Acute Toxicity and Hydrocarbon Composition of a Water-Based Drilling Mud Containing Diesel Fuel or Mineral Oil Additives

Abstract

A series of static and flow-through toxicity tests was conducted to determine the toxicity of drilling mud that contained three classes of hydrocarbon additives-low-sulfur diesel fuel, high-sulfur diesel fuel, or a commercial mineral oil additive-to four species of marine invertebrates. The hydrocarbon additives were chemically characterized by computerized gas chromatography/mass spectrometry. The base mud was a laboratory-formulated freshwater lignosulfonate mud (generic mud No. 8). Acute toxicity tests were performed with mysids (Mysidopsis bahia) by using the suspended particulate phase (SPP) of a 1 : 9 dilution of drilling mud with seawater. Ten-day solid phase (SP) toxicity tests were conducted with sand worms (Nereis virens). grass shrimp (Palaemonetes pugio), and soft-shell clams (Mya arenaria) by using mud solids that settled to the bottom of the mixing container during a 1-h settling period. Exposure concentrations of total hydrocarbons, biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total organic carbon (TOC) were confirmed analytically. Base mud without additives was practically nontoxic. Drilling mud that contained 5% mineral oil was less toxic than mud containing 5% of either low- or high-sulfur diesel fuel additive, with LC50 values of 3090, 451, and 276 mg/L, respectively. Drilling mud solids containing mineral oil were not acutely toxic to the test organisms, but lethality was observed when animals were exposed to the mud solids that contained 5% diesel fuel.