136
leaves of B. albicans narrow rather abruptly to a slender tip. H. lutescens is
characteristic of short, unimproved, calcareous grassland, especially on chalk and
limestone. It is also found in other open places, in quarries, and on sand dunes
(Mägdefrau 1982).
The focus of this research is on the uses of the two moss species Hypnum cupressiforme (Hedw.) and Homalothecium lutescens (Hedw.) for monitoring atmospheric
heavy metal deposition in lead-zinc mine environ. Sharing the same common name
“fern moss” with other monitoring mosses, this species similarly has extensive
branching, allowing for a large exposed surface area for ion exchange. These features make H. cupressiforme and H. lutescens a likely candidate for use as a biomonitor. The primary objective of this study was to evaluate the suitability of two
moss species as a bioindicator of heavy metals on a regional landscape scale in the
highly polluted area. To accomplish this objective, we tested the availability of
H. cupressiforme and H. lutescens and possibility of applying two types of moss
interchangeably to cover denser sampling network. Mosses as pollution bioindicators give only an overview of the areas where we found the presence of high content
of toxic metals in atmospheric dust, but not a real measurement of the content in the
ambient air. Because of that, the expressiveness of moss species to the metals content was monitored also.
5.2.2 Active Uptake of Metal Ions
Bryophytes accumulate heavy metals by several mechanisms, but the initial and
frequently limiting step is reversible adsorption on the cell surface (González and
Pokrovsky 2014). Adsorbed metals can be trapped as particulate matter within the
surface layer, dissolved in liquids or deposits surrounding cells (intercellular fraction), bound in exchangeable form to exchange or chelating sites on the cell wall
and outer surface of the plasma membrane (extracellular fraction), or transported
inside the cells and held in soluble or insoluble form (intracellular fraction)
(González and Pokrovsky 2014). The extracellular accumulation of heavy metals is
mediated by the ion exchange process and the formation of complexes between the
metals and the organic functional groups in the cell walls of bryophytes (Shakya
et al. 2008). The great binding capacities of mosses for some heavy metals are often
attributed to the functional groups of polygalacturonic acid and related polymers in
the cell walls (Shakya et al. 2008). Experiments exploring the acid-base properties
of the mosses resulted in the detection of several possible functional groups involved
in the binding of heavy metals. These include phosphodiester, carboxyl, phosphoryl, and amine groups, as well as polyphenols. Considering the organic composition
of the cell walls of mosses, carboxyl and phosphoryl groups could be regarded the
dominant metal-binding groups forming the complexes with heavy metals at the
surface of moss cells. Other groups, such as sulfhydryl and amine, could be determinants in the presence of small amounts of heavy metals or under extreme pH
conditions (González and Pokrovsky 2014). Greater amounts of uronic acids
B. Balabanova et al.
leaves of B. albicans narrow rather abruptly to a slender tip. H. lutescens is
characteristic of short, unimproved, calcareous grassland, especially on chalk and
limestone. It is also found in other open places, in quarries, and on sand dunes
(Mägdefrau 1982).
The focus of this research is on the uses of the two moss species Hypnum cupressiforme (Hedw.) and Homalothecium lutescens (Hedw.) for monitoring atmospheric
heavy metal deposition in lead-zinc mine environ. Sharing the same common name
“fern moss” with other monitoring mosses, this species similarly has extensive
branching, allowing for a large exposed surface area for ion exchange. These features make H. cupressiforme and H. lutescens a likely candidate for use as a biomonitor. The primary objective of this study was to evaluate the suitability of two
moss species as a bioindicator of heavy metals on a regional landscape scale in the
highly polluted area. To accomplish this objective, we tested the availability of
H. cupressiforme and H. lutescens and possibility of applying two types of moss
interchangeably to cover denser sampling network. Mosses as pollution bioindicators give only an overview of the areas where we found the presence of high content
of toxic metals in atmospheric dust, but not a real measurement of the content in the
ambient air. Because of that, the expressiveness of moss species to the metals content was monitored also.
5.2.2 Active Uptake of Metal Ions
Bryophytes accumulate heavy metals by several mechanisms, but the initial and
frequently limiting step is reversible adsorption on the cell surface (González and
Pokrovsky 2014). Adsorbed metals can be trapped as particulate matter within the
surface layer, dissolved in liquids or deposits surrounding cells (intercellular fraction), bound in exchangeable form to exchange or chelating sites on the cell wall
and outer surface of the plasma membrane (extracellular fraction), or transported
inside the cells and held in soluble or insoluble form (intracellular fraction)
(González and Pokrovsky 2014). The extracellular accumulation of heavy metals is
mediated by the ion exchange process and the formation of complexes between the
metals and the organic functional groups in the cell walls of bryophytes (Shakya
et al. 2008). The great binding capacities of mosses for some heavy metals are often
attributed to the functional groups of polygalacturonic acid and related polymers in
the cell walls (Shakya et al. 2008). Experiments exploring the acid-base properties
of the mosses resulted in the detection of several possible functional groups involved
in the binding of heavy metals. These include phosphodiester, carboxyl, phosphoryl, and amine groups, as well as polyphenols. Considering the organic composition
of the cell walls of mosses, carboxyl and phosphoryl groups could be regarded the
dominant metal-binding groups forming the complexes with heavy metals at the
surface of moss cells. Other groups, such as sulfhydryl and amine, could be determinants in the presence of small amounts of heavy metals or under extreme pH
conditions (González and Pokrovsky 2014). Greater amounts of uronic acids
B. Balabanova et al.