Assessment of biodegradation and toxicity of drill-muds used in an onshore active field located in Edo State,Nigeria

The biodegradation and toxicity of two drill-muds used in an onshore oil field located in edo state were examined. biodegradation of drill-muds by two bacterial and fungal isolates; citrobacter sp.,staphylococcus sp.,aspergillus sp. and penicillium sp. were carried in a shake flask experiment using mineral salts medium at 120 rpm for 28 days. the total viable counts were monitored and ultimate biodegradability was derived from the ratio of chemical oxygen demand and biological oxygen demand (bod5),after every four days. the water based mud was more degradable than non-aqueous based mud. this was shown by the highest total viable counts recorded in consortium amended with water based mud (126 ×103 cfu/ml),and also recording the lowest chemical oxygen demand and biological oxygen demand (45 mg/l and 0.38 mg/l,respectively). there were no significant differences (p > 0.05) in the degradation of the muds by the isolates. the 96 hrs and 24 hrs acute toxicity bioassay were carried out using juvenile fishes (tilapia guineensis) and microorganisms (staphylococcus sp.and aspergillus sp.),respectively. the different concentrations were prepared for fishes (in aquaria) and microorganisms (conical flask). mortality was recorded after 8,24,48,72 and 96 hrs and 0,2,4,8,12 and 24 hr at 30 0c to assess toxicity. the 96 hr lethal concentration,50 % (lc50) of water based mud and non-aqueous based mud (nabm) were greater than10,125 mg/l and 6000 mg/l for tilapia guineensis,respectively. the 24 hr lethal concentration,50 % (lc50) of water based mud was 370 mg/l for staphylococcus sp. and aspergillus sp. therefore,these selected isolates have the potential applications in the bioremediation of sites polluted by these drill-muds. also,in the interest of the environment,oil exploration and production companies operating in edo state and other parts of nigeria should strictly adhere to the use of non-toxic and biodegradable drilling muds during exploration activities. © 2017 jordan journal of biological sciences.