Deformities in cane toad (Bufo marinus) populations in Bermuda: Part II. Progress towards characterization of chemical stressors

An alarming high incidence of deformities in mature and newly metamorphosed Bufo marinus was identified in 2002 (29% in adults and 21% in metamorph specimens) in Bermuda. Suspicion of multiple chemical stressors in many of the effected ponds warranted identification of potential causative agents. Short-term embryo-larval, chronic exposure studies through hind limb development, and a battery of toxicity identification studies were performed with B. marinus and the surrogate species, Xenopus laevis, using sediment and water collected from four target ponds and one reference pond in Bermuda. Short-term embryo larval developmental toxicity studies based on a modified FETAX method indicated that samples from each of the target sites were capable of inducing abnormal development. Malformations induced in the early developmental tests were consistent amongst the species and included abnormal development of the craniofacial region, eye, mouth, and gut. Limb reduction deficit defects were identified in the chronic exposure studies with B. marinus and X. laevis. Toxicity characterization studies found that the toxicity of sediment extracts was variably filterable and reduced by C18-SPE, cation exchange, and zeolite treatments. Developmentally toxic samples contained elevated levels of petroleum hydrocarbons, metals (Al, As, Sn, Cd, Cr, Cu, Fe, Pb, Hg, Mn, Ni, and Zn), and ammonia. Sediment spiking studies with reference sediment confirmed that the levels of petroleum hydrocarbons and metals were capable of inducing developmental toxicity individually. Joint mixture interaction studies with sediment extracts prepared from the individually spiked reference sediment suggested however, that these extracts were potentially capable of acting synergistically, producing a greater level of toxicity than would normally be predicted based on the response to the individual spiked samples.