Methods for Deriving Pesticide Aquatic Life Criteria - Reviews of Environmental Contamination and Toxicology - page 68

address bioavailability of organic chemicals, and the associated influence of pH
and temperature on toxicity.
In the UK, EQS may be expressed either as total or dissolved concentrations,
though expert judgment determines how it is done. The Canadian protocol provides
no specific methodology to account for water quality factors that may affect toxicity
(CCME 1999). Pawlisz et al. (1998) derived Canadian water quality guidelines for
the pyrethroid insecticide deltamethrin [( S )-cyano(3-phenoxyphenyl)methyl (1 R ,3 R )-3-
(2,2-dibromoethenyl)-2,2-dimethylcyclopropanecarboxylate], and although they
acknowledged that deltamethrin toxicity to insects is temperature-dependent,
they did not address that issue in deriving the criteria. The EC's TGD on Risk
Assessment (ECB 2003) discusses effects of pH on bioavailability and toxicity of
ionizable organic chemicals in Appendix XI. It indicates that toxicity tests ought to
be conducted at pH levels above and below the p K a for the test substance. However,
because this is rarely done (because toxicity tests must be conducted in narrowly
prescribed pH ranges) effects of pH on toxicity can only be qualitatively discussed
as part of a risk assessment.
The Australia/New Zealand guidelines acknowledge that suspended solids,
dissolved organic matter, and total organic carbon levels in water may affect bioa-
vailability, and thus toxicity, of organic compounds. However, the guideline authors
did not believe that such solid-toxicant interactions are understood well enough to
allow specific quantitative guidance for national criteria setting. Guidance is only
given for case-by-case, site-specific evaluation of bioavailability. If quantitative
relationships exist between toxicity and a parameter affecting that toxicity, such as
pH or temperature, then factors may be applied to calculate a site-specific target
value. When a generally applicable quantitative relationship is absent, the use of
direct toxicity assessment (DTA) using local waters and local conditions is recom-
mended (ANZECC and ARMCANZ 2000).
A few methodologies offer specific guidance on how to express criteria as either
total or dissolved concentrations. In Germany, if a substance has a suspended par-
ticulate matter-water partition coefficient greater than 1000 L/kg, the target is
expressed as the level in suspended particulate matter, and is calculated as follows
(Irmer 1995, adapted from LAWA 1997):

K

QT ( g / kg) Μ = QT ( g / L) Μ (2.1) •

− 6

SPM water

10 K 25(mg / L) + 1

• •

where
QT SPM = quality target in suspended particulate matter (Μg/kg);
QT water = quality target in water, total (Μg/L)
K = partition coefficient (L/kg)
25 = default concentration of suspended particulate matter (mg/L)
10 -6 = conversion factor (kg/mg)
In the Netherlands, ERLs (MPC and NC) for water are reported, both for
dissolved and total concentrations, based on a standard amount of suspended matter
(30 mg/L). The total concentration is calculated as follows (RIVM 2001):