Dose-tissue relationships for dieldrin in nestling black-billed magpies

Environmental toxicologists have urged researchers to explicitly identify r elationships between dose level and tissue residues for wild birds (Peakall 1996). If relationships between dose and tissue residues are understood, t hen comparisons of differences in temporal and spatial dieldrin levels are more useful (Blus 1995). We believe it is important to understand the relat ionship between dose (exposure) and tissue residues for monitoring contamin ants in a field environment, particularly when linking exposure to ecologic al effects is a goal. Using non-lethal tissue samples (Fossi et al. 1994) to monitor wildlife exp osure offers several benefits compared to sampling tissues that require sac rificing the study animal. Non-lethal samples allow researchers to sample t he same individual over time and to examine ecological effects of exposure after the sample is collected (Frank and Lutz, 1999). Blood plasma is commo nly used as a non-lethal sample, and has been correlated to residue burdens in humans (Radomski et al. 1971) and several vertebrate species (Fossi et al. 1994), We conducted an "in-nest" closing study using dieldrin and nestling black-b illed magpies (Pica pica) to 1) examine the relationship between dose and t issue residues, and 2) evaluate lethal and non-lethal tissue samples as mea sures of exposure. Our study was conducted during the magpie breeding seaso n in 1997 as part of a larger project evaluating magpies as biomonitors for organochlorine contaminants at the Rocky Mountain Arsenal National Wildlif e Refuge (Refuge) in Denver, Colorado. The information gained from this stu dy will be used to aid in the interpretation of magpie tissue samples colle cted on the Refuge and in the design of a long-term biomonitoring program.