Methods for Deriving Pesticide Aquatic Life Criteria - Reviews of Environmental Contamination and Toxicology - page 44

6.4.1 Physical-Chemical Data

The Netherlands methodology (RIVM 2001) requires collection of specific physical-
chemical data. For each substance the following information is required: IUPAC
name (International Union of Pure and Applied Chemistry), CAS number
(Chemical Abstract Service), EINECS number (European Inventory of Existing
Commercial Substances), structural formula (including diagram), empirical
formula, molar mass, octanol-water partition coefficient ( K ow ), water solubility,
melting point, vapor pressure, Henry's law constant ( K H ), acid dissociation
constant(s) (p K a ), solid-water partition coefficients ( K p ) and degradation informa-
tion (i.e., hydrolysis, photolysis, and biodegradation). The methodology includes
procedures for calculation of a dimensionless K H , if experimentally derived
constants are not available.
Physical-chemical data and environmental fate information are used in the
Dutch methodology (RIVM 2001) in several ways. For example, if a substance has
a t 1/2 of less than 4 hr, then the criterion is derived for stable degradation products,
rather than for the parent compound. Moreover, if data are lacking for a particular
environmental compartment, partitioning data can be used to estimate concentra-
tions in another compartment. Water solubility data are used to judge the reliability
of aquatic toxicity studies, but may also be used together with vapor pressure and
molecular weight data to calculate a Henry's Law constant. Suspended matter-
water partition coefficients are used to calculate total toxicant concentrations in
water, based on the dissolved concentrations. K ow s are used to estimate aquatic
toxicity using QSARs, and for estimation of BCF values. K ow values may also be
used to determine the potential risk of secondary poisoning, and for estimating organic
carbon-water partition coefficients. Finally, partitioning constants are used for
harmonization procedures.
The OECD methodology (1995) recommends that the following information be
obtained for each compound: chemical structure, molecular weight, melting point,
water solubility, K ow , sediment-water partition coefficient ( K sw ), and p K a . K ow may
be used to estimate water solubility, or to derive QSAR estimates of toxicity. Van
Leeuwen et al. (1992) showed that by using QSAR estimates, it is possible to
develop a relationship between K ow and the hazardous concentration for nonpolar
narcotic chemicals; thus, it is possible to derive MTCs, and their associated confi-
dence limits, directly from K ow values.
In the Australia/New Zealand guidelines (ANZECC and ARMCANZ 2000), K ow
and BCF values are used to estimate bioaccumulative potential. The BCF also may
be used to calculate water concentrations that will protect fish-eating predators
from bioaccumulative chemicals. To derive low reliability target values for narcotic
chemicals (when little-to-no toxicity data are available), the Australia/New Zealand
guidelines utilize K ow values to derive (QSAR) estimates of toxicity. Beyond K ow
and BCF values, the Australia/New Zealand guidelines provide no specific require-
ments for collection and reporting of physical-chemical data.
For compounds with partition coefficients greater than 1000 L/kg, the German
derivation methodology utilizes the solid-water partition coefficient to express