Environmental Engineering Reference
In-Depth Information
bioindicator, of risk to human health. Plants also can be used
as bioindicators, of the effects of either acute or chronic
exposure to compounds. For example, in some water-quality
studies, the bioindicator has been algae, where blooms of
algae are associated with the release of excessive nutrients.
One area of research that has received attention is terrestrial
plants used as bioindicators of heavy-metal exposure. This is
because certain plants can accumulate high concentrations
of some heavy metals.
The application of using plants to indicate risk exposure
to decrease contaminant levels and, therefore, reduce risk is
an interesting story in itself. Initially, plant exposure to
chemicals was considered to be a direct route to wildlife
and human populations through ingestion. Plants also were
grown at contaminated sites to determine the extent of con-
taminant transfer, accumulation, and release of the specific
classes of contaminants found at the site. In fact, there are
many sites where plants have been added for the sole pur-
pose of determining the degree of plant exposure to the
chemicals at the site.
In many cases, whole plants are not necessary to deter-
mine the interaction between plants and contaminants. The
use of plant-tissue cultures to study the effect of plants on
chemicals is widespread. This is because tissue-culture tests
can be made with relative ease with respect to whole-plant
studies, and only small amounts of the chemical in question
need be used. Although algal cells typically have been the
focus of tissue-culture studies, the use of terrestrial plants
that make up phytoremediation systems have been
investigated (Wickliff and Fletcher 1991). As part of their
investigation, Wickliff and Fletcher (1991) used tissue
cultures of
Rosa cultivar
(Paul's Scarlet) to which they
added a surrogate for a xenobiotic, 1,3-dinitrobenzene
(DNB). The toxicity of DNB on plant-tissue culture was
examined, as well as the potential transformation of DNB
by plant tissues, by tracking the fate of radiolabel
14
C-1,3-
DNB. The plant growth rate, measured as dried cell weight,
was unaffected by DNB concentrations up to 1 mg/L. As the
concentration of DNB increased to 10 mg/L, however, the
dried cell weight decreased. Part of the explanation for
the lack of a deleterious effect on growth can be found in
the mineralization study results. Radiolabeled DNB was
transformed up to 90% by the plant-tissue cultures, possibly
into a gaseous fraction that did not affect the plant (Wickliff
and Fletcher 1991).
The production of CH
4
at manufactured gas plants pro-
duce wastes that contain cyanide (CN), which interacts
readily with iron. Most vascular plants naturally produce
cyanide as a byproduct during the plant-synthesis of ethyl-
ene. Therefore, plants possess the potential to tolerate CN if
it is released into the environment as a result of industrial use
of cyanide (Larsen and Trapp 2006). Poplar trees (
Populus
trichocarpa
) have been grown in the lab in a solution up to
Table 11.1
Common plants and their toxic compounds.
Plant name
Genus species
Toxin
Poison ivy
Toxicodendron
spp
.
Phenolics
Azalea
Rhododendron
spp.
Grayanotoxin
Oleander
Nerium oleander
L.
Cardiac glycosides
Philodendron
Philodendron
spp.
Oxalate
Foxglove
Digitalis purpurea
L.
Cardiac glycosides
Asparagus
Asparagus officinalis
Various toxins
Fig
Ficus carica
L.
Furocoumarins
Tomato
Lycopersicon
spp.
Alkaloids
Apple
Malus sylvestris
Mill.
Glycoside
Dumbcane
Dieffenbachia
spp
.
Oxalate
Privet
Ligustrum vulgare
L.
Glycosides
Lantana
Lantana camara
L.
Lantanine
Sago palm
Cycas circinalis
L.
Glycoside
Ginkgo
Ginkgo biloba
L.
Alkyl resorcinol
Yews
Taxus
spp.
Alkaloid
Caladium
spp
.
Caladium
Oxalate
Century plant
Agave
spp.
Oxalic acid
Daffodil
Narcissus
spp
.
Alkaloids
Hydrangea
Hydrangea
spp.
Cyanogenic glycoside
Wisteria
Wisteria
spp.
Glycoside
Boxwood
Buxus sempervirens
L.
Alkaloid
Holly
Ilex
spp.
Illicin
Eucalyptus
Eucalyptus
spp.
Glycosides and oils
English ivy
Hedera helix
L.
Saponin
Queen Anne Lace
Daucus carota
L.
Furocoumarins
Carolina Jessamine
Gelsemium simper.
L.
Alkaloids
Chili pepper
Capsicum frutescens
L. Alkaloids
Tobacco
Nicotiana tabacum
L.
Alkaloids
spelled out at the beginning of the environmental age in the
early 1970s that can be traced to the publication of topics
such as “Silent Spring” by Rachel Carson (1962). In that
topic, Carson portrayed a scenario where plants were the
unlucky recipients of the chemists' laboratory concoctions
when, in fact, the plants could produce their own toxic
compounds. Moreover, it is the very encounter of plants
with allelopathic compounds that can be considered as the
first natural analogy to the response of plants to exposure to
released xenobiotic contaminant compounds, especially in
groundwater. These reactions are discussed in Chap. 13.
11.2.2 Plants as Environmental Indicators
Coal miners used to carry canaries in cages as they
descended into mine shafts, because the bird would die
upon exposure to the odorless gas methane or to a lack of
oxygen, which would alert the miners to go no farther.
Today, the same task is carried out by portable gas detectors
that help miners determine when methane reaches levels
high enough to cause a risk of explosion or asphyxiation.
In this case, the canaries acted as a biological surrogate, or
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