Biotoxicity is mostly determined by the nature and bioavailability of
As species present in the contaminated habitat. An average toxicity threshold
of 40 mg kg
1 has been established for crop plants (Sheppard, 1992).
At high concentrations, As in plants inhibits plant metabolic processes,
such as photosynthesis through interference of the pentose–phosphate pathway,
thereby inhibiting growth and often leading to death (Marques and
Anderson, 1986; Tu and Ma, 2002). Arsenite penetrates the plant cuticle to
a greater degree than As(V) and generally results in the loss of turgor
(Adriano, 2001).