Crude oil is a highly complex mixture containing thousands of compounds, many of which remain unexplored. It is also highly toxic to marine life and poses a significant threat to fish species of both commercial and ecological importance. One of the greatest challenges for environmental scientists and policymakers is to predict the full consequences of oil spills on fish populations. While modeling approaches are valuable for risk and impact assessments, they often focus on a single life stage or generation, thereby overlooking long-term effects across generations. Recent insights into the complexity of oil compounds, their toxicity beyond early life stages, and the potential transfer of toxic effects from parents to offspring suggest that current models may lack the robustness and accuracy required.
To address this gap, the ToxiGen project seeks to answer key questions: How does oil exposure affect reproduction in adult fish? Which specific compounds are most toxic, and by what mechanisms do they cause harm? And most critically, do the effects of crude oil persist across multiple generations? Our research links molecular changes in exposed parents to the compounds they accumulate and investigates how these alterations influence the health and reproductive success of their offspring over several generations.
Large-scale in vivo studies on Arctic key species such as cod and polar cod have revealed profound disruptions in reproductive organs at both molecular and physiological levels, leading to adverse effects already in the early life stages of the first generation. Current work is focused on identifying epigenetic alterations induced by oil exposure and assessing their potential role in mediating toxicity within and across generations. In parallel, advanced transgenerational experiments in zebrafish are underway to examine changes at the methylome level and evaluate whether such modifications can be inherited across successive generations.
Our team has also identified chemical structures that bioaccumulate in brain, liver, and gonads. These analyses show a consistent distribution of compounds across tissues, with naphthalenes as the most dominant group, followed by alkylbenzenes, cyclic monoaromatics, and finally multicyclic aromatics and PAHs. Ongoing transcriptomic analyses indicate significant molecular effects in brain, liver, and gonads, while integration of multi-omics datasets is expected to provide a holistic understanding of the pathways driving the observed toxicity and their implications for long-term population health.
Preliminary ex vivo experiments on cod liver exposed to oil’s water-soluble fractions (WAF) and fractionated extracts suggest that the so-called “resin” fraction may play a prominent toxicological role alongside the traditionally emphasized PAH fraction, both in relation to it’s higher relative abundance and also varied chemical composition. These findings are consistent with behavioral impairments observed in zebrafish larvae exposed to the same extracts.
Finally, in silico modeling combined with in vitro assays and tissue culture systems are currently being applied to pinpoint the most potent WAF fractions and to identify individual compounds with the highest toxic potential through known pathways of toxicity and metabolic disruption. Computational screening has allowed to reduce the list of candidate compounds from more than 200 to 15 that appear most biologically active, paving the way for targeted mechanistic studies.
This knowledge is essential to understand the extent to which crude oil can impact marine organisms, particularly ecologically and economically important fish species, and may also contribute to the development of more realistic monitoring tools – especially through the use of chemical markers beyond the traditionally applied PAHs.
A fundamental and enduring challenge for ecosystem managers developing risk and impact assessment tools is to predict the extent of impact that spilled oil can have on the immediate fish populations and on future generations. Modelling approaches are important tools for these assessments, but they currently suffer from two major shortcomings: 1) the failure to acknowledge that effects can be transferred through several generations and 2) the assumption that a small group of toxic compounds, polycyclic aromatic hydrocarbons, can be used as chemical proxy for exposure to complex petroleum mixtures. Emerging understanding within petroleum ecotoxicology now suggests that model outputs lack robustness. Up until now studies have not been able to determine the effects over multiple generations, and to properly identify the causative agents within petroleum. ToxiGen is an interdisciplinary study that will determine the effects and toxic mechanisms of petroleum on the reproductive success of fishes and subsequent generations. Our ambition is to identify the compounds responsible for alterations in reproductive success in adults and survival and fitness of the progeny. We will work with Atlantic cod and polar cod that are of high ecological and commercial importance, respectively. Zebrafish will be used for high-risk and generational experiments. We will work at the frontier of analytical chemistry to characterize the toxic fractions of petroleum. To disentangle mechanisms of toxicity, novel methods such as micro-injecting compounds into eggs will be used. We will combine different approaches to identify new biomarkers of exposure and effects. The new knowledge will then be integrated into reproductive adverse outcome pathways to be available through an internationally harmonized knowledgebase. Ultimately, ToxiGen will provide environmental managers with knowledge and data for models, and methods to detect and monitor the presence and impact of these complex mixtures in situ.
