Distribution and risk assessment of trace metals in Leptodius exarata, surface water and sediments from Douglas Creek in the Qua Iboe Estuary

Five trace metals in Leptodius exarata, epipellic sediments and surface water from an intertidal ecosystem in the Niger Delta (Nigeria) were studied to evaluate their spatial distributions, degrees of contamination, and associated ecological and health risks. The results show that the Cd (cadmium), Cr (chromium), Ni (nickel), Pb (lead) and Zn (zinc) concentrations in sediment range from 0.550-1.142, 9.57-15.95, 9.15-13.96, 2.00-8.90 and 91.5-121.6 mg kg−1 dw, respectively, while the L. exarata tissue metal content varies from 0.162-0.931, 3.81-8.62, 4.45-17.15, 1.90-7.35, and 125.55-269.75 mg kg−1 dw, respectively. The bioconcentration factor ranking for trace metals was found to follow the Zn > Ni > Pb > Cr > Cd sequence. The high biota to sediment accumulation factor (BSAF) found for L. exarata reveals a sentinel metal bioindicator. Sediments from most sites were found to be uncontaminated to moderately contaminated (geoaccumulation, Igeo > 0), with Cd and Zn associated with anthropogenic intrusions. Low mean-ERM (effect range-median) and mean-PEL (probable effect level) quotients of sediments were found, indicating low-moderate degrees of contamination with 30% and 21% probabilities of toxicity. The multi-metal potential ecological risk index (RI) for the intertidal ecosystem denotes low-moderate risk. Health risks associated with crab (L. exarata) consumption are more significant for children than for adults.