Sulfates are compounds containing sulfur that cycle throughout the environment as part of natural biogeochemical cycles, which means they can enter aquatic ecosystems naturally. Methods of entry into freshwater ecosystems include saltwater intrusion, sea spray, and sea level rise. However, the majority of sulfates originate from surface runoff and air pollution, which is deposited into rivers through acid raid. Sulfates are often used in fertilizer, so pollution near these areas is the worst.
Sulfur compounds can have many detrimental effects on freshwater ecosystems. For instance, they promote the conversion of mercury into its most toxic form, methylmercury, and stimulate sediments to release nutrients, causing eutrophication. Some of the compounds themselves are also toxic to organisms within freshwater environments.