Wettable powders

Rya.nia., The root and stem of the plant yania speciosa family Flacourtiaceae, native to South America, contain from 0.16—0.2% of iasecticidal components, the most important of which is the alkaloid ryanodine [15662-33-9] C25H250 N (8) (mp 219—220°C). This compound is effective as both a contact and a stomach poison. Ryanodine is soluble ia water, methyl alcohol, and most organic solvents but not ia petroleum oils. It is more stable to the action of air and light than pyrethmm or rotenone and has considerable residual action. Ryania has an oral LD q to the rat of 750 mg/kg. The material has shown considerable promise ia the control of the European com borer and codling moth and is used as a wettable powder of ground stems or as a methanohc extract. Ryanodine uncouples the ATP—ADP actomyosia cycle of striated muscle. 

Wettable powders are prepared by blending the toxicant in high concentration, usually from 15 ndash 95%, with a dust carrier such as attapulgite which wets and suspends properly in water. One to two percent of a surface-active agent usually is added to improve the wetting and suspensibiUty of the powder. Sprays of wettable powders are used widely in agriculture because of their relative safety to plants. 

Pesticide Dispersants. Modified ligaosulfates are used ia the formulatioa of pesticides, la wettable powders, suspeasioa coaceatrates, and water dispersible granules, they act as dispersants and prevent sedimentation. They also act as biaders ia the productioa of granular pesticides. Typical usage levels ia these types of products range from 2—10%. 

All lnaphthalenesulfonic Acids. The aLkyLnaphthalenesulfonic acids can be made by sulfonation of aLkyLnaphthalenes, eg, with sulfuric acid at 160°C, or by alkylation of naphthalenesulfonic acids with alcohols or olefins. These products, as the acids or their sodium salts, are commercially important as textile auxiUaries, surfactants (qv), wetting agents, dispersants (qv), and emulsifying aids, eg, for dyes (qv), wettable powder pesticides, tars, clays (qv), and hydrotropes. 

The main purpose of pesticide formulation is to manufacture a product that has optimum biological efficiency, is convenient to use, and minimizes environmental impacts. The active ingredients are mixed with solvents, adjuvants (boosters), and fillers as necessary to achieve the desired formulation. The types of formulations include wettable powders, soluble concentrates, emulsion concentrates, oil-in-water emulsions, suspension concentrates, suspoemulsions, water-dispersible granules, dry granules, and controlled release, in which the active ingredient is released into the environment from a polymeric carrier, binder, absorbent, or encapsulant at a slow and effective rate. The formulation steps may generate air emissions, liquid effluents, and solid wastes. 

The bacterial culture converts a portion of the supplied nutrient into vegetative cells, spores, crystalline protein toxin, soluble toxins, exoenzymes, and metabolic excretion products by the time of complete sporulation of the population. Although synchronous growth is not necessary, nearly simultaneous sporulation of the entire population is desired in order to obtain a uniform product. Depending on the manner of recovery of active material for the product, it will contain the insolubles including bacterial spores, crystals, cellular debris, and residual medium ingredients plus any soluble materials which may be carried with the fluid constituents. Diluents, vehicles, stickers, and chemical protectants, as the individual formulation procedure may dictate, are then added to the harvested fermentation products. The materials are used experimentally and commercially as dusts, wettable powders, and sprayable liquid formulations. Thus, a... 

Methyl parathion is marketed as a technical grade solution (80% methyl parathion) or in emulsifiable concentrate, wettable powder, ultra-low volume (ULV) liquid, dustable powder, and encapsulated suspension forms (HSDB 1999). The technical grade solution contains 80% active ingredient, 16.7%... 

Wettable powder formulations can be mixed using the procedure described above with the exception that some of the second half of the water should be used to cream the test item into a paste type mixture which can then be poured into the first half of the water. Numerous rinsings will again be required to ensure that the entire test item is removed from its original container and, hence, thoroughly mixed with the second half of the water. 

End-use formulations should be used as the test substance. If an active ingredient is marketed in two commercial formulations, then both should be used in the study, since there may be differences in residue levels and dissipation rates, e.g., a wettable powder versus a liquid formulation. The best solution would be plots located at the same site for a side-by-side comparison. This should only be necessary at one of the sites. However, each formulation should be represented in the study unless a strong case can be made for a worst-case scenario. 

Acute Toxicity. The LD50 following oral administration of parathion, either in propylene glycol solutions or in aqueous suspensions of the 15% wettable powder, has been determined for rats, mice, and guinea pigs. The lethal dose was approximated for rabbits and dogs. The results of these experiments are summarized in Table I. Statistical evaluation was by the method of Wilcoxon and Litchfield (11). 

