EFFECTS OF MERCURY ON THE BIOSYNTHESIS OF PORPHYRINS IN BIVALVE MOLLUSKS (CERASTODERMA-EDULE (L) AND C-LAMARCKI (REEVE))

Growth of Cerastoderma (= Cardium) edule (L.) and C. lamarcki (Reeve) ''posed to mercury in situ in the western part of the Limfjord, Denmark, was compared with that of non-exposed populations. Physiological condition index values of cockles sampled during growth periods in 1990 and 1991 were not significantly different for exposed and non-exposed populations when species, length, and sampling date were taken into account (stepwise multiple regression analysis, and ANOVA). Mercury exposure in the laboratory confirmed these findings. Biosynthesis of porphyrin precursors, delta-amino levuleic acid (ALA) and porphobilinogen (PBG), detected by ion-exchange chromatography, was clearly perturbed by mercury exposure in the environment as well as in laboratory experiments; thus, the two biochemical components can be considered biomarkers of mercury exposure. For the porphyrins (uro-, proto-, and copro-porphyrins) detected by HPLC, no general effect could be established. The mechanistic basis of disturbance of the essential porphyrin biosynthesis (the prerequisite of cytochrome formation) and a possible alternative porphyrin source are discussed.