Effects of Organism Size and Weight on the Synthetic-Based Mud Sediment Toxicity Bioassay Using Leptocheirus Plumulosus

Abstract

Proposal The key objective of this study was to identify controllable test parameters that might reduce test variability for the 4-day sediment toxicity bioassay of synthetic-based drilling muds (SBM) required for offshore drill cuttings discharge into the Gulf of Mexico. The factors that produce an effect on the performance of the SBM-sediment toxicity bioassays include quality of mixing procedures, sediment composition, test organism health, size and weight. This study was designed to determine how different sieve sizes might affect the size and weight variability of selected Leptocheirus plumulosus and how this selection affected the LC50 test results of the SBMsediment bioassays. The design focused on organisms collected after passing through a 1000-micron sieve and retained on either 850-micron or 710-micron sieves. Weights of sieve-selected organisms were measured before each bioassay. The data from these bioassays was used to illustrate the relationships between organism sieve size, organism weight, variability of weights within sieve size, LC50 responses to SBMs and the variability of LC50 responses. These test parameters were evaluated for their degree of effect on the SBM-sediment toxicity bioassay test result variability.