In determining the health risks of a contaminated site it is important to know when the contamination occurred, or began occurring, and when toxic materials became available to the surrounding biota. Trees growing in the vicinity of a contaminated site may provide such a historic record. Chemical contaminants of soil or water may be picked up in the water entering trees and be deposited in their growth rings. The chemical content of individual tree rings can be examined using a new technique. Individual rings are sampled using laser ablation; the ablated material is then analyzed by mass or optical spectrometry. This study will examine the accuracy of using the laser ablation sampling technique and the ability of tree rings to monitor contamination. The first part of the proposed research will involve locating a suitable test site in Iowa and the second part will involve taking core samples of trees and analyzing the material.