Environmental Pollution and Degradation
This section covers Environmental Pollution and Degradation. The exam tests pollutant types, sources, health and ecosystem effects, and control measures, including indicators such as BOD, COD and PM2.5.
Core rules
- Pollution is the addition of a substance or energy at a rate that harms health or ecosystems. Sources may be point sources, such as a factory pipe, or non-point sources, such as farm runoff.
- Major air pollutants include PM10 and PM2.5, sulphur dioxide, nitrogen oxides, carbon monoxide and ground-level ozone. Thermal inversion traps pollutants near the ground.
- BOD measures the oxygen consumed by microbes decomposing biodegradable organic matter. High BOD means low dissolved oxygen. COD measures chemically oxidisable matter, including some non-biodegradable material.
- Eutrophication occurs when nitrogen and phosphorus enrich water, causing algal blooms; decomposition then crashes oxygen levels.
- Bioaccumulation is build-up in one organism; biomagnification is increasing concentration up a food chain.
- Noise is measured in decibels on a logarithmic scale; a 10 dB rise is about ten times the intensity. Control includes source reduction, barriers and hearing protection.
- Greenhouse gases enhance warming; CFCs deplete stratospheric ozone; sulphur dioxide and nitrogen oxides cause acid rain.
Worked example
A stream has 7 mg/L dissolved oxygen upstream. Untreated sewage with high BOD enters. Bacteria multiply and consume oxygen while decomposing the sewage, so dissolved oxygen downstream falls to 3 mg/L. Many fish need about 4-5 mg/L, so they die or leave. The reasoning is that BOD is an oxygen demand, not a direct poison; the oxygen sag is the mechanism of harm.
Traps
- BOD does not measure the volume of sewage; it measures biodegradable organic load through oxygen use.
- Do not confuse the greenhouse effect with ozone depletion; they involve different gases and mechanisms.
- Dilution is not treatment; the pollutant remains in the water body.
- PM2.5 is more dangerous than larger dust because it reaches deep lung tissue.
Odisha examples include hexavalent chromium contamination in the Sukinda chromite belt, emissions around Rourkela steel plant, and oil-spill risk at Paradip port.