353 



"<a) The total global level of mercuir in the environment is of less importance 

 than the fact of its uneven geographical distribution. Concentrated industrial 

 sources of mercury emissions, and the disposal of mercury contaminated muds 

 and sediments in particular constitute major problems. It must also be borne in 

 mind that with changes in technology, new pathways for the accumulation and 

 redistribution of mercury in the environment must be considered. 



"(b) Because of the widespread but as yet incompletely understood possibili- 

 ties of the methylation of inorganic mercury by micro-organisms in the natural 

 environment, any addition to the environmental mercury burden must be con- 

 sidered to represent an additional risk to the well-being of some species in the 

 environment, if not to man himself. 



"(c) The average long-term intake of mercury by humans not otherwise ex- 

 posed to mercury, does not appear to constitute a general health liazard at 

 the present time. Population groups in which predatory fish, or fish and shellfish 

 otherwise contaminated, constitute a major proportion of their diet, are however 

 particularly at risk. 



"(d) Methylmercury is highly toxic to many living species, the critical organs 

 being the brain and the nervous system. 



"(e) Laboratory experiments on animals indicate that even at concentrations 

 below those which cause manifest functional damage, methylmercury can bring 

 about losses from the irreplaceable reservoir of brain cells. 



"(f) Epidemics of poisoning by alkylmercury (particularly methylmercury) 

 comix>unds have occurred in the past, due to ignorance or misuse, and these con- 

 tinue to occur. In all several hundrp<l. if not thousands of deaths may have been 

 involved. Unborn children are particularly at risk because of the concentration of 

 the mercury in the foetus. 



"(g) The possibility of future repetition of such catastrophes as that in Iraq 

 will remain so long as stocks of methylmercury fungicides remain. UnoflScial esti- 

 mates suggest stocks of more than a hundred tons of this material, which would 

 be enough to cause another 50 catastrophes of the Iraq type. 



"(h) Laboratory experiments have demonstrated that organic mercury at 

 relatively low concentrations, can produce genetic aberrations in .some species. 

 Although this has been shown to occur in man (Skerfving, 1972), further elucida- 

 tion of the likelihood of these effects in humans and higher organisms is neces- 

 sary. The opportunity of examining damaged human material from the Iraq 

 catastrophe may provide valuable information in this regard. 



"(i) Although there is a substantial body of knowledge of the damage in 

 patients showing clinical symptoms of organic mercury poisoning, little is known 

 concerning the damage sustained by those showing subclinical symptoms. The 

 mechanism and early diagnosis of the delayed onset of mercury poisoning remain 

 unknown. 



"(j) There is no simple prescription for evaluating the risks of damage to 

 species in the environment, including man, consequent on the existence of mer- 

 cury. The problem is of its nature a complex one. 



"(k) In terrestrial systems it has been shown that the application of methyl- 

 mercury as seed dressing in accordance with prescription may give rise to in- 

 creased mortality of seed eating birds and birds of prey. Effects of mercury on 

 reproduction in wild birds has not been demonstrated so far. 



"(1) Aquatic ecosystems may become exposed to excessive levels of mercury 

 in areas where it is disposed of in surface waters. It has been shown that this 

 may give rise to increased risks to various organisms including phytoplankton 

 fish and other vertebrates. 



"(m) Legislative controls of mercufy use and discharge (not si)ecifically re- 

 viewed in this report) have had a beneficial effect on some environmental mer- 

 cury levels, both in water and in aquatic and avian .specie*. 



"(n) Recent findings indicate that a possible functional relationship might 

 exist between mercury and selenium, possibly resulting in protection against the 

 toxic action of methylmercury in the body. This may be important in relation 

 to the high mercury and selenium levels found in marine mammals. 



"(o) Particularly with respect to marine mammals, the question can be raised 

 to what extent any possible biochemical protective mechanism against mercury 

 toxicity will be functioning when the rate of exposure increases. The possibility 

 will have to be considered that for certain organisms, especially those whose 

 ability to excrete mercury compounds is limited (e.g. seals) even a minor In- 

 crease in the environmental load of mercury could represent a serious hazard. 



