Toxicological Effect of Oil and Water Based Drilling Muds on Soil Nitrosomonas and Nitrobacter spp.

Abstract

The toxic effect of used drill muds on soil Nitrosomonas and
Nitrobacter spp was studied. The 24 hr. acute toxicity test and the 28
day chronic toxicity tests were adopted. Findings revealed that the
drilling muds were relatively acidic with a pH of 4.94 and 6.03 for
oil based mud and water based mud respectively. Both types of mud
contain a wide range of heavy metals, aliphatic and polycyclic
aromatic hydrocarbons, petroleum hydrocarbons and volatile
organic compounds. There was a progressive toxic effect on the
organisms with increase in drill mud concentration. The 24 hr. acute
toxicity effect of the muds to Nitrosomonas sp. recorded EC50 of
503,500.0mg/kg and 398,100.0mg/kg for water based and oil based
muds respectively. The 24 hr. acute toxicity effect of the mud to
Nitrobacter sp. recorded EC50 of 384,500.0mg/kg and
234,400.0mg/kg for water based and oil based muds respectively.
The muds showed marked toxicological effect on the nitrogen
transformation activity in the soil. The percentage inhibition of
nitrite production in the soil by the drill muds ranges between 10.51
– 40.34% and 20.17- 50.28% for the water based mud and the oil
based mud respectively. The percentage inhibition of nitrate
production in the soil by the drill muds ranges between 11.94 –
45.63% and 20.68 – 56.08% percent for water based mud and oil
based mud respectively. Elimination of Nitrosomonas and
Nitrobacter organisms in drilling mud contaminated soil is a threat
to food production.