Ethylene is a colorless, flammable gas that occurs naturally and is a significant organic compound. It plays a role in various biological processes, particularly in plants, where it influences growth and development. Ethylene is also present in the environment from diverse sources, making an understanding of its origins and factors affecting its presence valuable for many applications.
Natural Sources of Ethylene
Ethylene is a naturally occurring plant hormone, synthesized from methionine. It is involved in various stages of a plant’s life, including seed germination, flower opening, and leaf shedding (abscission). A well-known role is its influence on fruit ripening, where it acts as a signaling molecule to trigger biochemical changes like softening, color transformation, and flavor development.
Different parts of higher plants, such as leaves, stems, roots, flowers, fruits, tubers, and seeds, can produce ethylene. Beyond living plants, decaying organic matter and stressed plant tissues also contribute to natural ethylene levels. Microbial activity in soil and marine environments further adds to these biogenic sources.
Human-Caused Sources of Ethylene
Human activities significantly contribute to the presence of ethylene in the atmosphere. Industrial processes are a major source, with over 95% of the worldwide commercial production of ethylene stemming from the steam cracking of petroleum hydrocarbons. This process uses feedstocks like ethane, propane, butanes, naphthas, and gas oils to produce ethylene, which is then used in manufacturing plastics, solvents, and textiles.
Combustion is another substantial human-caused source of ethylene. This includes vehicle exhaust, which is a primary contributor to urban ethylene levels. Burning fossil fuels, forest fires, savanna fires, and the combustion of crop residues also release considerable amounts of ethylene into the air. Even common activities like smoking tobacco can introduce ethylene into the environment.
Environmental Conditions Affecting Ethylene Levels
Environmental factors play a role in how ethylene concentrations build up or disperse. Ventilation is a primary factor; ethylene can accumulate in enclosed spaces like greenhouses, storage facilities, or homes. Poor air exchange allows ethylene levels to rise significantly, increasing exposure. Conversely, proper airflow and ventilation dilute ethylene concentrations, reducing its impact.
Temperature also influences ethylene levels. Higher temperatures can accelerate both plant ethylene production and the gas’s diffusion. For instance, ethylene’s impact on produce intensifies at higher temperatures, making temperature control a method to slow its effects. Humidity, while less direct, can affect plant processes that lead to ethylene production.
Understanding What Ethylene Exposure Is Not
Ethylene exposure is not influenced by factors that do not produce the gas, are not byproducts of ethylene-releasing processes, or do not affect its concentration or distribution. For example, the presence of inert gases like nitrogen or argon, which do not react to form ethylene and do not alter its atmospheric concentration, would not be a factor in ethylene exposure. Similarly, materials that are completely non-reactive and do not undergo combustion or decomposition to release ethylene would not contribute.
Understanding these distinctions helps in practical applications, such as food storage and maintaining air quality. For instance, storing non-ethylene-producing produce like leafy greens in sealed containers away from high ethylene emitters like apples helps prevent premature spoilage.