The introduction of synthetic-based drilling fluids has challenged both industry and the Environmental Protection Agency to investigate benthic toxicity testing. The need for a synthetic-based mud screening tool has been highlighted by the call for benthic testing to be included into offshore general permits by Coastal Effluent Limitation Guidelines. Outside of the oilfield, development of solid phase testing of dredged material has led to standardized benthic testing protocols accepted by the Agency. ASTM E1367-92, used with Ampelisca abdita and Corophium volutator on sediments spiked with various base fluids, was able to distinguish synthetic-based muds from oil-based muds. It is demonstrated in this paper that analysis of other test species using ASTM El 367-92, and additional testing with A. abdita, can lead to rapid development of a benthic screening tool for incorporation into the next round of offshore general permits. This should promote the continued positive development of synthetic-based drilling fluid technology.


The development and use of synthetic-based muds (SBMs) has resulted in significant advances in pollution prevention efforts for offshore drilling. The introduction of synthetic-based muds has challenged both industry and the Agency to look closely at existing test methods used in the regulation of mud and cuttings discharges offshore. The results of this study show that ASTM E-1367–92 with A. abdita is useful as a screening tool for SBM on the basis that the lower 95% confidence interval (CI) of the synthetic-based fluids was above the upper 95% CI of the diesel oil-based fluid. Continued development of ASTM E1367–92 using A. abdita, combined with investigation of other test species and protocols using the test analysis criteria described in this study, will lead to rapid development of a screening test for synthetic-based muds that will be acceptable to both the Agency and industry.

Development of a Benthic Toxicity Screening Test for Synthetic-Based Muds. Identification of a standardized protocol and test species that would be easily recognized by the EPA was a prime consideration. By using recognized test species and protocol much of the groundwork for meeting the criteria for a screening test would be addressed and validated allowing for rapid development and implementation of a benthic screening test for synthetic-based muds. From the currently available standardized protocols, this study would seek to identity a test that would be reproducible, sensitive to the materials tested and discriminate among potential benthic toxicities of various base fluids. An additional goal was the identification of a species that would have ecological relevance to the discharge environment and could be subject to field validation. Two recognized test protocols were closely examined ASTM E1367–923 (EPA/600/R-94/025) (Amphipods) and ASTM E1611–94 (Polychactous Annelids). The ASTM E1367–2 protocol was chosen as focus of this study. Species included in the test protocol are listed in Table 1. In addition to literature available on the various test species, data available from a field study of a SBM discharge site at North Padre Island Block 895 (NPI-895) was used to select the test protocol and species for this study.

When the mysid shrimp test was introduced, industry had considerable difficulty accepting the mysid shrimp test as a regulatory tool. Some of the key industry concerns that were identified were:

  • lack of validation of the test protocol;

  • lack of availability of the test species;

  • lack of purity in the test species;

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