Past paper

Administrative and Course Overview: BIO430

• Course Title: Ecotoxicology with an Emphasis on Ecology (Course Code: BIO430).

• Responsible Instructors: Ingela Dahllöf, Sam Dupont, Thomas Backhaus, Natàlia Corcoll, and Pedro Inostroza.

• Examination Assessment:

  • Maximum Score: $70$ points.

  • Grade Thresholds:

    • Fail (U): <42\,p (Less than $60\%$).

    • Pass (P): $\geq 42\,p$ ($60\%$

    • Pass with Honours (VG): $\geq 56\,p$ ($80\%$

• Examination Guidelines:

  • Answers must be provided in English.

  • Formatting requires brief, clear writing on the front side of the paper only; new pages should be used for each new question.

  • Evaluation is corrected anonymously via code numbers.

  • Standard aids are restricted to dictionaries only.

Fundamental Ecotoxicological Terminology and Acronyms

• ECx (Effect Concentration): The concentration of a substance that results in an observed effect in $x\%$ of the test population or a reduction of $x\%$ in a quantitative parameter (e.g., growth or reproduction).

• NEC (No Effect Concentration): The concentration below which no adverse effects are observed in the exposed organisms, often derived through statistical modeling from a concentration-response curve.

• Short-term Test: A toxicity test conducted over a brief period relative to the lifecycle of the organism, usually focusing on acute effects such as lethality or immediate physiological changes.

• Functional Redundancy: An ecological concept where multiple species within a community perform the same role or function (e.g., nitrogen fixation, primary production). This provides a "buffer" against the loss of individual species due to toxic stress.

• Community Composition: The specific identity and relative abundance of the different species present within a defined ecological community.

• Analytical Accuracy: A measure of how close a laboratory measurement of a chemical concentration is to the true or accepted value.

• Trophic Interactions: The feeding relationships and energy transfer pathways between different levels of a food web (e.g., predator-prey dynamics).

• Dose: The total amount of a substance administered to or received by an organism, typically expressed in terms of mass per body weight (e.g., $mg/kg$).

• Biomagnification: The process by which the concentration of a persistent, lipophilic substance increases as it moves up through successive levels of the food chain.

• Assessment Factor (AF): A numerical factor (safety factor) used in environmental risk assessment to account for uncertainties when extrapolating data, such as moving from laboratory data to field conditions or from acute to chronic effects.

Longitudinal Study: Pelagic Mesocosm Experiments

• Experimental Context: Testing the long-term effects of a single exposure to a specific insecticide (Insecticide X) at concentrations found in marine environments.

• Community Focus: Phyto- and zooplankton communities within a mesocosm.

• Temporal Endpoints:

  • Phase 1 (2 Days Post-Exposure): Evaluation of immediate impacts on copepod egg production and initial shifts in algal biomass.

  • Phase 2 (30 Days Post-Exposure): Evaluation of long-term community recovery or permanent shifts in the composition of algae and copepod species.

• Predictive Metrics:

  • Copepod Egg Production: Likely sensitive to insecticide exposure in the short term.

  • Algal Biomass: May exhibit indirect effects (e.g., increases due to reduced grazing pressure from impacted copepods).

  • Community Composition: Assessing the resilience and potential for taxonomic shifts in both the algae and copepod populations.

Hazardous Substance Monitoring and Chemical Fate

• Objectives of Monitoring:

  1. Assessing the effectiveness of mitigation measures and regulations.

  2. Tracking temporal and spatial trends in chemical concentrations.

  3. Evaluating potential risks to human health and environmental integrity.

• Concentration Variability: Variance in chemical concentration within a single site can occur due to:

  • Heterogeneity in environmental matrices (e.g., sediment vs. water column).

  • Temporal fluctuations in discharge or environmental conditions (e.g., currents, tides).

• Organic Chemical Fate: Guided by factors including the substance's physical-chemical properties and environmental degradation rates.

• Bioaccumulation vs. Bioconcentration:

  • Bioconcentration: The specific uptake of a chemical directly from the surrounding medium (e.g., water) into the organism.

  • Bioaccumulation: The net accumulation of a substance in an organism from all sources, including water, air, and dietary intake.

• The Grasshopper Effect: The process by which semi-volatile organic pollutants (like certain pesticides) undergo cycles of evaporation in warmer regions and subsequent deposition in colder regions, leading to long-range transport toward the poles.

Thresholds and Environmental Stressors: Ocean Acidification

• Threshold Definition Strategy: Setting thresholds for environmental stressors requires scientific justification similar to the Paris Agreement's limit of $1.5\,{^\circ}\text{C}$ above pre-industrial levels.

• Ocean Acidification Implementation: A strategy must define critical limits for $\text{pH}$ or saturation states of carbonate minerals that prevent irreversible damage to marine ecosystems and calcifying organisms.

