HEAVY METALS BURDEN IN WATER AND SEDIMENT, AND OXIDATIVE STRESS RESPONSES IN THE BLUE CRAB Callinectes amnicola ROCHEBRUNE, 1883 FROM LAGOS LAGOON

Abstract

Lagos Lagoon (LL) sustains a diverse array of fish and crustaceans but is vulnerable to anthropogenic activities from the hinterlands. Industrial facilities around the lagoon continuously discharge effluents laden with pollutants such as heavy metals, which may impact negatively on resident biota including the blue crab, Callinectes amnicola. Assessing indices of oxidative stress can reveal relative ecological risks of pollution to species in their natural habitat. However, the information on the use of Callinectes amnicola that could serve as sentinel species for assessing pollution in LL is scarce. This study was designed to determine heavy metal concentrations and oxidative stress responses inCallinectes amnicolafrom LL habitat.

Monthly samples of surface water, sediment (n=288 each) and crab (n=1750, using circular lift nets mesh 50-76mm) were collected between December 2011 and November 2013 from six sampling stations; Mid-lagoon, Makoko, Oko-Baba, Iddo, Ajah and Ikoyi. Cadmium, lead, copper and zinc were analysed in surface water, sediment and crab organs (hepatopancreas, gill, gonad and muscle) samples using Atomic Absorption Spectrophotometer. Biota Sediment Accumulation Factor (BSAF), condition factor and seasonal variation in Pollution Load Index (PLI) were calculated using standard formulae.Activities of oxidative stress enzymes: Superoxide Dismutase (SOD), Catalase,Glutathione Peroxidase (GPx), Reduced Glutathione(GSH) and Malondialdehyde (Lipid Peroxidation) in crab organs were determined using standard methods. Further assessment of tissue damage was carried out using histopathological method.Data were analysed using descriptive statistics and ANOVA at α 0.05.

Cadmium, lead, copper and zinc concentrations(0.4±0.02, 0.3±0.22, 0.1±0.1, 0.03±0.01mg/L) were lower in surface water than corresponding concentrations in sediment (2.7±1.2, 51.9±45.2, 60.1±53.9, 37.1±27.4 mg/kg) respectively. Heavy metals level in surface water were lower at Mid-lagoon (Cd-0.02±0.02, Pb-0.18±0.16, Cu-0.07±0.06, Zn-0.001±0.000) and higher in other stations (range: Cd-0.02-0.4, Pb-0.12-0.3, Cu-0.02-0.08, and Zn-0.01-0.03) than respective NESREA limits of 0.005, 0.01, 0.001 and 0.01 mg/L. Concentrations of cadmium, lead, copper and zinc (mg/kg) in organs of crabs from Mid-lagoon were lower (0.05-0.1, 0.03-0.29, 1.23-2.69, 1.18-3.18) and higher at all other stations (0.20-1.56, 1.11-5.17, 1.43-6.83, 5.17-40.24) respectively than NESREA limits. The BSAF was higher in organs of crabs from all stations (0.6-5.3) than those from Mid-lagoon (0.2-0.5).Condition factor was significantly highest at Mid-lagoon (0.8±0.3) than other stations (0.5±0.1-0.6±0.1). The PLI which incorporated metal concentrations in sediment revealed highest concentration (1.9) at Makoko followed by 1.2, 1.1, 0.7, 0.4 and 0.3 at Oko-Baba, Iddo, Ajah, Ikoyi and Mid-lagoon, respectively for the dry season. In the rainy season, highest PLI of 1.5 was at Iddo followed by 0.9, 0.6, 0.4, 0.3 and 0.2 at Makoko, Oko-Baba, Ikoyi, Ajah and Mid-lagoon, respectively. Levels of SOD, GPx, GSH and Catalase in crab organs were significantly low at the sampling stations; while Malondialdehyde concentrations were significantly higher in crab organs from all sampling stations except those from the Mid-lagoon. Pathological changes including necrosis were observed in crab organs, in all stations except Mid-lagoon.

The Lagos Lagoon was laden with heavy metals from industrial discharges. This could explain the induced oxidative damage inCallinectes amnicolafrom the Lagoon.