Heavy Metals and Arsenic in Sediment and Muscle Tissues of African Sharptooth Catfish (Clarias gariepinus) from Lake Ngami

Abstract

Concentrations of trace elements were determined in sediment and muscle tissues of African
sharptooth catfish (Clarias gariepinus) from Lake Ngami in Botswana. Sediment and tissue
samples were acid digested and analyzed using ICP-OES. Element concentrations followed
the order iron>>manganese>>zinc>copper>chromium>nickel>lead>arsenic in sediment and
iron>zinc>arsenic>chromium>copper>lead>manganese>molybdenum in fish. Levels in the sediment were
higher than in fish muscles for all but molybdenum, which was below detection in sediment; and arsenic,
which was 2.8 times more in fish muscles. The concentration of arsenic in muscle tissues was also 11 times
higher than reported in previous studies of catfish from African waters. The cancer risk and target hazard
quotient (THQ) for each element in four groups (two Okavango Delta communities, average persons in
Botswana and Sub-Saharan Africa) were assessed following the US-EPA risk assessment method. The THQ
for only arsenic and chromium were above 1, suggesting that the two elements pose an appreciable risk
of deleterious non-carcinogenic effects to human consumers of the fish. The cancer risk from exposure to
arsenic in fish exceeded the acceptable level of 10-4 and ranged from 0.0004 to 0.007. These results support
the need for future research of arsenic and chromium bioaccumulation in benthivorous fish species, which
may be posing health risks to the Okavango Delta communities who rely on these fish as a protein source.