Selected Pharmaceuticals Not Likely to Persist in Wild Fish: Results of Uptake and Elimination Testing

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Laboratory study shows that both uptake and elimination of selected pharmaceuticals within bluegill tissues is rapid indicating that persistence in bluegills in the environment is likely to be low except in those fish that reside downstream from a consistent, substantial, contaminant source.

Bluegill (Lepomis macrochirus)

Laboratory study shows that both uptake and elimination of selected pharmaceuticals within bluegill (Lepomis macrochirus) tissues is rapid indicating that persistence in bluegills in the environment is likely to be low except in those fish that reside downstream from a consistent, substantial, contaminant source.

(Credit: Trisha Shears. Public domain.)

Pharmaceutical use by humans, subsequent transport to wastewater treatment systems, and release to surface waters has been extensively studied and well documented globally. Chronic and subtle effects of pharmaceutical exposure through water have been reported for non-target fish including those related to reproduction, behavior, and growth. Although the effects of contaminants are related to the quantity of a contaminant that reaches an internal organ or tissue, little is known about the details of uptake and elimination of pharmaceuticals by exposed fish.

To this end, U.S. Geological Survey (USGS), Chinese Academy of Science, and St. Cloud State University scientists investigated the uptake and elimination of five pharmaceuticals in bluegill sunfish to aid in understanding the exposure risks, if any, to aquatic organisms or to humans through fish consumption.

A laboratory flow-through system was used to expose fish to pharmaceutical concentrations that mimicked those found in close proximity to continuously discharging wastewater outflows. Five commonly prescribed pharmaceuticals with different physio-chemical properties were used for the exposures:

  • diclofenac (nonsteroidal anti-inflammatory drug);
  • methocarbamol (a muscle relaxant);
  • rosuvastatin (a drug used to lower cholesterol levels);
  • sulfamethoxazole (an antibiotic); and
  • temazepam (a sleep aid).

Temazepam and methocarbamol were consistently detected in bluegill samples, so their uptake and elimination was studied in more detail. Over 30-day exposures, temazepam and methocarbamol demonstrated relatively rapid uptake and rapid elimination, indicating that internal tissue concentrations were driven by external environmental concentrations. This information indicates that overall persistence of the selected pharmaceuticals within bluegill tissues in the environment is likely to be low unless they reside downstream from a consistent, substantial, external contaminant source.

The pattern of rapid uptake and elimination observed for bluegill in this study is not dissimilar to that which is observed for human subjects indicating that the modeling of pharmaceutical uptake done as part of the drug approval process could be used to inform future study design and prioritize research needs for the Nation.

While this study provides a greater understanding of pharmaceutical persistence in fish tissue, the significance in terms of fish health has yet to be determined. This study was the first step in a longer-term a challenge for the USGS Environmental Health programs as they continue to provide the science to understand the sources, transport, fate, exposure, and adverse health effects, if any, of contaminants in the environment.

The USGS Toxic Substances Hydrology Program funded this study.

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