SUBLETHAL NARCOTIC IMPACTS OF DIETARY POLYCYCLIC AROMATIC HYDROCARBONS ON THE BIOENERGETICS OF AND POLYCHLORINATED BIPHENYL (PCB) BIOACCUMULATION IN FUNDULUS HETEROCLITUS

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2005-09-27

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Abstract

Accumulation of non-polar narcotic chemicals in organisms alters their metabolic rates and therefore, their energetic demands. It is hypothesized that decreases in standard metabolic rate from accumulation of narcotics reduces feeding. Thus, exposure to and accumulation of narcotics may cause a negative feedback, reducing net bioaccumulation. Three experiments were conducted to examine the consequences of narcotic exposure on the bioenergetics and bioaccumulation rates of Fundulus heteroclitus continuously challenged with sublethal levels of hydrophobic organic chemicals (HOCs).

In the final experiment (120 days), fish were exposed to two concentrations of a model narcotic, 3-aminobenzoic acid ester methanesulfonate (MS-222) (0 and 50 mg/L), and four concentrations of PAH-contaminated food treatments sampled over five time points. All food treatments contained background concentrations of polychlorinated biphenyl (PCB) congeners (40 ng/g -PCBs w/w) and were used as a tracer of bioaccumulation. No statistically significant differences in weight, length, or condition factors among treatments, except on day 120 where MS-222 exposed fish were longer than non-MS-222 exposed fish (p = 0.015). Standard metabolic rate responded in a non-linear manner. At low PAH doses (835 ng/g -PAH), SMR decreased significantly (p = 0.093,  = 0.10). Fish fed 100% PAH-contaminated food (regardless of MS-222), had significantly elevated SMRs (p = 0.02). MS-222 did not affect PCB accumulation. PAH-contaminated food enhanced PCB accumulation measured in fish. There was an overall interaction between the food treatment and aqueous MS-222 exposures (p = 0.004). The results indicate that total chemical burden from the MS-222 plus PAH-contaminated food exposures masked the sublethal narcotic effect of MS-222, and produced a net increase in the standard metabolic rates of Fundulus heteroclitus, perhaps because of increased energetic costs associated with detoxification and bioactiviation processes.

The results of the experiments were subtle and non-linear with respect to dose of PAH-contaminated food. To explore whether small changes in SMR (± 5 - 10 %) may be important costs, a bioenergetics model was developed.  The model tracks biomass (daily age classes) based on a balance of weight-specific consumption and bioenergetic costs (respiration, growth, and mortality).  The model projects population biomass as the main output for comparing different "impacts."

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