EFFECTS OBSERVED IN THE WHOLE ANIMAL 961 



The metabolism of the alkyl mercurials and PM in the body is of some 

 importance in understanding the pattern of their effects. PM is one of the 

 least stable mercurials in the body and much of it is split to inorganic 

 mercury, little being retained in any tissue but the kidneys (Miller et al., 

 1960; Gage and Swan, 1961). Very little MM, on the other hand, is split to 

 inorganic mercury; it is slowly excreted and cumulates in certain tissues, 

 such as the brain. Ethyl-Hg is also retained well by the tissues, but is ap- 

 parently split to inorganic mercury at a moderate rate (i.e., faster than MM 

 and slower than PM), so that by the seventh day only 21% of the total 

 mercury in the kidney is ethyl-Hg (Miller et al., 1961). It is odd that at the 

 seventh day all the mercury in the liver is ethyl-Hg, so that one concludes 

 that splitting does not occur in the liver. However, only 70% of the blood 

 mercury is ethyl-Hg, so it seems that the liver takes up some inorganic 

 mercury. It is possible, of course, that all the nonethyl-Hg mercury is not 

 inorganic mercury. 



Toxicity to Aquatic Organisms 



A discussion of the effects of mercurials on animals would not be complete 

 without mentioning briefly some of the interesting work done with marine 

 invertebrates, mainly in connection with antifouling programs, and with 

 fish. One would expect sea water not to be a favorable medium for the ac- 

 tion of Hg++ because of the high concentrations of complexing anions and 

 the elevated pH. The importance of the medium is apparent in the study 

 of the amphipod crustacean Marinogammarus marinus by Hunter (1949). 

 The minimal toxic concentration of Hg++ in sea water is 0.074 mM, while 

 in distilled water it is only 0.0093 vaM. Other factors, such as altered trans- 

 port activity, may contribute to the increased susceptibility. Hg++ at 0.18 

 milf does not depress the respiration of this organism, indicating that the 

 toxic effect is not to be attributed to a general metabolic inhibition. 



Marine invertebrates often show marked changes in susceptibility to Hg++ 

 during development. This is well illustrated by the results obtained on the 

 barnacle Balanus balanoides, the sensitivity to Hg++ reaching a minimum 

 during the free-swimming cyprid stage (see accompanying tabulation) (Pye- 



(Hg++) for 50% lethality 

 (mM) 



Nauplii 



Stage III 0.00033 



Stage IV 0.00085 



Stage V 0.0011 



Stage VI 0.0011 



Cyprids 0.011 



Barnacles 0.0026 



