The aim of the study is to assess the sublethal (chronic) ecotoxicological effects of Nigerian petroleum refinery sludge pollution on the biota of the terrestrial environment using the effects on bacteria nitrogen transformation activity and growth rate of the soil fauna, Earthworm (Aporrectodea longa) as bioindicators. The OECD TG 216 (2000) test method was used to determine the chronic effects(% inhibition and EC50) of the petroleum sludge on the nitrogen transformation activity of Nitrobacter sp. in the soil, while the OECD, 207method was used for the chronic effects of the sludge on the growth rate of the earthworms. Bioconcentration factor (BCF) of the sludge in the earthworms was also determined. Both tests were conducted for 28 days.Results from the test with multiple concentrations was analyzed using a regression model (ANOVA). EC5O was also determined using the Probit analytical software. Analyses were done using ASTM methods. Analysis of the Nigerian petroleum refinery sludge used for this research indicated that the sludge was acidic with a pH value of 5.91and had a high TPH content of 340,000mg/kg made mainly of between 10-40 carbon unit compounds. There was a progressive increase in the percentage (%) inhibition of the nitrogen transformation activities of the bacteria, from 18.0% (3125mg/kg) to 79.30% (5000mg/kg) with increase in concentration and time. The effective concentration that decreased 50% (EC50) of the nitrogen transformation activity was 13761.059mg/kg. The growth rate of the test earthworms decreased from 9.19 x 103g/day (375mg/kg) to 3.55 x 103g/day (3000mg/kg) for the test period. The BCF decreased from 5.168 (375mg/kg) to 1.22 (3000mg/kg) in the earthworms, while the EC50 for the earthworms was 825.02mg/kg as the concentration of the sludge increased with time. The sludge inhibited the nitrogen transformation activity of Nitrobacter sp. because it exceeded the 25% inhibition limit for chemicals with the potential to cause chronic effects on soil microbial activities as specified in OECD TG 216. Similarly, the sludge reduced the growth rate of the earthworm progressively as the sludge concentration increased in relation to the control. Bioaccumulation factor also increased with increasing sludge concentration and time.
Keywords: Petroleum Refinery Oily sludge, Chronic effects, Bio indicators, Bacteria, Earthworm
