Sublethal toxic effects of spent oil based drilling mud collected from an
abandoned oil drilling site in Mpanak, Akwa Ibom State, Nigeria were assessed in the
earthworm
Aporrectodea Longa
. The test annelid was exposed to sub-lethal Concentration of
0ppm SPP; 62,500ppm SPP; 125, 000ppm SPP; 250,000ppm SPP and 500,000ppm SPP of
drilling mud for 28 days. The procedure for the exposure was according to the Organisation
for Economic Co-operation and Development (OECD) recommended method for testing
chemicals No 207. There were three replicate jars per treatment and 10 earthworms per jar of
soil spiked with drilling mud. Control groups were also set up. At the end of the exposure,
bioaccumulation of the chemical constituents of the drilling mud (heavy metals and TPH)
increased (p<0.01) with increase drilling mud concentration. Mean weights of earthworms
increased in the 62,500 and 125,000SPP and decreased in the 250,000 and 500,000SPP.
Glucose levels increased with increase in the drilling mud concentration with the exception of
62,500ppm SPP. The elevated glucose levels could be due to hyperglycemia induced by the
toxicity of the drilling mud. Protein levels increased with increase in drilling mud
concentration except in the 125,000ppm SPP treatment. The increase in protein content could
be due to enhancement of microsomal protein synthesis prompted by the toxicity of the
drilling mud to test organisms. The results of this study have shown that drilling mud and
cuttings could cause serious health risk to
Aporrectodea longa. The discharge of drilling mud
into the terrestrial ecosystems should be discouraged.
