Toxicity of gold crew and SDS dispersants on Tilapia guineensis

Abstract

Oil spill impacted waterbodies are cleaned up using dispersants like Gold Crew® (GC) and sodium diodecyl sulphate (SDS). Since dispersants are chemicals, the potentials for negative impact on the applied environmental compartment cannot be ruled out. This study was a bioassay aimed at investigating the toxicity of Gold Crew and SDS dispersants on Tilapia guineensis. The weight of test organism (T. guineensis) was 222.5±2.11 mg while mean total and standard lengths were 2.20±0.47 and 1.75±0.03 cm respectively. Mean values for physiochemical parameters of habitat water were pH 7.25±0.06, conductivity 13.20± 0.85 μS/cm, alkalinity 18.04±1.12 mg/L, hardness 58.71± 3.24 mg CaCO₃/L, salinity 0.59±0.02 ppt and dissolved oxygen 3.96 ± 1.17 mg/L. All test organisms were first acclimated for 10 days at room temperature (28 ±2 °C). Range finding test was carried out to establish a preliminary working range by obtaining the least concentration that gives no effect and the minimum concentration that gives 100% death. Acute toxicity tests were carried out by exposing the organisms to test solutions containing various concentrations of the dispersants using the semi–static agitation test procedure. The number of test organism decreased with respect to time even at a particular concentration and also decreased as concentration increased. A comparative assessment of the two dispersants showed that Gold Crew was more toxic to the test organism Tilapia guineensis than SDS at the same concentration. A slight concentration of 0.05 ml/L of Gold Crew gave 90 % mortality after 48 h exposure while 100 mg/L SDS gave 100 % mortality at the same duration. Also at 0.05 ml/L Gold Crew and 100 mg/L SDS for exposure period of 72 and 96 h, both dispersants gave 100 % mortality. Gold Crew should be treated as a more toxic dispersant compared to SDS at various concentrations and exposure times and extreme care is needed if it is used during clean-up of oil impacted waterbodies. From the probit analysis of the toxicity results, the lethal concentrations at which 50% of test organism died (LC₅₀) for SDS at various time is given as LC₅₀ (24 h) 54.99 mg/L, LC₅₀ (48, 72 and 96 h) 22.29 mg/L while those of Gold Crew were LC₅₀ (24 h) 0.064, LC₅₀ (48 h) 0.048, LC50 (72 h) 0.029 and LC₅₀ (96 h) 0.025