Methods for Deriving Pesticide Aquatic Life Criteria - Reviews of Environmental Contamination and Toxicology - page 48

kinds of (acute and chronic) toxicity test data needed is important, and should be
considered in the context of what criteria may be derived from them.
The Netherlands guidelines define acute exposure as lasting a relatively short
period; chronic exposures continue through a complete or partial life cycle. Whether
an exposure is acute or chronic depends on the physiology and life-cycle character-
istics of the species (RIVM 2001). The Dutch guidelines further clarify that acute
tests generally last less than 4 d, and results are reported as an LC 50 or EC 50 .
Chronic tests generally last more than 4 d, and results are reported as an NOEC.
However, for single-celled organisms (e.g., algae or bacteria), chronic NOECs
may be obtained in less than 4 d. In addition, the guidelines are very specific in
stating the following: for algae, bacteria, or protozoa, tests of 3-4 d are defined as
chronic; for Crustacea and Insecta, tests of 48 or 96 hr are acute; and, for Pisces,
Mollusca, and Amphibia, tests of 96 hr are acute, while early life stage tests and
28 d growth tests are chronic (RIVM 2001). Only chronic NOECs are used for
refined effect assessments; acute data are used with application of AFs in
preliminary effect assessments.
Chronic toxicity data are preferred by OECD guidelines (1995), with acceptable
data presented either as NOECs or MATCs. However, acute data are also used, but
with appropriate application of AFs (i.e., ACRs). The guidelines caution that
substances with low water solubility, or log K ow > 5, a 96 hr acute exposure in
water, may not be long enough to see effects, and, therefore, only chronic data may
be appropriately used for such substances. Although not explicit, it appears that this
methodology considers exposures longer than 96 hr to be chronic. By this methodology,
NOECs may be estimated by conversion from LOEC values (e.g., NOEC =
LOEC/2), but only if the LOEC corresponds to a concentration causing an effect
more than 20%.
The Australia/New Zealand guidelines (ANZECC and ARMCANZ 2000) contain
the general description that acute tests are shorter than chronic tests. They proceed to
say that in applying the methodology, data from tests longer that 96 hr are considered
to be chronic, except for tests with single-celled organisms (for which 96 hr tests are
considered chronic). Chronic data are used to derive high reliability target values,
while acute data are used to derive moderate reliability target values. NOEC and LC 50
data are both used in statistical extrapolations, but the resulting hazardous concentra-
tion determined with LC 50 s is multiplied by an ACR.
The USEPA methodology (1985) utilizes acute LC 50 or EC 50 data to derive the
FAV. The EC 50 data, in this case, are based on the percentage killed plus the percent-
age immobilized. EC 50 data, relating to less severe effects, are not used to calculate
the FAV. Acute toxicity data are described as those from 48-h tests with daphnids
and other cladocerans, from 96 hr tests with embryos and larvae of various shellfish
species, or from 96 hr tests with older life stages of shellfish species. Tests with sin-
gle-celled organisms, of any duration, are not considered to be acute tests.
Expanding on this point, the Great Lakes guidance (USEPA 2003a) states that any
test that reports results giving the number of young produced (e.g., protozoan tests)
are not considered acute, even if the test duration is less than 96 hr. The USEPA
guidance (USEPA 1985) considers the following types of tests to be chronic: