Toxic Chemical Spills

Toxic chemical spills are accidental releases of potentially dangerous chemicals from some form of containment. Any spill involving toxic chemicals can have drastic effects on the environment, wildlife and people. How serious a spill is depends on the amount of the spill and the type of chemical.

Toxic Chemicals

• A toxic chemical is one that causes some kind of harm to living things. It may be poisonous, corrosive or carcinogenic or cause some other type of damage such as birth defects. One way of measuring toxicity is the LD50 of a chemical. This is the dose that is deadly to half of test animals during testing, so the more toxic the chemical, the lower its LD50. The LD50 of the poison potassium cyanide, for example, is only 6 mg per kilogram of body weight. Well-known toxic chemicals include mercury, lead and ammonia.

Types and Causes of Spills

• Although we think of a spill as involving a liquid, a chemical spill can also be a toxic gas or solid. A spill occurs when a chemical is unintentionally released into the environment. This can happen in many different ways; a container can break open due to a collision or fall, rust through from corrosion or burst due to pressure from a runaway reaction. Common causes of spills include improper storage, untrained employees and lack of planning or standard procedures.

Effects of Spills

• Some toxic chemical spills can be immediately dangerous to wildlife and humans, causing burns, poisoning or physical harm on contact. An oil spill would fall into this category. Other spills can be just as dangerous but work more slowly, causing long-term illnesses like cancer. How dangerous a spill is depends on the amount of chemical spilled and how toxic it is, but a spill is also more dangerous if the chemical is widely dispersed. Chemicals which are water soluble, for instance, will quickly dissolve in streams and lakes and spread widely. Chemicals with high persistence also make a spill worse, since they remain in the environment for a long time without breaking down or biodegrading.

Famous Chemical Spills

• One of the worst chemical spills in history happened when the Exxon Valdez oil tanker ran aground off the coast of Alaska in 1989. The broken tanker spilled around 30 million gallons of oil into the water, killing large numbers of animals, including over 100,000 seabirds. In 1984, a large cloud of chemical vapors escaped from the Union Carbide plant in Bhopal, India, killing thousands in the world's worst industrial disaster.