Patent Publication Number: US-4485103-A

Title: Controlled release acrylic polymer coated granular pesticidal compositions with attendant reduced dermal toxicity

Description:
This is a division of application Ser. No. 174,951 8/4/80 which is now U.S. Pat. No. 4,343,790 which is a continuation of Ser. No. 9883 2/6/79 now abandoned. 
    
    
     SUMMARY OF THE INVENTION 
     It is known that a number of phosphorus pesticidal compounds, such as 2-(diethoxyphosphinylimino)-1,3-dithiolane, 2-(diethoxyphosphinylimino)-4-methyl-1,3-dithiolane, 2-(diethoxyphosphinylimino)-1,3-dithietane, O,O-diethyl S-(ethylthiomethyl)phosphorodithioate and O,O-diethyl S-{[(1,1-dimethylethyl)thio]methyl}phosphorodithioate, are highly effective for the control of broad spectrum of insects and/or nematodes which attack and destory agriculturally imported food and fodder crops. It is, therefore, of advantage to utilize such compounds in various compositions useful in agriculture. Unfortunately, these otherwise highly effective pesticides are extremely toxic when introduced into the human circulatory system as by ingestion, inhalation, or dermal absorption. 
     Thus, the use of compositions containing the above referred-to compounds for the control of insect pests represents a distinct hazard to individuals engaged in the use and application thereof. Similar hazards are encountered by those who are engaged in storing, transporting and distributing to the ultimate user such compositions. 
     Practical use aspects of the above referred-to pesticide compounds for intended pest control often dictate the use of various granular carrier compositions in which the pesticidal compound is adsorbed or absorbed onto or into the carrier composition. These granular carrier compositions not only provide a more dilute composition of the active pesticide for appropriate applications in agronomic uses but also serve to reduce the potential hazard in use of the pesticide through dermal absorption. Even though such formulated compositions tend to reduce the potential hazard of dermal absorption of the above referred-to pesticides, it is highly desirable to reduce the potential hazard even more. 
     It is, therefore, a principal object of the invention to provide granular formulation compositions containing the aforementioned pesticides having low mammalian dermal toxicity while fully retaining their effectiveness. It is a further object to provide compositions which would offer a margin of safety otherwise not found in conventional compositions containing such pesticides. Other objects and advantages will become apparent from a reading of the ensuing description. 
     To these ends, it has been found that, when solid granular compositions containing the aforementioned pesticides are treated as by spraying, for instance, with certain acrylic latices, or with solutions of certain acrylic polymers in organic solvents, the resultant acrylic polymer coated compositions possess advantageously a two to three fold margin of safety due to their lowered mammalian dermal toxicity as compared to similar, uncoated compositions, while their pesticidal activity and physical integrity remains unchanged. These effects are accomplished in a straightforward manner by applying certain acrylic latex compositions or solutions of certain polymers in an organic solvent to the surfaces of said impregnated pesticidal granules. 
     According to the process of the invention, the compositions of the granular formulation, prior to acrylic polymer coating, are prepared by impregnating a toxicant ranging from about 2% to about 25%, by weight, and, preferably, from 2.5% to 20%, by weight, said toxicant being 2-(diethoxyphosphinylimino)-1,3-dithiolane, 2-(diethoxyphosphinylimino)-4-methyl-1,3-dithiolane 2-(diethoxyphosphinylimino)-1,3-dithietane, O,O-diethyl S-(ethylthiomethyl)phosphorodithioate, O,O-diethyl S-{[(1,1-dimethylethyl)thio]methyl}phosphorodithioate, and equivalents thereof, with a suitable granular carrier. Illustrative of the latter carrier is either (a) a sorptive material, such as attapulgite or montmorillonite (clays), brick chips, pumice, talc, volcanic cinders, corncob grits, or (b) a non-sorptive material, such as sand or limestone chips. If a sorptive material is selected, a deactivator such as ethylene glycol, di-, tri- or tetraethylene glycol and mixtures thereof can be added to neutralize intrinsic acidity in amounts ranging from about 3% to about 6%, by weight, of said compositions. In this event, the amount of granular carrier is decreased by an amount equal to that of the deactivator added to said composition. Advantageously, the above described granular composition may be blended and/or coated with from about 0.5%, by weight, to about 2%, by weight, of composition of a finely divided sorptive substrate, such as calcined powdered clays, diatomaceous earth, calcium silicate, fumed silica, and fumed silica which has been made hydrophobic by the replacement of most of the hydrophilic hydroxyl group, which normally populate the silica surface, with trimethylsiloxyl groups as well as mixtures of said substrate. It has been found that the addition of said sorptive substrate to the granular formulations aids in maintaining the free-flowformation of agglomerates in same particularly subsequent to treatment with a sprayed acrylic polymer, defined hereinbelow with particularity. 
