Will Chlorine Vapors Harm Tomato Plants?

Chlorine

• Chlorine is a halogen gas formed by two chlorine atoms. Chlorine changes from a solid state to a liquid state at approximately 147 degrees below zero Fahrenheit, and its boiling point, the point at which it becomes a gas, is 29 degrees below zero Fahrenheit. It must be bottled under pressure to transport it as a liquid. The gas is highly reactive, meaning that it breaks up when released in air or water to form hydrogen dioxide or hydrochloric acid. It also bonds with potassium or manganese to form salts used in fertilizer that provide micronutrients in soil.

Effects

• The most likely source of a chlorine gas release is around a swimming pool that uses pressurized chlorine or near a facility that produces or uses it for manufacturing. The release itself becomes obvious as a greenish cloud rolls out from the source, hugging the ground and dissipating as it travels. Once in the ground, chlorine stays in place. If its concentration is over 10 parts per million of air, the reactive vapors may "burn" fine roots. Lacy leaf edges of tomato plants may suffer oxidation, a process that robs plant tissue of oxygen and moisture. Chloroplasts, the organs that produce chlorophyll and give leaves their color, may also stop production. Damage depends on the concentration, length and frequency of exposure.

Benefits

• Chlorine vapor can also benefit tomato crops when used in a managed form during harvest. Pathogens may attach to the surface of the tomato fruit in the fields. They may also infect equipment in processing facilities where fruit is packaged for distribution. Experiments completed at Virginia State University and Purdue University, among others, established the effectiveness in chlorine dioxide gas in attacking certain pathogens. Chlorine dioxide, when combined with the water wash given tomato fruits at harvest, kills bacteria such as Salmonella enterica. Chlorine dioxide gas alone also kills Salmonella.

Considerations

• When vaporous chlorine occurs in nature, it quickly reacts with other molecules to form more stable molecules or evaporates quickly into the atmosphere where it may return to earth as hydrochloric acid (HCl) in acid rain. Plants do not store chlorine; in fact, they use trace amounts as a nutrient. Tomatoes, therefore, might survive an encounter with a vapor release if they are far enough away from its source. Vapors might damage sensitive plant tissue such as blooms or new growth, however, if exposure is concentrated or frequent.