Lecture 12: Plants, People and Planet - Plants, Pollution, and Plastics

Global Pollution and Human Health Impacts

• Scale of the Problem: According to Stephen Leahy ($2014$), pollution is the leading killer in the developing world, responsible for the deaths of over $8.4$ million people annually. This figure is nearly three times the number of deaths caused by malaria and fourteen times the mortality rate of HIV/AIDS.

• The Global Gap: Richard Fuller, president of the Pure Earth/Blacksmith Institute, notes that despite its severity, pollution receives only a fraction of the attention and funding provided by the global community to combat diseases.

• Definition of Pollution: The introduction of waste matter or surplus energy into the environment that, directly or indirectly, results in damage.

• Definition of a Pollutant: A substance or effect that adversely alters the environment. Specifically, it may:

  • Change the growth rate of specific species.

  • Interfere with the food chain.

  • Exhibit toxicity.

  • Interfere with human health, comfort, amenities, or property values.

• Types of Pollution:

  • Water Pollution.

  • Air Pollution.

  • Land Pollution.

  • Noise Pollution.

  • Thermal Pollution.

  • Electro Pollution.

  • Visual Pollution.

• Biological Impacts:

  • Environmental Damage: Negative impacts on plants/algae, microorganisms, and animals within air, soil, and water systems.

  • Human Health: Direct damage to human health caused by specific chemical substances found in air, food, and water supplies.

Environmental Challenges in New Zealand

• The "Clean and Green" Image: New Zealand faces significant environmental challenges, particularly from agricultural waste and high-nutrient runoff.

• Trophic States of Lakes: Lakes are classified based on nutrient levels and water clarity. Parameters include Secchi depth, Total Phosphorus ($TP$), Total Nitrogen ($TN$), and Chlorophyll a ($Chl\,a$):

  • Oligotrophic: Secchi depth > 7.0\,m; TP < 10\,mg/m^3; TN < 200\,mg/m^3; Chl\,a < 2\,mg/m^3.

  • Mesotrophic: Secchi depth $3.0-7.0\,m$; $TP \, 10-20\,mg/m^3$; $TN \, 200-300\,mg/m^3$; $Chl\,a \, 2-5\,mg/m^3$.

  • Eutrophic: Secchi depth $1.0-3.0\,m$; $TP \, 20-50\,mg/m^3$; $TN \, 300-500\,mg/m^3$; $Chl\,a \, 5-15\,mg/m^3$.

  • Supertrophic: Secchi depth $0.5-1.0\,m$; $TP \, 50-100\,mg/m^3$; $TN \, 500-1500\,mg/m^3$; $Chl\,a \, 15-30\,mg/m^3$.

  • Hypertrophic: Secchi depth < 0.5\,m; TP > 100\,mg/m^3; TN > 1500\,mg/m^3; Chl\,a > 30\,mg/m^3.

Serious Worldwide Pollution Case Studies

• Scientific American's Top 10 List: Includes locations suffering from toxic pollution related to electronic waste ($e$-waste), chemical weapons, and industrial complexes.

• Norilsk, Russia:

  • Located above the Arctic Circle.

  • Home to the world's largest metal-smelting complex.

  • The pollution is so severe that no living plants exist within a $30\,km$ radius.

• Rio Matanza-Riachuelo, Argentina:

  • Contains approximately $15,000$ small industrial operations.

  • Chromium levels reach $1,145\,ppm$ (for context, $200\,ppm$ is considered toxic in the U.S.A.).

  • Despite the contamination, the river provides drinking water for $20,000$ people.

Phytoremediation: Mechanisms and Applications

• General Definition: The direct use of green plants and their associated microorganisms to stabilize or reduce contamination in soil, sludges, sediments, surface water, or groundwater. It is often described as "using nature to clean itself."

• Specific Types of Phytoremediation:

  1. Phytoextraction: The uptake of substances from the environment with subsequent storage in the plant. This often involves hyperaccumulation of metals.

  2. Rhizofiltration: The use of plant roots to remove toxic materials from groundwater.

  3. Phytostabilization: Reducing the movement or transfer of substances in the environment, such as limiting the leaching of soil contaminants.

  4. Phytostimulation: Enhancement of microbial activity around plant roots to aid in the degradation of contaminants.

  5. Phytodegradation (Phytotransformation): The uptake of substances and their subsequent breakdown or degradation within the plant tissues.

  6. Phytovolatilization: The removal of substances from soil or water and their release into the atmosphere, often following internal degradation.

• Case Study: Sweden (Aronsson & Perttu, 2001): Willow (Salix) vegetation filters are used for treating urban wastewater, landfill leachate, industrial runoff (e.g., log-yard runoff), and sewage sludge, while simultaneously producing biomass.

• Case Study: Chernobyl Disaster: Sunflowers (Helianthus annuus) were cultivated on rafts in ponds to successfully remove radionuclides such as Cesium-137 ($^{137}Cs$) and Strontium-90 ($^{90}Sr$).

