Sub-chronic exposure to waterborne extracellular microcystin-LR impairs calcium homeostasis in rainbow trout.

Fish mortality is associated with harmful algal blooms, although whether toxicity is related directly to the presence of cyanotoxins or the prevailing water chemistry remains unclear. Similarly, while planktivorous fish may be exposed to toxin through the diet, the hazard posed by waterborne extracellular toxin to carnivorous fish is less well understood. In this study rainbow trout (Oncorhynchus mykiss) were exposed for up to 28 d to waterborne microcystin-LR at nominal concentrations of 1.5 and 50 µg L-1 (measured values 2 and 49 µg L-1, respectively). The former represents the Canadian drinking water guideline, and the latter an elevated environmental level. This study hypothesised that waterborne toxin exposure would specifically impact gill function, and given the importance of this tissue in freshwater fish ion regulation, effects on plasma ions and branchial ion transporter activity would be observed. Microcystin-LR exposure resulted in a significant and persistent hypocalcaemia at the higher exposure concentration, but plasma sodium and branchial activities of the sodium/potassium ATPase, proton ATPase and calcium ATPase enzymes remained unaffected. An in vitro assessment failed to show any effect of microcystin-LR on branchial calcium ATPase activity even at exposure concentrations as high as 1000 µg L-1. A transient increase in hepatic alkaline phosphatase activity was also observed at 49 µg L-1, but there were no effects of toxin exposure on branchial or hepatic lactate dehydrogenase activity. These results suggest that microcystin-LR exposure does not have a general effect on ion regulation, but instead produces a novel and specific impact on calcium metabolism in rainbow trout, although the mechanism underlying this effect remains unknown.

Factors Affecting the Binding of Diltiazem to Rainbow Trout Plasma: Implications for the Risk Assessment of Pharmaceuticals in Aquatic Systems.

The accumulation of organic toxicants in fish plasma, and how they partition between the bound and unbound fraction once absorbed, are important metrics in models that seek to predict the risk of such contaminants in aquatic settings. Rapid equilibrium dialysis of diltiazem, an ionizable weak base and important human pharmaceutical contaminant of freshwaters, was conducted with rainbow trout (Oncorhynchus mykiss) plasma. The effect of fed state, fish sex, fish strain/size, and dialysis buffer pH on the binding of radiolabeled diltiazem (9 ng ml-1 ) was assessed. In fed fish, 24.6%-29.5% of diltiazem was free, unbound to plasma proteins. Although starvation of fish resulted in a decrease in plasma protein, the bound fraction of diltiazem remained relatively constant. Consequently, the protein-bound concentration of diltiazem increased with length of starvation. In general, rainbow trout strain was a significant factor affecting plasma binding, although the two strains tested also differed markedly in size. Dialysis buffer pH significantly influenced plasma binding, with a higher unbound diltiazem fraction at pH 6.8 than pH 8.0. These data indicate that empirical measures of plasma binding in fish are important for accurate risk assessment and that the physiological status of a fish is likely to impact its sensitivity to toxicants such as diltiazem. Environ Toxicol Chem 2022;41:3125-3133. © 2022 SETAC.

Acute waterborne strontium exposure to rainbow trout: Tissue accumulation, ionoregulatory effects, and the modifying influence of waterborne calcium.

