Q.Name two ways in which industrial activity can contaminate soil, and explain why heavy-metal contamination of soil (for example by lead or cadmium) is particularly difficult to reverse.

Industrial activity contaminates soil in two principal ways: through solid waste and slag dumped or landfilled directly onto land, and through airborne particulate fallout or liquid effluent that settles into or is absorbed by soil over time. A particularly persistent form of this contamination is heavy-metal pollution -- soil contaminated with metals such as lead, cadmium, mercury or arsenic from smelting, battery manufacture, mining tailings or industrial effluent. Heavy metals are elements, not compounds that can be broken down into something harmless the way an organic pollutant sometimes can be degraded by micro-organisms; no natural chemical or biological process can convert a heavy-metal atom into a different, harmless element. This makes heavy-metal contamination of soil extremely difficult and expensive to remediate -- the metal has to be physically …

Distinguish direct solid-waste contamination from effluent/fallout contamination, then explain heavy-metal persistence in terms of it being an eleme …

Describing heavy metals as simply 'toxic' without explaining why they specifically resist remediation -- the key reason is that they are elements, immun …