Biomagnification of mercury in fish from Thruston Bay, Napoleon Gulf, Lake Victoria (East Africa)

Abstract

Total mercury concentrations (THg) were
measured in fish from Thruston Bay, Napoleon Gulf in northern Lake Victoria
between 1998 and 2000. Total Hg concentrations in Lates niloticus (Nile
perch) and Oreochromis niloticus (Nile tilapia) ranged from 10.6 to
77.5ng g^–1 and from 15.0 to 44.5ng g^–1 wet weight
respectively. These concentrations are lower than in the same fish species from
elsewhere in Napoleon Gulf and are in the middle of the range of THg
concentrations from across Lake Victoria. The rate of THg biomagnification, as
indicated by the regression slope of log-THg vs stable nitrogen isotope values
(0.28), is within the ranges of biomagnification rates observed in temperate
and tropical lakes, suggesting that THg is biomagnifying at a similar rate in
Thruston Bay as elsewhere. The low THg concentrations in fish were attributed
to the storage capacity, high oxygen concentrations and high organic matter
content of the wetlands surrounding Thruston Bay. However, caution is required
because the storage capacity and the methylation rates present in the wetlands
of Thruston Bay are unknown and the gradual accumulation of THg contamination
from other sources (e.g. atmospheric THg) may result in unexpected THg
increases in the biota of this system.



African Journal of Aquatic Science
2004, 29(1): 91–96