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DICHROMIC ACID: PRODUCT CHEMISTRY/ ENVIRONMENTAL FATE AND 

ECO-EFFECTS SCOPING DOCUMENT 

TABLE OF CONTENTS PAGE

No.

Dichromic Acid....................... 

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APPENDICES--------------------------------------------------------------------------------- 15
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Dichromic Acid 

Chemical Name Use Patterns/Use Sites 

 Dichromic Acid 

It is used as a wood preservative in commercial wood treatment 

plants, for end-use formulations of CCA, type A or type C 

It is tank-mixed at the use site for commercial wood treating 

establishments. v/v for chromium in both types A and C remains 

the same, i.e. = 0.0124 

REGISTRATION REVIEW DOCUMENT

PRODUCT CHEMISTRY, ENVIRONMENTAL FATE AND

 ECOLOGICAL EFFECTS SUMMARY: DICHROMIC ACID

PC Code: 068306; Case No. 5012

Regulatory History

Dichromic acid was first registered by the Agency in1994 as Sodium Bichromate Crystals (as a 

solid) by Occidental Chemical Company. In 2003 it was acquired by Elementis Chromium, LP. 

Elementis received conditional registration in 2005 but changed the name to Sodium Bichromate 

Liquid (69%) or as Sodium Bichromate Solution. Elementis is the only registrant and only two 

labels exist. Its final approval is pending. 

Important Notes: 1) With the change of the registrant, the new registrants decided to register 

sodium bichromate as Manufacturing Use Product (MUP) not as solid crystals but as a liquid or 

solution by mixing the sodium bichromate crystals with to the crystals (to make a 

100% solution). Adding to the sodium bichromate crystals forms dichromic acid, which 

exists in solution only and has never been crystallized.

2) The name Sodium Bichromate is more commonly used in European countries like Germany. 

The prevalent name in US is Sodium Dichromate. 

 3) Whether the term sodium bichromate liquid, sodium dichromate solution or dichromic acid is 

used, the underlying fact is chromium has the same oxidation state, i.e. +6 or Cr (VI). 

 4) The Agency has recently completed a RED on CCA (chromated arsenicals) which contains 

chromium as sodium bichromate. Hence, its database is complete for Cr (VI). 

5) Since the three names listed above are interchangeably used, for the remainder of the 

document it will be referred to as Dichromic acid 

This document describes the product chemistry of sodium bichromate crystals. 

*Manufacturing process inform

*Manufacturing

*Inert ingredient information may be entitled to confidential treatment*
Table 1: Registered Active Products of Dichromic Acid 

EPA Reg. 

Number

Product Name Formulation

Type

% Active 

Ingredient

Registrant

75449-1 Sodium Bichromate 

Liquid

MUP 69 Elementis Chromium LP 

75449-3 Sodium Bichromate 

Solution 

MUP 69 Elementis Chromium LP 

Table 2. Chemical Identity 

Common Name Sodium Bichromate/ Sodium Dichromate Dihydrate 

Chemical Name Disodium Dichromium(VI) oxide 

IUPAC Chromium (VI) oxide, disodium salt 

Molecular Weight 292.

PC Code 068306

CAS Registry Number 7789-12-0

Molecular Formula Na2Cr2O7.2H2O or H2Cr2O7

Registration Review Case No. 5012

Registration Review Case Name Dichromic acid/Sodium Bichromate Liquid or Sodium 

Bichromate Solution 

Classification: Inorganic

Structure: 

Science Findings:

The Agency recently completed and posted the RED on CCA, which includes chromium in + 6 

oxidation state. The Agency’s databases for product chemistry, environmental fate and 

ecotoxicity databases are complete and a Risk Assessment (RA) has been conducted and risk 

concerns have been identified. 

4
5

Product Chemistry Summary

Table 3: Physical and Chemical Properties of Sodium Bichromate Crystals 

Guideline

No. 

