Waste and Biodiversity

Define what a xenobiotic is and give two examples, explaining why decomposing organisms find it difficult to degrade these substances.

Differentiate between bioaccumulation and biomagnification using a three-level marine food chain of your choice.

The diagram shows the concentration of a persistent pesticide in a bay food chain. Calculate the biomagnification factor between water and fish-eating birds (marked with '?'), and explain why apex predators are always the most affected.

The authorities recommend limiting the consumption of tuna, swordfish and emperor fish, especially for pregnant women and children, because of their mercury content. Explain, using the concepts of persistence, bioaccumulation and biomagnification, why mercury concentrates precisely in large predatory fish and not in sardines.

List the waste management hierarchy (reduce, reuse, recycle, recover, and dispose) ordered from most to least recommended, and give an everyday example of each level.

Explain the difference between a controlled landfill and an uncontrolled dump, and point out two environmental risks of the latter (leachates, gases, fires, proliferation of vectors).

Explain what energy recovery from waste is (incineration with energy recovery) and analyse its advantages (less landfilling, electricity) and its drawbacks (emissions, ashes, disincentive to recycle) compared with prevention and recycling.

A landfill closed 15 years ago on fractured karst limestone lacks a basal geomembrane. Located 800 m downslope is a spring that supplies a town and feeds a protected wetland. Analysis of the spring water shows: electrical conductivity of 2400 µS/cm (natural baseline value: 450 µS/cm), ammonium at 12 mg/L (legal limit: 0.5 mg/L), traces of benzene, and a drop in dissolved oxygen to 1.8 mg/L in the wetland.

1. a) Justify hydrogeologically why the lithology of the substrate accelerates the impact, and predict the consequences of this chemical cocktail on the wetland's food web.
2. b) A town councillor proposes "pumping clean water into the landfill to dilute the groundwater contamination". Refute his proposal technically, demonstrating what hydrogeological risks it would trigger.
3. c) Design an urgent three-phase action plan (immediate hydraulic containment, leachate sealing/collection, and bioremediation), justifying the chronological order of each measure to prevent the collapse of the ecosystem.

Explain what the circular economy is and how it differs from the linear "extract, manufacture, use and throw away" model, giving an example of a product redesigned according to circular criteria.

What is composting? Indicate which waste it accepts and which it does not, explain what biological process occurs in the heap (aerobic decomposition) and what product is obtained and what it is used for.

Explain what ecodesign is and describe two examples of products redesigned to generate less waste (repairable appliances with spare parts, single-material packaging, refillable products), indicating which principle of the waste hierarchy they apply.

A fast food chain replaces its polypropylene (PP) packaging with polylactic acid (PLA)-coated cardboard containers and kraft paper bags, advertising: "100% eco-friendly and zero waste!". You have the following Life Cycle Assessment (LCA) data per 1000 units:

• Polyethylene bag (recycled): carbon footprint = 11 kg CO₂ eq; water consumption = 50 L; single use.

• Virgin kraft paper bag: carbon footprint = 26 kg CO₂ eq; water consumption = 1200 L; single use.

• PLA container: carbon footprint = 50 kg CO₂ eq (0.05 kg CO₂ eq per unit); it only biodegrades in industrial composting at >58 °C and 90% relative humidity; in the urban organic waste bin (anaerobic digestion at 37 °C) it is separated as non-target waste and ends up in a landfill.

• Reusable PP container: manufacturing carbon footprint = 1000 kg CO₂ eq (1 kg CO₂ eq per unit).

1. a) Refute the company's advertising claim using the LCA data: justify why replacing synthetic polymers with cellulose derivatives does not automatically imply an overall environmental improvement.
2. b) Predict the environmental impact that PLA will cause if users, confused by the prefix "bio", throw it into the yellow bin for conventional plastics during the mechanical extrusion recycling process.
3. c) Design an alternative for the establishment strictly based on the top of the European waste hierarchy (prevention and reuse) and calculate the minimum number of uses a reusable container must have to offset its higher manufacturing footprint compared to the disposable PLA container it replaces.

A municipality with 50 000 inhabitants generates 1.2 kg of waste per inhabitant per day (composition: 42% biowaste, 18% paper and cardboard, 14% lightweight packaging, 6% glass, 20% residual fraction). European regulations set a minimum municipal recycling target of 65% by weight and a 10% cap on landfilling for 2035. Three options are being debated:

• Option 1: Send the entire mixed fraction to a regional landfill (cost: 45 pesos/t plus an increasing levy per untreated ton; net generation of leachate and fugitive CH₄).

• Option 2: Build an energy recovery plant (incinerator) that burns the mixed waste and generates electricity (requires an investment of 60 million pesos and a guaranteed contractual flow of at least 20 000 t annually for 25 years to be amortized; generates 20% bottom ash and 3% toxic fly ash).

• Option 3: Implement door-to-door separate collection (5 fractions) with anaerobic digestion/composting of organic matter and landfilling only for non-recoverable rejects.

1. a) Analyze Option 2 in light of European targets: explain the concept of "technological lock-in or lock-in effect" and justify why this plant would contradict the reduction and recycling targets for 2035.
2. b) Calculate the amount of biowaste the municipality generates per year (in tons) and quantitatively demonstrate whether Option 3 would allow meeting the European 65% target, assuming an 80% citizen capture rate for recyclable fractions.
3. c) Justify which of the three options offers the best balance in terms of carbon footprint and return to the circular economy, considering greenhouse gas emissions (landfill methane vs. biogenic/fossil CO₂).

