Periwinkle, Tympanotonus fuscatus, was collected from the Cross River Estuary, allowed to acclimate to laboratory conditions for 7 days and exposed to Nigerian crude oil and detergent (Klin) at different concentration intervals of 50, 100, 150, 200, 250 and 20, 40, 60, 80, 100 ml/L of water, respectively for a period of 96 h. A total of 176 mortalities were observed for detergent out of 250 individuals during the entire experiment and 161 for crude oil with higher concentrations recording higher mortalities. Based on the derived toxicity indices, the detergent [96 h lethal concentration (LC50) = 12.42 ml/L] was found to be 7.1 times more toxic than Nigerian crude oil (96 h LC50 = 10.01 ml/L) and 5.8 times (96 h LC95 = 68.83 ml/L) more toxic (96 h LC95 = 396.7 ml/L). The two-way without replication analysis of variance (ANOVA) showed that there was significant difference (Fcrit = 3.5, P > 0.05) between all treatment of crude oil and detergent. One-sample t-test showed significant difference within 24 to 96 h (P < 0.05) mortality response of test animals exposed to toxicants at all concentrations. It is concluded that the detergent used as first generation oil dispersant is more toxic to shellfish than Nigerian light crude oil even at low concentration 20 ml/L of the estuarine water. Also, periwinkle may serve as useful in-situ sentinels for health assessment studies of organic pollutants in aquatic ecosystems.
Key words: Ecosystems, periwinkle, petroleum, crude oil.
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