• Case Study: Elizabeth City, U.S.A.: An active project at the Coast Guard Aircraft Repair & Supply Center uses poplar and willow trees to remediate soil and groundwater impacted by petroleum hydrocarbons.

Global Plastic Production and Usage

• Classification of Plastics:

  • Petroleum-based: Derived from oil and natural gas.

  • Bio-based: Derived from plants and microbes.

  • Composite: A mixture of petroleum-based and bio-based materials, or two different bio-based materials.

• Production Volume: Plastic production has surged from approximately $200$ million tonnes in $2000$ to over $380$ million tonnes in $2015$. More than half of all plastics ever produced have been manufactured since the year $2000$. Forecasts predict production will reach $600$ million tonnes by $2030$.

• Total Plastic Produced (1950-2017): Roughly $9,200$ million tonnes. Of this, $2,700$ million tonnes are currently in use, and only $600$ million tonnes (12\%\-20\%\ of waste) have ever been recycled.

• Industry Sector Usage (2017 Total: 438 Million Tonnes):

  • Packaging: $158$ million tonnes (mostly single-use).

  • Building and Construction: $71$ million tonnes.

  • Textiles: $62$ million tonnes.

  • Consumer Products: $45$ million tonnes.

  • Transportation: $29$ million tonnes.

  • Electrical/Electronics: $19$ million tonnes.

  • Industrial Machinery: $3$ million tonnes.

• Average Useful Life: Packaging lasts only $0.5$ years on average, whereas building materials last $35$ years.

The Environmental Impact of Plastics

• Soil Contamination: In a study of a field in northern Bavaria, Germany ($3,942\,m^2$), researchers found high densities of microplastics ($2-5\,mm$) and macroplastics (> 5\,mm). Common types included Polyethylene ($PE$), Polyvinyl chloride ($PVC$), and Polyethylene terephthalate ($PET$).

• Marine Life Impact: An average Arctic fulmar stomach contains $34$ pieces of plastic, weighing $31\,grams$. For a human, this would be equivalent to carrying $0.31\,grams$ of plastic in the stomach.

• Recycling Realities: In the United States ($2015$), $34,500$ thousand tons of plastic waste were generated. Only $3,140$ thousand tons were recycled (\approx 9\%\), while over $26,010$ thousand tons went to landfills.

• The China Ban: In early $2018$, China set stricter requirements for plastic waste imports, causing a massive drop in plastic scrap exports from Japan, the USA, and the EU.

Bio-based Polymers and Sustainable Alternatives

• Polymers Classification:

  • Plant Bio-based: Polylactic Acid ($PLA$) - from corn, Cellulosic plastics, Soy-based plastics, Starch plastics.

  • Microbial: Polyhydroxyalkanoates ($PHAs$), Polyhydroxybutyrate ($PHB$), Polyhydroxybutyrate co-valerate ($PHBV$).

  • Mixed: Sorona, Biobased Polyurethane.

• Polylactic Acid ($PLA$): Produced from corn via fermentation of dextrose to lactic acid, then polymerization. It is biodegradable and shares mechanical characteristics with polypropylene ($PP$), polyethylene ($PE$), and polystyrene ($PS$).

• Polyhydroxybutyrate ($PHB$):

  • A linear thermoplastic polyester produced through bacterial fermentation.

  • Discovered by Maurice Lemoigne in $1923$.

  • Current typical cost: $2-5\,\$/kg$.

  • Can be produced directly from plant waste or genetically engineered crops (e.g., Oil palm).

• Benefits of Bio-based Plastics:

  • Stable Prices: Generally more stable than petroleum plastics.

  • Shelf Life: $PLA$ packaging can increase the shelf life of lettuce by $2$ days.

  • Climate Impact: Production generally emits fewer greenhouse gases and uses less fossil energy.

  • Waste Streams: Can be made from beet pulp or industrial wastewater (e.g., Mars using potato waste starch).

Limitations and Challenges of Bioplastics

• Resource Intensity: Producing $1$ tonne of $PLA$ requires $2.39$ tonnes of maize, $0.37\,hectares$ of land, and $2,921\,m^3$ of water.

• Biodegradation Issues:

  • Less than 40\%\ of bio-based plastics are actually biodegradable.

  • They do not degrade in the sea or soil quickly enough to prevent pollution.

  • Many are not compostable at home and require industrial facilities.

• Synthetic Fibers and Climate: The textile industry produced $706\,billion\,kg$ of $CO_2e$ in $2015$. "Fast fashion" creates $50$ cycles per year compared to the traditional $2$ cycles, leading to massive environmental strain.

Global Resistance: Break Free From Plastic (BFFP)

• Movement Scope: A global resistance mapping reveals high concentrations of member organizations:

  • USA: $448$

  • EU: $412$

  • Indonesia: $70$

  • United Kingdom: $110$

  • New Zealand: $30$

• Conclusion: Plants represent the future for sustainable alternatives and environmental remediation to achieve a pollution-free world.