Ecotoxicology with an Emphasis on Ecology Examination Study Notes

Course Overview and Examination Protocols

• Course Metadata:

  • Course Name: Ecotoxicology with an Emphasis on Ecology.

  • Course Code: $BIO430$.

  • Responsible Teachers: Ingela Dahllöf (Primary Examiner), Sam Dupont, Thomas Backhaus, Natàlia Corcoll, and Pedro Inostroza.

  • Department: Department of Biological and Environmental Sciences.

  • Examination Date: 3rd June 2022 (also referenced as 2018 in some instructions).

• Grading Standards:

  • Maximum Points: $70$ points.

  • Fail (U): Less than $42$ points (less than $60\%$).

  • Pass (P): $42$ points or higher ($60\%$).

  • Pass with Honours (VG): $56$ points or higher ($80\%$).

• Examination Rules:

  • The exam consists of $15$ questions, and students are permitted to skip exactly one question. The skipped question must be clearly marked; otherwise, a random question will be excluded from the final score.

  • Responses must be in English.

  • A dictionary is the only allowed aid during the examination.

  • Strict requirements are in place for legible handwriting and the use of separate sheets for new questions, utilizing only the front side of the paper.

Fundamental Concepts and Ecotoxicological Terminology

To follow ecotoxicological literature, a firm understanding of specific acronyms and technical expressions is required:

• $EC_x$ (Effect Concentration): The concentration of a substance that causes a specific effect (e.g., mortality, growth inhibition) in $x \%$ of the test population compared to a control group.

• NEC (No Effect Concentration): The concentration at which no statistically significant effect is observed in the test organisms.

• Short-term test: A toxicity test conducted over a brief period relative to the organism's lifespan, often used to assess acute toxicity rather than chronic, long-term effects.

• Functional redundancy: A characteristic of an ecosystem where multiple species perform the same ecological function or process (e.g., nitrogen fixation). If one species is lost due to toxicity, the ecosystem process continues because other species fill the role.

• Community composition: The specific identification and relative abundance of different species present within a biological community.

• Analytical accuracy: The degree to which a measured value aligns with the actual, true value of the substance being analyzed.

• Trophic interactions: The biological interactions between different levels of a food web, such as predator-prey relationships or herbivory.

• Dose: The specific amount of a chemical or physical agent that is administered to or received by an organism.

• Biomagnification: The process by which the concentration of a persistent chemical increases as it moves up the food chain, resulting in higher concentrations in top predators than in lower-level organisms.

• Assessment factor: A numeric value (uncertainty factor) applied to laboratory toxicity data to account for uncertainties when extrapolating to real-world environmental risks (e.g., laboratory-to-field extrapolation, inter-species sensitivity).

Experimental Design: Pelagic Mesocosms

• Case Study Context: Designing a pelagic mesocosm experiment to test the long-term effects of a single exposure to Insecticide X at environmentally relevant concentrations.

• Target Community: Phyto- and zooplankton communities within a marine environment.

• Endpoints for Analysis:

  • Copepod egg production (zooplankton health/reproduction).

  • Algal biomass (phytoplankton productivity).

  • Community composition of both algae and copepods.

• Temporal Comparisons:

  • Short-term (2 days): Immediate physiological or behavioral shifts directly following exposure.

  • Long-term (30 days): Potential recovery, population-level shifts, or secondary community effects resulting from the initial pulse of Insecticide X.

Monitoring Hazardous Substances and Chemical Fate

• Objectives of Monitoring:

  • Identifying the presence and concentration of hazardous substances.

  • Assessing the effectiveness of environmental regulations and mitigation strategies.

  • Early detection of emerging contaminants to prevent ecological damage.

• Site Variability: Concentrations of a substance can vary within a single site due to:

  • Heterogeneity in sediment composition or organic matter content.

  • Hydrological factors (e.g., flow patterns, currents, or localized discharge points).

• Fate of Organic Chemicals: Three factors determining the fate of organic hazardous chemicals include their solubility (lipophilicity), volatility (evaporation rates), and degradation half-lives (persistence).

• Bioaccumulation vs. Bioconcentration:

  • Bioconcentration: The uptake of a substance directly from the surrounding medium (e.g., water) via respiratory or dermal surfaces.

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

• The Grasshopper Effect: A phenomenon where volatile or semi-volatile persistent organic pollutants (POPs) travel from warmer tropical or temperate regions to colder polar regions through successive cycles of evaporation and condensation.

Ocean Acidification and Environmental Thresholds

• Threshold Definition: Defining a threshold for ocean acidification is comparable to the $1.5 \, ^\circ\text{C}$ target set in the Paris Agreement for global temperature.

