Morphological and molecular analysis of the toxicity of pharmaceutical-derived aquatic contaminants (PPCPs)​ in zebrafish

Pharmaceutical chemicals, a subset of pharmaceuticals and personal care products (PPCPs), are aquatic contaminants of emerging concern (CECs) that have been detected at elevated concentrations in surface water globally, entering waterways primarily through sewage discharges containing unmetabolized drugs and improper drug disposal. However, the aquatic toxicity of these contaminants, especially in complex mixtures, is poorly understood; moreover, biomarker frameworks have not been largely applied to this class of contaminants. Here, the toxicity of two cardiac-specific medications, triamterene (diuretic) and gemfibrozil (fibrate), was examined both singly and in mixture concentrations in order to better understand the toxicological implications of PPCP mixtures and develop a biomarker framework. Zebrafish embryos (hpf) were exposed to single-chemical trials as well as binary mixtures. Morphometric measurements were extracted for various toxicological endpoints (eye area, length, yolk sac size, and cardiac abnormalities) and results from mixture trials were compared to single-chemical trials using the response addition model. Follow-up qPCR was conducted to inform molecular mechanisms of toxicity and identify potential biomarker responses. Gemfibrozil elicited a dose-dependent decrease in eye area and length (developmental delay), as well as an increase in yolk sac area, suggesting possible interference with lipid metabolism pathways; likewise, increased cardiac abnormalities were observed in a dose-dependent manner, indicating potential cardiotoxicity. Triamterene induced a similar dose-dependent increase in cardiac abnormalities, suggesting possible cardiotoxicity. Additive toxic effects were observed in multiple endpoints, with potential synergism evident in yolk sac and cardiotoxicity. These trends indicate that complex mixtures of PPCPs in the environment could interact in waterways to produce increased toxic effects and highlight the need for toxicity assays to take into account the effect of complex PPCP mixtures in order to more accurately predict environmental effects. This study also points to the need for increased policy regulating the disposal of pharmaceutical waste

Assessing the impacts of toxic mixtures over a broad geographic scale: challenges and first steps

Assessing the risks posed by chemical mixtures is a complex process. Ideally, details are available on exposure (e.g. which chemicals and what concentrations) and effects (e.g. mechanisms of action and toxicity data). This can be challenging even for a single location and time such as a lab or field site. Ecological risk assessments often need to cover much larger scales such as an entire watershed or a wide-ranging species. This increase in scale substantially increases the complexity. Thousands of chemicals in use lead to potential environmental mixture exposures, including pesticide runoff and municipal wastewater discharges. At the landscape scale the nature of chemical mixtures will vary across space and time; available monitoring data are inadequate for describing realistic exposure scenarios and effects on aquatic species. Therefore, creative solutions are required to utilize sources of data that are available to identify where and when risk is the greatest. Sources of data are available to develop a less-detailed, but still useful, landscape scale risk assessment for mixtures. These include data on potential use (e.g. pesticide labels) or release (e.g. mapping of NPDES permits) sites, as well as associated land use/cover. For example, the use of crop designations to represent where pesticide use is allowed can be a surrogate of actual use to establish where the greatest potential for exposure occurs. This landscape scale risk assessment for mixtures can establish priority watersheds for monitoring and further study. Similarly, exposure of aquatic species to complex mixtures discharged in wastewater can be related to urban land uses and permit distributions. The goal is to develop a process to prioritize the areas with increased relative risks of exposure to chemical mixtures in aquatic species and identify important data needs necessary for more detailed mixture analyses in the context of a landscape scale risk assessment

Recurrent Die-Offs of Adult Coho Salmon Returning to Spawn in Puget Sound Lowland Urban Streams

Several Seattle-area streams in Puget Sound were the focus of habitat restoration projects in the 1990s. Post-project effectiveness monitoring surveys revealed anomalous behaviors among adult coho salmon returning to spawn in restored reaches. These included erratic surface swimming, gaping, fin splaying, and loss of orientation and equilibrium. Affected fish died within hours, and female carcasses generally showed high rates (>90%) of egg retention. Beginning in the fall of 2002, systematic spawner surveys were conducted to 1) assess the severity of the adult die-offs, 2) compare spawner mortality in urban vs. non-urban streams, and 3) identify water quality and spawner condition factors that might be associated with the recurrent fish kills. The forensic investigation focused on conventional water quality parameters (e.g., dissolved oxygen, temperature, ammonia), fish condition, pathogen exposure and disease status, and exposures to metals, polycyclic aromatic hydrocarbons, and current use pesticides. Daily surveys of a representative urban stream (Longfellow Creek) from 2002–2009 revealed premature spawner mortality rates that ranged from 60–100% of each fall run. The comparable rate in a non-urban stream was <1% (Fortson Creek, surveyed in 2002). Conventional water quality, pesticide exposure, disease, and spawner condition showed no relationship to the syndrome. Coho salmon did show evidence of exposure to metals and petroleum hydrocarbons, both of which commonly originate from motor vehicles in urban landscapes. The weight of evidence suggests that freshwater-transitional coho are particularly vulnerable to an as-yet unidentified toxic contaminant (or contaminant mixture) in urban runoff. Stormwater may therefore place important constraints on efforts to conserve and recover coho populations in urban and urbanizing watersheds throughout the western United States

The Synergistic Toxicity of Pesticide Mixtures: Implications for Risk Assessment and the Conservation of Endangered Pacific Salmon

BACKGROUND: Mixtures of organophosphate and carbamate pesticides are commonly detected in freshwater habitats that support threatened and endangered species of Pacific salmon (Oncorhynchus sp.). These pesticides inhibit the activity of acetylcholinesterase (AChE) and thus have potential to interfere with behaviors that may be essential for salmon survival. Although the effects of individual anticholin-esterase insecticides on aquatic species have been studied for decades, the neurotoxicity of mixtures is still poorly understood. OBJECTIVES: We assessed whether chemicals in a mixture act in isolation (resulting in additive AChE inhibition) or whether components interact to produce either antagonistic or synergistic toxicity. METHODS: We measured brain AChE inhibition in juvenile coho salmon (Oncorhynchus kisutch) exposed to sublethal concentrations of the organophosphates diazinon, malathion, and chlorpyrifos, as well as the carbamates carbaryl and carbofuran. Concentrations of individual chemicals were normalized to their respective median effective concentrations (EC(50)) and collectively fit to a nonlinear regression. We used this curve to determine whether toxicologic responses to binary mixtures were additive, antagonistic, or synergistic. RESULTS: We observed addition and synergism, with a greater degree of synergism at higher exposure concentrations. Several combinations of organophosphates were lethal at concentrations that were sublethal in single-chemical trials. CONCLUSION: Single-chemical risk assessments are likely to underestimate the impacts of these insecticides on salmon in river systems where mixtures occur. Moreover, mixtures of pesticides that have been commonly reported in salmon habitats may pose a more important challenge for species recovery than previously anticipated