ABNORMAL PORPHYRIN PROFILE IN MUSSELS EXPOSED TO LOW CONCENTRATIONS OF CADMIUM IN AN EXPERIMENTAL PRECAMBRIAN SHIELD LAKE

Seven porphyrins previously suggested as biomarkers of chemical stress in mammals were identified and quantified in the freshwater mussels E lliptio complanata and Anodonta grandis grandis. Uroporphyrin, heptaca rboxyporphyrin, hexacarboxyporphyrin, pentacarboxyporhyrin, coproporph yrin, and protoporphyrin IX were determined using a method based on es terification of carboxylic acid moieties with BF3-methanol, extraction of the derivatives in chloroform, and HPLC-fluorescence analysis. Por phyrin profiles were compared in reference mussels sampled from nonpol luted lakes versus mussels exposed to 100 mu g Cd/L in iron deficient conditions in the laboratory for 1 month or 54-177 ng Cd/L for 4-5 yea rs in an experimental lake (northwestern Ontario, ELA, lake 382). The levels of protoporphyrin and mesoporphyrin were markedly elevated in s pecimens exposed to iron/salts deficiency and 100 mu g Cd/L. In mussel s sampled from lake 382, abnormal alterations in the relative proporti ons of uroporphyrin to heptacarboxyporphyrin, heptacarboxy- to meso-po rphyrin, heptacarboxy- to proto-porphyrin, coproporphyrin to mesoporph yrin, and copro- to proto-porphyrin were consistent with a cadmium-med iated response. Thus, differences in the relative proportions of porph yrins, especially those associated with the accumulation of heptacarbo xyporphyrin, indicate that Cd may be inhibiting uroporphyrinogen decar boxylase, suggesting potential applications of mussels' porphyrin prof ile as an ecotoxicological biomarker for Cd and possibly other metals.