On‐site, serial exposure of female fathead minnows to the Elkhorn River, Nebraska, USA, spring agrichemical pulse

Abstract

In the Midwestern United States, waterways such as the Elkhorn River experience an annual spring pulse of runoff that carries sediments, nutrients, and organic compounds downstream. The objective of the present study was to elucidate relationships between contaminant load in Elkhorn River water and biological impacts on female fathead minnows throughout the entire spring agrichemical pulse. Fish were maintained in on-site outdoor microcosms at the Elkhorn River Research Station. The start of the spring pulse was determined using commercially available atrazine strips that detected atrazine when concentrations exceeded 3 ppb. Once the pulse began, 5 serial 7-d exposures were conducted. Concentrations of atrazine, its metabolites, and 5 other herbicides were quantified using gas chromatography-mass spectrometry. Agrichemicals peaked during the first and second weeks of the pulse, with a smaller peak occurring during week 4, but the peaks were not directly associated with runoff events (as estimated from river discharge). Elevated agrichemical concentrations were associated with biological impacts, but not solely responsible. In the present study, differences in the abiotic environment were found to play a significant role in the defeminization of exposed female fathead minnows.

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

“…Briefly, beginning April 15, 2015 atrazine test strips were used to test whether concentrations of atrazine in surface water in the Elkhorn River were above or below 3 μg·L . These test strips have been demonstrated to accurately detect the presence of atrazine and other triazine herbicides at 3 μg·L −1 in surface water (US EPA 2004), with further confirmation of there accuracy by previously collected field data (Knight et al 2013;Ali and Kolok 2015). Tests were conducted every three to four days where the detection of three consecutive positive atrazine strips determined the start of the spring agrichemical pulse on May 8, 2015 (Fig.…”

“…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 start of the agrichemical pulse was determined using atrazine test strips (Abraxis, Warminster, PA) as described in previous studies within the Elkhorn River watershed (Knight et al 2013;Ali and Kolok 2015;Zhang et al 2015). Briefly, beginning April 15, 2015 atrazine test strips were used to test whether concentrations of atrazine in surface water in the Elkhorn River were above or below 3 μg·L .…”

“…A suite of pesticides was selected for measurement due to regional application practices and their regular detection during the spring pulse in previous studies within the Elkhorn River watershed Zhang et al 2015). Included in this suite of pesticides were atrazine, acetochlor, metolachlor all of which are consistently detected within spring to early summer runoff (Lerch et al 2011a;Lerch et al 2011b;Knight et al 2013;Ali and Kolok 2015;Fairbairn et al 2016). …”

“…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).…”