Human Impacts on Ecosystems and Environmental Pollution

Pollution occurs when human activities produce waste at a rate faster than ecosystems can break it down.
Human impacts are primarily driven by excessive consumption, industrial activities, and improper waste disposal.
Non-biodegradable pollutants are substances that are not easily eliminated or broken down by organisms.

Polychlorinated biphenyl (PCB): Organic molecules used in plastics since the 1920s; restricted in the 1980s. They seep from landfills into water, causing cancer and fertility issues in humans.
Dichlorodiphenyltrichloroethane (DDT): A synthetic insecticide used against malaria-carrying mosquitoes. Its impact on food webs was documented in Rachel Carson’s 1962 book Silent Spring.
Mercury: Enters aquatic environments through atmospheric deposition from burning fossil fuels. It targets the central nervous system and accumulates in top-level fish predators.

Bioaccumulation: The process where non-biodegradable pollutants build up in a single organism's body over time.
Biomagnification: The increase in toxin concentration as pollutants move up trophic levels. Apex predators exhibit the highest concentrations due to the loss of biomass along the food chain.
Ecosystems with high biomass and complex food webs have a greater potential for these processes to occur.

From 1932–1968, a chemical factory released industrial waste containing methylmercury into Minamata Bay.
The mercury bioaccumulated in fish and biomagnified in local cats and humans who consumed the fish.
Symptoms included numbness, hearing difficulties, and permanent brain damage.

Plastics are polymers (chains of linked components) that can be synthetic or natural.
Microplastics: Particles under $5\,mm$ in length. They are distributed globally via the hydrological and atmospheric systems.
Additives: Plastics contain endocrine-disrupting chemicals like bisphenol A (BPA) and phthalates, which interfere with hormonal systems and reproduction.
Organisms at all trophic levels ingest plastic; aquatic species often starve as their stomachs fill with non-nutritive materials.

Burning Fossil Fuels: Increases atmospheric $CO_2$ , leading to global warming and ocean acidification. Pollutants like nitrogen oxides contribute to acid rain.
Deforestation: Reduces ecosystem biomass, releases stored carbon, and disrupts the hydrological and nutrient cycles.
Agriculture: Clears native ecosystems and removes biomass for human consumption, preventing nutrients from returning to the soil.
Urbanisation: Destroys habitats and disrupts the base of food webs where light-to-chemical energy transformation occurs.

1. Define 'pollution'. [2]

Pollution is the production of waste by human activities at a rate faster than ecosystems can break it down (subtopic 7.3).

2. Explain how both biomagnification and bioaccumulation were involved with the mercury poisoning of cats and humans in Minamata Bay. [4]

Mercury entered the water and was absorbed by fish, where it bioaccumulated (built up in individual bodies over time). As cats and humans consumed large quantities of these contaminated fish, the toxin was biomagnified, reaching high, poisonous concentrations at these higher trophic levels.