Flowback and produced water (FPW) is an end-product of the hydraulic fracturing method of oil and gas extraction that is highly enriched in alkaline earth metals such as strontium (Sr). While Sr concentrations in FPW can exceed toxic thresholds for fish, the accompanying high concentrations of calcium (Ca) in FPW may ameliorate any toxicity. In this study, Sr bioaccumulation and molecular, biochemical, and physiological changes in ionoregulatory endpoints were investigated in rainbow trout (Oncorhynchus mykiss). Exposures were conducted over a 96-h period at Sr concentrations ranging from 1.7 to 1948 µM, with effects at the highest Sr exposure concentration also separately examined in waters of varying Ca concentration (10 to 958 µM). Plasma and gill Sr burdens increased as a function of increasing waterborne Sr, and accumulation increased further as water Ca concentrations were lowered. Despite this, there was no consistent, dose-dependent effect of Sr on plasma or gill Ca concentrations, although impacts on plasma and branchial sodium (Na) concentrations were observed. Waterborne Sr significantly inhibited branchial Ca2+-ATPase activity, albeit only at the highest tested Sr concentration (1948 µM). In exposure treatments where Sr was highly elevated and water Ca was reduced, the hepatic gene expression of Ca signaling receptors ß-2 adrenergic receptor (Adrb2) and inositol-1,4,5-triphosphate receptor-2 (Itpr2) were inhibited, highlighting novel potential pathways of Sr toxicity in rainbow trout. Overall, these data indicate that water Ca has a strong effect on Sr bioavailability, but over an acute exposure period there is limited evidence for an effect of Sr on Ca homeostasis. Although Sr is elevated in effluents associated with the oil and gas industry, the co-occurrence of high Ca concentrations might protect freshwater fish against acute effects related to Sr exposure.

Nutrients and salinity influence Prymnesium parvum (UTEX LB 2797) elicited sublethal toxicity in Pimephales promelas and Danio rerio.

The magnitude, frequency, and duration of harmful algal blooms (HABs) are increasing worldwide, primarily due to climate change and anthropogenic activities. Prymnesium parvum is a euryhaline and eurythermal HAB forming species that has expanded throughout North America, resulting in massive fish kills. Previous aquatic ecology and toxicology efforts supported an understanding of conditions resulting in P. parvum HABs and fish kills; however, the primary endpoint selected for these studies was acute mortality. Whether adverse sublethal responses to P. parvum occur in fish are largely unknown. To begin to address this question, molecular and biochemical oxidative stress (OS) biomarker responses and photomotor behavioral alterations were investigated in two common fish models, the fathead minnow (Pimephales promelas) and zebrafish (Danio rerio). Varying nutrient and salinity conditions influenced P. parvum related OS biomarkers and fish behavioral responses in zebrafish and fathead minnows, which were heightened by nonoptimal conditions for P. parvum growth. Such sublethal observations present important considerations for future aquatic assessments and management of P. parvum HABs.

Low dissolved oxygen increases uptake of a model calcium channel blocker and alters its effects on adult Pimephales promelas.

Human population growth accompanied with urbanization is urbanizing the water cycle in many regions. Urban watersheds, particularly with limited upstream dilution of effluent discharges, represent worst case scenarios for exposure to multiple environmental stressors, including down the drain chemicals (e.g., pharmaceuticals) and other stressors (e.g., dissolved oxygen (DO)). We recently identified the calcium channel blocker diltiazem (DZM) to accumulate in fish plasma exceeding human therapeutic doses (e.g., Cmin) in coastal estuaries impaired due to nonattainment of DO water quality standards. Thus, we examined whether DO influences DZM uptake by fish, and if changes in DO-dependent upatke alter fish physiological and biochemical responses. Low DO (3.0 mg DO/L) approximately doubled diltiazem uptake in adult fathead minnows relative to normoxic (8.2 mg DO/L) conditions and were associated with significant (p < 0.05) increases in fish ventilation rate at low DO levels. Decreased burst swim performance (Uburst) of adult fathead minnows were significantly (p < 0.05) altered by low versus normal DO levels. DO × DZM studies reduced Uburst by 13-31% from controls, though not significantly (p = 0.06). Physiological responses in fish exposed to DZM alone were minimal; however, in co-exposure with low DO, decreasing trends in Uburst appeared inversely related to plasma lactate levels. Such physiological responses to multiple stressors, when paired with internal tissue concentrations, identify the utility of employing biological read across approaches to identify adverse outcomes of heart medications and potentially other cardiotoxicants impacting fish cardiovascular function across DO gradients.

CRISPR-Generated Nrf2a Loss- and Gain-of-Function Mutants Facilitate Mechanistic Analysis of Chemical Oxidative Stress-Mediated Toxicity in Zebrafish.