     It is a good practice to coat impregnated granular formulations, hereinabove set forth by any suitable means, such as by spraying with an acrylic latex. The coating is accomplished by spraying either an aqueous emulsion of an acrylic polymer or a solution of an appropriate acrylic polymer in amounts sufficient to provide an acrylic polymer coating of from about 0.5% to about 5%, by weight, and, preferably, from about 1.5% to about 4%, by weight, of the overall granular formulation. Examplary of the above mentioned acrylic latices are (a) thermoplastic acrylic emulsion polymers with a solids content of from about 38% to about 43%, by weight, and having an intrinsic viscosity range of from 0.75 to 3.1 dl/g at 30° C. in THF (tetrahydrofuran), (b) crosslinking acrylic emulsion polymers with a solids content of about 45-46%, by weight, and having an intrinsic viscosity range of from 1.0 to 2.0 and, preferably, about 1.4 dl/g at 30° C. in DMF (dimethylformamide), and (c) solutions of acrylic polymers in tetrahydrofurfuryl alcohol, wherein said acrylic polymers have an intrinsic viscosity range of from about 0.05 to 0.1 dl/g and, preferably, about 0.085 dl/g at 30° C. in butanol. 
     It is an advantage of the process of the invention to prepare the coated granular compositions in a straightforward manner involving a plurality of steps. From about 2% to about 30%, by weight, and preferably from about, 2.5% to about 20%, by weight, of formulation of a toxicant selected from the above identified group, for instance, O,O-diethyl S-{[(1,1-dimethylethyl)thio]methyl}phosphorodithioate, is mixed with from about 3% to about 6%, by weight, of formulation of a deactivator selected from the group consisting of ethylene glycol, di-, tri- or tetraethylene glycol and mixtures thereof. The weight percent of the overall mixture is based on the weight of the carrier. This mixture is then sprayed on a granular carrier selected from the group consisting of clays, such as attapulgite and montmorillonite clays, brick chips, pumice, talc, volcanic cinders, corncob grits, sand and limestone chips, wherein said carrier is used in amounts from about 62%, by weight, to about 94% and, preferably, from about 68% to about 92%, by weight, of formulation. After the spraying has been completed, agitation of the mixture is continued until all of the liquid is absorbed. Thereafter, if so desired, from about 0.5% to about 2%, by weight, of a finely divided sorptive substrate is added and agitation of the mixture continued until a uniform blend is obtained. The latter sorptive substrate is illustrative calcined powdered clays, diatomaceous earth, calcium silicate, fumed silica and fumed silica which has been made hydrophobic as by the replacement of most of the hydrophilic hydroxyl groups which normally populate the silica surface with trimethylsiloxyl groups. The formulations so-prepared are then agitated by suitable means and sprayed with either one of a group of certain acrylic latices (an aqueous emulsion of an acrylic polymer) or a solution of said acrylic polymer in a solvent, such as tetrahydrofurfuryl alcohol, in amounts sufficient to provide an acrylic polymer coating of from about 0.5% to about 5%, by weight, and, preferably, from about 1.5% to about 4%, by weight, of said granular formulations. The latter latices are selected from hard thermoplastic acrylic emulsion polymers with a solids content ranging from about 38% to about 43%, by weight, and having an intrinsic viscosity range of from 0.75 to 3.1 dl/g at 30° C. in THF (tetrahydrofuran), from hard self-crosslinking acrylic emulsion polymers with a solids content of about 45-46%, by weight, and having an intrinsic viscosity range of from 1.0 to 2.0 and, preferably, about 1.4 dl/g at 30° C. in dimethylformamide (DMF), and from solutions of acrylic polymers in tetrahydrofurfuryl alcohol, wherein said acrylic polymers have an intrinsic viscosity range of from 0.05 to 0.1 dl/g and, preferably, 0.085 dl/g at 30° C. in butanol. If desired, the above formulations may be heated to accelerate and increase the hardening of said coatings. 
     It is found that, by utilizing the method of the present invention employing the above identified compounds in the combinations and percent weight ranges given above, a number of compositions can be prepared within which it is possible to select one wherein the toxicant is released rapidly into the surrounding environment over a relatively short period of time; or to alternatively select a composition which will release said toxicant slowly over a prolonged period of time. Thus, it is possible to adjust within certain practical limits, is so desired, the controlled release of toxicant from the novel compositions of the present invention by the selection of suitable formulations. 
     The coated granular pesticidal compositions also so shown reduced mammalian dermal toxicity. 
    