Physical and Chemical Properties Value

830.1550 Product identity and composition Refer to Table 2 

830.1600 Description of materials used to produce 

the product 

CBI

830.1620 Description of production process CBI 

830.1650 Description of formulation process CBI

830.1670 Discussion of formation of impurities CBI

830.1700 Preliminary analysis CBI

830.1750 Certified limits CBI

830.1800 Enforcement analytical method No data 

830.1900 Submittal of samples CBI 

830.6302 Color Bright Crystals, ruby red liquor 1

830.6303 Physical State Crystals as Sodium Bichromate solid and Liquid as 

dichromic acid1

830.6304 Odor Odorless1

830.6313 Stability to sunlight, normal and elevated 

temperature 

Stable up to relatively high temperature and not 

stable to sunlight1

830.6314 Oxidation/Reduction: Chemical 

Incompatibility 

Mildly oxidizing agent to metals, metal ions, organic 

s and inorganics 

830.6315 Flammability 

Flash Point 

Not flammable 

830.6316 Explodability Not explosive but can thermally decompose at high 

temperatures 

830.6317 Storage Stability No data 

830.6319 Miscibility Sodium bichromate crystals are miscible 

830.6320 Corrosion Characteristic No Data 

830.6321 Dielectric breakdown voltage Not used around energized electrical equipment 

830.7000 pH 4; ( For sodium Bichromate solution in water1)

830.7050 UV/Visible absorption No Data 

830.7100 Viscosity Not applicable 

830.7200 Melting Point 356 °C and decomposes at 400 o C 

830.7220 Boiling point Not applicable 

830.7300 Density 2.35 g/ml at 25 °C1 bulk density= 77.0 lb/ft3 (loose) 

830.7370 Dissociation Constants in water Not applicable 

830.7520 Particle size Not applicable; used as liquid 

830.7550 Octanol/water partition coefficient (KOW) Not applicable; an inorganic liquid 

830.7840 Solubility in water 74 g/100 ml water at 25o C 

830-7840 Solubility in organic solvents in g/100 ml No Data 

830.7950 Vapor pressure Not applicable to crystals or liquid form of this 

chemical 

Note: 1) The data is referenced in RASSB’s Memo on: Human Health Risk assessment 

and Ecological Effects for the Reregistration Eligibility Decision (RED) Document of 

Inorganic Arsenicals and/ or Chromium Based Wood Preservatives (March 31, 2008) 
6

Environmental Fate and Transport Data Summary:

The Database on the environmental fate and transport of sodium bichromate (as chromium (VI)) 

is complete and is included in the Agency’s RED Document on Chromated Arsenicals. The 

Bibliography is included in the present document. 

The CCA RED document, published in September 2008, as well as the AD Memo on: Human 

Health Risk Assessment and Ecological Effects Assessment for the RED of Inorganic Arsenicals 

and /or Chromium-Based Wood Preservatives (RASSB’s Memo of March 31, 2008) have stated 

the following for environmental fate risk assessment of chromium and other metals of chromated 

arsenicals:

 “the leaching of copper, chromium, and arsenic into water from CCA (chromate 

arsenical) has been widely investigated by laboratory and field studies, and although 

contradictory in results and interpretations, these studies generally indicate that leaching of the 

metals is a function of: pH, salinity (fresh water, sea water, estuaries, natural and synthetic water, 

sterile, buffered water), temperature, moisture content of the treated wood, wood type and wood 

texture. Results from a number of studies indicate that most of the leaching from the treated 

wood occurs in the first few days after the applications. Most of these studies have shown the 

extent and rate of leaching is: Cu> As> Cr. Leaching of chromium is the least from treated wood 

compared to the other metals. Leaching of the metals into soils is also dependent on: pH of the 

soil, soil type, and texture of soil as well as the organic content of the soil. However, studies on 

the sorption into soils from utility poles have shown that the release of metals into 

soils/sediments from the base of the treated wood, decks, or utility poles or from the pressure 

treatment plants, do not show a high degree of downward or ground level migration. In most 

cases, migrations of metals stops at a few meters down into the soils, the metals attain 

background level concentrations.” 

 “Bioaccumulation studies showed that copper bioaccumulation in various aquatic and 

benthic organisms are greater than arsenic which in turn is greater than chromium. 

 Copper, arsenic and chromium in water exist as all of these species: hydrated species, 

hydroxy species, bound to inorganic anions, bonded to organic ligands as metal complexes or as 

organometallics. Fate and transport processes, and interactions of these species with aquatic and 

benthic organisms will vary from one type of organism to the other. Metals attain background 

level concentration in water and soils, and it is harder to ascertain the source of contamination in 

water and soils. No comprehensive ground water monitoring of these metals have been 

conducted for the leaching of these metals into water and soils from the chromate arsenicals, it 

seems no significant possibility exists for ground water contamination in areas where utility 

poles have been placed and or where decks have been built.” 

