CHRONIC TOXICITY OF NICKEL-SPIKED FRESHWATER SEDIMENTS: VARIATION IN TOXICITY AMONG EIGHT INVERTEBRATE TAXA AND EIGHT SEDIMENTS JOHN M. BESSER,*y WILLIAM G. BRUMBAUGH,y CHRISTOPHER G. INGERSOLL,y CHRIS D. IVEY,y JAMES L. KUNZ,y NILE E. KEMBLE,y CHRISTIAN E. SCHLEKAT,z and EMILY ROGEVICH GARMANz yUS Geological Survey, Columbia, Missouri, USA zNickel Producers Environmental Research Association, Durham, North Carolina, USA (Submitted 26 October 2012; Returned for Revision 27 March 2013; Accepted 29 April 2013) Abstract: This study evaluated the chronic toxicity of Ni-spiked freshwater sediments to benthic invertebrates. A 2-step spiking procedure (spiking and sediment dilution) and a 2-stage equilibration period (10 wk anaerobic and 1 wk aerobic) were used to spike 8 freshwater sediments with wide ranges of acid-volatile sulfide (AVS; 0.94–38 mmol/g) and total organic carbon (TOC; 0.42–10%). Chronic sediment toxicity tests were conducted with 8 invertebrates (Hyalella azteca, Gammarus pseudolimnaeus, Chironomus riparius, Chironomus dilutus, Hexagenia sp., Lumbriculus variegatus, Tubifex tubifex, and Lampsilis siliquoidea) in 2 spiked sediments. Nickel toxicity thresholds estimated from species-sensitivity distributions were 97 mg/g and 752 mg/g (total recoverable Ni; dry wt basis) for sediments with low and high concentrations of AVS and TOC, respectively. Sensitive species were tested with 6 additional sediments. The 20% effect concentrations (EC20s) for Hyalella and Gammarus, but not Hexagenia, were consistent with US Environmental Protection Agency benchmarks based on Ni in porewater and in simultaneously extracted metals (SEM) normalized to AVS and TOC. For Hexagenia, sediment EC20s increased at less than an equimolar basis with increased AVS, and toxicity occurred in several sediments with Ni concentrations in SEM less than AVS. The authors hypothesize that circulation of oxygenated water by Hexagenia led to oxidation of AVS in burrows, creating microenvironments with high Ni exposure. Despite these unexpected results, a strong relationship between Hexagenia EC20s and AVS could provide a basis for conservative site-specific sediment quality guidelines for Ni. Environ Toxicol Chem 2013;32:2495–2506. # 2013 SETAC Keywords: Nickel Sediment toxicity Bioavailability Acid-volatile sulfide (AVS) Sediment quality guidelines INTRODUCTION A variety of approaches have been used to estimate sediment quality guidelines for protection of benthic invertebrates. Empirical guidelines such as Probable Effect Concentrations (PECs) [1] are based on biological effects data for large numbers of sediments with varying physicochemical properties and varying mixtures of chemical contaminants and are intended to estimate toxicity hazards of individual chemicals or chemical classes. Equilibrium-partitioning approaches, such as the US Environmental Protection Agency (USEPA) [2] equilibrium- partitioning sediment benchmarks (ESBs) attempt to reduce uncertainty in toxicity thresholds for specific contaminant classes by modeling the influences of sediment constituents on bioavailability. The European Commission is establishing sediment environmental quality standards for priority substances in water and sediment, including pesticides, industrial chem- icals, and metals [3]. The preferred approach for establishing these standards is to determine a predicted-no-effect concentra- tion (PNEC) based on chronic toxicity data from tests with multiple benthic species [4]. The starting point for development of environmental quality standards is to estimate a PNEC for “reasonable worst-case” (i.e., high-bioavailability) conditions, defined as the 10th percentile of factors that are known to affect the toxicity of a substance. Beyond worst-case conditions, estimation of environmental quality standards that can be applied on a regional or site-specific basis requires documentation of quantitative relationships between sediment characteristics and toxicity thresholds. Development of environmental quality standards for sediment metals has relied on tiered approaches, with PNECs for Zn modified to account for the influence of acid- volatile sulfide (AVS) [5] and PNECs for Cu modified to account for both AVS and total organic carbon (TOC) [6]. We characterized the toxicity and bioavailability of Ni in spiked sediments to support the development of European environmental quality standards for Ni and Ni compounds in sediments. Testing with spiked sediments is the preferred approach for characterizing toxicity of single chemicals in sediments, as opposed to extrapolation from water-only toxicity data [4]. This approach for characterizing Ni toxicity posed several technical challenges, including 1) development of appropriate methods for sediment spiking and equilibration, 2) selection of test organisms that are representative of major taxonomic and ecologic groups of benthic organisms and are amenable to laboratory testing, and 3) selection of sediments for spiking that adequately represent the range of physicochemical characteristics. The first phase of the present study, reported by Brumbaugh et al. ([7], this issue), optimized methods for spiking sediments with Ni to achieve realistic partitioning of Ni among sediment, porewater, and overlying water during toxicity tests. Previous sediment-spiking studies with Ni reported that equilibration with spiked sediments was slower than with several other metals (e.g., Cu, Zn, and Cd) [8] and that changes in pH during spiking and equilibration could alter Ni partitioning and bioavailabili- ty [9,10]. In addition, previous toxicity tests with Ni-spiked sediments indicated that high sediment:water ratios or All Supplemental Data may be found in the online version of this article. * Address correspondence to jbesser@usgs.gov. Published online 8 May 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/etc.2271 Environmental Toxicology and Chemistry, Vol. 32, No. 11, pp. 2495–2506, 2013 # 2013 SETAC Printed in the USA 2495