You are wrong as far as I can tell. Do you have a source of the claim you've made? My research is below:

USDA organic standard does not allow arsenic in use for pest control. It is explicitly barred from use in the National List:

Source: https://www.ams.usda.gov/grades-standards/organic-standards#Crop

The organic crop production standards require that:

Land must have had no prohibited substances applied to it for at least 3 years before the harvest of an organic crop.

Soil fertility and crop nutrients will be managed through tillage and cultivation practices, crop rotations, and cover crops, supplemented with animal and crop waste materials and allowed synthetic materials.

Crop pests, weeds, and diseases will be controlled primarily through management practices including physical, mechanical, and biological controls. When these practices are not sufficient, a biological, botanical, or synthetic substance approved for use on the National List may be used.

Operations must use organic seeds and other planting stock when available.

The use of genetic engineering, ionizing radiation and sewage sludge is prohibited

Now go look at the national list: https://www.ecfr.gov/current/title-7/subtitle-B/chapter-I/subchapter-M/part-205/subpart-G/subject-group-ECFR0ebc5d139b750cd

205.602 Nonsynthetic substances prohibited for use in organic crop production.

The following nonsynthetic substances may not be used in organic crop production:

(a) Ash from manure burning.

(b) Arsenic.

(c) Calcium chloride, brine process is natural and prohibited for use except as a foliar spray to treat a physiological disorder associated with calcium uptake.

(d) Lead salts.

(e) Potassium chloride—unless derived from a mined source and applied in a manner that minimizes chloride accumulation in the soil.

(f) Rotenone (CAS # 83-79-4).

(g) Sodium fluoaluminate (mined).

(h) Sodium nitrate—unless use is restricted to no more than 20% of the crop's total nitrogen requirement; use in spirulina production is unrestricted until October 21, 2005.

(i) Strychnine.

(j) Tobacco dust (nicotine sulfate).

[68 FR 61992, Oct. 31, 2003, as amended at 83 FR 66572, Dec. 27, 2018]

You are wrong as far as I can tell. Do you have a source of the claim you've made? My research is below:

USDA organic standard does not allow arsenic in use for pest control. It is explicitly barred from use in the National List:

Source: https://www.ams.usda.gov/grades-standards/organic-standards#Crop

The organic crop production standards require that:

Land must have had no prohibited substances applied to it for at least 3 years before the harvest of an organic crop.

Soil fertility and crop nutrients will be managed through tillage and cultivation practices, crop rotations, and cover crops, supplemented with animal and crop waste materials and allowed synthetic materials.

Crop pests, weeds, and diseases will be controlled primarily through management practices including physical, mechanical, and biological controls. When these practices are not sufficient, a biological, botanical, or synthetic substance approved for use on the National List may be used.

Operations must use organic seeds and other planting stock when available.

The use of genetic engineering, ionizing radiation and sewage sludge is prohibited

Now go look at the national list: https://www.ecfr.gov/current/title-7/subtitle-B/chapter-I/subchapter-M/part-205/subpart-G/subject-group-ECFR0ebc5d139b750cd

205.602 Nonsynthetic substances prohibited for use in organic crop production.

*The following nonsynthetic substances may not be used in organic crop production: *

(a) Ash from manure burning.

(b) Arsenic.

(c) Calcium chloride, brine process is natural and prohibited for use except as a foliar spray to treat a physiological disorder associated with calcium uptake.

(d) Lead salts.

(e) Potassium chloride—unless derived from a mined source and applied in a manner that minimizes chloride accumulation in the soil.

(f) Rotenone (CAS # 83-79-4).

(g) Sodium fluoaluminate (mined).

(h) Sodium nitrate—unless use is restricted to no more than 20% of the crop's total nitrogen requirement; use in spirulina production is unrestricted until October 21, 2005.

(i) Strychnine.

(j) Tobacco dust (nicotine sulfate).

[68 FR 61992, Oct. 31, 2003, as amended at 83 FR 66572, Dec. 27, 2018]

You are wrong as far as I can tell. Do you have a source of the claim you've made? My research is below:

USDA organic standard does not allow arsenic in use for pest control. It is explicitly barred from use in the National List:

Source: https://www.ams.usda.gov/grades-standards/organic-standards#Crop

The organic crop production standards require that:

Land must have had no prohibited substances applied to it for at least 3 years before the harvest of an organic crop.

Soil fertility and crop nutrients will be managed through tillage and cultivation practices, crop rotations, and cover crops, supplemented with animal and crop waste materials and allowed synthetic materials.

Crop pests, weeds, and diseases will be controlled primarily through management practices including physical, mechanical, and biological controls. When these practices are not sufficient, a biological, botanical, or synthetic substance approved for use on the National List may be used.

Operations must use organic seeds and other planting stock when available.

The use of genetic engineering, ionizing radiation and sewage sludge is prohibited

Now go look at the national list: https://www.ecfr.gov/current/title-7/subtitle-B/chapter-I/subchapter-M/part-205/subpart-G/subject-group-ECFR0ebc5d139b750cd

205.602 Nonsynthetic substances prohibited for use in organic crop production.

The following nonsynthetic substances may not be used in organic crop production:

(a) Ash from manure burning.

**(b) Arsenic. **

(c) Calcium chloride, brine process is natural and prohibited for use except as a foliar spray to treat a physiological disorder associated with calcium uptake.

(d) Lead salts.

(e) Potassium chloride—unless derived from a mined source and applied in a manner that minimizes chloride accumulation in the soil.

(f) Rotenone (CAS # 83-79-4).

(g) Sodium fluoaluminate (mined).

(h) Sodium nitrate—unless use is restricted to no more than 20% of the crop's total nitrogen requirement; use in spirulina production is unrestricted until October 21, 2005.

(i) Strychnine.

(j) Tobacco dust (nicotine sulfate).

[68 FR 61992, Oct. 31, 2003, as amended at 83 FR 66572, Dec. 27, 2018]