    
     The present invention is further illustrated by the following examples which are not to be taken as being limitative thereof. Unless otherwise stated, the percentages set forth are by weight. 
     EXAMPLE 1 
     Preparation of a granular formulation containing 15% by weight of O,O-diethyl S-{[(1,1-dimethylethyl)thio]methyl}-phosphorodithioate 
     A. 78.5 gms. of granular (25/50) montmorillonite having the composition set forth below are charged to a rotating type blender and agitated. While being agitated, the granules are sprayed with a mixture of the insecticide: O,O-diethyl S-{[(1,1-dimethylethyl)thio]methyl}phosphorodithioate (17.5 gms. 88.57% real=15.5 g. real) and a deactivator comprising a mixture of ethylene, di-, tri- and tetraethylene glycol, (4.0 gms.) 
     After the spraying has been completed, blending is continued until all the liquid is absorbed. There is obtained 100 gms. of a granular formulation containing 15.5 w/w of the above insecticide. 
     
         ______________________________________                                    
Montmorillonite Analysis                                                  
Component        % by weight, range                                       
______________________________________                                    
Silica (SiO.sub.2)                                                        
                   68-72.5                                                
Ferric oxide (Fe.sub.2 O.sub.3)                                           
                 5-7                                                      
Aluminum oxide (Al.sub.2 O.sub.3)                                         
                 11-15                                                    
Calcium oxide (Cao)                                                       
                 0.012-1.5                                                
Magnesium oxide (Mgo)                                                     
                 0.8-1.6                                                  
Sodium oxide (Na.sub.2 O)                                                 
                 0.08-0.4                                                 
Potassium oxide (K.sub.2 O)                                               
                 1.1-1.6                                                  
Phosphoric acid (P.sub.2 O.sub.5)                                         
                 0.1-0.2                                                  
Cr, Cu, Mn, Ni, Ti                                                        
                 trace                                                    
Ignition loss      3-7.5                                                  
______________________________________                                    
 
    
     B. Following above method, but substituting 78.5 gms. of attapulgite having the analysis set forth below, containing 15.5 w/w of the above insecticide is prepared. 
     
         ______________________________________                                    
Attapulgite Analysis                                                      
Component       % by weight                                               
______________________________________                                    
Silica          64.37                                                     
Aluminum        12.46                                                     
Ferric oxide    5.93                                                      
Magnesium oxide 5.28                                                      
Calcium oxide   0.99                                                      
Sodium oxide    0.05                                                      
Potassium oxide 1.58                                                      
Titanium dioxide                                                          
                0.73                                                      
Loss on ignition                                                          
                8.21                                                      
______________________________________                                    
 
