Toxicity assessment of individual ingredients of synthetic-based drilling muds (SBMs) Sajida Bakhtyar & Marthe Monique Gagnon Received: 1 August 2010 /Accepted: 30 August 2011 # Springer Science+Business Media B.V . 2011 Abstract Synthetic-based drilling muds (SBMs) offer excellent technical characteristics while providing improved environmental performance over other drilling muds. The low acute toxicity and high biodegradability of SBMs suggest their discharge at sea would cause minimal impacts on marine ecosys- tems, however, chronic toxicity testing has demon- strated adverse effects of SBMs on fish health. Sparse environmental monitoring data indicate effects of SBMs on bottom invertebrates. However, no environ- mental toxicity assessment has been performed on fish attracted to the cutting piles. SBM formulations are mostly composed of synthetic base oils, weighting agents, and drilling additives such as emulsifiers, fluid loss agents, wetting agents, and brine. The present study aimed to evaluate the impact of exposure to individual ingredients of SBMs on fish health. To do so, a suite of biomarkers [ethoxyresorufin-O- deethylase (EROD) activity, biliary metabolites, sorbi- tol dehydrogenase (SDH) activity, DNA damage, and heat shock protein] have been measured in pink snapper (Pagrus auratus) exposed for 21 days to individual ingredients of SBMs. The primary emulsifier (Emul S50) followed by the fluid loss agent (LSL 50) caused the strongest biochemical responses in fish. The synthetic base oil (Rheosyn) caused the least response in juvenile fish. The results suggest that the impact of Syndrill 80:20 on fish health might be reduced by replacement of the primary emulsifier Emul S50 with an alternative ingredient of less toxicity to aquatic biota. The research provides a basis for improving the environmental performance of SBMs by reducing the environmental risk of their discharge and providing environmental managers with information regarding the potential toxicity of individual ingredients. Keywords Petroleum exploration . Environmental management . Synthetic-based drilling mud (SBM) . Synthetic base fluids (SBF) . Chronic toxicity . Biomarkers . Pagrus auratus Introduction Drilling muds are an essential part of drilling operations for oil and gas exploration. During the drilling process, limited quantities of drill cuttings coated with drilling mud are discharged to the marine environment, a disposal method that requires environmental manage- ment as fluid-coated cuttings act as attracting devices for fish. Cuttings generated by using synthetic-based drilling muds (SBMs) are oil-wet and tend to clump together in large particles on their discharge in the ocean and settle rapidly in the bottom of sea (Neff et al. 1987; Boethling et al. 2007; Neff 2008). Environ Monit Assess DOI 10.1007/s10661-011-2342-x S. Bakhtyar : M. M. Gagnon (*) Department of Environment and Agriculture, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia e-mail: m.gagnon@curtin.edu.au