The transcription factor Nrf2a induces a cellular antioxidant response and provides protection against chemical-induced oxidative stress, as well as playing a critical role in development and disease. Zebrafish are a powerful model to study the role of Nrf2a in these processes but have been limited by reliance on transient gene knockdown techniques or mutants with only partial functional alteration. We developed several lines of zebrafish carrying different null (loss of function, LOF) or hyperactive (gain of function, GOF) mutations to facilitate our understanding of the Nrf2a pathway in protecting against oxidative stress. The mutants confirmed Nrf2a dependence for induction of the antioxidant genes gclc, gstp, prdx1, and gpx1a and identified a role for Nrf2a in the baseline expression of these genes, as well as for sod1. Specifically, the 4-fold induction of gstp by tert-butyl hydroperoxide (tBHP) in wild type fish was abolished in LOF mutants. In addition, baseline gstp expression in GOF mutants increased by 12.6-fold and in LOF mutants was 0.8-fold relative to wild type. Nrf2a LOF mutants showed increased sensitivity to the acute toxicity of cumene hydroperoxide (CHP) and tBHP throughout the first 4 days of development. Conversely, GOF mutants were less sensitive to CHP toxicity during the first 4 days of development and were protected against the toxicity of both hydroperoxides after 4 dpf. Neither gain nor loss of Nrf2a modulated the toxicity of R-(-)-carvone (CAR), despite the ability of this compound to potently induce Nrf2a-dependent antioxidant genes. Similar to other species, GOF zebrafish mutants exhibited significant growth and survival defects. In summary, these new genetic tools can be used to facilitate the identification of downstream gene targets of Nrf2a, better define the role of Nrf2a in the toxicity of environmental chemicals, and further the study of diseases involving altered Nrf2a function.

Toward Less Hazardous Industrial Compounds: Coupling Quantum Mechanical Computations, Biomarker Responses, and Behavioral Profiles To Identify Bioactivity of SN2 Electrophiles in Alternative Vertebrate Models.

Sustainable molecular design of less hazardous chemicals promises to reduce risks to public health and the environment. Computational chemistry modeling coupled with alternative toxicology models (e.g., larval fish) present unique high-throughput opportunities to understand structural characteristics eliciting adverse outcomes. Numerous environmental contaminants with reactive properties can elicit oxidative stress, an important toxicological response associated with diverse adverse outcomes (i.e., cancer, diabetes, neurodegenerative disorders, etc.). We examined a common chemical mechanism (bimolecular nucleophilic substitution (SN2)) associated with oxidative stress using property-based computational modeling coupled with acute (mortality) and sublethal (glutathione, photomotor behavior) responses in the zebrafish (Danio rerio) and the fathead minnow (Pimephales promelas) models to identify whether relationships exist among biological responses and molecular attributes of industrial chemicals. Following standardized methods, embryonic zebrafish and larval fathead minnows were exposed separately to eight different SN2 compounds for 96 h. Acute and sublethal responses were compared to computationally derived in silico chemical descriptors. Specifically, frontier molecular orbital energies were significantly related to acute LC50 values and photomotor response (PMR) no observed effect concentrations (NOECs) in both fathead minnow and zebrafish. This reactivity index, LC50 values, and PMR NOECs were also significantly related to whole body glutathione (GSH) levels, suggesting that acute and chronic toxicity results from protein adduct formation for SN2 electrophiles. Shared refractory locomotor response patterns among study compounds and two alternative vertebrate models appear informative of electrophilic properties associated with oxidative stress for SN2 chemicals. Electrophilic parameters derived from frontier molecular orbitals were predictive of experimental in vivo acute and sublethal toxicity. These observations provide important implications for identifying and designing less hazardous industrial chemicals with reduced potential to elicit oxidative stress through bimolecular nucleophilic substitution.

Influence of salinity and pH on bioconcentration of ionizable pharmaceuticals by the gulf killifish, Fundulus grandis.

