Ecological, toxicological and physiological effects of crude oil to polar cod on the basis of dynamic energy budgets
2016 - 2017This work takes place in the context of the POLARISATION project - Polar cod, lipid metabolism and disruption by polycyclic aromatic hydrocarbons
Summary
The energetics of polar cod is modelled using the standard DEB model extended to include metabolic acceleration between birth and metamorphosis. Different experimental setups (in terms of exposure routes, measurement of body residues) are compared and then a TK model is coupled to the DEB model in order to take into account dilution by growth, uptake via food and water as well as how effects relate to internal concentration. Each process in the DEB model has consequences for growth, development and reproduction. The impaired process is inferred from the time patterns of the combined effects on the different endpoints. The no effect concentration (NEC) of crude oil (and which process is impaired) is assessed from the empirical data.Two questions are explored:
- How does the NEC and the impaired process compare across the different experiments?
- How to obtain NECs from a crude oil mixture when toxicity of each compound separately is not available.
Background and approach
The Dynamic Energy Budget (DEB) theory starts from the premise that the mechanisms that are responsible for the organization of metabolism are not species-specific but will apply to all species. Every living organism has to take up resources from its environment and can use this to grow, reproduce and maintain itself. DEB-theory has solid roots in ecotoxicology as effects of organisms can reveal a great deal of information about the processes underlying the behavior of the blank. The different processes related to metabolism are tightly coupled in organisms through the conservation laws and the rules for metabolic organization, and cannot be understood in isolation. Modelling sub-lethal effects thus requires quantitative assumptions on energy budgets, and assumptions on how the metabolic processes are affected by toxicants Energetics impacts toxicological effects and these effects impact energetics. Therefore, two models must be coupled: (1) a DEB model the response of an organism to its environment and (2) a TK/TD model, which specifies the:- Uptake and elimination of the chemical (Toxico-Kinetic, TK parameters)
- Impaired process, e.g. growth, development, reproduction, maintenance
- No Effect Concentration, intensity of effect (Toxico-Dynamic, TD parameters)
Task 1 : DEB – TK/TD model for polar cod
Most teleost fish are modelled using the standard DEB model extended to include metabolic acceleration between birth and metamorphosis. The simplest TK model is the scaled one compartment model. The different experimental setups used in polarization are compared (exposure routes, measurement of body residues) and both scaled and unscaled TK models will be applied and we will take into account dilution by growth, and uptake via food and water.Task 2 : Parameter estimation of the blank
This task involves the synthesis of literature and laboratory data on polar cod life history traits. With the standard DEB-model the parameters that describe the energetic can be derived from life history traits of organisms. The parameters that describe the energy budgets using this model can be derived from life-cycle data:| Time to hatching | Physical length at birth | Weight at birth |
| Growth rate | Physical length at puberty | Age at puberty |
| Weight at puberty | Time to first reproduction | Ultimate length |
| Ultimate weight | Max reproduction rate | Lifespan |
These Life-Cycle data are then used to estimate the relevant DEB parameters that give a description over the life-cycle in terms of energy budgets, with in general very good model fits to the available data. These data are implemented into a matlab 'mydata file' and parameters of the DEB model will be estimated using the AmP set-up. The code, parameter values and goodness of fit to data will be submitted as a entry to the online library AmP (add-my-pet). As such it will be independently curated and the work will be transparent.
Task 3: Toxicity parameters
Both the ISO and the OECD say the NOEC but be out phased. ECx has severe drawbacks. The NOEC and ECx can only be derived using 'dose-response' data taken from standardized tests (constant exposure, constant time) and do not take into account that sublethal endpoints (feeding, growth, reproduction) are interlinked. No Effect Concentration (NEC) obtained from analyzing toxicity data using DEB-TK/TD models replaces the NOEC and ECx and is directly applicable for risk assessment purposes. Energy fluxes within the DEB-model cannot be directly measured however the different processes do have consequences for measurable properties such as body size and offspring production.The affected process is inferred from the time patterns of the combined effects on the different endpoints. Each physiological mode of action has specific consequences for the patterns of growth and reproduction over the life cycle.
The DEB-TK7TD models can be used to obtain NEC values from chronic and acute standardized assays as well as more complex experiments such as those performed on polar cod in this polarisation project. This is a unique opportunity to explore some very important questions:
- How does the NEC compare across the different experiments?
- What TK information can be extracted from the experiments (elimination rates, uptake through food, water)
- How does the metabolic mode of action compare across life-stages?
- How does it compare with published lethal NEC values for polar cod exposed to single compounds using the 4-day standardized assay?
In addition to these fundamental questions, some extra model development is needed to assess effects on reproduction. Energy/mass invested into reproduction cumulates inside the body into what is called a reproduction buffer. This reproduction buffer contributes to the total wet weight – the gonad weight can give some information on the size of the buffer, but this can only be known when the organism is dead. The fish is thus composed of structure, reserve and 'reproduction buffer'. The DEB model for the blank will be used to make educated guesses on how much of the initial wet weight of an adult is reproduction buffer and will predict how much more mass is created for a given feeding condition during the experiment. The only way to check the model predictions is to compare with the final observed weight and/or histological information. The problem of assessing effects on reproduction will entail some focused model development which will be of wider use for analysis of reproductive effects on fish in general.
Task 4 : Integrating to higher levels of organization.
The long-term health of populations and ecosystems is the starting point of environmental protections. However, toxicity tests at these higher levels of organization are complex, costly, difficult to interpret and for some species ethically unjustifiable or prohibited. So to extrapolate toxic effects at the individual level to meaningful consequences at the population level, model approaches are essential. These modelling approaches start from the seemingly simple question: ‘What harm does a small reduction of reproduction by toxic stress for an individual imply at the population level in the environment?’. Caluculate chronic effects on- Life-time reproduction
- Population growth rate (euler-lotka equation)
- Integration into a matrix population model
This work is supported by the POLARISATION - Polar cod, lipid metabolism and disruption by polycyclic aromatic hydrocarbons - (01/2012-03/2016) NFR FRIPRO/fellesløftet 214484.