EPA Extremely Hazardous Substances List. Selenium and its compounds are on the Community Right-To-Know List. Reported in EPA TSCA Inventory.

OSHA PEL: TWA 0.2 mg(Se)/m³
ACGIH TLV: TWA 0.2 mg(Se)/m³
DFG MAK: 0.1 mg(Se)/m³

The IUPAC name of this chemical is Selenious acid. With the CAS registry number 7783-00-8 and EINECS registry number 231-957-4, it is also named as Monohydrated selenium dioxide. In addition, the molecular formula is H₂O₃Se and the molecular weight is 128.97. It is a kind of white solid and belongs to the classes of Inorganics; AA Standard Solutions Alphabetic; Reference/Calibration Standards; Standard Solutions; AAS Spectroscopy; Matrix Selection; Nitrate Alphabetic; Spectroscopy.

Physical properties about Selenious acid are: (1)H-Bond Donor: 2; (2)H-Bond Acceptor: 3; (3)Exact Mass: 129.916916; (4)MonoIsotopic Mass: 129.916916; (5)Topological Polar Surface Area: 57.5; (6)Heavy Atom Count: 4; (7)Complexity: 26.3; (8)Covalently-Bonded Unit Count: 1; (9)Polar Surface Area: 35.53 Å².

Preparation of Selenious acid: it can be prepared by nitric acid and selenium at room temperature. Firstly, let nitric acid react with selenium until the nitrogen oxides does not overflow. And then after a series of evaporation, filtering, concentration, cooling, crystallization and recrystallization you can get the desired product. The equation as follows: 3Se+4HNO₃+H₂O → 3H₂SeO₃+4NO.

Uses of Selenious acid: The major use of this chemical is in changing the color of steel, especially the steel in guns. And it can be used as analytical reagent, reductant or oxidant. In addition, it is used in the chemical darkening and patination of copper, brass and bronze, producing a rich dark brown color that can be further enhanced with mechanical abrasion.

When you are using this chemical, please be cautious about it as the following:
This chemical is irritating to eyes and skin and has danger of cumulative effects. And it is toxic by inhalation and if swallowed. Moreover it is very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment. When you are using it, do not eat, drink or smoke. In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. And in case of accident or if you feel unwell, seek medical advice immediately (show label where possible). You should avoid release to the environment and can refer to special instructions safety data sheet. This material and its container must be disposed of as hazardous waste.

You can still convert the following datas into molecular structure:
(1)SMILES: O=[Se](O)O
(2)InChI: InChI=1/H2O3Se/c1-4(2)3/h(H2,1,2,3)
(3)InChIKey: MCAHWIHFGHIESP-UHFFFAOYAW

The toxicity data is as follows: