Assimilation and subcellular partitioning of elements by grass shrimp collected along an impact gradient

Abstract

Chronic exposure to polluted field conditions can impact metal bioavailability in prey and may influence metal transfer to predators. The present study investigated the assimilation of Cd, Hg and organic carbon by grass shrimp Palaemonetes pugio, collected along an impact gradient within the New York/New Jersey Harbor Estuary. Adult shrimp were collected from five Staten Island, New York study sites, fed 109Cd- or 203Hg-labeled amphipods or 14C-labeled meals and analyzed for assimilation efficiencies (AE). Subsamples of amphipods and shrimp were subjected to subcellular fractionation to isolate metal associated with a compartment presumed to contain trophically available metal (TAM) (metal associated with heat-stable proteins [HSP – e.g., metallothionein-like proteins], heat-denatured proteins [HDP – e.g., enzymes] and organelles [ORG]). TAM- 109Cd% and TAM- 203Hg% in radiolabeled amphipods were ∼64% and ∼73%, respectively. Gradients in AE- 109Cd% (∼54% to ∼75%) and AE- 203Hg% (∼61% to ∼78%) were observed for grass shrimp, with the highest values exhibited by shrimp collected from sites within the heavily polluted Arthur Kill complex. Population differences in AE- 14C% were not observed. Assimilated 109Cd% partitioned to the TAM compartment in grass shrimp varied between ∼67% and ∼75%. 109Cd bound to HSP in shrimp varied between ∼15% and ∼47%, while 109Cd associated with metal-sensitive HDP was ∼17% to ∼44%. Percentages of assimilated 109Cd bound to ORG were constant at ∼10%. Assimilated 203Hg% associated with TAM in grass shrimp did not exhibit significant variation. Percentages of assimilated 203Hg bound to HDP (∼47%) and ORG (∼11%) did not vary among populations and partitioning of 203Hg to HSP was not observed. Using a simplified biokinetic model of metal accumulation from the diet, it is estimated that site-specific variability in Cd AE by shrimp and tissue Cd burdens in field-collected prey (polychaetes Nereis spp.) could potentially result in up to ∼3.2-fold differences in the dose of Cd assimilated by shrimp from a meal in the field. The results of this study also suggest that chronic field exposure can impact mechanisms of metal transport across the gut epithelium that do not influence carbon assimilation. Differences in the assimilation and subcellular partitioning of metal may have important implications for metal toxicity in impacted shrimp populations.