Agriculture Reference
In-Depth Information
(e.g., sludge, fly ash, slag, etc.) are used as a fill material at numerous locations to
reclaim marshlands, for tank dikes, and for backfill at sites following demolition
(Salunkhe
1998
). Cr(VI) from the soils reaches into the groundwater. The tanning
industry is especially a large contributor of chromium pollution to water resources;
Chandra et al. (
1997
) estimated that in India alone about 2,000-3,200 tonnes of
elemental chromium escapes into the environment annually from the tanning indus-
tries, with a chromium concentration ranging between 2,000 and 5,000 mg L
−1
in
the effluents compared to the recommended permissible limit of 2 mg L
−1
. Cr(VI)
exerts toxic effects on biological systems. It was found that occupational exposure
to hexavalent chromium compounds leads to a variety of clinical problems. Inhala-
tion and retention of Cr(VI)-containing materials can cause perforation of the nasal
septum, asthma, bronchitis, pneumonitis, inflammation of the larynx and liver and
increased incidence of bronchogenic carcinoma. Skin contact of Cr(VI) compounds
can induce skin allergies, dermatitis, dermal necrosis and dermal corrosion (Lee
et al.
1989
). The toxic properties of chromates arise from the possibility of free
diffusion across cell membranes and strong oxidative potential. The toxicological
impact of Cr(VI) originates from the action of this form itself as an oxidizing agent,
as well as from the formation of free radicals during the reduction of Cr(VI) to
Cr(III) occurring inside the cell.
Chromium enters the food chain through consumption of plant material. A high
concentration of chromium in plants has been found to be harmful to vegetation. Both
metal forms cause serious damage to plant tissues and organs and adversely affect
several biological parameters, albeit at different concentrations (Fig.
14.1
). In this
chapter, concept and mechanism of phytotoxicity and the role of metal- binding pro-
teins, phytochelatins, metallothioneins along with other defense strategies that help
in imparting tolerance to plants to withstand chromium stress, has been presented.
2 Uptake and Accumulation of chromium in Plants
Environmental risk associated with increasing chromium concentration into the en-
vironment can be accessed through the study of uptake and accumulation of chro-
mium in plants. Interaction of chromium with plants begins with its uptake process.
The uptake of chromium, especially in + VI oxidation state, is active and is a meta-
bolically driven process (Aldrich et al.
2003
; Diwan et al.
2008
). As chromium is
a nonessential element to plants, they do not possess specific mechanisms for its
uptake. Its uptake is mediated through carriers used for the uptake of essential met-
als for plant metabolism. In barley plants, chromate influx shows Michaelis-Menten
kinetics at an external concentration ranging between 0.52-8.32 µg ml
−1
, and it
is competitively inhibited by sulphate (Shewry and Peterson
1974
; Chatterjee and
Chatterjee
2000
; Cervantes et al.
2001
). Smith et al. (
1989
) reported that Cr(VI)
uptake is a metabolically-mediated process via the sulphate pathway. This suggests
that chromate enters root cells using the same transport system as sulphate. As both
sulphate and chromate appear to be transported by the same transport system (Skef-
fington et al.
1976
), the higher initial uptake of chromate in sulphate-deprived pre-
