Categorizing Pollution . . . by Jan Weaver
Pollution is typically categorized based on the medium where it is found - air, water or land. While useful because it identifies a route of exposure, this classification has the unfortunate consequence that the focus becomes reducing pollution in whichever medium is attracting federal or state regulatory attention. Sometimes the easiest and cheapest way to do this is to shift the pollution into a different medium. For example, an incinerator might be used to reduce the volume of solid hazardous waste, but could end up polluting the air. Regulatory agencies are hip to this tactic, but most people still think in terms of air, water and land-based pollution. Below is one rule to remember about pollution and three alternative categories for classifying it that might be useful when communities we care about are threatened by pollution.
Rule to Remember: Stuff never disappears. This is a law of nature known as "Conservation of Matter". It is a law because despite rigourous testing over several centuries, no one has been able to make something from nothing and no one has been able to make nothing out of something. However, it is possible to convert one kind of stuff to another, and even convert tiny amounts of stuff to energy. What it means for pollutants is that we should never be satisfied just because the pollutant we were concerned about disappeared from the air, or the water, or is no longer solid. It may have simply changed phase (solid to liquid, liquid to gas) or it may have been converted into another substance which could be less or more toxic than the original pollutant.
Category 1: Chemical pollutants: This includes molecular and elemental pollutants. Molecular pollutants are made up of atoms of different elements, so they can be broken down by the action of air, water, light, heat, pressure, chemical processes, and/or biological agents. Some are easily degraded by air, water or light, others require intense heat and pressure, or the specialized enzymes of biological agents. Sometimes breakdown of the original pollutant can produce more toxic agents. Elemental pollutants cannot be broken down, they are already atoms of one element. Once contaminated with an elemental pollutant (like lead or arsenic, anything on the Periodic Table), an area can only be cleaned up by removing the element and putting it somewhere else.
Category 2: Radioactive pollutants: (a special case of elemental pollutants). They are particular forms of particular elements that spontaneously give off particles and/or rays that have enough energy to damage living cells. A radioactive element gives off rays and particles until it decays into a stable daughter element, like Uranium 238 decaying into Lead 206. The rate of decay is measured in half-lives, the time it takes half of a measured mass of radioactive parent element to decay into daughter element. Each parent-daughter pair has a specific half life, which cannot be speeded up by any of the processes used to break down molecular pollutants. In practice this means that eventually all radioactive waste decays to safe daughter elements on its own - we don't need to do anything but store it until it decays. However, while some half-lives are minutes, others are thousands, millions, or even billions of years. It is unlikely we will be around long enough to supervise storage for that long, so eventually radioactive elements could escape to the environment.
Category 3: Biological pollutants: (work with me). These are living species whose activities have the potential to drive newly exposed species to extinction. Diseases and parasites transported to new environments can attack host species that have not evolved any defenses against them. For example, Chestnut Blight effectively eliminated the American Chestnut over its natural range. Other biological pollutants are invasive aliens that outcompete native species. Purple loosestrife crowds out native plants and the animal species dependent on them in wetlands. Biological pollutants are especially pernicious, because once established, they have the ability to multiply, something we don't need to worry about with chemical and radioactive pollutants. Rapid globalization and expansion of trade and transportation have significantly aggravated this problem.
To learn more:
Other Laws of Nature it would be useful to know - http://www.csicop.org/si/2000-09/laws.html
Chemical Clean-Ups - http://clu-in.org/products/nairt/
Radioactive Waste - http://www.iclei.org/efacts/radioact.htm
Invasive Aliens - http://www.usgs.gov/invasive_species/plw/
BioRegional Quiz: In terms of watershed pollution, what is nonpoint source water pollution?
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Answer to BioRegional Quiz: Nonpoint source water pollution cannot be traced back to a specific point of discharge. For example, nonpoint source pollution includes pollutants in water that runs off crop land, water that comes from failing septic systems, from parking lot or construction site runoff, irrigation systems and storm drain systems.
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