    
     EXAMPLE 2 
     Preparation of acrylic polymer coated granular pesticidal formulations 
     a. A granular insecticidal formulation (100 g) prepared by the method of Example 1A above is tumbled in a rotating type blender and sprayed with a hard, thermoplastic acrylic emulsion polymer with a solids content of 38% and with an intrinsic viscosity of 3.1 dl/g at 30° C. in THF (10 ml of latex is used). There is obtained 110 g of free-flowing and dry granules containing 14.09%, by weight, of toxicant. 
     b. A sample of the above formulation is stored at 45° C. for 2 hours. 
     c. A granular insecticidal formulation (100 g) prepared by the method of Example 1A above is sprayed as above with a mixture of a hard thermoplastic acrylic emulsion polymer, solids content 43%, by weight, and with an intrinsic viscosity of 0.75 dl/g at 30° C. in THF and dibutyl phthalate (6 ml of a 60:40 mixture). There is obtained 106 g of formulation containing 14.6% by weight of toxicant. 
     By the methods of a, b and c above, granular formulations are prepared, containing 15.5%, by weight, or 20.5%, by weight, of O,O-diethyl S-{[(1,1-dimethylethyl)thio]methyl}-phosphorodithioate, respectively. 
     EXAMPLE 3 
     Preparation of acrylic polymer coated granular pesticidal formulations 
     Procedure 
     A granular insecticidal formulation (100 g) prepared by the method of Example 1A, above, and a finely divided hydrohobic silica (0.5 g; 0.5%) in which most of the surface hydroxyl groups have been replaced by trimethylsiloxyl groups, are mixed and blended for 5 minutes prior to being sprayed with the respective coatings. 
     a. A granular formulation (100.5 g) prepared by the above procedure is agitated and sprayed with a hard self-crosslinking acrylic emulsion polymer with a solids content of 45%, by weight, and with an intrinsic viscosity of 1.4 dl/g at 30° C. in DMF (4 ml of latex used for coating). The thus obtained formulation (104.5 g; 14.83% real) is free-flowing, dry, and shows no tendency to form agglomerates; 
     b. The procedure of a above is followed except that 6 ml of latex are used to coat the granules (106.5 g; 14.55% real); or 
     c. A granular formulation (100.5 g) prepared by the above procedure is agitated and sprayed with a hard self-crosslinking acrylic emulsion polymer with a solids content of 45%, by weight, and with an intrinsic ciscosity of 1.4 dl/g at 30° C. in DMF (6 ml of latex used for coating). The thus obtained formulation (106.5 g; 14.55% real) is free-flowing, dry, and shows the presence of only trace amount of agglomerates. 
     By the methods of a, b or c above, a granular formulation is prepared which contains 15.5%, by weight, or 20.5%, by weight, of O,O-diethyl S-{[(1,1-dimethylethyl)thio]mety}-phosphorodithioate, respectively. 
     EXAMPLE 4 
     Preparation of acrylic polymer coated granular pesticidal formulation 
     Procedure 
     A granular insecticidal formulation (100 g) prepared by the method of Example 1A, above, and a finely divided hydrophobic silica in which most of the surface hydroxyl groups have been replaced by trimethylsiloxyl groups (1.0 g; 1%) are blended for 5 minutes prior to being sprayed with the respective coatings. 
     a. A granular formulation (101 g) prepared by the above procedure is tumbled in a rotating type of blender and sprayed with a hard, self-crosslinking acrylic emulsion polymer with a solids content of 45%, by weight, and with an intrinsic viscosity of 1.4 dl/g at 30° C. in DMF (4 ml of latex used). The thus obtained composition (105 g; 14.76% real) is free-flowing, dry, and shows no tendency to form agglomerates; 
     b. A granular formulation (101 g) prepared by the above procedure is tumbled and sprayed with a hard, self-crosslinking acrylic emulsion polymer with a solids content of 45%, by weight, and with an intrinsic viscosity of 1.4 dl/g at 30° C. in DMF (6 ml of latex used). The thus obtained composition (107 g; 14.48% real) is free-flowing, dry, and does not form aggregates. 
     EXAMPLE 5 
     Preparation of acrylic polymer coated granular pesticidal formulations 
     Procedure 
     There are admixed 100 gms of a granular insecticidal formulation prepared by the method of Example 1A, above, together with 0.5 gm of a finely divided hydrophobic silica in which most of the surface hydroxyl groups have been replaced by trimethylsiloxyl groups. The admixing takes place within 5 minutes prior to being sprayed with the respective coatings. 
     a. A granular formulation (100.5 g) prepared by the above procedure is agitated and sprayed with a hard thermoplastic acrylic emulsion polymer with a solids content of 43%, by weight, and with an intrinsic viscosity of 0.75 dl/g at 30° C. in THF (6 ml of latex used). The thus obtained composition (106.5 g; 14.55% real) is dry and forms only a few agglomerates. 
     b. As under a except that 1.0 g (1%) of the above hydrophobic silica is used in the formulation. The thus-obtained composition (107 g; 14.48% real) is dry and forms no agglomerates. 
     EXAMPLE 6 
     Preparation of a granular formulation containing 20% by weight of O,O-diethyl S-{[(1,1-dimethylethyl)thio]methyl}-phosphorodithioate 
     Granular (25/50) montmorillonite clay (66.2 g) is agitated in a blender and while being agitated, the granules are sprayed with a mixture of O,O-diethyl S-{[(1,1-dimethylethyl)thio]methyl}phosphorodithioate (22.8 g; 90.38% real=20.6 g real) and a deactivator comprising a mixture of ethylene, di-, tri- and tetraethylene glycol (4.0 g). After the spraying step has been completed, finely divided hydrophobic silica in which most of the surface hydroxyl groups have been replaced by trimethylsiloxyl groups (1.0 g; 1%) is added and blending is continued for 5 minutes. The thus-obtained blend is tumbled and sprayed with a hard, self-crosslinking acrylic emulsion polymer with a solids content of 45% by weight and with intrinsic viscosity of 1.4 dl/g at 30° C. in DMF (6 ml of latex used). The composition is free-flowing and dry. 
     EXAMPLE 7 
     Preparation of a granular formulation containing 10% by weight of O,O-diethyl S-(ethylthiomethyl)phosphorodithioate 
     a. Brick chips (79.07 g) are charged to a rotating type blender. While being agitated, the chips are sprayed with the insecticide: O,O-diethyl S-(ethylthiomethyl)phosphorodithioate (11.93 g of 88% real=10.5 g real, and diethylene glycol (5.0 g). Next, the so-treated chips are sprayed with a 37.5% w/w solution of an acrylic polymer in tetrahydrofurfuryl alcohol (4.0 g) to provide a polymer coating for said chips. The acrylic polymer is characterized by having an intrinsic viscosity of 0.085 dl/g at 30° C. in butanol. There is obtained 100 g of a granular formulation containing 10% w/w of the above insecticide (with a 5% overage). 
     The above formulation has an LD 50  of &gt;200 mg/kg by the method of Example 9, whereas a similar, but uncoated, sample has an LD 50  of 110 mg/kg. 
     b. By the method of a, but substituting O,O-diethyl S-{[(1,1-dimethylethyl)thio]methyl}phosphorothioate (10.5 g real) for the above insecticide, a granular formulation can be prepared. 
     c. The preparation under a is repeated except that the sprayed brick chips are blended for 5 minutes with 0.5%, by weight, of a finely divided hydrophobic silica in which most of the surface hydroxyl groups have been replaced by trimethylsiloxyl groups, and the thus prepared blend is then sprayed with a hard thermoplastic acrylic emulsion polymer with a solids content of 38% and with an intrinsic viscosity of 3.1 g dl/g at 30° C. in THF, to provide 1.9%, by weight, of formulation of said polymers. 
     The thus obtained composition has a dermal LD 50  of from &gt;120 to &lt;200 mg/kg by the method of Example 9. 
     The properties of the acrylic resins employed in the above Examples 2a, 2b and 7c, for instance, are further characterized below. The resins, manufactured by the Rohm and Hass Co. is sold under the trademark, RHOPLEX® B-85. It has the following typical physical properties: 
     
