134
is costly because it requires a lot of money and is time-consuming. Biomonitoring
has been the alternative method (Markert et al. 2003). Moss, lichens, and plants are
biomonitors available to entrap air pollutants. However, different species of mosses
have been used for biomonitoring in a number of different ways which may lead to
rather different results, and some kind of classification seems necessary at this point.
Epigeic mosses (growing on the ground) are preferred in the regional surveys in
Europe (Fernandez et al. 2007; Harmens et al. 2008, 2010). Trace elements may be
either absorbed on the moss from the atmosphere as soluble chemical species in wet
deposition or contained in particles from dry deposition. Part of the trace element
content of particulates may eventually be released by weathering and reabsorbed by
the moss (Onianwa 2001). Whereas uptake efficiencies for particulate-bound trace
elements are generally poorly known, ions may be subject to active uptake into cells
or attached on the moss surface by physical and chemical forces. Methods are available to distinguish between intracellular and surface-bound fractions of elements.
The main problem with the issue of moss biomonitoring is revealed as (a) the transport of soluble compounds from the soil into moss tissue, particularly during periods with excessive soil/water contact (Onianwa 2001). Although mosses do not
have a root system, influence from this source cannot be disregarded, in particular
in areas with low atmospheric deposition and (b) windblown mineral dust from
local soil.
As far as the surface-bound fraction is concerned, little is known about the binding mechanisms, but the fact that different metals show rather large differences in
their retention capacities indicates that both simple cation exchange on negative
surface charges and complex formation with ligands on the moss surface are
involved. Furthermore, for the last two decades in developed countries, mosses have
been increasingly tested as bio-filters for airborne toxins, with emphasis for the
xenobiotics molecules and heavy metals.
5.2 Mosses as Biomonitors
Bryophytes are non-vascular plants (without conductive vessels) that include
mosses as a separate group. At the organizational level, bryophytes are found among
green algae (of which their offspring are very likely) and among simpler lower vascular plants such as lycopods. Unlike higher plants, the gametophyte (sexual form)
is the dominant generation. The sporophyte (asexual form) develops above the
gametophyte and remains almost entirely dependent on it. Bryophytes do not have
true conductive tissues because they are found in ferns and taller plants (Mägdefrau
1982). Some species of bryophytes are aquatic, and others are able to survive in
warm and dry regions. Although its size varies from microscopic to 30 cm, the average bryophyte measures approximately 1.2–5 cm, with color ranging from green to
black to almost colorless. Hepatic are the most primitive bryophytes and have a flat
shape; sometimes their thickness is only one cell (Mägdefrau 1982).
B. Balabanova et al.
is costly because it requires a lot of money and is time-consuming. Biomonitoring
has been the alternative method (Markert et al. 2003). Moss, lichens, and plants are
biomonitors available to entrap air pollutants. However, different species of mosses
have been used for biomonitoring in a number of different ways which may lead to
rather different results, and some kind of classification seems necessary at this point.
Epigeic mosses (growing on the ground) are preferred in the regional surveys in
Europe (Fernandez et al. 2007; Harmens et al. 2008, 2010). Trace elements may be
either absorbed on the moss from the atmosphere as soluble chemical species in wet
deposition or contained in particles from dry deposition. Part of the trace element
content of particulates may eventually be released by weathering and reabsorbed by
the moss (Onianwa 2001). Whereas uptake efficiencies for particulate-bound trace
elements are generally poorly known, ions may be subject to active uptake into cells
or attached on the moss surface by physical and chemical forces. Methods are available to distinguish between intracellular and surface-bound fractions of elements.
The main problem with the issue of moss biomonitoring is revealed as (a) the transport of soluble compounds from the soil into moss tissue, particularly during periods with excessive soil/water contact (Onianwa 2001). Although mosses do not
have a root system, influence from this source cannot be disregarded, in particular
in areas with low atmospheric deposition and (b) windblown mineral dust from
local soil.
As far as the surface-bound fraction is concerned, little is known about the binding mechanisms, but the fact that different metals show rather large differences in
their retention capacities indicates that both simple cation exchange on negative
surface charges and complex formation with ligands on the moss surface are
involved. Furthermore, for the last two decades in developed countries, mosses have
been increasingly tested as bio-filters for airborne toxins, with emphasis for the
xenobiotics molecules and heavy metals.
5.2 Mosses as Biomonitors
Bryophytes are non-vascular plants (without conductive vessels) that include
mosses as a separate group. At the organizational level, bryophytes are found among
green algae (of which their offspring are very likely) and among simpler lower vascular plants such as lycopods. Unlike higher plants, the gametophyte (sexual form)
is the dominant generation. The sporophyte (asexual form) develops above the
gametophyte and remains almost entirely dependent on it. Bryophytes do not have
true conductive tissues because they are found in ferns and taller plants (Mägdefrau
1982). Some species of bryophytes are aquatic, and others are able to survive in
warm and dry regions. Although its size varies from microscopic to 30 cm, the average bryophyte measures approximately 1.2–5 cm, with color ranging from green to
black to almost colorless. Hepatic are the most primitive bryophytes and have a flat
shape; sometimes their thickness is only one cell (Mägdefrau 1982).
B. Balabanova et al.