Estuaries routinely receive discharges of contaminants of emerging concern from urban regions. Within these dynamic estuarine systems, salinity and pH can vary across spatial and temporal scales. Our previous research identified bioaccumulation of the calcium channel blocker diltiazem and the antihistamine diphenhydramine in several species of fish residing in multiple urban estuaries along the Gulf of Mexico in Texas, where field-measured observations of diltiazem in fish plasma exceeded human therapeutic plasma doses. However, there remains a limited understanding of pharmaceutical bioaccumulation in estuarine environments. Here, we examined the influence of pH and salinity on bioconcentration of three pharmaceuticals in the Gulf killifish, Fundulus grandis. F. grandis were exposed to low levels of the ionizable pharmaceuticals carbamazepine, diltiazem, and diphenhydramine at two salinities (5 ppt, 20 ppt) and two pH levels (6.7, 8.3). pH influenced bioconcentration of select weak base pharmaceuticals, while salinity did not, suggesting that intestinal uptake via drinking does not appear to be a major exposure route of these pharmaceuticals in killifish. Compared to our previous pH dependent uptake observations with diphenhydramine in the fathead minnow model, killifish apparent volume of distribution values were markedly lower than fatheads, though killifish bioconcentration factors were similar at high pH and four fold higher at low pH than freshwater fish. Advancing an understanding of environmental gradient influences on pharmacokinetics among fish is necessary to improve bioaccumulation assessments and interpretation of toxicological observations for ionizable contaminants.

Spatial and temporal influence of onsite wastewater treatment systems, centralized effluent discharge, and tides on aquatic hazards of nutrients, indicator bacteria, and pharmaceuticals in a coastal bayou.

In the rapidly urbanizing watersheds and estuaries flowing to the Gulf of Mexico in Texas, USA, instream flows are increasingly influenced by point source and nonpoint source discharges. Spatial and temporal tidal influences on water quality, especially for contaminants of emerging concern (CECs), is poorly understood in estuaries and coastal systems. We selected Dickinson Bayou, an urban estuary in Galveston County, Texas, for study because it has historically impaired water quality, receives point source discharge from one major wastewater treatment plant (WWTP), while also being influenced by high densities of onsite sewage facilities upstream in the watershed. We explored the occurrence and potential hazards of aquatic contaminants, including nutrients, indicator bacteria for pathogens, and CECs, in relation to this point source discharge, across seasons and at high and low tides. Aquatic contaminants and associated hazards varied significantly in relation to the WWTP discharge, and were influenced by onsite systems. In fact, spatiotemporal water quality varied by class of contaminants (e.g., nutrients, indicator bacteria, CECs), which indicates that traditional surface water monitoring activities should account for such environmental complexity. This study provides a diagnostic approach for future studies of emerging water quality challenges across gradients of rapidly urbanizing coastal bays and estuaries.

Comparative behavioral toxicology with two common larval fish models: Exploring relationships among modes of action and locomotor responses.

Behavioral responses inform toxicology studies by rapidly and sensitively detecting molecular initiation events that propagate to physiological changes in individuals. These behavioral responses can be unique to chemical specific mechanisms and modes of action (MOA) and thus present diagnostic utility. In an initial effort to explore the use of larval fish behavioral response patterns in screening environmental contaminants for toxicity and to identify behavioral responses associated with common chemical specific MOAs, we employed the two most common fish models, the zebrafish and the fathead minnow, to define toxicant induced swimming activity alterations during interchanging photoperiods. Though the fathead minnow (Pimephales promelas) is a common model for aquatic toxicology research and regulatory toxicology practice, this model has received little attention in behavioral studies compared to the zebrafish, a common biomedical model. We specifically compared behavioral responses among 7 different chemicals (1-heptanol, phenol, R-(-)-carvone, citalopram, diazinon, pentylenetetrazole (PTZ), and xylazine) that were selected and classified based on anticipated MOA (nonpolar narcosis, polar narcosis, electrophile, specific mechanism) according to traditional approaches to examine whether these comparative responses differ among chemicals with various structure-based predicted toxicity. Following standardized experimental guidelines, zebrafish embryos and fathead minnow larvae were exposed for 96 h to each compound then were observed using digital behavioral analysis. Behavioral observations included photomotor responses, distance traveled, and stimulatory, refractory and cruising locomotor activity. Though fathead minnow larvae displayed greater behavioral sensitivity to 1-heptanol, phenol and citalopram, zebrafish were more sensitive to diazinon and R-(-)-carvone. Both fish models were equally sensitive to xylazine and PTZ. Further, the pharmaceuticals citalopram and xylazine significantly affected behavior at therapeutic hazard values, and each of the seven chemicals elicited unique behavioral response profiles. Larval fish behaviors appear useful as early tier diagnostics to identify mechanisms and pathways associated with diverse biological activities for chemicals lacking mechanistic data.