Dermal Absorption. To determine the toxicity of parathion following dermal application, the method of Draize, Woodard, and Calvery (3) was followed. Variables considered in the design of these experiments were concentration as a factor of area, solvent, exposure time, and number of exposures. In some cases the wettable powder was applied in the dry form, while in other cases sufficient water was added to produce a viscid paste. All doses in the table are presented as milligrams per kilogram of parathion, regardless of the concentration or solvent. 

As the concentration of parathion in the propylene glycol solutions is increased, it follows that the area covered by the solution is decreased. That this is a factor in toxicity is indicated by the greater toxicity of the 10 mg. per ml. solution than the 50 mg. per ml. solution. This relationship appears to be true also of the various dry preparations, in that the 1% powder is somewhat more toxic than the 15%. The addition of water to convert the powder to paste does not appreciably influence the toxicity. In comparable concentrations the wettable powder formulation is less toxic than the propylene glycol solution. 

Skin of abdominal area was closely clipped and parathion preparation applied under rubber sheeting. All doses are as parathion. Dust suspension is an aqueous suspension of 15% wettable powder comparable to a spraying application of 3 pounds per 100 gallons)... 

Following oral administration of a lethal dose to a dog (25 mg. per kg. wettable powder) tissues taken immediately after death analyzed as follows no parathion recovered from bladder bile, liver, kidney, abdominal fat, saliva, or intestine small quantities (2 to 7 p.p.m.) of parathion recovered from oxalated blood, spleen, lung, brain, and spinal cord. The urinary bladder was strongly contracted and no urine could be collected. The results of these two experiments indicate a universal distribution of parathion following acutely lethal doses. 

The agricultural chemicals in general are more dangerous to handle in solution than in wettable powder or dust form. Parathion and nicotine are the only exceptions to this as they seem to be about equally toxic in wet or dry form. 

The substrate was Valencia orange leaves, with 2500 leaves per sample selected in a carefully prescribed manner (4). The trees involved were field sprayed in a conventional manner with 4 pounds of a 25% wettable powder of parathion, then sampled after 7 days and again after 11 days. Each sample was mixed thoroughly and subsampled into 125-leaf units in 2-quart Mason jars. To all units were added 250 ml. of benzene each, and they were sealed, stripped for various lengths of time, then restripped with fresh benzene, again for various lengths of time. The strip solutions were analyzed in the usual manner. 

It was also established in laboratory work that this product could be readily formulated into dusts, wettable powder, or liquid formulations. Liquid formulations were more readily made with this than with the commercial benzene hexachloride, because of the higher concentration of the gamma isomer. 

The residual toxicity of the pure gamma isomer was found to be equivalent to that of ordinary commercial benzene hexachloride. Commercial usage has shown that the residual action is effective for a longer time with dust or wettable powder spray applications than with emulsive solvent-type formulations. The over-all residual life of the chemical is on the order of 4 to 8 days as compared to 14 to 21 days for DDT. This is, of course, adequate residual life for good insect control in most cases and the shorter... 

The use of pure gamma isomer of hexachlorocyclohexane on livestock has also been worked out. It has been found possible to use the wettable powder formulation dispersed in water as a spray on livestock for control of flies, lice, and ticks. Proper dosage and application must be used, of course, but this is again indicative of the safety factor of this insecticide. 

As wettable powder containing 50% technical DDT. b Since final application. 

As wettable powder supplied by American Cyanamid Co. containing 25% technical parathion. 

As wettable powder containing 25% parathion. First application 9/15/47, second application 10/15/47. 

The authors are indebted to the American Cyanamid Company for supplies of the wettable powder of parathion used in these trials. 

Spray schedules applied on experimental plots at the Yakima, Wash., and Vincennes, Ind., laboratories of the United States Bureau of Entomology and Plant Quarantine were studied to determine the magnitude of parathion and DDT spray residues at harvest. The parathion sprays were prepared from 25% vet table powder and the DDT sprays from 50% wettable powder, except in one series of tests, when a 25% DDT wettable powder was used. All spray treatments were planned and made by members of the Division of Fruit Insect Investigations. Conventional hydraulic sprayers were used in this work. 

The harvest residue in plot 1, in which a 50% DDT wettable powder was used, was only slightly less than where the same amount of DDT in a 25% wettable powder was applied in plot 2. Reduction of the concentration of actual DDT in the spray mixture (plots 3 and 4) resulted in lower residues at harvest. 

Parathion has been recommended in the state of Washington (3) for the control of various species of mites and orchard aphids. Wettable powders, containing 15 or 25% of parathion, have been used at concentrations ranging from 0.25 to 4 pounds per 100 gallons of water on an experimental basis and from 0.25 to 0.5 pound on a commercial basis. 

Although parathion has not been recommended to date for insect control on soft fruits, there are indications that some injurious insects may be controlled by applications of parathion. Experimental sprays of 1 pound of the 25% wettable powder per 100 gallons of water were applied to soft fruits to determine the amount of parathion residue that would remain on the surface at harvest time. The parathion residue at harvest time is presented in Table I. 

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