Regulatory Limits and Applications - Fundamental QSARs for Metal Ions - page 262

to categorization together with iT criteria. The goal was to ensure that the most
harmful substances posing an environmental risk were adequately identified, and
those that were not posing an environmental risk were also identified. The IWG
noted that persistence and bioaccumulation criteria for organic chemicals were not
suitably discriminatory for inorganic chemicals; transformation relative to stabil-
ity constants may be an appropriate substitute for persistence; biomagnification
was not an issue for inorganic chemicals; chronic toxicity was important; an acute
aquatic toxicity LC 50 or EC 50 ≤ 1 mg/L and nominal concentrations of inorganic
chemicals could be used to determine or predict aquatic toxicity provided the
nominal concentrations did not exceed water solubility values. The IWG consid-
ered the use of LSERs to estimate the solution properties of inorganic chemicals
(IWG 2001). The LSERs developed by Hickey (2005) for estimating water solu-
bility and toxicity of cations are discussed in Section 5.3 and listed in Table 5.4.
The most recent information on Environment Canada's assessment of metals was
included in a 2009 presentation to the Society of Environmental Chemistry and
Toxicology (Gauthier et al. 2009) and provided to a 2011 OECD Workshop on
Metals Specificities in Environmental Risk Assessment ( http://www.oecd.org/
dataoecd/42/13/48719530.pdf ) . The workshop report was published in January
2012 ( http://www.oecd.org/oficialdocuments/publicdisplaydocumentpdf/?cote=
ENV/JM/MONO(2012)2&docLanguage=En ) .
7.2.2 epA
To predict the health effects of metal ions, the US EPA's Office of Chemical Safety
and Pollution Prevention uses mechanism-based SAR. A metal ion's bioavailability,
as it exists in inorganic and organic metal compounds, is estimated by considering
the ion's solubility, oxidation state, dissociation, and reactivity. To predict potential
carcinogenicity, the EPA developed the OncoLogic Cancer Expert system, which has
a metals/metalloids subsystem that includes major carcinogenic metals ( http://www.
epa.gov/oppt/sf/pubs/oncologic.htm ) .
7.2.3 itc
Since it was established in 1976, the Interagency Testing Committee (ITC) is
probably the oldest government organization that has a statutory requirement to
apply SARs and QSARs to identify potentially toxic chemicals. The ITC must
apply SARs and QSARs before adding chemicals to the TSCA Section 4(e)
Priority Testing List and recommending testing of these chemicals to the US EPA
Administrator (Walker 1993). As required by TSCA, the ITC must determine:
(1) the extent to which the substance or mixture is closely related to a chemical
substance or mixture that is known to present an unreasonable risk of injury to
health or the environment, and (2) the extent to which testing of the substance
or mixture may result in the development of data upon which the effects of the
substance or mixture on health or the environment can reasonably be determined
or predicted. The ITC used QSARs to predict the sorption of antimony and related
metals and the potential toxicity of other metal ions.