In the USA, an estimated 2000 to 2500 tons of simazine are applied to agricultural crops (mainly on corn, fruits and nuts) each year, and an additional 500 tons are applied for nonagricultural uses. It mainly enters the marine environment through run off from application sites. 
Simazine is moderately soluble (3,5 mg/L) and has a low tendency to be absorbed to organic matter or into the soil, although it can adsorb to clay particles. Therefore simazine is highly mobile and can leach into ground water systems. It has low volatility and losses of simazine by evaporation into the atmosphere are therefore expected to be rather low. According to laboratory studies simazine is persistent and able to persist into the environment for months, as it takes 90 days to half its concentration.
Simazine is moderately toxic to aquatic animals. Some fish species only start dying when exposed to concentrations above 100 mg/l, although others can't tolerate concentrations above 3 mg/l. Oysters die at concentration above 3,7 mg/l. Algae however are highly affected by low concentrations of the herbicide. Concentrations of only 6 µg/l are already toxic for some algae species. 
Environmental standards and legislation