The uptake, tissue distribution and retention patterns of
cadmium, mercury and zinc were examined in the freshwater mussel,
Margaritifera margaritifera. All three of these heavy metals are
found in the environment. Both cadmium and mercury are toxic at
low environmental concentrations. Zinc may also be toxic at low concentrations
but is also a required microelement in plants and animals.
The mussels were maintained in separate solutions containing
radioisotopes of these metals at 14.5°C. The uptake was followed for
39 to 80 days of chronic exposure, at which time a near equilibrium
was reached in most experiments. At this point all animals were
placed in uncontaminated water. Half of them were sampled at intervals
to determine changes in tissue distribution. The remainder
were regularly counted to determine the pattern of retention. An
Armac liquid scintillation whole-body counter was used for all determinations.
The tissue distribution. was remarkably constant over separate
studies lasting from 67 to 150 days. Multicomponent retention
patterns were observed for each metal. The percent of original
whole-body activity remaining after 81 days was 87% for methylmercuric
chloride, 69% for mercuric nitrate, 76% for cadmium
chloride and 57% for zinc chloride. Retention studies were terminated
after approximately 81-150 days. The long term retention
components for cadmium chloride, methylmercuric chloride, mercuric
nitrate and zinc chloride revealed biological half-lives of 835,
860, 194 and 103 days, respectively.
The inhibition of zinc uptake in mussels was demonstrated when
2.0 ppm cadmium was added to the experimental solution. This level
of cadmium also proved toxic to the mussels with a median survival
time of 88 hours. When the cadmium concentration was doubled (4.0
ppm) the median survival time was reduced to 61 hours
