Page 186 - Plant-Based Remediation Processes

178 A. Branzini and M.S. Zubillaga

Fig. 10.1 Contamination sources of the soil–plant–animal system

soil–plant–animal–human), drinking of contaminated groundwater, reduction in
food quality (safety and marketability) via phytotoxicity, reduction in land usability
for agricultural production causing food insecurity, and land tenure problems (Ling
et al. 2007). In fact, one of the most important problems of heavy metals’ contami-
nation, related with their nondegradable condition, is that their accumulation in the
food chain will have a significant effect on human health in the long term (Gleyzes
et al. 2001).
In an ecological research, any metal or metalloid that causes environmental
problem, which cannot be biologically degraded, should be considered as a heavy
metal. Therefore, heavy metals represent an ill-defined group of inorganic chemical
hazards, and those most commonly found at contaminated sites are lead (Pb),
chromium (Cr), arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu), mercury
(Hg), and nickel (Ni) (McLaughlin et al. 1999). Out of the 92 known elements
present on the earth crust, some metals are well known to be essential
micronutrients for plants and animals, and others have no known biological
function.
Essential nutrients could be defined as those without which plants and animals
cannot complete their life cycle, irreplaceable by other elements, and directly
involved in plant/animal metabolism. Consequently, certain levels of micro-
nutrients are necessary to mediate the numerous biochemical reactions essential
for growth and development. Based on the quantity required, nutrients are divided
into macro- and micronutrients. Micronutrients have also been called minor or trace
elements, indicating that their concentrations in tissues are minor or in trace
amounts relative to the macronutrients (Mortvedt 2000). For plants, recycling
organic matter such as grass clippings and tree leaves is an excellent way of