Lost Circulation Specialists, Inc.

LC-50 Test

Acute Toxicity of Drilling Fluid Sample 218-14-1

Drilling Specialties Company
309 Short Street
Bartlesville, Oklahoma 74004
Enseco Incorporated
Doaks Lane at Little Harbour
Marblehead, Massachusetts 01945
May 1987


Exposure of mysids (Mysidopsis bahia) to the suspended particulate phase of the drilling fluid (the unfiltered fraction of the nonsettleable portion of a 1:9 mixture of drilling fluid and seawater) resulted in a 96-hr LC50 of greater than 1,000,000 ppm

The test with mysids was conducted according to methods of the U.S. Environmental Protection Agency (1985) as defined in the Enesco Aquatic Toxicology standard operating procedure 085-110. The test was conducted at 20°C using seawater adjusted to a salinity of 20 parts per thousand (ppt). Mysids were purchased from a commercial supplier and cultured in Enseco's Aquatic Toxicology Laboratory under test conditions. All data analysis for the test was performed using nominal concentrations of suspended particulate phase.

Methods and Materials

The drilling fluid (Enseco Sample Number AM0518) was delivered to Enseco Marblehead on April 17, 1987. It was packed in a polyethylene container, shipped in an ice chest, and was immediately placed in cold storage at 2°C in Enseco's Aquatic Toxicology Laboratory in Marblehead, Massachusetts. The drilling fluid had a pH of 8.4 and did not emit a foul odor. Black spots were not present on the container walls. The label attached to the container bore the following information:

Drilling Specialties Preparation II 218-14-1
Generic Mud #7 + 20 lbs/BBL Magma Fiber

The drilling fluid was prepared for biological testing according to procedures described in Draft Methodology: Drilling Fluids Toxicity Test (U.S. EPA, 1985) as defined in Enseco SOP 085-110. All glassware was cleaned according to methods detailed in the
procedure. The drilling fluid was thoroughly homogenized for 30 min with a four-bladed mixer. The homogenized material was then combined with seawater (salinity = 20.0 ppt, 1.0 micron filtered) in a 1:9 ratio by volume in a 2-liter, large-mouth Erlenmeyer flask. The drilling fluid-seawater mixture, which was characterized by a pH of 8.1, was mixed for 5 min with a magnetic stirrer and allowed to settle for 1 hr. During the 5-min mixing period, the pH was adjusted to the pH of the seawater. Following the settling period, the suspended particulate phase was carefully decanted and mixed for 5-min. The pH was
measured, and a dissolved oxygen concentration above 4.9 ppm was verified. The phase was diluted to test concentrations, which were each mixed for an additional 5 min and used immediately in the toxicity test.

The test with the suspended particulate phase was conducted during May 13-17, 1987. Mysids employed as test organisms were 3-6 days old. They were purchased from a commercial supplier and cultured in seawater at Enseco's Aquatic Toxicology Laboratory. Testing occurred at 20°C with mysids that were fed 10-12 live Artemia (brine shrimp) nauplii per mysid every day. Tests were conducted with five concentrations of suspended particulate phase, a control, and the standard toxicant, sodium lauryl sulfate, with 60 mysids randomly distributed among three replicates of each treatment. Tests were performed in 2-liter Caroline Culture Dishes which contained 1 liter of test solution. Culture dishes were randomly arranged during the 96-hr test. Filtered (1 micron) seawater with a salinity of 20 ppt was used to dilute the suspended particulate phase to test concentrations and as the control. A 14-hr light and 10-hr dark photoperiod was maintained with cool-white fluorescent lights (1200 microwatts/cm2). Aeration was employed in each test container. Air was supplied by a model SL4P-33 Roton blower and delivered through a 1-ml disposable pipette (surface area = 1 mm2) at the rate of approximately 10 cm2/min. Mysids were confined in Nitex cages during testing. The number of surviving mysids could not always be determined by means of visual counts after 24, 48 and 72 hr, because concentrations of suspended solids precluded observation. At a minimum, the number of survivors was determined at 0 and 96 hr. Dissolved oxygen, pH and salinity were measured daily, and temperature of the environmental chamber was continuously recorded.

Results of the text (Appendix A) could not be interpreted by standard statistical techniques (Finney, 1971; Stephan, 1983) because greater than 50% survival occurred at the highest tested concentration.


Data generated by the acute toxicity test with mysids are presented in Appendix A. Greater than 90 percent survival occurred in the control exposure.

The 96-hr LC50 for the standard toxicant, sodium lauryl sulfate, was 8.3 ppm toxicant. The 96-hr LC50 for this sample of drilling fluid tested with mysids was greater than 1,000,000 ppm suspended particulate phase. The suspended particulate phase of the drilling fluid contained 10,000 mg/1 filterable residue and 20,000 mg/l unfilterable residue.

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