Mixture Toxicity: Concepts and Modeling

• The Three Core Concepts:

  1. Concentration Addition (CA): Assumes chemicals have the same mode of action; they act as dilutions of each other. Concentrations are summed by scaling them to their individual potencies.

  2. Independent Action (IA): Assumes chemicals act on different target sites or through different modes of action. The effects are treated as statistically independent probabilities.

  3. Effect Summation: A flawed concept that simply adds up the observed percentage effects of components. This fails because it can lead to predictions exceeding $100\%$ effect and does not account for the non-linear nature of dose-response curves.

• Comparison of Approaches:

  • Commonalities: Both CA and IA allow for the prediction of mixture toxicity based on the properties of individual components.

  • Differences: CA is generally used for similar-acting compounds, while IA is used for dissimilar-acting compounds.

  • Whole-Mixture Testing vs. Modeling: Testing a whole mixture (e.g., wastewater dilution) provides the actual toxicity (EC50) of that specific sample but does not identify the causative agents. IA/CA models are used to understand the contributions of specific chemicals and predict effects in complex environmental mixtures where testing every possible combination is impossible.

Pollution-Induced Community Tolerance (PICT)

• Requirement for PICT: Differential sensitivity among species in a community is essential. The toxicants must eliminate the most sensitive species/individuals, allowing the more tolerant ones to dominate; without this specific selection pressure, the community-level tolerance cannot increase.

• PICT Endpoints for Detection: Short-term toxicity tests may utilize:

  1. Inhibition of photosynthesis in algae.

  2. Leucine incorporation (protein synthesis) in bacteria.

  3. Enzyme activities or respiration rates.

• Laboratory Methodologies for PICT Samples:

  • Dilution to same fluorescence units: Normalizes biomass to ensure valid comparisons between different samples.

  • Formaldehyde addition: Used as a killed control to account for non-biological uptake or background radiation in $^{14}\text{C}$-carbonate uptake experiments.

  • River water incubation: Maintains environmental realism and provides the natural chemical matrix found at the site.

  • Short-term incubations (30–60 minutes): Captures immediate physiological responses while preventing the community from adapting or shifting composition during the laboratory test itself.

  • Light and shaking: Ensures optimal conditions for photosynthetic activity and prevents the settling of organisms, maintaining oxygen and nutrient distribution.

Ecological Processes, Resilience, and Pulsed Exposures

• Environmental Influence: Ecological processes are shaped by environmental conditions; distinguishing these is relevant to ecotoxicology to understand if an effect is due to chemical toxicity or natural environmental stressors.

• Pulsed Pesticide Exposure: Pulse events (e.g., spray drift or runoff during rain) require assessment methods that focus on:

  • Physiological Response: The immediate, often reversible, stress at the individual level.

  • Biodiversity Changes: Long-term shifts in the community structure due to the loss of sensitive species during peak concentration events.

• Resilience and Recovery: A system is considered recovered when both its function and its taxonomic composition return to a state indistinguishable from control (unexposed) communities.

Diversity Metrics and Statistical Analysis

• Shannon-Weaver Index ($H'$): Calculated using $p_i$, where $p$ is the relative proportion of individuals found in species $i$. It measures both species richness and evenness.

• Bray-Curtis Dissimilarity Index: used to compare the difference between two communities ($A$ and $B$).

  • $n$ = number of species.

  • $X_i$ = abundance of species $i$ in community $A$ or $B$.

• Why Ecotoxicologists Prefer Bray-Curtis: Unlike some indices, Bray-Curtis reflects changes in the actual species identities and their abundances between a control and a treated group, making it highly sensitive to community shifts caused by chemical exposure.

• Data Visualization:

  • Total Abundance: Shows the gross number of individuals across doses.

  • Multidimensional Scaling (MDS): Uses Bray-Curtis dissimilarity on log-transformed data (e.g., chlorpyrifos exposure) to map community distance in a 2D space, illustrating how communities diverge from the control over time (weeks) and dose levels.

Molecular Biodiversity Monitoring for Pollinators

• Context: The EU aims to reduce pesticide use by $50\%$ by 2030 to protect pollinators.

• Molecular Methods:

  • Advice: Implementation of DNA metabarcoding.

  • Components: Requires specific primers (e.g., targeting the COI gene region) and Next-Generation Sequencing (NGS) technology.

  • Justification: Allows for the rapid, high-throughput identification of thousands of individuals and multiple species simultaneously from bulk samples without manual taxonomic expertise.

• Metrics:

  • Alpha-diversity: Species richness within a single site.

  • Beta-diversity: The variation in species composition between different sites or across a temporal gradient.

  • Recommendation: Using both metrics provides a comprehensive view of how pollinator communities are recovering across landscapes and through time.