Markus Hecker

Markus Hecker
University of Saskatchewan | U of S · School of Environment & Sustainability and Toxicology Centre

PhD

About

296
Publications
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7,692
Citations

Publications

Publications (296)
Article
Early-life stage (ELS) avian toxicity tests have been proposed as a more ethical alternative to traditional standardized tests with adult birds. At the same time, 'omics approaches are gaining traction in the field of avian toxicology, but little has been done to characterize the metabolome and transcriptome at different life stages. The present st...
Article
Selenium (Se) is an environmental contaminant of global concern that can cause adverse effects in fish at elevated levels. Fish gut microbiome play essential roles in gastrointestinal function and host health and can be perturbed by environmental contaminants, including metals and metalloids. Here, an in-situ Se exposure of female finescale dace (P...
Preprint
Toxicity testing is under transformation as it aims to harness the potential of New Approach Methods (NAMs) as alternative test methods that may be less resource-intensive (i.e., fewer animals, cheaper costs, quicker assays) than traditional approaches while also providing more data and information. While many stakeholders are of the opinion that t...
Article
Current ecotoxicity testing programs are impeded as they predominantly rely on slow and expensive animal tests measuring adverse outcomes. Therefore, new approach methodologies (NAMs) increasingly involve short-term mechanistic assays that employ molecular endpoints to predict adverse outcomes of regulatory relevance. This study aimed to elucidate...
Article
Reptiles represent the least-studied group of vertebrates with regards to ecotoxicology and no empirical toxicity data existed for dioxin-like chemicals (DLCs). This lack of toxicity data represents a significant uncertainty in ecological risk assessments of this taxon. Therefore, the present study assessed early-life sensitivity to select DLCs and...
Article
Full-text available
This proof-of-concept study characterizes the Japanese quail (Coturnix japonica) hepatic metabolome following exposure to benzo[a]pyrene, chlorpyrifos, ethinylestradiol, fluoxetine hydrochloride, hexabromocyclododecane, lead(II)nitrate, seleno-L-methionine, and trenbolone in embryos and adults. The analysis revealed effects on lipid metabolism foll...
Article
Hazardous chemicals are one of the greatest environmental challenges facing our planet, testing governments in the face of economic and social development. Chemical risks are often complex systemic risks, which require particular governance processes, stakeholder participation mechanisms, and communication procedures to manage. In this article we e...
Article
Current approaches in chemical hazard assessment face significant challenges because they rely on live animal testing, which is time-consuming, expensive, and ethically questionable. These concerns serve as an impetus to develop new approach methodologies (NAMs) that do not rely on live animal tests. This study explored a molecular benchmark dose (...
Article
The microbiome of the gut is vital for homeostasis of hosts with its ability to detoxify and activate toxicants, as well as signal to the immune and nervous systems. However, in the field of environmental toxicology, the gut microbiome has only recently been identified as a measurable indicator for exposure to environmental pollutants. Antidepressa...
Article
Information on the effects of silver nanoparticles (AgNPs) in fish have mostly been generated from standard laboratory species and short‐term toxicity tests. However, there is significant uncertainty regarding AgNP toxicity to native species of concern in North America, particularly in northern freshwater ecosystems. Here, we assessed the chronic t...
Article
The assessment of the exposure of aquatic wildlife to complex environmental mixtures of chemicals originating from both point and diffuse sources and evaluating the potential impact thereof constitutes a significant step towards mitigating toxic pressure and the improvement of ecological status. In the current proof-of-concept study, we demonstrate...
Article
Modern 21st century toxicity testing makes use of omics technologies to address critical questions in toxicology and chemical management. Of interest are questions relating to chemical mechanisms of toxicity, differences in species sensitivity, and translation of molecular effects to observable apical endpoints. Our study addressed these questions...
Article
While it is well recognized that the frequency and intensity of flood events are increasing worldwide, the environmental, economic, and societal consequences of remobilization and distribution of pollutants during flood events are not widely recognized. Loss of life, damage to infrastructure, and monetary cleanup costs associated with floods are im...
Article
Standardized laboratory tests with a limited number of model species are a key component of chemical risk assessments. These surrogate species cannot represent the entire diversity of native species, but there are practical and ethical objections against testing chemicals in a large variety of species. In previous research, we have developed a mult...
Article
Full-text available
Despite the global toxicology community discussing New Approach Methodologies (NAMs) for chemical hazard and risk assessment, such as in vitro, in silico, and ‘omics-based approaches, for some 30 years, their formal adoption by regulators remains limited. Previous research suggests that insufficient validation, complexity of interpretation, and lac...