         ______________________________________                                    
Appearance           White milky liquid                                   
Solids               38.0 ± 0.5 percent                                
pH (as shipped)      9.5 to 10.0                                          
Weight per gallon    8.9 lbs.                                             
Dry bulking value (gal/lb.)                                               
                     0.102 (calculated)                                   
Tukon hardness (KHN) 18                                                   
Colloidal charge     Anionic                                              
Minimum film-formulation tem-                                             
                     &gt;90° C.                                       
perature                                                                  
______________________________________                                    
 
    
     In Examples 2c, 5a and 5b, above, the acrylic resin is manufactured by Rohm and Haas Co. and is sold under the trademark RHOPLEX® B-88. It has the following typical physical properties: 
     
         ______________________________________                                    
Appearance           White milky liquid                                   
Solids content       42 to 43%                                            
Viscosity            Less than 100 cps.                                   
pH (as shipped)      8.5 to 9.0                                           
Ionic nature         Nonionic                                             
Minimum film-forming tem-                                                 
                     Greater than 90° C.                           
perature                                                                  
Tukon hardness (approx.)                                                  
                     18 KHN                                               
______________________________________                                    
 
    
     In Examples 3a, 3b and 4a, above, the acrylic resin manufactured by the Union Carbide Co. and is sold under the trademark UCAR® Latex 189. It has the following typical physical properties: 
     
