Deformities in cane toad (Bufo marinus) populations in Bermuda: Part III. Microcosm-based exposure pathway assessment

Abstract

Short-term embryo-larval, limb development, and a battery of toxicity identification studies using sediment and water collected from selected ponds found that developmentally toxic samples contained elevated levels of petroleum hydrocarbons and As, Cu, Pb, Cr, Cd, Hg, Fe, and Zn. Sediments spiked with diesel fuel or metals confirmed that the levels of petroleum hydrocarbons and metals found in the sediment were capable of inducing developmental toxicity individually. However, joint mixture interaction studies indicated that the metals and petroleum hydrocarbons acted synergistically. To more rigorously evaluate exposure pathways and the effects induced, chronic laboratory-based microcosm experiments were performed using B. marinus from early embryo to metamorphosis. Results from these microcosm studies indicated that reasonably consistent frequencies of malformations were induced by exposure to contaminated media samples from four contaminated sites compared with frequencies found in field-collected specimens. The frequencies of specific types of deformities in newly metamorphosed organisms from the microcosm studies and in free-roaming field-collected specimens were also similar. Exposure to contaminated media from three of the four sites decreased the frequency of metamorphic completion and at one site reduced the metamorphic rate, compared to exposure to laboratory controls or reference media. Elevated whole body petroleum hydrocarbons and metals tissue residues were detected in organisms from the laboratory microcosms, as well as in the free-roaming specimens collected. To evaluate the impact of maternal contaminant transfer as an exposure route, cross-over exposure studies in which reference organisms were raised, from embryos through metamorphosis, in contaminated media and organisms from a contaminated site were cultured in reference media were conducted. Results from these studies indicated that environmental exposure and maternal toxicant transfer were the potential exposure routes. Overall, the present studies suggested the petroleum hydrocarbons and metals that accumulated in B. marinus during development in microcosms corresponded with increased frequencies of malformation.