Spatio-temporal bioaccumulation and trophic transfer of ionizable pharmaceuticals in a semi-arid urban river influenced by snowmelt.

Bioaccumulation of pharmaceuticals in aquatic organisms is increasingly reported in the peer-reviewed literature. However, seasonal instream dynamics including occurrence and bioaccumulation across trophic positions are rarely studied, particularly in semiarid streams with flows influenced by seasonal snowmelt and municipal effluent discharges. Thus, we selected East Canyon Creek in Park City, Utah, USA to examine spatio-temporal bioaccumulation of select ionizable pharmaceuticals across trophic positions using trophic magnification factors calculated at incremental distances (0.15, 1.4, 13 miles) downstream from a municipal effluent discharge during spring (May), Summer (August), and fall (October). Nine target analytes were detected in all species during all sampling events. Trophic dilution was consistently observed for amitriptyline, caffeine, diphenhydramine, diltiazem, fluoxetine, and sertraline, regardless of seasonal instream flows or distance from effluent discharge. Calculated TMFs ranged from 0.01-0.71 with negative slopes observed for all regressions of chemical residue in tissue and trophic position. We further presents the first empirical investigation of normalizing pharmaceutical concentrations to lipid, phospholipid or protein fractions using pair matched fish samples. Empirical results identify that normalization of ionizable pharmaceutical residues in aquatic tissues to neutral lipids, polar lipids, or the total protein fraction is inappropriate, though bioaccumulation studies examining influences of internal partitioning (e.g., plasma proteins) are needed.

Influence of Diltiazem on Fathead Minnows Across Dissolved Oxygen Gradients.

Water resources in many arid to semi-arid regions are stressed by population growth and drought. Growing populations and climatic changes are influencing contaminant and water chemistry dynamics in urban inland waters, where flows can be dominated by, or even dependent on, wastewater effluent discharge. In these watersheds, interacting stressors such as dissolved oxygen and environmental contaminants (e.g., pharmaceuticals) have the potential to affect fish physiology and populations. Recent field observations from our group identified the calcium channel blocker (CCB) diltiazem in fish plasma exceeding human therapeutic doses (e.g., Cmin ) in aquatic systems impaired because of nonattainment of dissolved oxygen water quality standards. Therefore our study objectives examined: 1) standard acute and chronic effects of dissolved oxygen and diltiazem to fish, 2) influences of dissolved oxygen at criteria levels deemed protective of aquatic life on diltiazem toxicity to fish, and 3) whether sublethal effects occur at diltiazem water concentrations predicted to cause a human therapeutic level (therapeutic hazard value [THV]) in fish plasma. Dissolved oxygen × diltiazem co-exposures significantly decreased survival at typical stream, lake, and reservoir water quality standards of 5.0 and 3.0 mg dissolved oxygen/L. Dissolved oxygen and diltiazem growth effects were observed at 2 times and 10 times lower than median lethal concentration (LC50) values (1.7 and 28.2 mg/L, respectively). Larval fathead minnow (Pimephales promelas) swimming behavior following low dissolved oxygen and diltiazem exposure generally decreased and was significantly reduced in light-to-dark bursting distance traveled, number of movements, and duration at concentrations as low as the THV. Individual and population level consequences of such responses are not yet understood, particularly in older organisms or other species; however, these findings suggest that assessments with pharmaceuticals and other cardioactive contaminants may underestimate adverse outcomes in fish across dissolved oxygen levels considered protective of aquatic life. Environ Toxicol Chem 2018;37:2835-2850. © 2018 SETAC.