         ______________________________________                                    
Polymer Type         Hard, self-crosslinking                              
                     acrylic                                              
Emulsifier           Anionic                                              
Total Solids         45% by wt.                                           
Viscosity (Brookfield,                                                    
                     &lt;100 cp                                              
Model LVT, Spindle No. 2; 60 rpm)                                         
pH at 25° C.  4.0                                                  
Apparent Specific Gravity at                                              
                     1.07                                                 
20/20° C.                                                          
Weight per Gallon at 20° C.                                        
                     8.9 lb                                               
Particle Size (microns)                                                   
                     0.3                                                  
Surface Tension (dynes per cm.)                                           
                     38                                                   
______________________________________                                    
 
    
     In Examples 3c, 4b and 6, above, the acrylic resin is manufactured by the Union Carbide Co. and is sold under the UCAR® Latex 879. It has the following typical physical properties: 
     
         ______________________________________                                    
Total Solids, % by weight                                                 
                       46                                                 
Brookfield Viscosity (maximum),                                           
                      100                                                 
Model LVT, Spindle No.                                                    
1,60 rpm., cps                                                            
pH at 25° C.   4.5                                                 
Apparent Specific Gravity at                                              
                      1.07                                                
20/20° C.                                                          
Weight per Gallon at 20° C.                                        
                      8.90                                                
Surface Tension, dynes per cm.                                            
                       50                                                 
at 30% total solids                                                       
______________________________________                                    
 
    
     In Example 7a and 7b, the acrylic resin is manufactured by the American Cyanamid Co. and is designated as XG4011 Acrylic Resin as having the following typical physical properties: 
     
         ______________________________________                                    
Appearance           Clear, viscous liquid                                
Solids, % by weight  75 ± 2                                            
Solids, % by volume  70 ± 2                                            
Solvent              N--Butanol                                           
Viscosity, Gardner-Holdt, 25° C.                                   
                     Z.sub.5 Z.sub.7                                      
Color, Gardner, 1963, maximum                                             
                     1                                                    
Acid number, (resin solids)                                               
                     100-120                                              
Pounds per gallon, approximate                                            
                     8.5                                                  
Flash point (Tag Open Cup)                                                
                     &gt;172° F.                                      
Intrinsic Viscosity in Butanol                                            
                     .085                                                 
at 30° C.                                                          
______________________________________                                    
 
    
     EXAMPLE 8 
     General method for the evaluation of dermal toxicity of the formulations of the present invention using male albino rabbits as the test animals 
     Materials 
     a. Five male albino rabbits weighing approximately 2.2 to 3.5 kilogram are selected for each dosage level. The hair is shaved from the entire trunk. 
     b. Saran tubing or &#34;Vinylite&#34; film VU1900. 30.5 cm (12&#34;) wide, 0.04 millimeter in thickness and long enough to fit around the rabbit. 
     c. One felt cloth bandage measuring approximately 22.9×45.7 cm (9&#34;×18&#34;). 
     d. Four pieces of 3.8 cm (1.5&#34;) adhesive tape approximately 35.6 cm (14&#34;) long. 
     Procedure 
     a. The granular material is placed in the center of the plastic film and is moistened with water. 
     b. The rabbits underside is moistened with water and the animals are placed belly down on the material. 
     c. The plastic is then brought up and around the animal and secured at each end with strips of adhesive tape. The felt cloth is then placed under the belly and brought up around the animal and secured to the body with the remaining two strips of adhesive tape. 
     Evaluation 
     Twenty-four hours after dosing, the &#34;cuff&#34; is removed and any remaining material is brushed away. If the test material cannot be removed, the animal is fitted with a fiber collar which prevents the animal from licking the treatment area. The animals are observed for 14 days, post dosing, noting signs to toxicity, skin irritation and mortality. At the end of 14 days, the animals are sacrificed and weighed. 
     From the data thus obtained, the dermal LD 50  values (mg/kg body weight) are calculated for the formulations (compositions) of Examples 2 to 6, and are summarized in Table I below, along with the LD 50  value of the toxicant itself and a granular (non-coated) formulation thereof. 
     
