Influences of prey- and predator-dependent processes on cadmium and methylmercury trophic transfer to mummichogs (Fundulus heteroclitus)

Factors affecting CH3Hg and Cd trophic transfer from six invertebrates and a juvenile fish prey to mummichogs (Fundulus heteroclitus) were investigated using prey-dependent and predator-dependent approaches. Prey-specific trophic availability of metals to mummichogs was estimated using a subcellular partitioning approach (i.e., trophically available metals (TAM), as originally proposed by Wallace and Luoma (2003)). The proportions of CH3Hg partitioned to TAM (CH3Hg-TAM%) ranged from 39.7% to 82.7%, while the proportions of Cd partitioned to TAM (Cd-TAM%) ranged from 51.8% to 67.4%. CH3Hg-TAM% and Cd-TAM% were significantly correlated with the proportions of metals released from prey by in vitro solubilization with mummichog gut fluid (i.e., gut solubilizable metals (GSM)), CH3Hg-GSM% and Cd-GSM%, respectively. This relationship suggests that the majority of CH3Hg and Cd partitioned as TAM in prey were solubilized in the digestive tract of mummichogs. Mummichogs retained 52.7% to 73.7% of the ingested CH3Hg, which was comparable with prey-specific CH3Hg-TAM% and CH3Hg-GSM%. However, mummichogs retained only 3.2%-11.0% of ingested Cd, which was substantially lower than Cd-TAM% or Cd-GSM%. These results suggest that solubilizable, prey-associated CH3Hg was transported through the gut membrane of mummichogs, whereas the majority of prey-associated Cd was excluded and subsequently eliminated, regardless of its subcellular partitioning.