Agriculture Reference
In-Depth Information
Chapter 14
Chromium Toxicity and Tolerance
in Crop Plants
Ishrat Khan, Hema Diwan and Altaf Ahmad
1 Introduction
Industrialization and technological advancements, the hallmarks of civilization
have been increasing heavy metal releases into the environment, that pose a signifi-
cant threat to environment and public health because of their toxicity, accumulation
in the food chain and persistence in nature. Chromium (Cr) is of particular concern
as it, when accumulated at high levels, can generate serious trouble and diseases
and, as concentration reaches a saturation point, it can become lethal. Within the
environment, chromium is found primarily in two oxidation states: Cr(VI) and
Cr(III). These two oxidation states of chromium are drastically different in charge,
physicochemical properties as well as chemical and biochemical reactivity. Cr(III)
results from the weathering of minerals and is the most stable state of environ-
mental chromium. Cr(VI) in the environment is man-made, the result of contami-
nation by industrial emissions (Bartlett
1991
; Kotas Stasicka
2000
), and is more
toxic (EPAUS
1984
). Examples of Cr(III) compounds include chromium acetate,
chromium chloride, chromic oxide, and chromium sulfate; examples of Cr(VI)
compounds include ammonium chromate, calcium chromate, potassium chromate,
potassium dichromate, and sodium chromate. Although chromium contamination
can originate from natural sources (e.g., in situ weathering of rock minerals can
lead to metal contamination in soils), it mainly comes from several industrial and
agricultural activities such as ore refining, electroplating, tanning, phosphate fertil-
izers and waste disposal on land (Shanker et al.
2005
). Chromium(VI) is used on
a large scale in many different industries, including metallurgical, electroplating,
production of paints and pigments, tanning, wood preservation, chromium chemi-
cals production, and pulp and paper production. Often wastes from such industries
