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Wednesday, November 21, 2018

Biomarker Response of Pink Snapper to Chronic Exposure to Synthetic-Based Drilling Muds


Department of Environmental and Aquatic Sciences, Curtin University of Technology, Perth, Western Australia

In Western Australia, the discharge of drill cuttings at sea is permitted under certain conditions set by regulatory authorities. These drill cuttings are coated with the drilling muds used during the drilling process. Synthetic-based drilling muds (SBMs) are increasingly used in exploration drilling. However, very little is known of their long-term toxicity in the marine environment. The impetus for the present study arose from the concerns raised regarding the long-term environmental impacts of SBMs on marine biota. The project investigated the chronic toxicity of two SBMs, Syndrill 80:20 and Syndrill 90:10, to a marine fish, the pink snapper (Pagrus auratus Forster). Juvenile fish were exposed under laboratory conditions to the two SBMs for 21 days, after which biomarkers of exposure (ethoxyresorufin-O-deethylase [EROD] activity and biliary metabolites) and biomarkers of effects (condition factor, liver somatic index, serum sorbitol dehydrogenase [SDH], DNA damage and heat shock stress proteins HSP-70) were measured and compared to an unexposed group. Results demonstrated that exposure of juvenile pink snapper to the drilling muds Syndrill 80:20 and Syndrill 90:10, did not result in changes in condition factor and liver somatic index. Similarly it did not induce EROD activity nor heat shock stress protein HSP-70 levels, relative to the unexposed group. However, chronic exposure to the SBMs did result in elevated serum SDH levels, as well as increased DNA damage in fish blood. In addition, exposure of fish to the two SBMs resulted in the presence of biliary metabolites, which may potentially interfere with the measurement of polycyclic aromatic hydrocarbon (PAH) metabolites in petroleum-exposed fish. The results of this exploratory study into the chronic exposure of fish to SBMs indicate that SBMs have the potential to affect fish health, and that SBMs should be tested on an individual basis to assess their potential chronic toxicity to fish.

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