Impact of Sediment on Agrichemical Fate and Bioavailability to Adult Female Fathead Minnows: A Field Study

Abstract

Precipitation induced runoff is an important pathway for agrichemicals to enter surface water systems and expose aquatic organisms to endocrine-disrupting compounds such as pesticides and steroid hormones. The objectives of this study were to investigate the distribution of agrichemicals between dissolved and sediment-bound phases during spring pulses of agrichemicals and to evaluate the role of suspended sediment in agrichemical bioavailability to aquatic organisms. To accomplish these objectives, suspended sediment and water samples were collected every 3 days from a field site along the Elkhorn River, located at the downstream end of a heavily agricultural watershed, and were screened for 21 pesticides and 21 steroids. Adult female fathead minnows (Pimephales promelas) were exposed in field mesocosms to river water containing varying sediment loads. Changes in organism hepatic gene expression of two estrogen-responsive genes, vitellogenin (VTG) and estrogen receptor alpha (ERα), as well as the androgen receptor (AR) were analyzed during periods of both low and high river discharge. Trends in agrichemical concentrations of both the dissolved and sediment phases as a function of time show that, while sediment may act as both a source and a sink for agrichemicals following precipitation events, the overall driver for molecular defeminization in this system is direct exposure to the sediment-associated compounds. This study suggests that endocrine disrupting effects observed in organisms in turbid water could be attributed to direct exposure of contaminated sediment.

Compensatory response of fathead minnow larvae following a pulsed in-situ exposure to a seasonal agricultural runoff event

“…Exposure of all fathead minnow larvae was conducted at the Elkhorn River Research Station (ERRS) where previous field studies have identified biological impacts and changes in endocrine responsive gene expression following in situ exposure to agricultural runoff (Knight et al 2013;Ali and Kolok 2015;Zhang et al 2015;Ali et al 2016). The ERRS is an open-air facility located approximately 10 km upstream from the confluence of the Elkhorn and Platte Rivers, Nebraska, USA.…”

“…The ERRS is an open-air facility located approximately 10 km upstream from the confluence of the Elkhorn and Platte Rivers, Nebraska, USA. The station is equipped to pump water continuously from the Elkhorn River into stainless steel mesocosms capable of supporting aquatic organisms Zhang et al 2015;Ali et al 2016).…”

“…The short-term peaks in agrichemicals tend to overlap with dramatic fluctuations in physicochemical parameters (e.g. temperature, dissolved oxygen, salinity, suspended solids) related to increased river discharge (Blann et al 2009;Zhang et al 2015). Early life stage fish may be particularly sensitive to the covariation among stressors, as larvae are balancing the metabolic demands of growth and organogenesis while simultaneously responding to their unpredictable surroundings.…”

“…In the Midwestern United States, agrichemical pulses follow precipitation events from May until July (Crawford 2001;Smiley et al 2014;Zhang et al 2015) making a predictable and natural setting for investigating their biological impacts. Indeed, field studies exposing fish to seasonally occurring agricultural runoff have documented endocrine disruption in the reproductive axis of otherwise intact adult females (Sellin et al 2009;Sellin Jeffries et al 2011a;Sellin Jeffries et al 2011b;Knight et al 2013;Ali and Kolok 2015;Zhang et al 2015).…”

“…Indeed, field studies exposing fish to seasonally occurring agricultural runoff have documented endocrine disruption in the reproductive axis of otherwise intact adult females (Sellin et al 2009;Sellin Jeffries et al 2011a;Sellin Jeffries et al 2011b;Knight et al 2013;Ali and Kolok 2015;Zhang et al 2015). Periods of elevated discharge and pesticide loads were associated with decreased expression of the steroid responsive genes vitellogenin (VTG), estrogen receptor subtype α (ERα) and androgen receptor (AR) (Knight et al 2013;Ali and Kolok 2015;Zhang et al 2015).…”