Concerns about water quantity and quality for aquaculture are increasing due to climate change and population growth. Surface water sources are increasingly dominated or dependent on treated wastewater effluent, potentially influencing downstream uses. Wastewater effluent generally contains trace levels of anthropogenic compounds, typically referred to as contaminants of emerging concern (CEC), for which our knowledge of their impacts is still evolving. Therefore, introduction of CEC from surface waters influenced by wastewater effluent is a potential concern for cultured fish health as well as humans who consume farmed fish.
Bioconcentration and depuration of the pharmaceutical diltiazem (DTZ) and the perfluorinated compound GenX (ammonium 2,3,3,3-tetrafluoro-2-heptafluoropropoxy propanoic acid) were examined in fingerling tilapia (Oreochromis mossambicus) using a controlled time sequence exposure (1 µg L-1, 1, 3, 6, 12, 24, 48, 78 and 96 hr) and non-exposure (1, 12, 48 and 96 hrs after max exp time) in freshwater (DTZ & GenX) and brackish water (~16 ppt, GenX only). A semi-static flow-through tank system was utilized that consisted of triplicate 10-gal tanks connected to a single 30-gal sump tank for each exposure and depuration experiment. Fish carcass, blood plasma, liver, and muscle were analyzed in both exposure and depuration phases.
DTZ bioconcentration was greatest in liver >plasma >carcass >muscle. The biological half-life (t1/2) of DTZ in tilapia muscle was 18.8 hrs, indicating the compound is processed relatively quickly. Based on the 96 hr DTZ uptake by fingerlings, human exposure to the highest DTZ muscle concentration would be ~6 orders of magnitude below the lowest daily human therapeutic (120 ppb) dose. Plasma values were on the same order of magnitude as the human therapeutic dose, implying potential effect on the fish and productivity (verification needed).
GenX bioconcentration was greatest in plasma >liver >carcass >muscle. Muscle was found to have the highest t1/2 followed by carcass, plasma, and liver. The rate of uptake and depuration was affected by salinity, raising concern for euryhaline organisms. Fish muscle (fillet) GenX concentration at 96 hrs in freshwater was 0.14 ppb and at 16 ppt it was 0.312 ppb. Based on the 96 hr GenX uptake by fingerlings, human exposure to the highest GenX muscle concentration would be ~2 orders of magnitude below the chronic daily exposure limit (0.08 ug kg-day-1).
The projections and improved bioaccumulation models for farmed fish from this research will provide aquaculturists with knowledge to make pro-active management decisions regarding water quality in the future, while improving our general understanding of human exposure to CEC from nontraditional water use. This project was supported by a USDA-NIFA.