ACUTE TOXICITY OF OILY DRILL CUTTINGS ON MANGROVE LITTORAL PERIWINKLE (Pachymelania aurita) OF THE LAGOS LAGOON

Abstract

Acute toxicity of oily drill cuttings against the littoral mangrove periwinkle (Pachymelania. aurita) of the Lagos
Lagoon was evaluated in the laboratory bioassay. 450 specimens of P. aurita were collected from Lagos lagoon
and mangrove swamp, put in different holding tanks, half-filled with lagoon water, and aerated. Sand was placed
at the bottom of the holding tanks serving as substrate. 20 litres of oily drill cuttings were collected. The bioassays
were carried out in glass tanks. The result showed that the acute toxicity of drill mud cuttings based on the
immobility response of P. aurita increased with time of exposure. The concentration that caused 50 % immobility
in the organisms at 24 hours, 48 hours, 72 hours, and 96 hours was 2057.93 ml/L 394.11 ml/L, 321.85 ml/L, and
122.15 ml/L respectively. The median lethal concentration of drill cuttings and fluids against P. aurita decreased
as the duration of exposure increased. There was a significant difference (p< 0.05) between all the treatments at
24, 48, 72, and 96 hours of exposure. There is a need to include bio accumulators such as P. aurita in monitoring
programmes to establish the environmental level of drill cuttings in Aquatic Ecosystems.