Assessment of toxicity of two types of drill cuttings from a drilling rig on the Trinidad East coast using Metamysidopsis insularis

Abstract

This study investigated the relative toxicity of water-based cuttings (WBC) and synthetic oil-based cuttings (SOBC) to the marine species, Metamysidopsis insularis. Results obtained indicate that SOBC (LC₅₀ 1.2 (0.85–1.6)%) was more toxic to M. insularis than WBC (LC₅₀ 9.9 (8.3–11.8)%), with similar metal contents in both types of cuttings. The elevated levels of metals found in the cuttings when compared to surficial sediments may be due to both drilling fluids, as well as the rock strata from which the cuttings were obtained. Furthermore, total petroleum hydrocarbon (TPH) analyses demonstrated significantly higher concentrations of TPH present in SOBC (14,680 ± 1250 mg kg⁻¹) compared to WBC (860 ± 115 mg kg⁻¹). This may also be due to the increased depth and hence oil bearing rock formations in the selected sampling area, along with the associated synthetic oil-based drilling fluid. These findings therefore supply evidence that drill cuttings after treatment prior to discharge are potentially toxic to marine organisms.

Keywords:

• cuttings
• metals
• toxicity
• offshore drilling
• hydrocarbons

Acknowledgments

We would like to thank Baroid Trinidad Services Limited for their kind support in providing the drill cutting samples.