Explain what microplastics are, what their two main sources are, and why it is so difficult to remove them from the ocean. Propose two effective measures to reduce their entry into the sea.

The so-called "plastic islands" form at the center of the great ocean gyres. Explain how the currents concentrate floating waste there, why plastic does not disappear but fragments into microplastics, and what difficulties its large-scale cleanup faces.

Define biodiversity and explain its three levels — genetic, species and ecosystem diversity — giving an example of each.

Relate loss of biodiversity to loss of ecosystem services using two specific examples (for example pollinators, wetlands, or reefs), and indicate which type of service is degraded in each case.

The current rate of species extinction is estimated to be tens or hundreds of times higher than the background rate of the fossil record. Explain what the background extinction rate is, name the major causes of the current crisis (habitat destruction, overexploitation, invasive species, pollution, climate) and discuss why there is talk of a possible sixth mass extinction.

Explain what an exotic species is and under what conditions it comes to be considered invasive, citing an example of a non-invasive exotic species in the Dominican Republic and an example of an invasive one.

The zebra mussel and tiger mosquito are invasive alien species in the Dominican Republic. Explain what characteristics make a species invasive, how these two damage biodiversity and ecosystems, and what control measures are applied against them.

The sea otter controls the sea urchins that devour the kelp forests; the wolf controls the deer that prevent the forest from regenerating. a) Explain what a keystone species is and why its disappearance causes disproportionate cascading effects. b) Apply it to the debate on the recovery of the Iberian wolf in Spain: ecological arguments in favor and conflicts with livestock farming. c) Propose measures that make the presence of the large predator compatible with human activity.

Following a diesel spill in a peri-urban sandy soil, three in situ bioremediation plots are tested over 90 days, monitoring the concentration of total petroleum hydrocarbons (TPH) starting from an initial value of 15 000 mg/kg:

• Plot A (natural attenuation, no intervention): final TPH = 13 800 mg/kg; degrading bacterial population = 10⁴ CFU/g.

• Plot B (biostimulation with the addition of N and P at a C:N:P ratio of 100:10:1 and periodic tilling for aeration): final TPH = 1200 mg/kg; degrading population = 10⁸ CFU/g.

• Plot C (bioaugmentation with a commercial inoculum of allochthonous degrading bacteria, without nutrient correction or tilling): final TPH = 11 500 mg/kg; introduced bacteria drop to undetectable levels after 20 days.

1. a) Interpret the results by comparing B and C: justify which factor was limiting biodegradation in the original soil and identify why bioaugmentation failed.
2. b) Reasonably predict what would have happened in Plot B if the soil had become waterlogged due to continuous torrential rains, indicating which microbial metabolic pathways would be affected.
3. c) If the hydrocarbons had migrated to the saturated zone (a deep anoxic aquifer), justify why physicochemical methods (such as multi-phase extraction or permeable reactive barriers) would compete advantageously against standard aerobic biostimulation.

A ravine receives discharges from tanneries containing hexavalent chromium [Cr(VI)]. Ecotoxicological analyses reveal:

• Surface water: total Cr = 0.08 mg/L (virtually all in the form of Cr(VI)).

• Surface sediment (top 10 cm): total Cr = 1450 mg/kg.

• Benthic macroinvertebrates (mayfly larvae): Cr = 320 mg/kg dry weight.

• Benthic fish (barbels, muscle): Cr = 45 mg/kg; nektonic carnivorous fish (trouts, muscle): Cr = 18 mg/kg.

1. a) Interpret the distribution pattern: justify why the concentration in the sediment exceeds that of the water by four orders of magnitude. Analyze the data for barbels and trouts: are we observing a bioaccumulation or a trophic biomagnification process? Contrast this behavior with that of organochlorine pollutants such as DDT.
2. b) A technical report suggests "applying phytoremediation by planting willows directly in the ravine bed". Discuss the feasibility and the risks of transferring the pollutant to terrestrial food webs via leaf litter.
3. c) Propose a technical remediation sequence that combines an initial reducing chemical treatment (Cr(VI) to Cr(III)) with subsequent phytostabilization, justifying the change in solubility and bioavailability between both ionic forms.

An ecotoxicological trial evaluates the impact of the neonicotinoid insecticide imidacloprid on foraging honey bee colonies (Apis mellifera):

• Median lethal concentration (48-h LC50 in the laboratory): 40 ng/bee.

• Mean concentration detected in pollen and nectar of treated crops: 4 ng/g.

• In field trials at doses of 1.5 ng/g: the rate of return to the hive after 1-km flights decreases by 62% and the frequency of the "waggle dance" drops by 75%.

• After 6 months, hives in the treated agricultural environment suffer a 40% loss of their brood mass and a drastic increase in the opportunistic parasite Nosema ceranae.

1. a) Interpret these data: demonstrate why using the LC50 as the sole environmental safety indicator masks population collapse caused by sublethal effects, and how this relates to immunosuppression in the colony.
2. b) Analyze the conflict of interests: a farmer argues that replacing this preventive seed treatment with conventional broad-spectrum aerial spraying increases production costs and kills insects through direct contact. What are the medium-term consequences of each model on pest resistance and the loss of wild pollinators?
3. c) Design an Integrated Pest Management (IPM) program for that agricultural region that dispenses with preventive chemical treatment, incorporating economic injury levels and ecological infrastructure measures (hedgerows and reservoir floral strips).