 the richest uranium ore bodies ever discovered ( cigar lake and mcarthur river ) are presently under development in northeastern saskatchewan . 
 this subarctic region is also home to several operating uranium mines and aboriginal communities , partly dependent upon caribou for subsistence . because of concerns over mining impacts and the efficient transfer of airborne radionuclides through the lichen - caribou - human food chain , radionuclides were analyzed in tissues from 18 barren - ground caribou ( rangifer tarandus groenlandicus ) . 
 radionuclides included uranium ( u ) , radium ( 226ra ) , lead ( 210pb ) , and polonium ( 210po ) from the uranium decay series ; the fission product ( 137cs ) from fallout ; and naturally occurring potassium ( 40k ) . 
 natural background radiation doses average 2 - 4 msv / year from cosmic rays , external gamma rays , radon inhalation , and ingestion of food items . 
 the ingestion of 210po and 137cs when caribou are consumed adds to these background doses . 
 the dose increment was 0.85 msv / year for adults who consumed 100 g of caribou meat per day and up to 1.7 msv / year if one liver and 10 kidneys per year were also consumed . 
 we discuss the cancer risk from these doses . 
 concentration ratios ( crs ) , relating caribou tissues to lichens or rumen ( stomach ) contents , were calculated to estimate food chain transfer . 
 the crs for caribou muscle ranged from 1 to 16% for u , 6 to 25% for 226ra , 1 to 2% for 210pb , 6 to 26% for 210po , 260 to 370% for 137cs , and 76 to 130% for 40k , with 137cs biomagnifying by a factor of 3 - 4 . 
 these crs are useful in predicting caribou meat concentrations from the lichens , measured in monitoring programs , for the future evaluation of uranium mining impacts on this critical food chain.imagesfigure 1figure 2figure 3figure 4figure 5figure 6figure 7figure 8figure 9 
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