Methods for Deriving Pesticide Aquatic Life Criteria - Reviews of Environmental Contamination and Toxicology - page 97

but few are for current-use pesticides. Other countries also derive aquatic life criteria
utilizing a variety of methodologies. As a prelude to developing a new criteria
derivation methodology, this chapter explores the current state of aquatic life criteria
derivation around the world. Rather than discussing each methodology independ-
ently, this review is organized according to critical elements that must be part of a
scientifically defensible methodology.
All of the reviewed methodologies rely on effects data to derive aquatic life
criteria. Water quality criteria may be derived from single-species toxicity data by
statistical extrapolation procedures (for adequate data sets), or by use of empirically
based AFs (for data sets of any size). Assessment factor methods are conservative
and have a low probability of underestimating risk, with a concomitant high prob-
ability of overestimating risk. Extrapolation methods may also under-, or overestimate
risk, but uncertainty is quantifiable and is reduced when larger data sets are used.
Although less common, methods are also available for criteria derivation using
multispecies toxicity data.
Environmental toxicity of chemicals is affected by several factors. Some of these
factors can be addressed in criteria derivation, and some cannot. For example,
factors such as magnitude, duration and frequency of exposure may be incorporated
into criteria, either through use of time-to-event and population models or by deri-
vation of both acute and chronic criteria that have duration and frequency compo-
nents. Aquatic species may be exposed to hydrophobic organic chemicals by
multiple routes. They may take up residues directly from water, or may be exposed
dietarily, or combinations of both. Unfortunately, to properly address such multiple
routes in criteria derivation, food web models are needed that work for chemicals
that have specific modes of action. Similarly, both bioavailability and toxicity
parameters may contribute to derivation of criteria, providing sufficient data are
available.
Ecotoxicological effects and physical-chemical data are needed for criteria deri-
vation. The quality and quantity of required data are clearly stated in existing meth-
odologies; some guidelines provide very specific data quality requirements. The level
of detail provided by guidelines varies among methodologies. Most helpful are those
that provide lists of acceptable data sources, descriptions of adequate data searches,
schemes for rating ecotoxicity data, specifications of required data types (e.g., acute
vs chronic), and instructions for data reduction. Many methodologies present proce-
dures for deriving criteria from both large and small data sets. Very small data sets
may be supplemented through the use of QSARs for selected pesticides, and through
the use of models such as ICE (for prediction of toxicity to under-tested species), and
ACE (for estimation of chronic toxicity from acute data).
The toxicity of mixtures is addressed by several existing methodologies. In some
cases, additional AFs are applied to criteria to account for exposure to mixtures,
whereas in others, concentration addition models are used to assess compliance.
Multiple stressors and bioaccumulation are also addressed in some methodologies, by
providing for application of additional safety factors. Methods are also available for
translating dietary exposure limits for humans or other fish-eating animals into water
concentrations. Options for addressing the safety of TES exist, and rely heavily on data