Ponderosa Pine Tree Rings as Historical Monitors of Zinc and Cadmium Pollution

Abstract

AbstractConcentrations of Zn and Cd were determined in growth rings of 13 ponderosa pines (Pinus ponderosa Dougl.) from two watersheds impacted by the discharge of heavy‐metal laden waste. Trees growing along rivers with contaminated sediments have greater concentrations of Zn and Cd than trees growing at uncontaminated reference sites. Concentrations of Zn and Cd in trees from the Coeur d'Alene region (Idaho, USA) decline progressively in younger growth rings. This indicates that reductions in mining activity and implementation of pollution control technologies have reduced Zn and Cd loading in this system. Samples from the Coeur d'Alene region contain Zn and Cd concentrations greater than those found trees from contaminated sites in the Lake Roosevelt (Washington, USA) region. Clearly, the effects of soil and other environmental conditions cannot be accounted for over the past 60 yr. However, dendrochemical analyses suggest that heavy‐metal sulfide wastes in the Coeur d'Alene region have a greater susceptibility to mobilization than siliceous slag wastes in Lake Roosevelt. Concentrations of Zn and Cd measured in a tree growing along an intervening river suggest that Zn and Cd from the Coeur d'Alene basin are diluted before reaching Lake Roosevelt. Radial translocation of Zn and Cd to the heartwood cannot be excluded as a possible influence on elemental distribution of Zn and Cd in ponderosa pine. Nonetheless, the data demonstrates that ponderosa pine can effectively integrate mobile Zn and Cd present in their environment during wood formation.