The present invention relates to completely or partially water-based organophosphate pesticide formu¬ lations or solid organophosphate pesticide formulations comprising one or more organophosphate pesticides as active ingredients and the usual formulation, carrier and auxiliary agents.

It is well-known that organophosphate pesticides, for instance alathion, methyl parathion, dimethoate and chlorpyrifos carry or develop, when stored, an obnoxious odour, which for the major part is probably due to the formation of decomposition products of the mercaptan and sulphide type.

Inhibition of the development or removal of the unpleasant odour in organophosphate pesticides or from organic solvent-based organophosphate pesticide formu- lations may at least partially be achieved by adding small amounts of oxidation agent, for instance perox¬ ides, nitrites, nitrogen oxides or ozone, to the pesticides (US 3,714,301, US 2,962,521, US 2,879,284 and GB 960,013). The oxidation agents oxidize the unpleasantly smelling mercaptans and sulphides into odourless compounds.

It is known to use peroxides for removal of bad odour from organophosphate-containing, for instance malathion-containing, sewage (US 4,263,136). The patent leaves the impression that malathion in the sewage water may be decomposed in connection with the peroxide treatment.

Problems of destabilizing organophosphate pesti¬ cides by adding oxidation agents are described in US 3,714,301 and US 2,879,284.

Gratzel C.K. et al. (J. Mol. Catal., 60(1990) 375- 387) proved that addition of oxidation agent, for instance hydrogen peroxide, to aqueous organophosphate pesticide dispersions of for instance malathion and parathion increased the decomposition of the pesticide considerably, i.a. on account of a direct oxidation of the compounds.

Jensen-Holm J. (Ugeskr. Laeg. (Doctors' Weekly) 143(48) (1981) 3206-3211) described the catalytic effect of hydrogen peroxide on the decomposition of organophosphate pesticides in aqueous waste products.

Destruction of organophosphate pesticides in waste water by means of oxidation agents is likewise described by Lion C. et al. (Bull. Soc. Chim. Belg. 103(1994) 115-118). Egli S. et al. (Chem. Oxid. 1992(1994) 264-277), Hu K. et al. (Huanjing Huaxue 9(1990) 13-19) and Go aa H.M. et al. (Advan. Chem. Ser. (1972), 111, Fate of Org. Pestic. in the Aquatic Environ., 189-209). According to Pilar Aires et al. (J. Photochem. Photobiol. A: Chem., 68(1992) 121-129) the presence of only 0.6% hydrogen peroxide in an aqueous malathion solution increased the decomposition of pesticide by a factor 10, which meant that practically all malathion had been decomposed in the course of a few days of storing at room temperature, even though pH - in respect of the stability of malathion - was near optimum.

The above-mentioned pesticides are often used in the form of solutions in organic solvent. The solutions are diluted with water immediately before spraying. For both environmental reasons and for reasons concerning the working environment there is a widespread desire to use, instead of solutions of pesticides in organic solvent, completely or partially water-based formula-

tions, for instance oil-in-water emulsions or aqueous microcapsule suspensions of the pesticides or to use solid formulations without any content of water or organic solvent. The chemical stability of organophosphate pesti¬ cides and their properties as to toxicity and smell are considerably impaired by the presence of water in formulations and in solid formulations, for instance wettable powders and water-soluble and water-dispers- ible granules. In addition to the fact that the prob¬ lems mentioned above in respect of odours are substan¬ tially more pronounced in aqueous or solid organophos¬ phate pesticide formulations compared to organic solvent-based formulations, there is a marked tendency that the decomposition of the pesticides into human and animal toxic iso ers occurs considerably faster in both aqueous as solid formulations than in formulations based on organic solvents.

The formation of isomalathion in malathion formu- lations and the formation of isomethyl parathion are examples of decomposition of organophosphate pesticides to isomers which are more toxic than the active com¬ pounds, from which the isomers are formed. The problem is therefore not only that for instance isomethyl parathion and isomalathion per se are most toxic compounds. The iso compounds are also to a considerable degree known for potentiating the inherent toxicity of the active agents on human beings and animals.

The consequence is that both the initial content and the formation of the isomeric compounds in organo¬ phosphate pesticide formulations are to be limited as much as possible, and that the authorities only allow very limited concentrations of the toxic isomeric compounds in commercial pesticide formulations. It is possible to a certain degree to limit both

