Summary
Highlights
Human activities often have negative environmental consequences due to chemicals, trash, and air pollution, impacting organisms and ecosystems. Organisms have a 'range of tolerance,' illustrating optimal and sub-optimal conditions. Exceeding this range leads to physiological stress, reduced reproduction, or death, as seen with polar bears and pH changes affecting amphibians.
Climate change causes coral bleaching due to increasing ocean temperatures. Oil spills, like Deepwater Horizon, spread rapidly, harming birds, sinking to cover the seafloor, and making fishing unsafe. Plastics photodegrade into smaller pieces, are ingested by marine animals, and release toxins. Endocrine disruptors interfere with hormones, leading to birth defects, developmental, reproductive, or immune system issues.
Point source pollution comes from an identifiable source, like a smokestack or outflow pipe. Non-point sources are diffuse, often from runoff, such as fertilizers from farm fields entering waterways, leading to nutrient excess (nitrogen and phosphorus).
Nutrient runoff causes algae blooms, blocking sunlight, killing plants, and leading to the decomposition of algae. This decomposition consumes dissolved oxygen, creating hypoxic (oxygen-lacking) conditions that result in fish and plant die-offs. Extreme eutrophication can form dead zones, like in the Gulf of Mexico, where water stratification prevents oxygen mixing.
Biological Oxygen Demand (BOD) measures oxygen used by organisms. Low BOD indicates clean water, while high BOD signifies pollution and rapid oxygen consumption. An oxygen sag curve illustrates how dissolved oxygen levels drop near a pollution source (high BOD) and then recover downstream as the BOD decreases.
Mercury released from burning coal settles in waterways and converts to methylmercury, which bioaccumulates (builds up in an organism's tissues over time). Biomagnification occurs when these toxins increase in concentration up the food chain, leading to very high levels in top predators.
Thermal pollution is caused by the discharge of hot water, typically from power plants, into cooler natural water bodies. This can cause fish to avoid the area and, more significantly, reduces the water's capacity to hold dissolved oxygen, leading to physiological stress and oxygen depletion for aquatic life.
Solid waste is often managed in sanitary landfills, which are engineered pits with liners, leachate collection systems, and methane collection (which can be burned for electricity). Landfills are capped and can be reverted to green space. Incineration reduces trash volume but causes air pollution. Recycling is energy-intensive and expensive, but reuses some materials.
Sewage undergoes three levels of treatment before release. Primary treatment physically removes large objects. Secondary treatment uses bacteria to break down organic waste. Tertiary treatment removes nutrients. Finally, disinfection (using chlorine, ozone, or UV light) sterilizes the water before it's returned to the environment.
Climate change expands the range of vector-borne diseases (e.g., West Nile, Zika, malaria) to new areas. Pathogens also spread with poverty, lack of sanitation, and dirty drinking water, particularly in developing countries. The LD50 (Lethal Dose 50) is the dose of a chemical required to kill 50% of a test population, used to determine safe dosing levels.
The Clean Water Act prohibits discharging pollutants from point sources into navigable waters. The Safe Drinking Water Act protects underground drinking water sources. RCRA (Resource Conservation and Recovery Act) ensures cradle-to-grave management of hazardous waste. CERCLA (Superfund) holds companies responsible for cleaning up hazardous waste. The Delaney Clause bans food additives known to cause cancer.