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 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).

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.

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 centre 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 clean-up faces.

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.

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

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 Spain and an example of an invasive one.

Four years after the natural recolonization of the Iberian wolf (Canis lupus) in a Cantabrian mountain district, a scientific team gathers the following quantitative data:

• The density of red deer and roe deer has decreased by 22%, but the time spent by ungulates in riverbanks and open clearings has fallen by 70% ("landscape of fear" effect).

• The regeneration of willows, birches, and yews along riverbanks has increased by 55%, reducing summer river turbidity by 40% and doubling the diversity of aquatic macroinvertebrates.

• Wild boar damage to peri-urban corn crops has decreased by 35% due to changes in their nocturnal foraging routes.

• Concurrently, recorded attacks on extensive sheep farms without guarding have increased from 2 to 31 per year.

1. a) Explain the concept of a top-down trophic cascade using these data, distinguishing the direct predatory effect from the indirect behavioral effect on river morphology and biodiversity.
2. b) Refute both the stance of those who advocate for the "total eradication of the predator to save the rural environment" and those who promote "strict protection without management or compensation", using arguments from ecosystem ecology and rural socioeconomics.
3. c) Design a coexistence proposal based on predator behavior (use of livestock guardian dogs trained with the flock of sheep, electrified night enclosures, and birthing synchronization) and biologically justify why non-selective hunting or poison usually disrupts wolf family groups and paradoxically increases attacks on domestic livestock.