Application of tracer techniques to continuous-flow toxicity testing

Chemical control of nuisance aquatic vegetation has long been the most widely utilized management tool due to its high level of efficacy, limited environmental impacts, and relatively low cost. However, unprecise application of herbicides can lead to uncontrolled invasive plants and unintended management costs. Therefore, precision herbicide delivery techniques are being developed to improve invasive plant control and minimize impacts to non-target plants. These technological advancements have the potential to enhance aquatic ecosystem protection from invasive species while reducing associated management costs. Despite the benefits of using registered herbicides for aquatic plant control in efforts to restore aquatic habitats, their use is often misunderstood and opposed by public stakeholders. This can lead to significant challenges related to chemical control of nuisance aquatic vegetation. Thus, US Army Corps of Engineers (USACE) Districts seek improved methods to monitor and quantify the distribution (i.e., amount of herbicide retained on plant foliage compared to those deposited into the water column) of herbicides applied in aquatic systems. Monitoring herbicide movement in aquatic systems can be tedious and costly using standard analytical methods. However, since the inert fluorescent tracer dye Rhodamine WT (RWT) closely mimics product movement in the aquatic environment it has been used as a cost-effective surrogate for herbicides tracing. The use of RWT (or other inert tracer dyes) can be an efficient way to quantify herbicide retention and deposition following foliar treatments. However, the collection of operational spray deposition data in large populations of invasive floating and emergent plant stands is labor intensive and costly. One proposed solution is the use of remote sensing methods as an alternative to traditional in situ samples. Specifically, using unmanned aircraft systems (UAS) in conjunction with RWT could provide more efficient monitoring and quantification of herbicide spray distribution and in-water concentrations when using RWT in combination with herbicides. A better understanding of UAS capabilities and limitations is key as this technology is being explored for improved and integrated management of aquatic plants in the U.S. This technical note (TN) provides a review of literature to assess the state of knowledge and technologies that can assist USACE Districts and partners with tracking herbicide movement (using RWT as a surrogate or additive), which could improve operational monitoring, thus reducing the level of uncertainty related to chemical applications and non-target impacts, and thus improve management in aquatic systems.

To have accurate runoff velocity, there is need to improve dye tracer method for estimating surface runoff velocity. This can enhance the calculations of relevant hydrologic parameters that will lead to a better understanding of hydrological processes and soil erosion. In this study, an integrated dye tracer and image processing method (IPV) and dye tracer method (AOV), respectively, were used to estimate runoff velocity under three slope gradients (5°, 10°, and 15°) and three slope positions (up-slope, mid-slope, and down-slope). The results showed more variation in runoff velocity under IPV than AOV. Both IPV and AOV were positively correlated with slope gradient. IPV values were close to AOV ones for slope gradients ≤5°, but were significantly different for slope gradients ≥10°. The mean AOV value was 10.6% higher than that of IPV. Regression analysis showed that compared with AOV, IPV overestimated and underestimated runoff under low and high runoff velocity conditions, respectively. The use of image processing in IPV was advantageous because of its ease of use with fewer artificial errors and its suitability for lateral diffusion of runoff. Irrespectively, additional studies are needed to verify and/or improve further the use of this method in runoff velocity analysis.

Effects of progesterone on sperm motility in fathead minnow ( Pimephales promelas)

Acidification effects on macroinvertebrates and fathead minnows ( Pimephales promelas) in outdoor experimental channels

Comparing biological effects and potencies of estrone and 17β-estradiol in mature fathead minnows, Pimephales promelas

The relationship between the toxicity of 68 organic chemicals to fish and luminescent bacteria was evaluated. Chemicals for which 96-h median lethal concentration (LC50) values had been measured for fathead minnows (Pimephales promelas) in flow-through tests at the U.S. Environmental Protection Agency (EPA) Environmental Research Laboratory-Duluth, Minn., were tested using the Microtox toxicity analyzer (Beckman Instruments, Inc.). The Microtox system measures the decrease in luminescence of the bacterium Photobacterium phosphoreum in response to a toxicant. The toxicity end point is the 5-min median effective concentration (EC50), which is the concentration that causes a 50 percent reduction in light output. The correlation between fish and bacteria toxicity for a composite of industrial chemicals and pesticides had an R2 value of 0.65. However, the relationship of these two end points for a semihomologous series of industrial chemicals appeared to be firm, with R2 being 0.96 for common alcohols. The feasibility of using the bacterial bioassay as a screening test in a cost-effective testing scheme is discussed.

