Simazine and Simazine Degradates
|CAS Number: 122-34-9|
|Synonyms: Aquazine, Framed, Gesatop, Premazine, Primatol, Princep, Simadex|
|Contaminant Type: Chemical|
Simazine is an s-triazine herbicide and is used extensively as a pre-emergent on a variety of crops, and on broad-leaf and grassy weeds. It is used to control weeds in turf grasses, and to control algae in ponds and fish hatcheries. It is principally used for corn, but also for vegeatbles, fruits and berries. For corn, it is often used in combination with atrazine, the most commonly used s-triazine herbicide. Simazine acts by inhibiting photosynthesis.
Simazine is 6-chloro-2,4-diethyl-1,3,5-triazine-2,4-diamine.
Simazine and its degradates reach source waters largely through runoff, typically one to three months following agricultural application. 
The transformation of simazine to its degradates is complex, invloving not only simazine but possibly other triazine herbicides. They are:
An ethyl group may be cleaved resulting in deethylsimazine (6-chloro-4-ethyl-1,3,5-triazine-2,4-diamine) (CAS Number 1007-28-9). Deethylsimazine is an identical molecule to deisopropylatrazine (DIA) which results from the degradation of atrazine. DIA may be detected with simazine as its degradate or as a degradate of atrazine commonly used in combination with simazine.  Literature for control of deethylsimazine were not found, but were found for DIA. DIA results will be reported in the Treatment tab.
Cleaving both ethyl groups results in diaminochlorotriazine (6-chloro-1,3,5-triazine-2,4-diamine) (CAS Number 3397-62-4). Diaminochlorotriazine can also be named didealkylsimazine, or didealkylatrazine (DDA) or didealkyltriazine. This molecule may result from degradation of any of the four most commonly used triazines: atrazine, simazine, propazine or cyanazine. Literature for control of diaminochlorotriazine were not found, but were found for DDA. DDA results will be reported in the Treatment tab.
Biotic action is the most common means of simazine degradation.  By microbial action, hydroxysimazine may result (6-hydroxy-2,4-diethyl-1,3,5-triazine-2,4-diamine) (CAS Number 2599-11-3). This degradate may only result from simazine. One of the ethyl groups may be cleaved and deethylhydroxysimazine may result (6-hydroxy-4-ethyl-1,3,5-triazine-2,4-diamine).  This degradate may also result from other triazines with a single ethyl group, i.e., atrazine and cyanazine. Literature for control of these latter two degradates were not found.
Simazine is commonly detected in ground and surface source waters in numerous states.  In a literture review reporting on California monitoring in 2001, it was detected in 166 of 460 surface waters with a median of 0.024 ug/L and a maximum of 3.7 ug/L, and in 87 of 1173 wells with a median of 0.104 ug/L and a maximum of 0.244 ug/L. In another study, of 131 wells monitored in California, simazine was detected in 85, diaminochlorotriazine in 105 and deethylsimazine (as DIA) in 110. Hydroxysimazine and deethylhydroxysimazine were not monitored.  Concentrations of simazine reaching 1 to 2 ug/L have been reported in ground water in the USA. 
The US EPA states that simazine's acute effects are changes in blood and weight loss, and that its chronic effects involve damage to testicles, liver, thyroid and kidneys.  It is implicated in gene mutation. [2011, 2013] There is some evidence of carcinogenic effects of simazine , but its carcinogenic effects are unclassifiable. [2012, 2013] There are no reported reproductive or teratogenic effects.  It is suspected to have endocrine disruptive mechanisms, as are its deethylsimazine degradate. [1428, 2013] Simazine and its degradates deethylsimazine, hydroxysimazine and deethylhydroxysimazine are reported not to be cholinesterase inhibitors. 
Simazine is regulated in drinking water in the US at 4 ug/L because of its blood-associated problems. Simazine degradates were on Contaminant Candidate Lists 1 and 2 under the umbrella of triazine degradates. Simazine's and other triazine degradates did not appear on Contaminant Candidate List 3.
The best available technology for control of simazine is granular activated carbon. There is signifcant literature on the control of simazine in drinking water, but only scant literature on control of its degradates.
Photodegradative effects of simazine are small [2011-2013], but possibly result in the formation of deethylsimazine (deisopropylatrazine) and diaminochlorotriazine.  Simazine hydrolyzes only at low pH [2010, 2011], so would not be expected to be controlled during precipitative softening. It is has a low Henry's coefficient [2010, 2011] so would not be expected to be controlled by air stripping. It is poorly bound to soils, clays and organic matter [2010-2012], so moves readily to ground waters , and would not be expected to be well controlled by conventional treatment. In surface waters it may persist for months following agricultural application. 
Date of Literature Search: June 2009
Miltner, R., Baker, D., Speth, T. and Fronk, C.;
Treatment of seasonal pesticides in surface waters;
1428 Jiang, H and Adams, C; 2006; Treatability of chloro-s-triazines by conventional drinking water treatment technologies; Water Research 40; pg. (1657-1667); Input May 2009
2010 Gunasekara; 2004; Environmental Fate of Simazine; California Environmental Protection Agency; Department of Pesticide Regulation, 1001 I St, Sacramento, CA 95812
2011 USEPA Office of Ground Water ands Drinking Water; 2011; Technical Fact Sheet on Simazine; http://www.epa.gov/safewater/pdfs/factsheets/soc/tech/simazine.pdf;
2012 Oregon State University; 1996; Simazine; http://extoxnet.orst.edu/pips/simazine.htm; Pesticide Information Project
2013 PAN Pesticides Database; 2009; Simazine; http://www.pesticideinfo.org/Detail_Chemical.jsp?Rec_ID=PC34340;