There is also the possibility of delayed effects as has been shown in certain animal experiments. Other systems besides the nervous system are affected but these have been less well studied. The threshold for mercury effects is not well known. The threshold for neurological effects due to mercury may vary with the pattern of exposure, whether the exposure is acute, subacute, chronic or intermittent and seasonal as in Canadian Indians. Most of the studies are done during epidemics and in these epidemics exposure is often determined by retrospective analysis with all the uncertainties that this implies.
Many questions remain about the effects of mercury on adults.
The Crees have even greater concerns about the effects of mercury on the foetus. Mercury is presumably toxic at lower doses on the foetus and can cause delays in walking and speaking, and abnormal reflexes. Boys are possibly more sensitive than girls. In higher doses it can cause cerebral palsy. The threshold for effects on the foetus is also the subject of debate.