Modeling solute reactivity in a phreatic solution conduit penetrating a karst aquifer

In ovo exposure of fathead minnow (Pimephales promelas) to selenomethionine via maternal transfer and embryo microinjection: A comparative study

Aquatic ecosystems are threatened by environmental contaminants, and many heavy metals can influence both the structure and function of sense organs in fishes. The use of these senses is vital to the survival and reproductive success of fish and therefore affects the health of the ecosystem as a whole. The current study examines the effects of cadmium on auditory structure and function in the fathead minnow (Pimephales promelas). In the laboratory, fish were exposed for 96 h to a range of cadmium concentrations and both hearing sensitivity and hair cell morphology were quantified. While hair cell numbers were unaffected, cadmium caused an increase in auditory threshold, with a critical range for toxic effects of cadmium estimated at 2.1-2.9 µg L(-1). Cadmium exposure also caused a decrease in response latency at higher cadmium concentrations. The current study demonstrates the sublethal effects of cadmium on fish sensory function while also pointing to the need for more careful interpretation of cadmium impacts on aquatic populations.

Individual and combined effects of heat stress and aqueous or dietary copper exposure in fathead minnows ( Pimephales promelas)

Hydrazine is widely used in commercial industries and is employed as a missile fuel in Air Force operations. The widespread use of hydrazine suggests a need for assessing its potential impact upon the aquatic environment. We designed this investigation to simulate conditions of an accidental spill which might occur during the spawning season of the fathead minnow, Pimephales promelas. This study was undertaken to determine the sensitivity of cleaving eggs to hydrazine, in particular morphological abnormalities and how they affect hatching, growth rate and certain physiological functions which may possess survival value.

Mercury (Hg) is a ubiquitous environmental contaminant and potent neurotoxin. In aquatic environments, Hg can be transformed into methylmercury (MeHg), which bioaccumulates in aquatic food webs, including fish. Methylmercury has been shown to transfer from female fish to developing eggs; however, relatively little is known regarding the effects of maternally transferred MeHg on fish embryos. The present study evaluated the effects of maternally transferred MeHg on fathead minnow (Pimephales promelas) embryos. Embryos were collected from adult fatheads exposed for 30 d to 1 of 3 diets spiked with MeHg: a control diet (0.02 ppm Hg dry wt), a low diet (0.87 ppm Hg dry wt), or a high diet (5.5 ppm Hg dry wt). No effects on spawning frequency, clutch size, or total egg output were observed. In embryos, Hg concentration was a function of female diet and the duration (number of days) of female exposure. Compared with controls, embryos from the low-diet treatment displayed altered embryonic movement patterns (hyperactivity) and decreased time to hatch. Embryos from the high-diet treatment had delayed hatching and increased mortality compared with the other treatments. Collectively, these results suggest that maternally transferred Hg may impact survival, behavior, and developmental milestones of the embryo-larval stages of fish. Environ Toxicol Chem 2016;35:1436-1441. © 2015 SETAC.

