5.1 The USEPA's policy for whole-effluent monitoring stresses, an integrated approach to toxicity testing ( 1 , 5 ) tests and other measures of toxicity, should be systematically employed and should be related to certain aquatic-system factors, such as the type of habitats available (benthic and water column), flow regime, and physicochemical quality of the site water and sediment. The determination of toxicity is generally accomplished with a few surrogate species for four major reasons: a regulatory agency can compare test results between sites and over time in order to help prioritize enforcement efforts, tests using these species are relatively inexpensive since the organisms can be cultured year-round under laboratory conditions, the reliability of test methods utilizing surrogate species is better established than for other species, and surrogate species are better integrated into toxicity identification evaluations than other species. For regulatory purposes, under the National Pollution Discharge Elimination System (NPDES), USEPA considers it unnecessary to conduct whole effluent toxicity tests with resident or indigenous species ( 6 ) . An alternate testing procedure protocol is provided by USEPA for validating toxicity methods using species not already approved ( 6 , 7 ) . In systems where surrogate species are not found, erroneous predictions might be obtained of environmental impact or water and sediment quality impairment based on toxicity tests using surrogate species ( 8 ) .

5.2 This guide is intended to assist researchers and managers in selecting appropriate resident species for site-specific toxicity assessments. This guide could be used to select a resident species for use in predicting the potential toxic effects of a substance in certain types of aquatic environments. Another use might be for selecting a number of indigenous species from the aquatic community, that when tested, might indicate potential toxic effects of the test substance or material on the ecological integrity of that community. Selection of a suitable test species is very important because species might respond quite differently to toxic compounds ( 9 ) . Species suggested as test organisms by regulatory agencies might not occur in the receiving waters of interest and their sensitivity to a toxic substance might not be representative of the sensitivity exhibited by resident species. Since aquatic ecosystem structure and function is often determined by a few key species ( 10 , 11 , 12 , 13 ) , toxicological tests with these resident species might be very important.

5.3 This guide can be used in the selection of representative test species for certain site-specific assessments, such as the Resident-Species Criteria Modification Procedure ( 1 ) , the Recalculation Procedure ( 14 ) , and ecological risk assessment studies.

5.4 This guide can be used as a general framework for researchers who desire to develop or modify existing toxicity test methods for previously untested species.

5.5 Researchers in countries other than the United States and Canada might obtain useful information from this guide regarding potential test species or test methods for sites of local interest.

1.1 This guide along with Guide E1192 and guidance from the U.S. Environmental Protection Agency ( 1 , 2 ) ² covers the use of resident species in toxicity testing, particularly if site-specific information is desired. For example, in those systems where particular species are considered to be economically or aesthetically important, it might be more appropriate to utilize resident species for testing ( 3 ) . For this reason, the USEPA allows development of site-specific chemical standards, using resident species, in order to reflect local conditions ( 1 ) . This guide is designed to guide the selection of resident species for use as test organisms in aquatic and sediment toxicity tests. It presupposes that the user is familiar with the taxonomy of aquatic and benthic species and has some field experience.

1.2 Because toxicological information is often limited for many aquatic species, it is assumed that the majority of testing applications will be acute tests. Therefore, much of the guidance presented in this guide pertaining to the species selection process is applicable when acute toxicity testing is the desired goal. However, the principles discussed in this guide pertain to chronic toxicity test applications as well, although it should be clearly understood that such testing requires substantially greater effort, time, and resources than acute testing.

1.3 The procedures for selecting resident species in toxicity testing are necessarily general at this time because information is often lacking for specific taxa or groups of taxa. This guide attempts to give specific information when appropriate.

1.4 This guide is not intended to be inclusive. References listed provide a starting point from which to approach the literature. This guide deals solely with aquatic toxicity test situations. Terrestrial, arboreal, or atmospheric species are not considered in this guide.

1.5 This guide is arranged as follows:

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. All safety precautions and health-related practices are the responsibility of the user. Specific safety practices are suggested in Section 8 .