Lead uptake and the effects of EDTA on lead-tissue concentrations in the desert species mesquite (Prosopis spp.).

Experimental results have shown that the desert plant species mesquite (Prosopis spp.) is capable of accumulating high levels of lead in the roots, translocating it to the aerial portion of the plant. One-week-old mesquite seedlings were treated for 7 d in a hydroponic culture using a modified Hoagland solution. Six treatments were used; three treatments contained only Pb [as Pb(NO3)2] at 25-, 50-, and 75-mg L(-1) levels and three treatments contained the same levels of Pb, but with equimolar concentrations of disodium ethylenediamine tetraacetic acid (EDTA). Our results showed that the plants exposed to 25-, 50-, and 75-mg Pb L(-1) treatments without EDTA concentrated in stems 524, 3726, and 1417 mg kg(-1), respectively. However, the plants treated with Pb-EDTA concentrated in stems 480-, 607-, and 1247-mg Pb kg(-1) for the 25-, 50-, and 75-mg Pb L(-1) treatments, respectively. Results for the roots followed a similar trend; without EDTA the Pb levels ranged from 16,055, 89,935, and 63,396 for the 25-, 50-, and 75-mg Pb L(-1) treatments, respectively, and with EDTA these levels were 9,562, 49,902, and 39,181 mg kg(-1) for the three treatments. However, the addition of EDTA increased lead movement to the leaves. The levels of Pb without EDTA were 20, 35, and 51 mg kg(-1) for the 25-, 50-, and 75-mg Pb L(-1) levels, respectively. Treatments with EDTA showed uptake levels of 105, 124, and 313 for the 25-, 50-, and 75-mg Pb L(-1) treatments. Further, the percent Pb in dry leaf tissues for all EDTA treatments were greater than 0.1%. However, only the 25-mg Pb L(-1) treatment was greater than 0.1%, compared to 0.04 and 0.08% for the 50- and 75-mg Pb L(-1) treatments, respectively. Preliminary transmission and scanning electron microscopy corroborate the presence of lead.