Effects of Pb in Tagetes minuta L. (Asteraceae) leaves and its relationship with volatile compounds

Abstract

Soil has traditionally been the disposal site for most heavy metal waste. Since metals can not be degraded, soil remediation requires their removal with phytoextraction, being a cost effective alternative in which metal accumulator plants are used to remove toxic metals from soil. Aromatic crops, used for the production of essential oils, may be a suitable alternative to be used in agricultural soils contaminated with heavy metals, since after removal, a marketable product is left. The present study investigated the effects that high concentrations of lead (Pb) have on the volatile compounds in leaves of Tagetes minuta L., growing near a battery recycling plant and also determined whether Pb was present in its essential oil. In this way, it could be evaluated whether the use of this species for Pb phytoremediation supports safe production. To carry this out, it was determined whether the essential oil obtained by hydrodistillation contained Pb, which was also checked for each individual of T. minuta, by measuring the amount of this metal in leaves using the technique of X-ray Fluorescence and calculating the percentages of volatiles by the HS-SPME technique.The essential oils extracted by hydrodistillation did not have any detectable Pb, there by demonstrating that it is not transferred to the essential oil. Regarding the volatiles, the highest concentrations encountered were for cis-tagetone, dihydrotagetone and verberone. Furthermore, the compounds β-ocimene and α-thujone correlated significantly with the Pb concentration in leaves, indicating that the increase of Pb in T. minuta may favor synthesis of these compounds. In conclusion, T. minuta is a resistant plant that can grow in Pb polluted soils and accumulate the contaminant in aerial tissues, while providing an economic return through the production of essential oil free of Pb.