The Molecular Design Research Network.

Herein, we provide an overview of a research network that is aimed at fostering interdisciplinary collaboration between chemists and toxicologists with the goal of rationally designing safer commercial chemicals. The collaborative is the Molecular Design Research Network (MoDRN) that was created in 2013 with funding from the EPA-National Science Foundation Networks for Sustainable Molecular Design and Synthesis (NSMDS) program. MoDRN is led by 4 universities, Baylor University, University of Washington, The George Washington University, and Yale University. The overarching goal of the network is to enable and empower the design of safer chemicals based on the fourth Principle of Green Chemistry that states, "chemical products should be designed to preserve efficacy of function while minimizing toxicity."

Revisiting inland hypoxia: diverse exceedances of dissolved oxygen thresholds for freshwater aquatic life.

Water resources in many regions are stressed by impairments resulting from climate change, population growth and urbanization. In the United States (US), water quality criteria (WQC) and standards (WQS) were established to protect surface waters and associated designated uses, including aquatic life. In inland waters of the south central US, for example, depressed dissolved oxygen (DO) consistently results in impaired aquatic systems due to noncompliance with DO WQC and WQS. In the present study, we systematically examined currently available DO threshold data for freshwater fish and invertebrates and performed probabilistic aquatic hazard assessments with low DO toxicity data that were used to derive the US Environmental Protection Agency's (EPA) Ambient Water Quality Criteria (AWQC) for DO and newly published information. Aquatic hazard assessments predicted acute invertebrate DO thresholds for Ephemeroptera, Plecoptera, or Trichoptera (EPT) taxa and species inhabiting lotic systems to be more sensitive than fish. For example, these organisms were predicted to have acute low DO toxicity thresholds exceeding the US EPA guidelines 17, 26, 31 and 38% and 13, 24, 30 and 39% of the time at 8.0, 5.0, 4.0 and 3.0 mg DO/L, respectively. Based on our analysis, it appears possible that low DO effects to freshwater organisms have been underestimated. We also identified influences of temperature on low DO thresholds and pronounced differences in implementation and assessment of the US EPA AWQC among habitats, seasons, and geographic regions. These results suggest some implemented DO guidelines may adversely affect the survival, growth, and reproduction of freshwater aquatic organisms in a region susceptible to climate change and rapid population growth. Given the global decline of species, particularly invertebrates, low DO threshold information, including sublethal (e.g., reproduction, behavior) responses, for additional species (e.g., mollusks, other invertebrates, warm water fish) across seasons, habitats, and life history stages using consistent experimental designs is needed to support more sustainable environmental assessment efforts and management of biodiversity protection goals in inland waters.

Global scanning assessment of calcium channel blockers in the environment: Review and analysis of occurrence, ecotoxicology and hazards in aquatic systems.

As an urban water cycle is increasingly realized, aquatic systems are influenced by sewage and wastewater effluent discharges of variable quality. Such urbanization results in exposures of non-target aquatic organisms to medicines and other contaminants. In the present study, we performed a unique global hazard assessment of calcium channel blockers (CCB) in multiple environmental matrices. Effluent and freshwater observations were primarily from North America (62% and 76%, respectively) and Europe (21% and 10%, respectively) with limited-to-no information from rapidly urbanizing regions of developing countries in Asia-Pacific, South America, and Africa. Only 9% and 18% of occurrence data were from influent sewage and marine systems, though developing countries routinely discharge poorly treated wastewater to heavily populated coastal regions. Probabilistic environmental exposure distribution (EED) 5th and 95th percentiles for all CCBs were 1.5 and 309.1 ng/L in influent, 5.0 and 448.7 ng/L for effluent, 1.3 and 202.3 ng/L in freshwater, and 0.17 and 12.9 ng/L in saltwater, respectively. Unfortunately, global hazards and risks of CCBs to non-target organisms remain poorly understood, particularly for sublethal exposures. Thus, therapeutic hazard values (THV) were calculated and employed during probabilistic hazard assessments with EEDs when sufficient data was available. Amlodipine and verapamil in effluents and freshwater systems exceeded THVs 28% of the time, highlighting the need to understand ecological consequences of these CCBs. This global scanning approach demonstrated the utility of global assessments to identify specific CCBs, chemical mixtures with common mechanisms of action, and geographic locations for which environmental assessment efforts appear warranted.

