Mg. Spalding et al., Methylmercury accumulation in tissues and its effects on growth and appetite in captive great egrets, J WILDL DIS, 36(3), 2000, pp. 411-422
To test the hypothesis that fledging wading birds would be more at risk fro
m mercury toxicosis than younger nestlings, captive great egret nestlings w
ere maintained as controls or were dosed from 1- to 14-wk-old with 0.5 or 5
mg methylmercury chloride/kg wet weight in fish. Birds dosed with 5 mg/kg
suffered from subacute toxicosis at wk 10-12. Growing feather concentration
s were the most closely correlated with cumulative mercury consumed per wei
ght. Blood concentrations of mercury increased more rapidly after 9 wk in a
ll groups when feathers stopped growing. Total mercury accumulated in tissu
es in concentrations in the following order: growing scapular feathers > po
wderdown > mature scapular feathers > liver > kidney > blood > muscle > pan
creas > brain > bile > fat > eye. The proportion of total mercury that was
methylated depended upon tissue type and dose group. Selenium accumulated i
n liver in direct proportion to liver mercury concentrations. After wk 9, a
ppetite and weight index (weight/bill length) declined significantly in bot
h dosed groups. At current exposure levels in the Everglades (Florida, USA)
mercury deposited in rapidly growing feathers may protect nestlings from a
dverse effects on growth until feathers cease growing.