and Cu at selected urban and suburban sites
of Varanasi, India, using a dust collector. Average fluxes of 2.88, 0.34, 2.96, 12.22,
22.27, and 2.89 g/h
/ year were measured for Pb, Cd, Cr, Ni, Zn, Mn, and Cu,
respectively. The result showed that the dust load was significantly higher in summer
and winter as compared to rainy season. Rohbock (1982) evaluated mass balances of
dry and wet deposition rates separately at 13 sites in Germany. They reported that
metals bound to large PM are deposited mainly via dry deposition, whereas metals
bound to submicron PM are deposited by wet deposition.
After falling on soil surface, the metal-PMs can have different fates in the soil.
This fate of metal-PM is controlled both by soil physicochemical properties as well
as the type, size, and composition of metal-PM. In most cases, the metal-PM is
sorbed on the upper soil surface. For example, Cecchi et al. (2008b) reported that the
soil in the vicinity of a Pb recycling plant was contaminated by Pb, Cu, As, Zn, Sb,
and Sn in the upper horizons.
Inside the soil, heavy metal(loid)s deposited by atmospheric deposition may
occur in different chemical forms. Speciation of atmospheric deposited metal may
vary with the type of metal and the soil characteristics (Jung 2008; Olaniran et al.
2013; Shahid et al. 2013). Cecchi et al. (2008b) reported that 40–60% Pb was mainly
found in the acid-soluble fraction (carbonates and phosphates) between 0 and 50 cm,
while 20–50% Pb was contained mainly in the form of iron oxides. Similarly,
Clemente et al. (2006) found 42% Pb in the same acid-soluble fraction near a
Pb-Zn mine area. It is reported that the heavy metal(loid) fraction deposited on
soil from the atmosphere is generally present in the soil solution (Shahid et al. 2013).
These metals deposited from atmosphere do not become the structural part of soil
constituents. Therefore, it is believed that the heavy metal(loid) contents introduced
to soil via atmospheric deposition or other human activities are more bioavailable
than those present in parent materials or minerals (Cecchi et al. 2008a). However,
this bioavailable/exchangeable fraction of atmospheric deposited metal may vary
with the type of soil and metal as well as the size of PM.
It is also observed that the size of PM attached to metal affects metal bioavailability in soil. Uzu et al. (2009) carried out a microculture experiment with numerous
calcareous soils spiked with micronic and submicronic PM containing
1,650 Æ 20 mg/kg Pb. They reported a higher soil-plant transfer with the finest
PM. This shows that size and composition of PM emitted from industrial units must
be monitored for their possible environmental pollution and associated health risks.
In addition to direct atmospheric deposition of metal-PM on soil, these metalPMs may get attached on plant canopy and then fall on soil with plant litter. In this
case the speciation and fate of metal may vary greatly compared to direct fall of
metal-PM on soil. A study conducted by Shahid et al. (2013) indicated high metal
contamination of topsoil from the decaying of industrially contaminated popular
leaves (litter containing metal-PM). It was demonstrated that organic matter
Ecotoxicology of Heavy Metal(loid)-Enriched Particulate Matter: Foliar. . .
79