                       TABLE I                                                     
______________________________________                                    
Dermal toxicity of coated granular compositions containing                
0,0-diethyl S--{[(1,1-dimethylethyl)thio]methyl}phosphoro-                
dithioate.                                                                
Composition         LD.sub.50 mg/kg                                       
______________________________________                                    
0,0-diethyl S--{[(1,1-dimethyl-                                           
                    1-2                                                   
ethyl)thio]methyl}phosphorodi-                                            
thioate (technical)                                                       
Non-coated, granular; 15%                                                 
                    &lt;20                                                   
toxicant.                                                                 
Example 2a          &gt;80                                                   
Example 2b          &gt;80                                                   
Example 2c          &lt;80&gt;40                                                
Example 3a          &gt;80                                                   
Example 3b          &gt;80                                                   
Example 4a          &gt;80                                                   
Example 4b          &gt;80                                                   
Example 5a          &lt;80&gt;40                                                
Example 5b          &lt;80&lt;40                                                
Example 6           &lt;80&gt;40                                                
______________________________________                                    
 
    
     It can be seen from Table I above, that the coated granular compositions of the present invention are at least two to three-fold less toxic as are the comparable non-coated compositions. 
     EXAMPLE 9 
     Southern corn rootworm soil residual test 
     One quart (950 ml) of moist (about 25% of moisture holding capacity) potting soil is placed in a stainless steel beaker approximately 22 cm deep×18 cm diameter. A weighed amount of granular is distributed over the soil. The beaker is then capped and rotated on a mechanical mixer for 2 minutes (60 revolutions). Two 1-ounce (29.7 ml) jars of soil are removed for 0 days mortality evaluation with southern corn rootworm (Diabrotica undecipunctata howardi) larvae. The remainder of the treated soil is divided between 2 wide-mouth pint (475 ml) treated paper containers. Each container of soil received 100 ml of tap water, bringing the soil to near field moisture holding capacity. A regime of moistening and drying continues throughout the test period. The treated soils plus the untreated control are held in the holding room at about 26.7° C. At weekly intervals the duplicate containers of soil are removed, the soil thoroughly mixed, moistened to about 25% moisture holding capacity, and two 1-ounce (29.7 ml) jars of soil are removed for bioassay with southern corn rootworm larvae. 
     The data obtained are summarized in Table II below. 
     
                       TABLE II                                                    
______________________________________                                    
Evaluation of the soil residual activity of acrylic polymer coated        
pesticidal granules, containing 15% by weight of 0,0-diethyl              
S--{[(dimethylethyl)thio]-methyl}phosphorodithioate against               
southerncorn rootworm larvae.                                             
      Concen-                                                             
      tration                                                             
      mg. a.i./                                                           
               Residual Activity (average of two replicates)              
Exam- 950 ml** Percent kill, days past start of week                      
ple   soil     0      7    21   42*  70   91   131                        
______________________________________                                    
control                                                                   
      --       0      0    30   5    0    0    0                          
uncoated                                                                  
      1         50    100  100  100   30   0   0                          
      2        100    100  100  100  100  67   0                          
      4        100    100  100  100  100  100  100                        
2a    1        100    100  100  100  100  44   0                          
      2        100    100  100  100  100  78   0                          
      4        100    100  100  100  100  100  50                         
3a    1         20    100  100   95   10   0   0                          
      2         90    100  100  100   90  44   0                          
      4        100    100  100  100  100  100  17                         
3b    1         50    100  100  100  100  67   0                          
      2         70    100  100  100  100  100  0                          
      4         80    100  100  100  100  100  83                         
3c    1         85    100  100  100  100  11   0                          
      2         80    100  100  100  100  78   0                          
      4        100    100  100  100  100  100  100                        
4a    1         85    100  100  100   90   0   0                          
      2        100    100  100  100  100  56   0                          
      4        100    100  100  100  100  100  83                         
4b    1        100    100  100  100   70   0   0                          
      2        100    100  100  100  100  67   0                          
      4        100    100  100  100  100  100  83                         
5a    1         45    100  100  100   40  22   0                          
      2         75    100  100  100   70  11   0                          
      4        100    100  100  100  100  100  50                         
______________________________________                                    
 *After this day only single tests are run                                
 **Corresponds to 1.12, 2.24 and 4.48 kg/ha, respectively                 
 
    
     Advantageously, from the biological data presented in Table II above, it can be seen that certain of the coated granular formulations may be utilized to provide short term controlled release of toxicant, especially at the lower rates applied (e.g. 3a,4b and 5a; at 1 mg. a.i., 6 to 10 weeks); while others provide long term controlled release of toxicant, especially at the higher rates applied (e.g. 3b, 3c, 4a and 4b; at 4 mg. a.i., 13-19 weeks).