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EC number: 231-901-9
CAS number: 7778-39-4
There are no existing studies
investigating the environmental fate of arsenic acid (AA), however there
is an extensive array of published information on the environmental fate
of arsenic (As). The published data on As has been previously compiled
and reviewed in several published reviews. The technical dossier of AA
compiles some of these reviews and recommendations. The relevant
reviews/publications are listed here under:
-ATSDR, 2007, Toxicological profile
for Arsenic, In: Agency for toxic substances and disease registry,
Division of toxicology and environmental medicine/applied toxicology
branch, 297, Atlanta, USA.
-Lepper P, Sorokin N, Maycock D, Crane
M, Atkinson C, Hope S-J, Comber, S, 2007, Proposed EQS for Water
Framework Directive Annex VIII substances: arsenic (total dissolved),
Published by UK Environment Agency, Science report: SC040038/SR3, 101 p.
-United States Environmental
Protection Agency (US EPA), 2004, Volume II - Geochemistry and Available
Kd Values for Selected Inorganic Contaminants, In: Understanding
Variation in Partition Coefficient, Kd, Values, Office of Air and
Radiation, EPA 402-R-04-002C, July 2004, 188p.
-United States Environmental
Protection Agency (US EPA), 2004, Technical Summary of Information
Available on the Bioaccumulation of Arsenic in Aquatic Organisms, Office
of Science and Technology, Office of Water, EPA-822-R-03-032.
-WHO, 2001, Arsenic and arsenic
compounds, Environmental Health Criteria 224, United Nations Environment
Programme, International Labour Organisation, World Health Organization,
International Programme on Chemical Safety.
The environmental fate of arsenic
species and bioavailability
are influenced by environmental factors such as redox conditions, pH,
and presence of ligands and biotransformations reactions. Irrespective
of the species that As is introduced into the environment, the actual
species present vary according to various reversible equilibria which
are driven according to the local conditions. In addition, arsenic is a
naturally occurring chemical which concentration varies greatly
according to region.
Concentrations of As in the
The FOREGS Database provides the
median concentrations of As in the environment: 6.02 mg/kg (subsoil),
7.03 (topsoil), 0.63 µg/L (water, filtered < 0.45 µm), 6 mg/kg (stream
sediment, floodplain sediment). The FOREGS Data provide a present
overview of As in the environment. Since they do not provide a
historical variation, these concentrations cannot be considered as true
natural background concentration. Furthermore, those concentrations
include several fractions as bioavailable and non bioavailable ones.
in contact with water
is a thermodynamically stable form of As. In water and under aerobic
conditions, arsenic acid exists as a mixture of arsenate ions based on
<-> H+ H2AsO4- pKa1=2.22
<-> H+ +
<-> H+ +
the influence of pH alone, the protonated form H3AsO4 is the dominant
form of arsenate at very low pH. Under most environmental conditions (pH
5 - 9), H2AsO4- and HAsO42- are the dominant forms of arsenate ions.
Stability in contact with light
Photolysis has no influence on the
behaviour and transformation of arsenate in waters.
Modes of biotransformation involve
redox transformation between arsenite and arsenate, reduction and
methylation of As, biosynthesis of organoarsenic compounds. The
biomethylation and bioreduction are considered the most important
pathways. Such biotransformation of As species occurs in the soil, in
sediments, in plants and animals, and in zones of biological activity in
Under aerobic conditions, the mixed
microbial cultures of lake sediments were able to reduce arsenate (the
predominant from of arsenic in water) to arsenite and a variety of
methylated arsenicals, and also to oxidise arsenite to
arsenate. Under anaerobic conditions, however, only reduction occurs.
Partitioning and distribution
Partitioning and distribution of
arsenic will depend upon the oxidation state of arsenic and the
interactions with the ligands present in the system. All forms of
arsenic are adsorbed to most types of soil and sediment to a greater or
a lesser degree. The following discussion aims to give an overview of
the main current understandings.
Partitioning in water/sediment
In water, As is mainly found in the
particulate phase and it is suggested that sorption/desorption and
co-precipitation processes are responsible of the regulation of the
dissolved concentrations of As. Precipitation of As may occur with
calcium, sulphur, iron, aluminium and barium unless these reactions are
low. Adsorption is believed to be an important removal process of As from
solution with 80% being removed on entering estuarine waters.
In aerobic conditions, As cycle in
sediment is dominated by inorganic forms. Both adsorption of As on
iron-rich oxides on the surface of sediments and incorporation of As
into sediments by co-precipitation with hydrous iron oxides are factors
controlling mobilisation of As in sediment. Aluminium compounds and
organic matter have also been implicated in adsorption of As to
sediments. The amount of arsenate adsorbed increases as the pH of the
system increases. The major As species leached is arsenate which is
found to be related to total iron and free iron oxides in the sediments.
Finally, not all the adsorbed As is non bioavailable and it is expected
that a fraction may be bioavailable to benthic organisms.
Partitioning in soil system
As compounds tend to adsorb to soils
to a greater or a lesser degree being stronger adsorbed in clay soil
than in sandy soil. The main factors that affect As adsorption to soil
include: Fe and Al soil content, OC content, soil clay content, soil pH,
phosphate concentrations and concentrations of other cations. Among
them, the most influential factor is the iron content of the soil.
Under oxidizing conditions, leached As
from soil is transported over only short distance. Therefore, leaching
does not appear to be a significant route of As loss from soil. In
agricultural soils, As is largely immobile and it tends to concentrate
and remain in upper soil layers.
Under reducing conditions, arsenite
compounds are dominant forms in soil but As(-3) and As(0) can also be
present. As would be present as H2AsO4 - in well-drained and acids soil
or as HAsO42 - in well-drained and alkaline soils. In the porewater of
aerobic soils, arsenate is the dominant form of As. The amount of As
sorbed from solution increases as the free iron oxide, magnesium oxide,
aluminium oxide or clay content of the soil increases.
As is emitted to atmosphere as dust
and fine particles which can be transported by winds and air prior to
deposition to terrestrial compartment.
As bioaccumulation depends on various
factors such as the compartment considered (e.g. freshwater, seawater),
the exposure concentration and the route of exposure. The range of BCF
values for aquatic organisms suggest that As is accumulated to a greater
or a lesser degree with fish BCF being generally below 2000. As does not appear
to biomagnify between trophic levels.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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