Response of Marine Microalgae and Copepod to Toxicity of an Effluent

Discharges of treated effluents from producing industries is a continuous source of pollutants to the marine ecosystems. Typically, effluents comprise of one or more pollutants such as hydrocarbons, heavy metal rinses and detergents of which after treatment, the pollutants may be at a level that could affect the marine ecosystem. This study aimed to determine the acute toxicity of the treated effluent and the response of Microalgae (Skeletonema costatum) and Copepod (Acartia tonsa) when exposed to the treated effluent in a marine system. The microalgae and copepod which are standard test organisms for acute toxicity testing as selected by Nigerian Upstream Petroleum Regulatory Commission were sourced from the Nigerian Institute for Oceanography and Marine Research, Buguma in Rivers State, acclimatized to laboratory conditions and utilized in whole effluent acute toxicity test of the effluent. Utilizing different concentrations of the treated effluent, growth inhibition test (for microalgae) and mortality test (for copepod) were performed using static without renewal option at 22oC under continuous white light for 72 hours. Thereafter, median inhibition/lethal concentration (IC50/LC50) was calculated. The treated effluent was more toxic to Acartia tonsa (72 hours - LC50 473.19 mg/l) when compared to Skeletonema costatum which had 72 hours - IC50 > 100,000 mg/l. The study revealed that the treated effluent displayed moderate toxicity to the copepod and was non-toxic to the microalgae. Hence, more efforts should be put in place by the regulatory agencies to ensure that operators adhere strictly to effective guidelines of waste water treatment to avoid extinction of sensitive species.