INORGANIC AND ORGANIC SOIL AMENDMENTS USED FOR THE IMMOBILIZATION OF CADMIUM IN CONTAMINATED SOILS - Management of Hazardous Residues Containing Cd - page 101

Hazardous Wastes Law (law 24051). Like most other metals, Cd does not
undergo microbial or chemical degradation and therefore persists in soils for a
long time after its introduction. Cadmium has been identified as a major toxic
trace element reaching the food chain, directly through crop uptake or
indirectly through animal transfer (Adriano 2001). Furthermore, Cd is the only
metal that might pose human or animal health risks at plant tissue
concentrations that are not generally phytotoxic (Peijnenburg et al. 2000).
Once ingested or absorbed by humans, it has a long biological half-life and
causes numerous health concerns (Goyer, 1997).
Due to the growing size of the population of Buenos Aires City,
horticulture in urban areas and its surroundings is a means of employment of
migrants from agricultural areas or inmigrants from neighboring countries
(Schnitzler et al., 1999). According to the United Nations (2001), nearly all of
the expected growth in population in the next two decades (2010-2030) will
take place in urban areas, with almost no growth in the rural population. As a
result, peri urban environments are conducive to intensive production of
perishable foods (fruits, vegetables, meat and dairy products) to be consumed
by urban inhabitants. Many studies have shown that Cd is readily taken up by
roots crops and translocated to aerial organs where it accumulates to high
levels (Jiang et al, 2010; Perilli et al, 2010). In particular, vegetables are
capable of accumulating relatively high levels of Cd in the edible portion at
concentrations that may exceed food safety limits (McLaughlin et al., 2006,
Peralta-Videa et al., 2009; Yang et al, 2009).
2. C ADMIUM A VAILABILITY IN C ONTAMINATED S OILS
Soils normally contain 0.1-1.0 mg Cd kg −1 (Kabata-Pendias, 2004). Total
Cd concentration over 10 mg kg −1 may be toxic for plants, inhibiting root and
shoot growth (Palágyi et al., 2006), decreasing soil microbial activity and soil
fertility (Belimov et al, 2005). Nevertheless, total soil concentration of PTE
gives some indication of the level of contamination, but provides no insight
into element bioavailability or mobility. Traditionally, bioavailability refers to
the biologically available fraction that may be taken up by organisms and may
react with its metabolic machinery (Campbell, 1995), or it refers to the fraction
that can interact with a biological target. The chemodynamics of Cd in the soil
environment is controlled by its interactions with both solid and aqueous
phases. Processes such as adsorption/desorption, ion exchange,
precipitation/dissolution, soil and solution phase composition regulate the