Toxic Effects of Water-Based Drilling Fluid and Its Components on Skeletonema costatum

In order to explore the toxic effects of a water-based drilling fluid and its components,the fluorescence technique was used to measure the toxicity of the water-based drilling fluid—WBF,and its seven principal components (HXJ,PAC141,KPAM,PolyAL,XC,PolyA,Mud)on marine microalgae—Skeletonema costatum,and the median effective concentrations(EC50)of WBF and its seven components at different times were calculated with the fluorescent intensity of Skeletonema costatum without WBF or its components as the control.The following results can be indicated through the calculation: 1) Among the seven components,PolyA has the most intensive toxic effect on Skeletonema costatum with the 96h EC50 equaling to 2×103mg·L-1;PolyAL has a middle toxicity with the 96h EC50 of 3×104mg·L-1,and the other five components are non-toxic substances.2) The joint toxicity of the intensive and middle toxic components changes with time.The joint toxicity of PolyA and PolyAL appears to be synergistic within 24 hours and then turns to be antagonistic.3) The overall toxicity of WBF mainly depends on the toxic component PolyA,while the middle and non-toxic components can be synergistic.