Relationships between Changes of Three Organic Acids (Oxalic Acid, Citric Acid and Tartaric Acid) and Phytoextraction by Sunflower (Helianthus annuus L.) in Sand Cultures Contaminated with Cadmium and Lead

Sand culture was used to investigated the Cd and Pb phyto extraction by sunflower, and changes of organic acids including oxalic acids, citric acids and tartaric acids. The results showed that bioconcentration factors (BCF) of Cd or Pb increased with time and decreased with concentrations, the highest Cd-BCF and Pb-BCF appeared in Cd5 (21) and Pb50(7.95), respectively. The contents of oxalic acids in Cd 40 were the highest (152.20 mg·L
^-1
) at the 90th day. Citric acids in Cd10and Pb400 treatments were higher than other Cd and Pb treatments, which was 578.12 mg·L
^-1
, 413.87 mg·L
^-1
, respectively at the end of the test. Tartaric acids in single Cd or Pb treatments showed increasing trend with time obviously, the highest (474.15 mg·L
^-1
) appeared in Cd5 treatments at the end of this experiment. The presence of heavy metals may influence organic acids secretion from roots. And organic acids could promote bio availability of heavy metals or impact the mechanism of metals uptake, which might result the distinction of Cd or Pb phyto extraction by sunflower. This study may supply useful information for phytoremediation of soil contaminated with cadmium and lead in situ.