Leveraging comparative physiology and genomics to predict species sensitivity: A novel framework for interspecies extrapolation in ecotoxicology

The idiom of a 'miner's canary'
A miner holds a canary as an alert for toxic gas; from experience he knows that the canary will stop singing before the gas causes lasting harm. The idiom of a 'miner's canary' is used throughout toxicological risk assessment, whether testing for potential risks to human health or for environmental impacts. A restricted range of organisms are used as 'canaries' or sentinels to assess the risk chemicals pose to entire ecosystems. However, unlike 'the canary and the miner' we often do not know the relative affect of the chemical on the sentinels in relation to other organisms. To account for this uncertainty in risk assessment, a 'safety factor', an arbitrary 100 or 1000-fold adjustment, is applied to the lowest observed toxicological effect on sentinel species in an attempt to protect more sensitive species. This extrapolation has no mechanistic grounding being itself entirely a pragmatic response to the number of chemicals entering the environment & variety of organisms present. In this application we propose to develop a novel framework that may be used to provide an objective measure of comparative species sensitivity. The framework is based on three components; i) the measurement of where a chemical goes when it enters an organism; ii) the specific interactions of the chemical with its biological receptor molecules & how this is affected by subtle differences in the receptors observed between species, & iii) the pathways that transmit the affect of the chemical from the interactions with receptor through to eventual impact on the organism.

The where & the how much
To calculate the amount of a chemical that resides in a target tissue we will use radio-labelled compounds & also detailed chemistry to determine the rates of chemical Accumulation (into the organism), Distribution (especially to the target site), Metabolism (to form more or less toxic metabolites) & Excretion (from the body). These measurements will allow us to determine the relative where & how much of a compound is present in response to a precise level of exposure.

Pushing the first domino
Many chemicals affect a biological system through interaction with specific biomolecules termed receptors. In the same way as pushing on a single domino can lead to exotic patterns, a chemical-receptor interaction can act as a "Molecular Initiating Event" that ultimately produces a cascade of biological responses. This means that the precise characteristics of the chemical-receptor interaction are crucial to transmission of chemical affect. The structure of receptor molecules differs between species & this significantly influences the potency of the chemical to the organism. We will use genomics tools & modelling techniques developed for the pharmaceutical industry to predict the relative strength of the chemical-receptor interaction & therefore the effectiveness to transmit its affect.

Mapping affect pathways
Chemical affect is transmitted from a molecular interaction with receptor(s) to the final observed biological effect through a complex series of biological pathways, now termed the Adverse Outcome Pathways (AOP). We will use computational approaches to derive the effective AOP for our chemical linking the exposure amount & its potency to transmit the biological impact.

Case studies: Selecting chemicals & earthworms
We have selected different earthworm species as sentinels because they are widely used for chemical risk assessment in soils, they are key ecosystem engineers & they show a significant diversity of sensitivity to a range of chemicals. The chemical we have selected to study: a) show significant differential sensitivity amongst earthworm species; b) represent a range of chemical modes-of-action; &, c) have receptors of varying complexities. Furthermore, the chemical classes selected have significant environmental relevance especially as this relates to 'non-target' impacts in terrestrial ecosystems.

Parties who can benefit from our research include chemical companies in some of the most economically important sectors, chemical regulatory bodies responsible and also the interested general public.

For Chemical companies there are strong regulatory and reputational drivers to improve current understanding of species sensitivity to chemicals hazards. For these companies, a scientifically robust approach for predicting sensitivity in ecotoxicology would be a valuable addition to current risk assessment strategies.

Regulators and stakeholders involved in chemical management have a specific interested in understanding (and being able to predict) species sensitivity. The novel quantitative perspective on safety factor validity and the overall framework and tools for sensitivity assessment and prediction we will develop can be of tremendous value to such organisations.

Policy makers involved in "3Rs" R&D are seeking solutions to some of the ethical workload issues that have arisen during the implementation of policies such as REACH in Europe. Our work has the potential to address some of these concerns. In particular our overall framework and the in vivo, in vitro and in silico tools for species sensitivity assessment we will develop has the potential to refine and replace traditional toxicity testing approaches through use of surrogate toxicokinetic, toxicodynamic and AOP based endpoints.

The general public are concerned about chemical in the environment, from a health and also an environmental protection perspective. Our project is intended to support development of an approach that can help to identify sensitivity species and develop prediction of possible sensitivity for these organisms to ensure they are included in more complete risk assessments.

Our strategy to reach these organisations will be four fold.

Scientific publication: All project data will be submitted to appropriate data repositories and published in high impact journals in ecotoxicology, molecular ecology, risk assessment and general biology.

Presentation at meetings: We will present our results at meetings affiliated with appropriate societies, such as Society of Experimental Biology (SEB), Society of Toxicology (SOT) and Society of Environmental Toxicology and Chemistry (SETAC) as fora where scientists with industrial, policy and academic backgrounds meet to share the latest research on chemical effects and risk assessment.

Specific workshops: We will hold two specific workshops to showcase the result of our project. The first will be held in parallel with a meeting of SETAC to maximise industry and regulator attendance and will set out the overall theoretical basis for our framework and the tools included. This, and the associated publicity we will generate, will raise awareness of our work with the intention of creating an audience interested in obtaining more information. The second event will build on this groundswell and will be held as a hands-on data analysis course that will allow participants to work with the kinds of toxicokinetic, toxicodynamic and adverse outcome pathway data-sets that we will develop and use within the project.

Public engagement: We will maintain a project web page building on Lumbribase, which is already the most comprehensive resources of earthworm toxicogenomic information. The information on the range and causes of species sensitivity we will generate will also be enable us to participate in current debates on chemical safety, including for neonicotinoids and their alternatives.

The success of our activities can be tracked by monitoring published and conference paper outputs, the number and diversity (industry and regulatory) of organisations attending both our SETAC special symposium and the training workshop and the public responses to the press releases that arise from our work.