Article
There is increasing pressure to develop alternative ecotoxicological risk assessment approaches that do not rely on expensive, time-consuming, and ethically questionable live animal testing. This study aimed to develop a comprehensive early life stage toxicity pathway model for the exposure of fish to estrogenic chemicals that is rooted in mechanis...
Article
Selenium (Se) is both an essential micronutrient and a contaminant of concern that is of particular interest in mining-influenced waterbodies in Canada. The objective of this research was to characterize the trophic dynamics of selenium along a gradient of exposure concentrations in a Canadian boreal lake ecosystem. From June 20 to August 22, 2018,...
Article
Recent studies have shown that white sturgeon (Acipenser transmontanus) are more resistant to cadmium (Cd) compared to rainbow trout (Oncorhynchus mykiss), whereas they are more sensitive than rainbow trout when exposed to copper (Cu). Differences in the subcellular distribution of metals among species could be one of the factors responsible for th...
Article
Full-text available
Although withdrawn from the market in the 1980s, polychlorinated biphenyls (PCBs) are still found ubiquitously in the aquatic environment and pose a serious risk to biota due to their teratogenic potential. In fish, early life-stages are often considered most sensitive with regard to their exposure to PCBs and other dioxin-like compounds. However,...
Article
Environmental risk assessment is often challenged by a lack of toxicity data for ecological species. The overall goal of this research project was to employ an avian early‐life stage toxicity test to determine the effects of four chemicals (benzo[a]pyrene [BaP], chlorpyrifos [CPF], fluoxetine hydrochloride [FLX], ethinylestradiol [EE2]) in an ecolo...
Article
Understanding internal dose metrics is integral to adequately assess effects environmental contaminants might have on aquatic wildlife, including fish. In silico toxicokinetic (TK) models are a leading approach for quantifying internal exposure metrics for fishes; however, they often do not adequately consider chemicals that are actively biotransfo...
Article
Full-text available
Background: Some 20 y ago, scientific and regulatory communities identified the potential of omics sciences (genomics, transcriptomics, proteomics, metabolomics) to improve chemical risk assessment through development of toxicogenomics. Recognizing that regulators adopt new scientific methods cautiously given accountability to diverse stakeholders...
Article
Uptake and effects of ionizable organic chemicals (IOCs) that are weak acids in aqueous solution by fish can differ as a function of pH. While the pH-dependent behavior of select IOCs is well-understood, complex mixtures of IOCs, e.g., from oil sands process-affected water (OSPW), have not yet been studied systematically. Here, we established an in...
Article
Full-text available
Because compounds accumulate through dry periods and enter aquatic systems in just a few seasonal events such as snowmelt and summer storms, surface waters in semi-arid, cold regions, such as the Canadian Prairies, are particularly vulnerable to loading of contaminant from runoff events from surfaces. This study assessed concentrations of metals an...
Article
In addition to aiding in digestion of food and uptake of nutrients, microbiota in guts of vertebrates are responsible for regulating several beneficial functions, including development of an organism and maintaining homeostasis. However, little is known about effects of exposures to chemicals on structure and function of gut microbiota of fishes. T...
Article
Traditional results from toxicogenomics studies are complex lists of significantly impacted genes or gene sets, which are challenging to synthesize down to actionable results with a clear interpretation. Here we defined two sets of 21 custom gene sets, called the functional and statistical EcoToxModules, in fathead minnow (Pimephales promelas) to 1...
Article
Early life-stages of the endangered white sturgeon (Acipenser transmontanus) have been shown to be among the most sensitive fishes to aqueous copper (Cu) exposure. In a recent analogous study, we examined the role of whole-body Cu accumulation and Na homeostasis in species-specific differences between the sensitivity of white sturgeon and a common...
Article
Sturgeons (Acipenseridae) are ancient fishes that have tissue-specific profiles of transcriptional responses to dioxin-like compounds (DLCs) that are unique from those generally measured in teleost fishes. Because DLCs exert their critical toxicities through activation of the aryl hydrocarbon receptor (AHR), this transcription factor has been the s...
Article
Background: Given current legislative mandates to assess the safety of thousands of chemicals and the slow pace at which conventional testing proceeds, there is a need to accelerate chemical risk assessment. Governments and businesses are increasingly interested in New Approach Methodologies (NAMs) that promise to reduce costs and delays. Aim: W...
Poster
Full-text available
The use of toxicogenomic endpoints and increased reliance on early-life stage (ELS) animal exposures are two strategies that have been proposed to improve toxicity testing for regulatory risk assessment. However, it is unknown whether transcriptomic measures in ELS organisms are predictive of those measured in their adult counterparts. The present...
