Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance or energy. Pollutants, the components of pollution, can be either foreign substances/energies or naturally occurring contaminants.
Litter on the coast of Guyana
Smog in the center of Moscow, Russia in August 2010
An industrial area, with a power plant, south of Yangzhou's downtown, China
A litter trap catches floating waste in the Yarra River, east-central Victoria, Australia.
Agricultural pollution refers to biotic and abiotic byproducts of farming practices that result in contamination or degradation of the environment and surrounding ecosystems, and/or cause injury to humans and their economic interests. The pollution may come from a variety of sources, ranging from point source water pollution to more diffuse, landscape-level causes, also known as non-point source pollution and air pollution. Once in the environment these pollutants can have both direct effects in surrounding ecosystems, i.e. killing local wildlife or contaminating drinking water, and downstream effects such as dead zones caused by agricultural runoff is concentrated in large water bodies.
Aerial application of pesticide
Soil erosion: soil has washed from a ploughed field through this gate and into a watercourse beyond.
Centaurea solstitialis, an aggressively invasive weed, was probably introduced to North America in contaminated fodder seed. Agricultural practices such as tilling and livestock grazing aided in its rapid spread. It is toxic to horses, prevents native plants from growing (decreasing biodiversity and degrading natural ecosystems), and is a physical barrier to the migration of indigenous animals.