Soil contamination by heavy metals is a problem that has long been a concern for the population, and has increased the number of contaminated sites due to the large increase in industrial activities that use these elements during finishing processes. The big issue is that not all heavy metal is purely toxic, and several micronutrients are heavy metals , such as copper (Cu2+) which is part of enzymes involved in oxidation-reduction reactions. This element can have its increased concentration in the soil due to anthropogenic activities and also by excessive use of chemical fertilizers and pesticides. According to CETESB (2005) Cu concentrations from 60 mg kg-1 are considered to have high and require intervention agricultural areas should not have concentrations greater than 200 mg kg-1, and industrial areas 600 mg kg-1. In plants, concentrations between 20 and 30 mg kg-1 are considered to be phytotoxic, but still not known concentration in soil could lead to toxicity. An environmentally friendly alternative is phytoremediation, in which crops are tolerant to heavy metal removal or stabilization of contaminants in the soil. The species Cajanus cajan is a herbaceous legume, which has the favorable characteristics mentioned above, is also used as green manure in agricultural systems, but haven't data about its tolerance to potential toxic elements. Thus, the main objective of this study is to characterize the tolerance and phytoremediation potential of C. cajan heavy metal copper to the potential application of this plant as phytoremediation.
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