The Agency does not anticipates requiring any additional environmental fate studies for sodium 

bichromate liquid (solution) as Cr (VI): 
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Ecological Effects Data Summary:

The RED document and the Memo of March 31, 2008, also state the following observations for 

the ecological effects of chromium bichromate (as Cr (VI) or Cr (III)): 

“CCA (chromate arsenicals) can be used to treat freshwater or marine piling, bulkheads, and 

bracing timbers underneath non-residential docks, decks, and walkways. The results of the 

terrestrial risk assessment indicate that the potential for adverse acute effects to birds and 

mammals from exposure to average concentrations of arsenic or chromic acid is low. Average 

residual levels are not expected to result in chronic impacts to birds; however there is slight 

concern for chronic effects to mammals based on soil residue levels under existing CCA 

(chromate arsenicals) treated decks. Average soil concentrations are considered more likely to 

represent the exposure level for mobile receptor species such as bird and mammals than 

maximum soil concentrations. A quantitative assessment of risks to birds and mammals from 

arsenic acid or chromic acid from direct contact (oral) with CCA-treated (chromate arsenicals) 

lumber was not conducted but is considered to be minimal. The Residential decks built after 

2004 are not expected to leach arsenic or chromium. Non-residential structures build from CCA 

(chromate arsenicals)treated lumber (bracing, bulkheads, pilings, support poles) are not expected 

to pose an adverse risk to non-target birds or mammalian species due to very limited surface area 

exposure and greatly reduced surface area wood volumes (absent dimensional lumber).” 

“As and Cr are typically found in most soils and sediments in the US at background 

levels that approximate those leaching from CCA wood. Water column concentrations of these 

metals in aquatic habitats would likely be much lower than values obtained in leaching studies 

conducted in small laboratories vessel due to dispersion in water body by tidal flow and wave 

action, and the degree of portioning into biota and sediments. Risk quotients (RQ) were not 

calculated because of a high degree of variability in available data and inability to predict metals 

speciation and bioavailability in aquatic environments. The bioavailability of As and Cr is 

considered to be relatively constant regardless of CCA wood contribution due to steady 

background environmental levels. Aquatic organisms eliminate arsenic and chromium with little 

bioaccumulation. Published studies on the effects of CCA wood on aquatic organisms indicate 

that the metals released from treated wood are localized within sediments typically 10 meters 

around the treated wood. Of the three metals copper is considered most toxic to aquatic 

organisms. CCA metals are released at higher concentrations from new woods than from old 

wood, and benthic levels are higher in poorly flushed tidal areas close to the treated wood. 

Leachates from piling in well flushed tidal areas do not appear to have adverse effects on the 

benthic community. Benthic community impacts may occur from copper leachates in aquatic 

areas having high CCA wood usage that are poorly flushed (Weis et al, 1991; 1995, 1996, 2002, 

2004, Brown et al 2001).” 

“Some research indicates that making sure that wood is properly conditioned (completing 

the fixation process) prior to instillation in water, and collections of saw dust during 

construction/maintenance would help reduce the impact of CCA metals in the environment 

(Elbow et al, 2000, Elbow 2004). It is not known if the 3 metals in CCA wood are antagonistic 

or synergistic upon exposure to terrestrial or aquatic organisms. The uptake of arsenic, chromium 

and copper by plants and subsequent impacts on food chain are not well understood either.” 
8

The database on the ecological effects of sodium bichromate (as Chromium (VI)) is not 

complete and is included in the Agency RED on Chromated Arsencials (CCA) 

RED document lists the ecological effects data gaps.

The Agency does not anticipate requiring any additional ecological effects data, if the use for the 

chemical remains the same at the same application rate. 

Science Conclusions:

Sodium dichromate solution or Cr (VI) ( ) was addressed, and risks 

were identified in CCA RED, issued in 2008. The RED document lists some data gaps for the 

use pattern of this chemical. The anticipated data for eco-effects noted in this document are the 

same as were required for Cr (VI) in the CCA RED. It is concluded that the Agency will not 

require any addition data for product or eco-effects.

*Manufacturing process information may be entitled to confidential trea

*Inert ingredient information may be entitled to confidential treatment*
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