Ontogenetic dietary shifts and bioaccumulation of diphenhydramine in Mugil cephalus from an urban estuary.

Though bioaccumulation of pharmaceuticals has received attention in inland waters, studies of pharmaceutical bioaccumulation in estuarine and marine systems are limited. Further, an understanding of pharmaceutical bioaccumulation across size classes of organisms displaying ontogenetic feeding shifts is lacking. We selected the striped mullet, Mugil cephalus, a euryhaline and eurythermal species that experiences dietary shifts with age, to identify whether a model base, diphenhydramine, accumulated in a tidally influenced urban bayou. We further determined whether diphenhydramine accumulation differed among size classes of striped mullet over a two year study period. Stable isotope analysis identified that ontogenetic feeding shifts of M. cephalus occurred from juveniles to adults. However, bioaccumulation of diphenhydramine did not significantly increase across age classes of M. cephalus but corresponded to surface water levels of the pharmaceutical, which suggests inhalational uptake to diphenhydramine was more important for bioaccumulation than dietary exposure in this urban estuary.

Toward the Design of Less Hazardous Chemicals: Exploring Comparative Oxidative Stress in Two Common Animal Models.

Sustainable molecular design of less hazardous chemicals presents a potentially transformative approach to protect public health and the environment. Relationships between molecular descriptors and toxicity thresholds previously identified the octanol-water distribution coefficient, log D, and the HOMO-LUMO energy gap, ΔE, as two useful properties in the identification of reduced aquatic toxicity. To determine whether these two property-based guidelines are applicable to sublethal oxidative stress (OS) responses, two common aquatic in vivo models, the fathead minnow (Pimephales promelas) and zebrafish (Danio rerio), were employed to examine traditional biochemical biomarkers (lipid peroxidation, DNA damage, and total glutathione) and antioxidant gene activation following exposure to eight structurally diverse industrial chemicals (bisphenol A, cumene hydroperoxide, dinoseb, hydroquinone, indene, perfluorooctanoic acid, R-(-)-carvone, and tert-butyl hydroperoxide). Bisphenol A, cumene hydroperoxide, dinoseb, and hydroquinone were consistent inducers of OS. Glutathione was the most consistently affected biomarker, suggesting its utility as a sensitivity response to support the design of less hazardous chemicals. Antioxidant gene expression (changes in nrf2, gclc, gst, and sod) was most significantly (p < 0.05) altered by R-(-)-carvone, cumene hydroperoxide, and bisphenol A. Results from the present study indicate that metabolism of parent chemicals and the role of their metabolites in molecular initiating events should be considered during the design of less hazardous chemicals. Current empirical and computational findings identify the need for future derivation of sustainable molecular design guidelines for electrophilic reactive chemicals (e.g., SN2 nucleophilic substitution and Michael addition reactivity) to reduce OS related adverse outcomes in vivo.

Predicted and observed therapeutic dose exceedances of ionizable pharmaceuticals in fish plasma from urban coastal systems.