• Strategic Approach: Formulating a threshold involves identifying critical pH levels or carbonate saturation states (e.g., aragonite saturation levels) beyond which marine organisms (calcifiers like corals or shellfish) experience irreversible physiological stress or population decline.

Mixture Toxicity Concepts and Application

In ecotoxicology, chemicals rarely occur in isolation. Understanding how mixtures interact is essential:

• Concentration Addition (CA):

  • Assumes all chemicals in a mixture act via the same mode of action ($MoA$).

  • Chemicals are effectively dilutions of one another; the toxic effect of the mixture can be predicted by summing the concentrations of individual components weighted by their relative potency.

• Independent Action (IA):

  • Assumes chemicals act via different, statistically independent modes of action.

  • The toxicity is predicted based on the probability of effects from individual components, often expressed by the formula for combined probabilities.

• Effect Summation: This concept involves simply adding the observed percentage effects of components. It is generally considered flawed because it ignores the non-linear nature of dose-response curves and cannot account for effects exceeding $100\%$.

• Comparison of Approaches:

  • Direct Testing: (e.g., testing raw wastewater) is beneficial because it captures unknown interactions and the "toxic cocktail" effect without needing to know every ingredient.

  • Modeling (CA/IA): Necessary when dealing with complex mixtures where only list-based data is available. Advantages include the ability to identify the primary drivers of toxicity; disadvantages include the requirement for detailed dose-response data for every single component.

Pollution-Induced Community Tolerance (PICT)

• Core Principle: PICT assumes that exposure to a toxicant will eliminate sensitive species, leaving behind more tolerant individuals or species, thereby increasing the overall community tolerance.

• Requirement for PICT: Differential sensitivity among community members is essential. If all species had identical sensitivity, the entire community would collapse simultaneously rather than shifting toward a more tolerant state.

• Detection Endpoints (Short-term):

  • Photosynthetic inhibition in algae.

  • Respiration rates in bacteria or fungi.

  • Enzyme activity (e.g., phosphatase or glucosidase activity).

• Laboratory Methodologies for PICT Support:

  • Normalization: Diluting periphyton slurry to identical fluorescence units ensures that biomass is standardized across treatments, allowing for direct comparison of toxic effects.

  • Controls: Formaldehyde is added to some control samples before incubation with $^{14}\text{C}$-carbonate to kill the organisms, providing a measure of non-biological (abiotic) carbon uptake.

  • Incubation Conditions: Short-term incubations ($30$ minutes to $1$ hour) are used to measure immediate physiological responses before the community can adapt or shift composition during the lab test. Light and shaking provide optimal environmental conditions for photosynthesis and nutrient exchange.

Ecological Processes and Biodiversity Metrics

• Environmental Influence: Ecological processes (such as nutrient cycling) are influenced by environmental conditions (temperature, light, moisture). It is critical to distinguish between effects caused by chemical toxicity and those caused by natural environmental fluctuations to avoid misattributing ecological changes.

• Pesticide Pulses in Agricultural Streams: Exposure often occurs in "pulses" (spray events). Assessment requires looking at both physiological responses (immediate health of organisms) and long-term biodiversity changes (loss of sensitive species like macroinvertebrates).

• Diversity Indices:

  • Shannon-Weaver Index ($H'$): Measures diversity based on species richness and evenness. Formula: $H' = -\sum p_i \ln(p_i)$, where $p_i$ is the relative proportion of species $i$.

  • Bray-Curtis Dissimilarity Index: Measures the difference in community composition between two sites (e.g., treated vs. control). Ecotoxicologists prefer this in microcosm experiments because it focuses specifically on shifts in composition and abundance caused by treatment rather than just overall richness.

• Multidimensional Scaling (MDS): A visualization technique used to plot the similarity/dissimilarity of communities. If points representing different doses or time intervals cluster together, the communities are similar. If they move apart, it indicates a shift in community structure due to the toxicant.

Advanced Monitoring and Molecular Tools

• Pollinator Resilience Strategy: The European Commission's "Farm to Fork Strategy" aims to reduce pesticide use by $50\%$ by $2030$. Monitoring pollinator biodiversity (e.g., bees, butterflies) is vital for food security.

• Molecular Methods:

  • Environmental DNA (eDNA) / Metabarcoding: Involves extracting DNA from environmental samples (water, soil, or trap residues) and using universal primers to amplify specific barcodes (e.g., $COI$ gene for invertebrates).

  • Sequencing: High-throughput sequencing (e.g., Illumina) allows for the identification of entire communities from a single sample.

• Diversity Metrics:

  • Alpha-diversity ($\alpha$): Local diversity within a single site.

  • Beta-diversity ($\beta$): The variation in species composition between different sites or along an environmental gradient. Both are necessary to understand how pesticide reduction affects local health and regional distributions.