The ecological impact of tire wear particles in aquatic ecosystems is a growing environmental concern. We combined toxicity testing, using fathead minnow (Pimephales promelas) embryos, with nontarget high‐resolution liquid chromatography Orbitrap mass spectrometry to characterize the toxicity and chemical mixture of organic chemicals associated with tire particle leachates. We assessed: 1) exposure to tire particle leachates after leaching for 1‐, 3‐, and 10‐d; and 2) the effect of the presence and absence of small tire particulates in the leachates. We observed a decrease in embryonic heart rates, hatching success, and lengths, as well as an increase in the number of embryos with severe deformities and diminished eye and body pigmentation, after exposure to the leachates. Overall, there was a pattern whereby we observed more toxicity in the 10‐d leachates, and greater toxicity in unfiltered leachates. Redundancy analysis showed that several benzothiazoles and aryl‐amines were correlated with the toxic effects observed in the embryos. These included benzothiazole, 2‐aminobenzothiazole, 2‐mercaptobenzothiazole, N,N′‐diphenylguanidine, and N,N′‐diphenylurea. However, many other chemicals characterized as unknowns are likely to also play a key role in the adverse effects observed. Our study provides insight into the types of chemicals likely to be important toxicological drivers in tire leachates, and improves our understanding of the ecotoxicological impacts of tire wear particles. Environ Toxicol Chem 2022;41:1144–1153. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Environmental contextMercury, a globally important pollutant, undergoes transformations in the environment to form methylmercury that is toxic to humans. Naturally occurring dissolved organic matter is a controller in these transformations, and we demonstrate that its strength of interaction with mercury is time dependent. These changes in complexation with dissolved organic matter are likely to affect mercury’s reactivity in aquatic systems, thereby influencing how mercury is methylated and bioaccumulated. AbstractMercury interactions with dissolved organic matter (DOM) are important in aquatic environments but the kinetics of Hg binding to and repartitioning within the DOM remain poorly understood. We examined changes in Hg–DOM complexes using glutathione (GSH) titrations, coupled with stannous-reducible Hg measurements during Hg equilibration with DOM. In laboratory prepared DOM solutions and in water from a Hg-contaminated creek, a fraction of the Hg present as Hg–DOM complexes did not react to GSH addition. This unreactive Hg fraction increased with time from 13 % at 1 h to 74 % after 48 h of equilibration with a Suwannee River DOM. In East Fork Poplar Creek water in Oak Ridge, Tennessee, ~58 % of the DOM-complexed Hg was unreactive with GSH 1 h after the sample was collected. This time-dependent increase in unreactive Hg suggests that Hg forms stronger complexes with DOM over time. Alternatively the DOM-complexed Hg may become more sterically protected from the ligand exchange reactions, as the binding environment changes within the DOM over time. These results have important implications to understanding Hg transformations in the natural environment, particularly in contaminated aquatic systems due to non-equilibrium interactions between Hg and DOM.

Pentachlorophenol (PCP) is used extensively as a biocide and has been detected in toxic concentrations in aquatic environments. PCP is a potent uncoupler of oxidative phosphorylation (WEINBACH 1954, 1956) and this effect has been considered to be at least partly responsible for its toxic effects (WEINBACH and NOLAN 1956). Apart from the effect on oxidative phosphorylation stimulation or inhibition of a large number of enzyme systems has been described (KRUEGER et al. 1966, ISHAK et al. 1970, ISHAK 1972, BOSTROM and JOHANSSON 1972). According to HOLMBERG et al. (1972) the effect of subtlethal concentrations of PCP in the eel Anguilla anguilla L. is comparable to an exercise or stress situation. According to GOODNIGHT (1942), MANN (1957) and WEBER (1965) the lethal concentrations of PCP for a number of fishes vary between 0.2 and I ppm. For Anguilla anguilla it must lie somewhat above 0.1 ppm (HOLMBERG et al. 1972) while DAVIS and HOOS (1975) showed that for a number of salmonids the LC50 96 h at 10vC varies from 0.037 to 0.130 ppm. WEINBACH and NOLAN (1956) mention that a concentration of 3 ppm kills a number of water snails. According to MANN (1957) and WEBER (1965) Tubifex sp. can survive at 0.5 ppm. According to GOODNIGHT (1942) insect larvae survive at 5 ppm and according to MANN (1957) at 1.1 to 2.2 ppm. GOODNIGHT (1942) stated that Cambaris virilis Hagen, the amphipod Hyelella knickerbockeri (Bate), Daphnia pulex (de Geer) and Asellus communis Say survived at 5 ppm Na-PCP. MANN (1957) mentions that Cladocerans and Amphipods survive at 0.5 ppm, while WEBER (1965) exposed Daphnia magna to 1.0 ppm and found 30% mortality after 6 h and 100% mortality after 21 h, but no mortality at 0.5 ppm. In the present paper the toxicity of Na-PCP for two marine decapods i.e. Crangon crangon (Linnaeus) and Palaemon elegans (Rathke) and one brackish water decapod i.e. Palaemonetes varians (Leach) has been