Future water quality challenges to aquaculture and influences on product safety
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Concerns about water quantity and quality are increasing due to climate change and population growth. Climate change is driving changes in evapotranspiration and precipitation patterns. This is exacerbated as population growth, particularly in arid and semi-arid regions, increases water extraction and consumption. After human consumption, water is treated and discharged to the environment, but generally at lower quality than what was originally extracted. This could cause trouble for consumers of surface waters. One such consumer is the aquaculture industry, which is growing to support human protein consumption demands, while depending on surface water.Aquaculture is growing both globally and within the U.S. (worldwide 9.2% yr-11990-2000 & 6.2% yr-12000-2012). Freshwater aquaculture in the U.S. is largely dependent on surface water (80.78%) compared to ground water sources (19.32%). 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, the introduction of CEC in aquaculture from surface waters influenced by wastewater effluent is a potential concern for cultured fish health as well as for humans when consuming farmed fish. Studies were conducted to improve our understanding of future water resource quality and quantity in relation to the aquaculture industry and safety of farmed fish. Initially, wastewater effluent data was collected (e.g., USGS), consolidated, and analyzed (e.g., GIS) to understand its influence on surface water quantity and quality, which was utilized to project potential future water quality and quantity scenarios in the USA and its potential effect on aquaculture. This was followed by laboratory-based studies to quantify the bioaccumulation and depuration in tilapia of diltiazem, an ionizable calcium channel blocker, and GenX, a perfluorinated compound, at environmentally relevant concentrations. To broadly examine the extent of U.S. surface waters to dilute wastewater treatment plant (WWTP) effluent, data from wastewater discharge and surface flow from 2007-2017 was used to calculate a WWTP wastewater dilution factor (WWDF) within United Sates Geological Society (USGS) hydrologic unit code (HUC). A WWDF less than 10 indicates poor quality water when classified on <1 to >100 DF scale. The 4 HUCs with the lowest WWDF (i.e., <2) were located in the West or Southwest U.S. and were among the 10 HUCs with the highest proportional population growth from 2010-2016, with similar projections for the future. To identify the end water user impact, U.S. aquaculture farm area with WWDF < 2 was mapped. It was quantified at ~ 2.71% of total freshwater area, out of which 69% and 44% of the area was occupied by aquaculture farms with 100-and 1000-acre areas, respectively. Water availability for the contiguous U.S. was estimated for each HUC during 2015 using a model developed from the earlier analysis of water quantity and quality in the U.S. The Mississippi River generally served as a dividing line for surface water availability, with five of the six HUC regions with very low water availability (<24,000 L/D/Km2) residing in the west. These same areas also experience more drought as well as more severe droughts than regions in the east. In regions with lower surface water flows, water quality is more susceptible to the influence of wastewater effluent discharge, especially near large and growing population centers like San Antonio, Texas. A prediction model was established for this city, which found that from 2009-2017 wastewater effluent increased by 1.8%. Diltiazem(DTZ)bioconcentrationanddepurationintilapiawasexaminedusingacontrolledtimesequence(maxtime=96hr)exposure(1μgL-1)andnon-exposure(maxtime=96hr)infreshwater.Fishcarcass,bloodplasma,liver,andmusclewereanalyzedinbothexposureanddepurationphases.Diltiazembioconcentrationwasgreatestinliver>plasma>carcass>muscle.Depurationratesweregreatestforliver>carcass>plasma>muscle.Thebiologicalhalf-life(t1/2)indicatesthatDTZtookthelongesttodepuratefrommuscleandleastfromtheliver,whichissimilarforthestablebioconcentrationfactor(BCFa)valueorder.Thet1/2ofDTZintilapiamusclewas18.8hrs,indicatingthecompoundisprocessedrelativelyquickly.Basedonthe96hrDTZuptakebytilapiafingerlingsinthisstudy,humanexposuretothehighestDTZmuscleconcentrationwouldbe~6ordersofmagnitudebelowthelowestdailyhumantherapeutic(120ppb)dose,resultinginverylowhumanexposure. GenX (ammonium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy))bioconcentrationanddepurationintilapiawasexaminedusingacontrolledtimesequence(maxtime=96hr)exposure(1μgL-1)andnon-exposure(maxtime=96hr)infreshwaterandbrackishwater(16ppt).GenXbioconcentration (BCFa) was greatest in plasma > liver > carcass > muscle, with higher distribution in liver compared to carcass and muscle. Bioconcentration in all tissues examined increased with increasing salinity, raising concern for euryhaline organisms. Muscle was found to have the highest t1/2followed by carcass, plasma, and liver. The rate of uptake and depuration was affected bysalinity. Fish muscle (fillet) GenX concentration at 96 hrs at 0 ppt was 0.14 ppb whereas at 16 ppt it was 0.312 ppb. Therefore, a fillet serving size of ~3.5 oz (100 g) would contain 14.0 μg GenX from freshwaterfish and 31.2 μg GenX from saltwater (16 ppt) fish. This would result in a single serving exposing a person to more than the subchronic oral reference dose of 0.2 ppb as recommended by U.S. EPA. Water quality is a growing concern along with changing climate and increasing population. 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. It also helps to understand environmental exposure and ecological impacts of pharmaceuticals and other industrial chemicals for sustainable management of environmental quality, particularly in urbanizing ecosystems.
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