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60 O.P. Abioye et al.

Pb ore as eyeliner with therapeutic properties and cosmetic kohl; Pb-based
pigments were used as part of yellow red and white paint. In ancient Rome, Pb
was used to build pipes for water transportation (Rehren 2007).
Plants are the target of a wide range of pollutants that vary in concentration,
speciation, and toxicity. Such pollutants mainly enter the plant system through the
soil (Arshad et al. 2008) or via the atmosphere (Uzu et al. 2010). Among common
pollutants that affect plants, lead is one of the most toxic and frequently encoun-
tered (Cecchi et al. 2008; Grover et al. 2010; Shahid et al. 2011). Lead continues to
be used widely in many industrial processes and occurs as a contaminant in all
environmental compartments (soils, water, the atmosphere, and living organisms).
The prominence of environmental lead contamination results both from its persis-
tence (Islam et al. 2008; Andra et al. 2009; Punamiya et al. 2010) and from its
present and past numerous sources. These sources have included smelting, com-
bustion of leaded gasoline, or applications of lead-contaminated media (sewage
sludge and fertilizers) to land (Piotrowska et al. 2009; Gupta et al. 2009; Sammut
et al. 2010; Grover et al. 2010). In 2009, production of recoverable lead from
mining operations was 1,690, 516, and 400 thousand metric tons by China,
Australia, and the USA, respectively. Despite a long history of its beneficial use
by humankind, lead has no known biological function in living organisms (Maestri
et al. 2010) and is now recognized as a chemical of great concern in the new
European REACH regulations (EC 1907/2006; Registration, Evaluation, Authori-
zation, and Restriction of Chemicals). Moreover, lead was reported as being the
second most hazardous substance, after arsenic, based on the frequency of occur-
rence, toxicity, and the potential for human exposure by the Agency for Toxic
Substances and Disease Registry (ATSDR 2003). The transfer of lead from polluted
soils to plants was therefore widely studied, especially in the context of food quality
use in phytoremediation, or in bio-testing (Arshad et al. 2008; Uzu et al. 2009).
Lead is known to induce a broad range of toxic effects to living organism, including
those that are morphological, physiological, and biochemical in origin. This metal
impairs plant growth, root elongation, seed germination, seedling development,
transpiration, chlorophyll production, lamellar organization in the chloroplast, and
cell division (Sharma and Dubey 2005; Krzeslowska et al. 2009; Gupta et al. 2009,
2010; Maestri et al. 2010). However, the extent of these effects varies and depends
on the lead concentration tested, the duration of exposure, the intensity of plant
stress, the stage of plant development, and the particular organs studied. Plants have
developed various methods for responding to toxic metal exposures. They have
internal detoxification mechanisms to deal with metal toxicity that includes selec-
tive metal uptake, excretion, and complexation by specific ligands, and compart-
mentalization (Gupta et al. 2009; Krzesłowska et al. 2010; Maestri et al. 2010;
Singh et al. 2010; Jiang and Liu 2010). The various responses of plants to lead
exposure are often used as tools (bio indicators) in the context of environmental
quality assessment.