Abnormal porphyrin profile in mussels exposed to low concentrations of cadmium in an experimental Precambrian Shield lake

Abstract

Seven porphyrins previously suggested as biomarkers of chemical stress in mammals were identified and quantified in the freshwater mussels Elliptio complanata and Anodonta grandis grandis. Uroporphyrin, heptacarboxyporphyrin, hexacarboxyporphyrin, pentacarboxyporhyrin, coproporphyrin and protoporphyrin IX were determined using a method based on esterification of carboxylic acid moieties with BF3-methanol, extraction of the derivatives in chloroform, and HPLC–fluorescence analysis. Porphyrin profiles were compared in reference mussels sampled from nonpolluted lakes versus mussels exposed to 100 μg Cd/L in iron deficient conditions in the laboratory for 1 month or 54–177 ng Cd/L for 4–5 years in an experimental lake (northwestern Ontario, ELA, lake 382). The levels of protoporphyrin and mesoporphyrin were markedly elevated in specimens exposed to iron/salts deficiency and 100 μg Cd/L. In mussels sampled from lake 382, abnormal alterations in the relative proportions of uroporphyrin to heptacarboxyporphyrin, heptacarboxy- to meso-porphyrin, heptacarboxy- to proto-porphyrin, coproporphyrin to mesoporphyrin, and copro- to proto-porphyrin were consistent with a cadmium-mediated response. Thus, differences in the relative proportions of porphyrins, especially those associated with the accumulation of heptacarboxyporphyrin, indicate that Cd may be inhibiting uroporphyrinogen decarboxylase, suggesting potential applications of mussels' porphyrin profile as an ecotoxicological biomarker for Cd and possibly other metals.