Abstract
Ecotoxicological effects of the discharge of Nigerian petroleum refinery oily sludge on biological sentinels were examined. The ecotoxicological effects examined included acute toxicity tests on Nitrobacter sp., fresh water shrimp (Desmoscaris trispinosa) and brackish water shrimp (Palaemoneles africanus) from the aquatic environment. It also covered chronic toxicity tests on microbial nitrogen transformation activity in soil and the growth of the terrestrial fauna, earthworm (Apporectoda longa) in pristine soils spiked with predetermined concentrations of the sludge. Analysis of the Nigerian petroleum refinery oily sludge used in this study indicated that the sludge is slightly acidic with a high total petroleum hydrocarbon (TPH) content of 340,000 mg/kg made up mainly between 10-40 carbon unit compounds. The sludge reduced the growth of Nitrobacter sp. in aqueous medium and also caused chronic effect on microbial nitrogen transformation activity in soil because it exceeded the 25% inhibition limit for chemicals with the potential to cause chronic effects on soil microbial activities. Similarly, the sludge exhibited toxicity on fresh and brackish shrimp. The freshwater shrimp was however more affected with an LC50 of 1097.375 ± 0.62 mg/kg when compared with an LC50 of 1590. 37±0.92 mg/kg obtained for the brackish water shrimp. It also reduced the growth rate of the earthworm (A. longa) progressively as the sludge concentration increased. Key words: Toxic effects, petroleum refinery oily sludge, biological sentinels.
Highlights
Petroleum sludge are oily and viscous residues, which are formed during production, transportation, refining of petroleum and storage
In view of the problems encountered in the management of petroleum refinery sludge, this study examined the acute and chronic ecotoxicological effects of Nigerian Petroleum refinery oily sludge on biological sentinels
The physicochemical and microbial qualities of Nigerian petroleum refinery oily sludge shown in Table 1 indicates the sludge was acidic with a pH value of 5.81 ± 0.28 and total petroleum hydrocarbon (TPH) of 340000 ± 50000 mg/kg
Summary
Petroleum sludge are oily and viscous residues, which are formed during production, transportation, refining of petroleum and storage. Petroleum refinery oily sludge is composed basically of oil, water and solids (Ururahy et al, 1998). The oil industry is responsible for the generation of high amounts of oily sludge as waste by-product. One of the problems faced by the oil industry is the safe disposal of the oily waste generated. It is estimated that approximately 1% of the total oil processed in a refinery is discarded as oily sludge (Ururahy et al., 1998). These oily wastes are expensive to store or destroy and previously contaminated areas have required expensive remediation processes to minimize contaminant dispersion
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