Pollution — UPSC Mains Model Answer

Phytoremediation employs plants to extract, stabilise, or degrade soil contaminants through mechanisms such as phytoextraction, phytostabilisation, and rhizofiltration. It is particularly effective for heavy metal contamination because metals cannot be chemically degraded and must be physically removed via plant uptake. Hyperaccumulator species like Thlaspi caerulescens concentrate zinc and cadmium at levels far exceeding tolerance thresholds of ordinary vegetation, making them valuable tools for metal-contaminated sites.

Microbial bioremediation is highly effective for organic pollutants — petroleum hydrocarbons, pesticides, and chlorinated solvents — because microorganisms can metabolise carbon-based compounds. However, heavy metals are not biodegradable; microbes can only alter their speciation or mobility through processes like biosorption or reduction, not eliminate them. Treating bioremediation as equally effective for both pollutant classes is therefore a significant technical misconception with policy consequences for site management decisions.

Soil washing involves excavating contaminated soil and treating it with water, surfactants, or chelating agents to physically and chemically separate contaminants from soil particles. As an ex-situ method, it offers controlled processing conditions and faster turnaround but entails higher costs and risks of secondary contamination from wash effluents requiring further treatment.

India's Hazardous Waste Management Rules and the National Green Tribunal have increasingly mandated site-specific remediation plans for industrial brownfields. Selecting the wrong technique — applying bioremediation to heavy-metal-dominant sites, for instance — wastes public resources and leaves residual risk. Standardised site characterisation protocols are essential before remediation technology selection.