the mercaptan and the sulphide smell and the conversion of the active compounds into toxic isomers by adequate¬ ly choosing auxiliary compounds, for instance carriers and emulgators and by adequately choosing the type of packaging and pH in the formulation. For a number of aqueous or solid organophosphate pesticides the above- mentioned solutions will not, however, be sufficient for obtaining a product with acceptable properties as to stability, toxicity and smell. It has most surprisingly been found that addition of oxidation agents, for instance peroxides to inor¬ ganic solvent-based organophosphate pesticide formula¬ tions improves the chemical stability of the pesticide, and thus does not impair the chemical stability, which might have been expected in view of the above (US 4,263,136, US 3,714,301, US 2,879,284, J. Mol. Catal. 60(1990) 375-387, Ugeskr. Laeg. (Doctors' Weekly) 143(48) (1981) 3206-3211, Bull. Soc. Chim. Belg. 103(1994) 115-118, Chem. Oxid. 1992(1994) 264-277, Huanjing Auaxue 9(1990) 13-19, Advan. Chem. Ser. (1972) , 111, Fate of Org. Pestic. in the Aquatic Environ., 189-209, J. Photochem. Photobiol. A: Chem. 68(1992) 121-129). The addition of oxidation agent eliminates the mercaptan and sulphide smell of the formulations even during a lengthy storage over a long period at high temperature.

Likewise it has most surprisingly been found that addition of oxidation agent, for instance peroxides, considerably reduces the concentration of the toxic organophosphate isomeric compounds, such as for instance isomalathion and isomethyl parathion, even after a lenghty storage at high temperature.

The fact that it has been found that an auxiliary compound, the oxidation agent, for instance peroxides, can improve the properties as to stability, smell and

toxicity of the organophosphate pesticide formulations is in itself most surprising.

As addition of only small concentrations of an auxiliary compound may considerably impair the physio- chemical and chemical stability of a formulation and consequently make the development of formulations with optimal properties difficult, it is of essential value that addition of only one auxiliary compound solves three fundamental problems - decomposition of organo- phosphate pesticides, formation of toxic isomeric compounds and development of mercaptan and sulphide smell - without having any substantial impact on the remaining properties of the formulations.

Thus, the formulations according to the invention are characterized in that to the formulations is added 0.01-10, preferably 0.05-3 and in particular 0.3-1 percentage by weight, of an oxidation agent, said agent improving the chemical stability and/or minimizing the concentration of human- and animal toxic isomeric compounds and/or removes and prevents the development of mercaptan and sulphide smell.

Peroxides, for instance hydrogen peroxide, has proved most suitable in the above-mentioned pesticide formulations, but other oxidation agents may also be used.

Autoxidation of peroxide into water and oxygen may limit the effect of the peroxide on the smell, the active compound stability and toxic characteristics of the formulation. The autoxidation may, however, be considerably limited by addition of stabilizing agents, which stabilize the peroxide without limiting its effect on the chemical stability of the organophosphate pesticide, on the mercaptan and the sulphide smell and on the formation of toxic organophosphate isomers like for instance isomalathion and isomethyl parathion.

Among peroxide-stabilizing agents may for instance be mentioned EDTA, salicylic acid, propylgallate, acetanilide, 8-hydroxyquinoline, phenacetin and mix¬ tures thereof. In formulations consisting of two or more phases it may be advantageous to use a combination of oxida¬ tion agents which have different solubilities in the phases and differing distribution coefficients in between the phases. Addition of oxidation agent, for instance perox¬ ides alone or together with peroxide-stabilizing auxiliary agents, makes possible the development of both completely or partially water-based organophos¬ phate pesticide formulations and solid organophosphate pesticide formulations with substantially improved properties as to stability, toxicity and smell.

Among specific active agents may be mentioned malathion, methyl parathion, ethyl parathion, di- methoate, chlorpyrifos, ethion, fenitrothion, eth- amidophos, acephate, diazinone and prophenophos. From said active compounds malathion, methyl parathion, ethyl parathion, dimethoate, chlorpyrifos, ethion and fenitrothion are preferred.

The formulations according to the invention may in addition to one or more organophosphate pesticides also contain one or more pesticides of a different type.

Among specific formulation types may be mentioned oil-in water emulsions, liposomes, micelles, microemul- sions, aqueous suspensions, suspension concentrates, microcapsules, microcapsule suspensions, wettable powders, powders and granules, in particular oil-in- water emulsions and microcapsule suspensions.

The invention will be further illustrated by means of the following examples. The concentration of pesti- cides and decomposition products is determined by means

of gas and/or liquid chromatography and NMR spectro- scopy.

Example 1

Malathion 40% by weight oil-in-water emulsions were prepared lege artis. An optimal combination of e ulgators was used. The stirring velocity during the emulsion formation was regulated such that the volume surface-middle diameter was 10-12 μm. A suitable viscosity was obtained by addition of viscosity in¬ creasing compounds. The pH value was regulated in view of obtaining an optimum malathion stability.

The concentration of hydrogen peroxide in the emulsions was varied. The contents of isomalathion was analytically determined after storing of the formu¬ lations for 6 and 14 days at 54°C (accelerated storing test) . Likewise, the malathion content was analytically determined before and after storing. Fig. 1 shows the relationship between initial hydrogen-peroxide concentration and isomalathion concentration after 6 days of storing. A considerable reduction of the isomalathion concentration was obtained by addition of hydrogen peroxide. A pronounced reduction of the isomalathion concentration is obtained even after 14 days of storing at 54°C.

