Aquatic Toxicology 81 (2007) 117–125 Dynamic multipathway modeling of Cd bioaccumulation in Daphnia magna using waterborne and dietborne exposures Richard R. Goulet a,∗ , Susannah Krack b , Patrick J. Doyle a , Landis Hare c , Bernard Vigneault b , James C. McGeer d a Environment Canada, Existing Substances Division, 451 St. Joseph Blvd., Gatineau, Quebec, Canada K1A 0H3 b CANMET Mining and Mineral Sciences Laboratories, 555 Booth Street, Ottawa, Ontario, Canada K1A 0G1 c INRS-ETE, Universit´ e du Qu´ ebec, 490 de la Couronne, Quebec City, Quebec, Canada G1K 9A9 d Department of Biology, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario, Canada N2L 3C5 Received 15 September 2006; received in revised form 16 November 2006; accepted 17 November 2006 Abstract We tested the predictive ability of the dynamic multipathway bioaccumulation model (DYMBAM) to characterize Cd accumulation in Daphnia magna, a species commonly used in toxicity tests and because of its sensitivity, particularly to metals, a species that is relied upon in ecological risk assessments. We conducted chronic exposure experiments in which D. magna were exposed to either dietborne Cd alone or to both dietborne and waterborne Cd. In the food-only treatments, the algae Chlamydomonas reinhardtii or Pseudokirchneriella subcapitata were pre-exposed to free Cd ion concentrations, [Cd 2+ ], from 0.001 to 100 nM (0.001–11 gL -1 ) then, on a daily feeding renewal basis, fed to D. magna over 21 days. In the water plus food treatment, D. magna were exposed for 21 days to the same range of [Cd 2+ ] and fed with the same algal species that had been exposed to Cd at various concentrations. In the algal exposure media, Cd concentrations in algae were directly related to those in water and were characterized by a linear regression model using the log transformed concentration of the WHAM predicted Cd 2+ concentration. The DYMBAM was used with estimated values of the model constants for ingestion rate (0.08–0.34 g g -1 day -1 ) and growth rate (0.085–0.131 day -1 ) based on our experimental data and with literature values for rate constants of Cd influx and efflux as well as Cd assimilation efficiency. Measured Cd concentrations in D. magna agreed with model predictions within a factor of 3. Using the model, we predict that food is an important contributor of Cd burden to D. magna, particularly at lower Cd exposure concentrations over an environmentally realistic gradient of free Cd in water. However, this cladoceran also takes up Cd from water and this exposure route becomes increasingly important at very high concentrations of free Cd (>10 nM or 1.1 gL -1 ). Nevertheless, Cd produced lethal effects in D. magna that were exposed to this metal in water and diet, but exposure to Cd in food only did not result in toxic effects (as measured by survival and reproduction). © 2006 Elsevier B.V. All rights reserved. Keywords: Daphnia magna; Bioaccumulation; Dietary toxicity; Waterborne toxicity; Cadmium 1. Introduction Many water-quality guidelines for trace metals assume that dissolved metals are the main contributor to toxic effects in aquatic organisms (Janssen et al., 2003). Where this is the case, the free ion activity model (reviewed in Campbell, 1995) and its extension, the biotic ligand model (BLM, e.g., Di Toro et al., 2001), are often adequate for predicting the toxicity of metals. Thus, the BLM has successfully been used to predict the effects of short-term (acute) exposures to sensitive animals (Di Toro et ∗ Corresponding author. Tel.: +1 819 994 9556; fax: +1 819 953 4936. E-mail address: richard.goulet@ec.gc.ca (R.R. Goulet). al., 2001; Santore et al., 2001, 2002; De Schamphelaere et al., 2002, 2006; De Schamphelaere and Janssen, 2002; Heijerick et al., 2002b, 2005), which explains its increasing use in establish- ing acute water-quality guidelines. In contrast, most ecological risk assessments focus on long- term exposures. During chronic exposures, animals take up metals from both water and food, both of which can potentially contribute to toxic effects. Waterborne metals usually cause respiratory impairment in fish (Pagenkopf, 1983). The mech- anism of toxicity of many cationic metals is mainly related to specific inhibitory effects on ion transport functions in fish gills (Wood, 2001). This mechanistic information helped guide the development of the biotic ligand model (BLM) framework, which resulted in the development of chronic BLMs for risk 0166-445X/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2006.11.008