Poster
Full-text available
Incorporation of toxicogenomics into ecological risk assessment requires a good understanding of the genes/pathways that are commonly affected by exposure to toxic chemicals. Studies comparing transcriptomic responses across environmental chemicals are available for fish but less research has been done for birds. The present study aims to reveal un...
Article
Full-text available
There is growing interest within regulatory agencies and toxicological research communities to develop, test, and apply new approaches, such as toxicogenomics, to more efficiently evaluate chemical hazards. Given the complexity of analyzing thousands of genes simultaneously, there is a need to identify reduced gene sets. Though several gene sets ha...
Article
Selenium (Se) is a contaminant of concern in many aquatic ecosystems due to its narrow range between essentiality and toxicity in oviparous (yolk-bearing) vertebrates. The objective of the present study was to determine the effects of Se, experimentally added to in situ limnocorrals as selenite, on invertebrate communities and fathead minnow (Pimep...
Article
Selenium (Se) enrichment has been demonstrated to vary by several orders of magnitude among species of planktonic algae. This is a substantial source of uncertainty when modelling Se biodynamics in aquatic systems. In addition, Se bioconcentration data are largely lacking for periphytic species of algae, and for multi-species periphyton biofilms, a...
Article
Full-text available
Selenium (Se) is an essential trace element of concern that is known to contaminate aquatic ecosystems as a consequence of releases from anthropogenic activities. Selenium is of particular toxicological concern for egg-laying vertebrates as they bioaccumulate Se through the diet and deposit excess Se to embryo-offspring via maternal transfer, a pro...
Article
Early‐life stage (ELS) toxicity tests are recognized as an advancement over current testing methodologies in terms of cost, animal use, and biological relevance. However, standardized ELS tests are not presently available for some vertebrate taxa, including birds. This manuscript describes a Japanese quail (Coturnix japonica) ELS test that is a pro...
Article
Recent studies have demonstrated that white sturgeon are more sensitive to acute exposure to Cu than rainbow trout (Oncorhynchus mykiss), especially during early life-stages. However, the physiological mechanisms underlying this difference in sensitivity to Cu is not known. In the present study, we first confirmed the higher sensitivity (lower 96 h...
Preprint
There is growing interest within regulatory agencies and toxicological research communities to develop, test, and apply new approaches, such as toxicogenomics, to more efficiently evaluate chemical hazards. Given the complexity of analyzing thousands of genes simultaneously, there is a need to identify reduced gene sets.Though several gene sets hav...
Preprint
Full-text available
There is growing interest within regulatory agencies and toxicological research communities to develop, test, and apply new approaches, such as toxicogenomics, to more efficiently evaluate chemical hazards. Given the complexity of analyzing thousands of genes simultaneously, there is a need to identify reduced gene sets.Though several gene sets hav...
Article
Nanosized alumina (Al2O3-NPs), a widely used nanoparticle in numerous commercial applications, is released into environment posing a threat to the health of wildlife and humans. Recent research has revealed essential roles of physicochemical properties of nanoparticles in determining their toxicity potencies. However, influence of shape on neurotox...
Chapter
Legislation in North America and Europe, such as the Canadian Environmental Protection Act (CEPA), the US Safe Drinking Water Act (SDWA), and the European Registration, Evaluation, and Authorization of Chemicals (REACH) program, mandates the assessment of risks of chemicals to the environment and human health. Current testing strategies within thes...
Article
Human activities have increased the release of selenium (Se) to aquatic environments, but information about the trophic transfer dynamics of Se in Canadian boreal lake systems is limited. In the present study, Se was added as selenite to limnocorrals (2 m diameter, 3000 L in situ enclosures) in a boreal lake in northwestern Ontario to reach nominal...
Article
Understanding the mechanistic basis of differences in the sensitivity of fishes to metals is important for developing informed ecological risk assessment approaches for metals. Whole body metal accumulation, metallothionein induction, oxidative stress and associated antioxidant response, as well as heat shock proteins (mainly HSP70) are known to pl...
Article
Full-text available
Hydroxylation of polyaromatic compounds through cytochromes P450 (CYPs) is known to result in potentially estrogenic transformation products. Recently, there has been an increasing awareness of the importance of alternative pathways such as aldehyde oxidases (AOX) or N-methyltransferases (NMT) in bioactivation of small molecules, particularly N-het...
Poster
Full-text available
The production and release of chemicals by our society has been described as one of the greatest threats to the sustainability of human activities on this planet. Legislations of varying rigor have been implemented globally and seek to minimize impacts of chemicals on the environment through ecological risk assessments (ERA). The foundation of ERA...
