A positive linear relation between size and mercury
content of fish is well documented. However, for low
levels of mercury in fish (below 0.2 lg/g) no increase, or
a very moderate increase in mercury content was found
to occur as fish weight increased. As the level of mercury
increased, the mercury level in relation to the weight
increased noticeably. At extremely high levels of mercury,
caused by manifest contamination, no relation to
age or weight was found. This indicates that there is a
threshold level of mercury in the environment, above
which fish cannot eliminate mercury from their muscular
tissues faster than it is incorporated and accumulation
thus occurs. This relationship also indicates that
fish are adapted to a mercury concentration of less than
0.2 lg/g. All past data indicated that the maximum
natural concentration in fish is 0.2 lg/g or less. It should
be noted that 23.3% of fishes caught in the vicinity of the
natural gas platforms in the Gulf of Thailand had
mercury above 0.2 lg/g.