Use of this information is subject to copyright laws and may require the permission of the owner of the information, as described in the ECHA Legal Notice.
EC number: 223-267-7
CAS number: 3794-83-0
Endpoint waived on the basis that the study is technically unfeasible.
The essential nutrients present in the test medium will be complexed by
the phosphonates and as a result the test organisms will be exposed to
phosphonate-metal complexes. Adverse effects seen in the studies are
therefore likely to be the result of nutrient complexation rather than a
reflection of the true toxicity of the test substance.
In accordance with Section 2 of REACH Annex
XI, the study does not need to be conducted because an assessment of the
toxicity to aquatic algae and cyanobacteria is technically not possible
due to substance's complexing properties of essential nutrients present
in the test media.
It is a functional property of phosphonate
substances that they form stable complexes (ligands) with metal ions. In
algal toxicity tests essential nutrients will thus be bound to the
phosphonates according to the Ligand binding model
(PFA 2009). In algal growth medium some metals form
strongly-bound complexes and others form weakly-bound ones (PFA 2009).
The phosphonates possess multiple metal-binding capacities, and pH will
affect the number of binding sites by altering the ionisation state of
the substance. However, the phosphonate ionisation is extensive
regardless of the presence of metals (PFA 2009).
The phosphonate-metal complexes may be very
stable due to the formation of ring structures ("chelation"). This
behaviour ensures that the phosphonic acids effectively bind and hold
the metals in solution and renders them biologically less available As a
result when a trace metal is complexed, its bioavailability is likely to
be negligible (PFA 2009, SIAR 2005). However, there is no evidence of
severe toxicity from metal complexes of the ligands (PFA 2009).
In algal growth inhibition tests,
complexation of essential trace nutrients (includingFe,
Cu, Co, and Zn) by phosphonate substances can lead to inhibition
of cell reproduction and growth. Guidelines for toxicity tests with
algae typically do not describe procedures for mitigating against this
behaviour. For example the standard OECD Guideline 201, describing the
algal growth inhibition test, only specifies that the “chelator content”
should be below 1 mmol/l in order to maintain
acceptable micronutrient concentrations in the test medium (SIAR 2005).
OECD guidance on the testing of difficult
substances and mixtures (OECD, 2000) does include an annex describing
“toxicity mitigation testing with algae for chemicals which form
complexes with and/or chelate polyvalent metals”. The procedure is
designed to determine whether it is the toxicity of the substance or the
secondary effects of complexation that is responsible for any observed
inhibition of growth. It involves testing the substance in its standard
form and as its calcium salt in both standard algal growth medium and in
medium with elevated CaCO3hardness. Calcium is non-toxic to
aquatic organisms and does not therefore influence the result of the
test other than by competitively inhibiting the complexation of
nutrients (SIAR 2005). By increasing the calcium content it may be that
the nutrient metals are released from their complexed form although this
may not always apply. The outcome of the test however only determines
whether nutrient complexation is the cause of apparent toxicity and does
not determine the inherent toxicity of the test substance for the
reasons explained by the Ligand binding model (PFA 2009).
The SIAR (2005) provides two tables of
stability constants (effectively the strength of the complexation), one
from Lacour et al. (1999) and one from Gledhill and Feijtel (1992). The
Gledhill and Feijtel constants show a range of important divalent metal
ions, cited as having been obtained from Monsanto internal reports
(Owens, 1980). Values reported below are log10of the overall
stability constant (Table 1 a and b).
The complexation constant for phosphonates
with iron (III) has been estimated by TNO (1996a) to be around log K =
25 (PFA 2009).
The magnitude of the stability constants
depends on the properties of the metal and also of the ligand, in
respect of the type of bonding, the three dimensional shape of the
complexing molecule, and the number of complexing groups.
Table 1a Stability constants of
phosphonatesfrom Lacour et al. (1999)
ATMP (X )
HEDP (Y )
Table 1b Stability constants of phosphonates
from Gledhill and Feijtel (1992)
Calculation based on the known stability
constants shows that even where the OECD-recommended approach to add
additional calcium to the test media is used, the complexation
properties of these ligands mean that key nutrients would still be
complexed by the phosphonates in preference to complexation of calcium
and magnesium, and therefore the calcium complex (most representative of
the environmental species) can never be maintained in the test medium in
the presence of other key nutrient ions such as Co, Zn, Mn and Fe (PFA
2009). The resulting complexed nutrients will almost certainly not be
bioavailable to aquatic plants and this can result in inhibited algal
growth. Growth inhibition via this mechanism is a secondary
effect and does not reflect the inherent toxicity of the test substance
A study designed to ensure adequate levels
of bioavailable nutrients with either of the phosphonates would result
in the actual substance tested being a phosphonates-Fe complex. Under
conditions where iron is readily available to counteract the effects of
nutrient complexation it is unlikely that the substance will have a
negative effect on algal growth (PFA 2009). The nutrient complexing
behaviour of phosphonate substances therefore renders testing to
determine their intrinsic toxicity to algae impractical. The
available evidence suggests that toxic effects observed in the tests are
a consequence of complexation of essential nutrients and not of true
toxicity (SIAR 2005).
is a general term used to describe a molecule that bonds to a metal;
in the present case the phosphonate can form several bonds and the
resultant chelated complex can be a very stable entity. It is
possible that two molecules could bind to the individual metal, or
that one molecule could bind two metals. In dilute solution a 1:1
interaction is the most probable. To simplify discussion, the ligand
is considered to be able to form a strongly-bound complex with some
metals, and a more weakly-bound complex with others.
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.
Tällä verkkosivustolla käytetään evästeitä parhaan mahdollisen käyttäjäkokemuksen varmistamiseksi.
Welcome to the ECHA website. This site is not fully supported in Internet Explorer 7 (and earlier versions). Please upgrade your Internet Explorer to a newer version.
Do not show this message again