Article
There are huge variations in life-stage- and species-specific sensitivities among the fishes to the exposure with metals; however, the physiological mechanisms underlying these differences are not well understood to date. This study revealed significant life-stage (larval, swim up and juvenile) and species-specific differences between two evolution...
Article
Full-text available
Background: Freshwater sediments have been recognized as a long-term sink and potential source for environmen- tal pollutants released into the aquatic ecosystems. In this study, the sediment quality of Taihu Lake, which is sus- ceptible to anthropogenic contamination, was assessed by a combination of chemical analytical and biological end points....
Article
Full-text available
Background Eutrophication of freshwater systems can result in blooms of phytoplankton, in many cases cyanobacteria. This can lead to shifts in structure and functions of phytoplankton communities adversely affecting the quality of drinking water sources, which in turn impairs public health. Relationships between structures of phytoplankton communit...
Article
Dioxin-like compounds (DLCs) elicit adverse effects through activation of the aryl hydrocarbon receptor (AHR). Prior investigations demonstrated that sensitivity to activation of AHR1 in an in vitro AHR transactivation assay is predictive of early life stage mortality among birds. The present study investigated the link between sensitivity to activ...
Article
Full-text available
Endocrine-disrupting chemicals are known to impact multiple hormonal axes of vertebrates, among which the thyroid system is crucial for multiple developmental and physiological processes. Thus, the present study focused on the semi-quantitative visualization of intrafollicular triiodothyronine (T3) and thyroxin (T4) in zebrafish embryos as a potent...
Article
Freshwaters worldwide are under increasing pressure from anthropogenic activities and changing climate. Unfortunately, many inland waters lack sufficient long-term monitoring to assess environmental trends. Analysis of sedimentary ancient DNA (sedaDNA) is emerging as a means to reconstruct the past occurrence of microbial communities of inland wate...
Article
Full-text available
In the original article wrong unites were quoted in Table 3 (page 508) and Table 4 (page 510) as well as in the paragraph 3.2 Core chemical exposure experiments on page 509. Also in paragraph 2.3 Selection and testing of chemicals the link to the Supplemental Materials (ESM) was missing.
Article
Full-text available
Background Managing and recycling electronic waste (e-waste), while useful and necessary, has resulted in significant contamination of several environments in China. The area around Tianjin, China has become one of the world's largest e-waste disposal centers, where electronics are processed by manually disassembly or burning, which can result in s...
Chapter
Ecological risk assessors are increasingly recognizing the need for objectively characterizing the sensitivity of specific ecological receptors of interest to environmental contaminants. Current testing strategies in support of ecological risk assessments primarily rely on extensive animal testing, and on extrapolation from standard laboratory mode...
Article
Full-text available
In ecotoxicology, transcriptomics is an effective way to detect gene expression changes in response to environmental pollutants. Such changes can be used to identify contaminants or contaminant classes and can be applied as early warning signals for pollution. To do so, it is important to distinguish contaminant-specific transcriptomic changes from...
Article
Full-text available
The implementation of in vitro bioassays for the screening of dioxin-like compounds (DLCs) into management guidelines of dredged material is of increasing interest to regulators and risk assessors. This study reports on an intra- and inter-laboratory comparison study between four independent laboratories. A bioassay battery consisting of RTL-W1 (7-...
Article
Previous research has characterized the important role of aldehyde oxidases (AOX) in biotransformation of N-heterocyclic therapeutic drugs and environmental contaminants in mammals. Research pertaining to AOX activity in non-mammalian vertebrates, however, is scarce, despite its biological role as a potentially important metabolic pathway for xenob...
Article
Cell-based bioanalytical tools are considered one alternative to overcome limitations of sensitivities of instrumental, analytical chemistry for monitoring estrogenic chemicals in the environment. Because these tools also reflect non-additive interactions of chemicals in mixtures, their outcomes often deviate from outcomes of chemical analytical ap...
Article
Full-text available
Protecting our water resources in terms of quality and quantity is considered one of the big challenges of the twenty-first century, which requires global and multidisciplinary solutions. A specific threat to water resources, in particular, is the increased occurrence and frequency of flood events due to climate change which has significant environ...
Article
Gene expression analysis represents a powerful approach to characterize the specific mechanisms by which contaminants interact with organisms. One of the key considerations when conducting gene expression analyses using quantitative real-time reverse transcription-polymerase chain reaction (qPCR) is the selection of appropriate reference genes, whi...
Article
Our ability to conduct whole-organism toxicity tests to understand chemical safety has been outpaced by the synthesis of new chemicals for a wide variety of commercial applications. As a result, scientists and risk assessors are turning to mechanistically based studies to increase efficiencies in chemical risk assessment and making greater use of i...