Environmental monitoring of soil contaminated with heavy metals using laser-induced breakdown spectroscopy

Research on the detection of heavy metals in soils and water using laser-induced breakdown spectroscopy (LIBS) has been carried out. LIBS is based on a Nd:YAG laser operating at 50-100 mJ at λ=1.06 μm. The beam is focused on the surface of the sample to produce a laser spark (plasma). The atomic emission lines are recorded using an optical multichannel analyzer (OMA) after specific gate delay times. Gating delay times of a few microseconds allow broadband emissions to decay before detecting heavy metal emission lines. This remote sampling technique has application in monitoring both land and ocean sites containing heavy metals. Research has been performed on the detection of As, Cd, Cr, Hg, Pb, and Zn. Results are reported on the detection levels of Cr in soil samples. In addition, computer software has been developed to automate the identification of atomic emission lines for mixed matrices of these heavy metals in background emissions from elements typically in soil. Future plans are to determine the minimum limits of detection for various heavy metals by a typical LIBS system based on a Nd:YAG laser and a fiber-optic collection system for the plasma emissions.