Simazine leaching

Groundwater. According to the U.S. EPA (1986) simazine has a high potential to leach to groundwater. 

The most ubiquitous pesticide was simazine, present in 80% of the samples, followed by atrazine, diuron, DEA and diazinon, present in more than 50% of the samples (64%, 56%, 56% and 50%, respectively). Cyanazine, molinate, fenitro-thion and mecoprop were detected in less than 5% of the samples. The maximum individual concentrations were observed for alachlor (9,950 ng/L in M33, 2008), dimethoate (2,277 ng/L in M35, 2010), DEA (1,370 ng/L in M48, 2007) and linuron (1,010 ng/L in M33, 2008), while many others, such as terbuthylazine, DIA, atrazine and metolachlor, presented levels also higher than 500 ng/L. Results are consistent when evaluated with the GUS index (see Table 2). Mots triazines and metolachlor, i.e., the compounds with GUS index > 3 and therefore with higher leaching potential, were among the most ubiquitous an abundant compounds. In contrast, fenitrothion, which according to its GUS index (0.64) is a nonlixiviable pesticide, was detected at low levels in less than 5% of the samples. 

Simazine also became widely used in industrial weed control. It was effective, stable, and did not leach as readily as alternatives. Highway departments sprayed simazine under guardrails to eliminate the need for mowing. Railroads and utilities used simazine in mixes with other herbicides to get longer-lasting control of shallow germinating weeds. 

Simazine is widely used for preemergence control in field-grown nursery stock in North America. Selective use in container nurseries also has been demonstrated (Ahrens, 1972 Fretz, 1974 Wadsworth, 1975 Bing, 1983). It is less widely used in container-grown nursery production because of potential leaching (Elmore et al., 1976), but is especially effective when applied in the fall or winter to control winter annual weeds in containers. Simazine currently is registered in the United States for 50 species of woody ornamental nursery stock and Christmas trees. Tables 18.1 and 18.2 list selected species of conifers and deciduous ornamental plants, respectively, and their observed tolerance to simazine at rates of 2.2-3.3kg/ha. Information for these tables was obtained from personal observations and the literature, including those references by Ries et al. (1959) Ahrens (1961) Ticknor (1972) and Schubert et al. (1986). 

The triazine herbicides simazine, atrazine, and hexazinone are commonly used in Christmas tree plantings in North America. Hexazinone is widely used in certain pines and on other conifer species in natural stands in regions where the organic matter content in soil is adequate to prevent excessive leaching to conifer root zones. Simazine and... 

Reddy, K.N., M. Singh, and A.K. Alva (1992). Sorption and leaching of bromacil and simazine in Florida flatwoods soils. Bull. Environ. Contam. Toxicol., 48 662-670. 

Burnside, O.C., C.R. Fenster, and G.A. Wicks (1963). Dissipation and leaching of monuron, simazine, and atrazine in Nebraska soils. Weeds, 11 209-213. 

Cornejo, L., R. Celis, C. Dominguex, and J. Cornejo (2007). Clay-based formulations of simazine to reduce herbicide leaching in sport turfgrasses. Proceedings of the International Conference on Water Pollution in Natural Porous Media at Different Scales, Barcelona, Spain, April 11-13, pp. 1-5. 

Stearman, G.K. and M.J.M. Wells (1997). Leaching and runoff of simazine, 2,4-D, and bromide from nursery plots. J. Soil Water Cons., 52 137-144. 

Figure 5. Relative leaching of simazine and terbacil, showing effects of added water, soil texture, and (possibly) pH. Adapted from reference 52.

Simazine and propazine are the two triazine herbicides with the longest duration of action In a dose of 10-15 kg/ha the residual life is 2-3 years. Under dry climatic conditions their weed-control activity is unsatisfactory because with their poor water-solubility they are not leached by the low soil moisture to the roots of the weeds. 

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