Instream flows of the rapidly urbanizing watersheds and estuaries of the Gulf of Mexico in Texas (USA) are increasingly dominated by reclaimed waters. Though ionizable pharmaceuticals have received increasing attention in freshwaters, many research questions remain unanswered, particularly in tidally influenced urban coastal systems, which experience significant spatiotemporal variability in pH that influences bioavailability and bioaccumulation. The authors coupled fish plasma modeling of therapeutic hazard values with field monitoring of water chemistry variability and pharmaceutical occurrence to examine whether therapeutic hazards to fish existed within these urban coastal ecosystems and whether therapeutic hazards differed within and among coastal locations and seasons. Spatial and temporal fluctuations in pH within study sites altered the probability of encountering pharmaceutical hazards to fish. Significant water quality differences were consistently observed among traditional parameters and pharmaceuticals collected from surface and bottom waters, which are rarely sampled during routine surface water quality assessments. The authors then compared modeling predictions of fish plasma concentrations of pharmaceuticals to measured plasma levels from various field-collected fish species. Diphenhydramine and diltiazem were observed in plasma of multiple species, and diltiazem exceeded human therapeutic doses in largemouth bass, catfish, and mullet inhabiting these urban estuaries. Though the present study only examined a small number of target analytes, which represent a microcosm of the exposome of these fish, coastal systems are anticipated to be more strongly influenced by continued urbanization, altered instream flows, and population growth in the future. Unfortunately, aquatic toxicology information for diltiazem and many other pharmaceuticals is not available for marine and estuarine organisms, but such field observations suggest that potential adverse outcomes should be examined.

Bioaccumulation of human pharmaceuticals in fish across habitats of a tidally influenced urban bayou.

Though pharmaceuticals and other contaminants of emerging concern are increasingly observed in inland water bodies, the occurrence and bioaccumulation of pharmaceuticals in estuaries and coastal ecosystems are poorly understood. In the present study, bioaccumulation of select pharmaceuticals and other contaminants of emerging concern was examined in fish from Buffalo Bayou, a tidally influenced urban ecosystem that receives effluent from a major (∼200 million gallons per day) municipal wastewater treatment plant in Houston, Texas, USA. Using isotope dilution liquid chromatography-tandem mass spectrometry, various target analytes were observed in effluent, surface water, and multiple fish species. The trophic position of each species was determined using stable isotope analysis. Fish tissue levels of diphenhydramine, which represented the only pharmaceutical detected in all fish species, did not significantly differ between freshwater and marine fish predominantly inhabiting benthic habitats; however, saltwater fish with pelagic habitat preferences significantly accumulated diphenhydramine to the highest levels observed in the present study. Consistent with previous observations from an effluent-dependent freshwater river, diphenhydramine did not display trophic magnification, which suggests site-specific, pH-influenced inhalational uptake to a greater extent than dietary exposure in this tidally influenced urban ecosystem. The findings highlight the importance of understanding differential bioaccumulation and risks of ionizable contaminants of emerging concern in habitats of urbanizing coastal systems.

Bioaccumulation and trophic dilution of human pharmaceuticals across trophic positions of an effluent-dependent wadeable stream.

Though pharmaceuticals are increasingly observed in a variety of organisms from coastal and inland aquatic systems, trophic transfer of pharmaceuticals in aquatic food webs have not been reported. In this study, bioaccumulation of select pharmaceuticals was investigated in a lower order effluent-dependent stream in central Texas, USA, using isotope dilution liquid chromatography-tandem mass spectrometry (MS). A fish plasma model, initially developed from laboratory studies, was tested to examine observed versus predicted internal dose of select pharmaceuticals. Pharmaceuticals accumulated to higher concentrations in invertebrates relative to fish; elevated concentrations of the antidepressant sertraline and its primary metabolite desmethylsertraline were observed in the Asian clam, Corbicula fluminea, and two unionid mussel species. Trophic positions were determined from stable isotopes (δ(15)N and δ(13)C) collected by isotope ratio-MS; a Bayesian mixing model was then used to estimate diet contributions towards top fish predators. Because diphenhydramine and carbamazepine were the only target compounds detected in all species examined, trophic magnification factors (TMFs) were derived to evaluate potential trophic transfer of both compounds. TMFs for diphenhydramine (0.38) and carbamazepine (1.17) indicated neither compound experienced trophic magnification, which suggests that inhalational and not dietary exposure represented the primary route of uptake by fish in this effluent-dependent stream.