It appears from Table 1 that the chemical stabil¬ ity during storing test at 54°C is improved by addition of hydrogen peroxide.

Table 1

Decomposition of malathion in 40% by weight oil-in- water emulsion at storing for 14 days at 54°C.

% hydrogen peroxide in formulation 0 0.1 0,3

% malathion decomposed rela¬ tive to initial content 7,0 3,4 1,4

Example 2

In selected malathion oil-in-water formulations the chemical stability of malathion and the formation of isomalathion were examined during storing for months at 23°C. The results appear from Table 2. Addition of hydrogen peroxide considerably reduces the isomalathion concentration and improves the chemical stability of malathion.

Table 2

Decomposition of malathion and isomalathion concentra¬ tion in malathion 40% by weight oil-in-water emulsion when stored for 4 months at 23°C.

% hydrogen peroxide in formulation 0 0,1 0,3

% malathion decomposed relative to initial content 1,4 0,73 0,24 pp isomalathion after storing 1404 217 <10

Example 3

Malathion oil-in-water emulsions are prepared lege artis. The emulsions were prepared without hydrogen peroxide, with 0.1 or 0.3% hydrogen peroxide. Moreover,

EDTA was added to some of the emulsions to prevent autoxidation of the peroxide.

The odour of the emulsions after storing at 23°C and 54°C, respectively, was concurrently assessed by a

panel. The results are given below in Table 3.

Table 3

The results of odour test with malathion oil-in-water emulsions

Hydrogen peroxide Peroxide Odour Odour % stabi lizer After 10 days After 14 days 23'C 54 ^* C 23 C 54 C

0 - u u u u

0 EDTA 0.01% u u u u

0 EDTA 0.1% u u u υ

0 EDTA 1% u u u u

0,1 - a a a u

0.1 EDTA 0.01% a a a a

0,1 EDTA 0.1% a a a a

0,1 EDTA 1% a a a a

0,3 - a a a a

0,3 EDTA 0.01% a a a a

0,3 EDTA 0.1% a a a a

0,3 EDTA 1% a a a a

a: acceptable odour u: unacceptable odour

Example 4

Water-based malathion formulations, i.a. oil-in- water emulsions and microemulsions and water-based chlorpyrifos and methyl parathion formulations were prepared lege artis. Considerable improvements of the properties as to odour were achieved by addition of oxidation agent to the formulations. The improvements were obtained both in accelerated storing tests and in storing tests at 23°C.

Example 5

A methyl parathion microcapsule suspension with an active ingredient content of 39% by weight was prepared under use of usual auxiliary compounds. The microcapsule suspensions contained different concentra¬ tions of hydrogen peroxide. The formation of isomethyl parathion at 14 days of storing at 54°C was analytical¬ ly determined, se Table 4

Table 4

Isomethyl parathion in methyl parathion microcapsule suspension formed during storage for 14 days at 54°C.

% hydrogen peroxide in formulation 0 0.2 0.4 0.6

% Isomethyl parathion 1.16 0.90 0.72 0.52

Example 6

Methyl parathion 40% by weight oil-in-water emulsions was prepared in accordance with the same method and by use of the same auxiliary compounds mentioned in connection with Example 1.

Formulations without hydrogen peroxide and with 0.3% hydrogen peroxide were prepared. To some of the formulations 5 mg/ml isomalathion was added. The concentrations of isomethyl parathion and isomalathion were determined before and after storing at 54°C for 6 days or at 23°C for 6 days. The results in Table 5 show that the function of the hydrogen peroxide in connection with a reduction of the concen- tration of the isomeric compounds is not to increase the decomposition speed of the isomeric compound itself

(isomalathion) , but on the contrary to inhibit the transformation of pesticide (methyl parathion) into an isomeric compound (isomethyl parathion) .

Table 5

Methyl parathion 40% by weight oil-in-water emulsion with differing initial contents of hydrogen peroxide and isomalathion. The isomethyl parathion and isomal- athion concentration after storing for 6 days at 23°C and at 54°C.

Formulation After 6 days at After 6 days After 6 days After 6 days composition 23 C at 23-C at 54-C at 54 ^* C initial ly Isomethyl Isomalathion Isomethyl Isomalathion parathion (ppm) parathion (ppm)

(ppm) (ppm)

0% H ₂ 0 ₂ 0% Isomalat¬ 2700 <10 23400 <30 hion

0% H.,0., 2 2 0.5 Isomalat¬ 4600 5591 17500 2153 ion

0.3% H^ 0% Isomalat¬ 2100 <10 8500 <30 hion

0.3% H 0, 22 0.5% Isomal¬ 3500 4352 6600 2793 athion

Example 7

A malathion 40% by weight oil-in-water emulsion was prepared as described in Example 1. To the formula¬ tion 0.1 sodium nitrite was added. The isomalathion concentration after 6 days of storing at 54°C was substantially smaller than the concentration in a corresponding formulation without sodium nitrite.