Many human and natural processes increase the levels of sulfates in waters. Sulfates are used, produced or of concern in many processes e.g. mining, oil & gas, and the manufacturing of fertilizers, dyes, paper, soaps, cosmetics, pesticides, and more. In fossil fuel power plants, sulfates are collected in flue-gas desulfurization (FGD) systems. In mining, metals are often extracted from minerals containing sulfur—and processing means oxidation to sulfates.
Although not generally very dangerous to humans, moderate levels (250–500 mg/L) of sulfates in drinking water are associated with an undesirable taste, and higher levels can cause illnesses such as diarrhea (>1000 mg/L). In recent years, elevated sulfate levels have been closely associated with negative environmental outcomes. Sulfates can kill aquatic plants while feeding algal blooms, causing severe disruptions to eco-systems. Sulfates can be very dangerous to ruminants like moose and cattle because their digestive systems can convert sulfates to toxic hydrogen sulfide. Sulfates can also form precipitants on stream beds, covering spaces that aquatic organisms need for habitat and breeding.
For these reasons, sulfates are increasingly being subjected to regulatory guidelines and public scrutiny. Sulfate discharge limits are imposed on many wastewater flows to ensure that environmental and health impacts of sulfates are minimized. These limits are often dependent on hardness; in British Columbia for example, maximum sulfate limits typically range from 128–429 mg/L. Safety, regulation-compliance, and cost-effectiveness must all be considered in finding appropriate solutions for sulfates in industrial, mining, and other wastewater processes.