PERFORMANCE AND SENSITIVITY OF RAPID SUBLETHAL SEDIMENT TOXICITY TESTS WITH THE AMPHIPOD MELITA PLUMULOSA AND COPEPOD NITOCRA SPINIPES STUART L. SIMPSON* and DAVID A. SPADARO Centre for Environmental Contaminants Research, CSIRO Land and Water, Kirrawee, New South Wales, Australia (Submitted 22 May 2011; Returned for Revision 5 July 2011; Accepted 11 July 2011) Abstract —Sublethal whole-sediment toxicity tests are an important tool for assessing the potential effects of contaminated sediments. However, the longer duration required for evaluating potential chronic effects may increase endpoint variability and test costs compared to survival endpoints. In the present study we compare the performance and sensitivity to contaminants of 10-d sublethal sediment toxicity tests with the amphipod Melita plumulosa and harpacticoid copepod Nitocra spinipes. For both tests, sublethal effects were consistently observed when sediment contaminant concentrations exceeded sediment quality guideline (SQG) concentrations. The response of these bioassays in metal-contaminated sediments was shown to conform ideally with respect to the mean SQG quotient calculated on the basis of the Australian and New Zealand lower SQG trigger value, with toxicity being observed only in those sediments where the mean quotient exceeded one. Better predictions of nontoxicity were obtained when dilute acid-extractable rather than total metal concentrations were used. Using the upper SQG, toxicity frequently occurred at mean quotients below one. The effects were generally consistent with predictions from the acid-volatile sulfide and simultaneously extracted metal model. Effects on reproduction of M. plumulosa were detected for sediments that did not cause effects on survival and highlighted the environmental relevance and importance of using these sublethal endpoints. When using four replicates for M. plumulosa and five replicates for N. spinipes, the endpoint variability (standard error) was less than 10%. Variations in sediment particle size and organic carbon content did not affect endpoint variability. Both species are relatively easily cultured in the laboratory, and the estimated effort and cost of achieving the sublethal endpoints is 1.5 times that of the acute survival test endpoints. Environ. Toxicol. Chem. 2011;30:2326–2334. # 2011 SETAC Keywords —Sublethal toxicity Metals Acid-volatile sulfide Sediment quality guideline INTRODUCTION Whole-sediment toxicity tests are an important tool in all sediment quality assessment frameworks [1–4]. Toxicity tests can be conducted for acute or chronic exposure durations. While acute toxicity methods that assess the survival of amphipods after 10 d are by far the most commonly used [5,6], chronic tests are generally considered to be more sensitive to contaminated sediments [7–11]. Chronic tests, which use exposure periods that last for a substantial portion of an organism’s life cycle, typically assess sublethal endpoints, such as reproduction, development, or growth, in addition to survival. Longer exposure durations are expected to provide results that are of greater ecological relevance and amenable to modeling contaminant effects on population dynamics [12–14]. However, chronic tests have not always been determined to be more sensitive than acute methods [9,15], and long test durations sometimes result in greater variability in the performance of these tests [9,15,16]. Increased variability usually requires that greater test replica- tion is undertaken to meet quality assurance criteria and this increases labor intensiveness and costs [16]. Chronic methods have been described for a large variety of benthic marine organisms, including 28-d growth and repro- duction of the amphipods Leptocheirus plumulosus test [5] and Corophium volutator [8], 20-d growth of the polychaete Nean- thes arenaceodentata [17], 14-d reproduction of the copepod Amphiascus tenuiremis [18], and 7-d growth of the juvenile clam Mercenaria mercenaria [19]. However, these Northern Hemisphere species are not frequently used in the Southern Hemisphere [2]. Melita plumulosa is an epibenthic, detritivorous amphipod, native to estuaries in eastern Australia [20], and Nitocra spinipes is a harpacticoid copepod that is common in estuaries and has a worldwide distribution [21,22]. Recently, test procedures have been developed that rapidly assess the potential for chronic effects from sediment contaminants to M. plumulosa [10] and N. spinipes [11]. Both methods are suitable for assessing effects on repro- duction and survival following exposure to whole sediments for just 10 d, which is considerably shorter than the 20 to 28-d periods used in most sublethal sediment toxicity tests [9,16]. In the present study we assessed the performance of these two chronic whole-sediment toxicity tests for use in the assess- ment of sediment quality. The variability in their reproductive output was assessed on control sediments that were largely uncontaminated and exhibited wide ranges of sediment particle size (0–100% silt) and total organic carbon (0–8% TOC). Toxicity tests on a range of predominantly metal-contaminated sediments were used to compare the sensitivity of the test endpoints. The results were interpreted in relation to sediment quality guidelines [23], total or dilute acid-extractable metal concentrations, the acid-volatile sulfide (AVS) – simultaneously extractable metals (SEM) model [24], and the extension of the AVS-SEM model that incorporates the partitioning of metals to sediment particulate organic carbon [25]. MATERIALS AND METHODS Test organisms Melita plumulosa was collected from the Hawkesbury River (New South Wales [NSW], Australia) and was cultured in silty Environmental Toxicology and Chemistry, Vol. 30, No. 10, pp. 2326–2334, 2011 # 2011 SETAC Printed in the USA DOI: 10.1002/etc.633 All Supplemental Data may be found in the online version of this article. * To whom correspondence may be addressed (stuart.simpson@csiro.au). Published online 30 July 2011 in Wiley Online Library (wileyonlinelibrary.com). 2326