B.3 Effluent Elutriate for Water Column Toxicity

B.3 Effluent Elutriate for Water Column Toxicity

For effluent toxicity evaluations, an effluent elutriate for the suspended phase

is prepared and used as a test medium for water column toxicity tests. This

procedure is essentially the same as that for water quality evaluations, except that

the elutriate sample is handled differently following extraction. The volume of

effluent elutriate required for toxicity testing will be influenced by the number of

species to be tested, their size, and requirements for water change during the test.

A 4-L cylinder is normally used to prepare the effluent elutriate, and the resulting

supernatant volume will vary from approximately 500 to 1,000 mL, depending on

the sediment properties, settling times, and initial concentration of the slurry. It

may be necessary to composite several extracted sample volumes or to use large

diameter cylinders to obtain the total required volume.

B.3.1 Effluent elutriate apparatus

The apparatus necessary for preparation of effluent elutriate is described in

Section B.2.1. However, for biological testing the effluent elutriate is not filtered,

so only items a through d are required to prepare effluent elutriate for toxicity

testing.

Prior to use, all glassware should be thoroughly cleaned. Wash all glassware

with detergent, rinse five times with tap water, place in a clean bath for a minimum

of 4 hr, rinse five times with tap water, and then rinse five times with distilled or

deionized water.

B.3.2 Effluent elutriate procedure

The step-by-step procedure for preparing the effluent elutriate for use in

toxicity tests is outlined below.

Step 1 - Slurry preparation. Same as Section B.2.2.

Step 2 - Mixing. Same as Section B.2.2.

Step 3 - Aeration. Same as Section B.2.2.

Step 4 - Settling. Same as Section B.2.2.

Step 5 - Sample extraction. After the appropriate period of quiescent settling,

an interface will usually be evident between the supernatant water, with a low

concentration of suspended solids above, and the more concentrated settled

material below the interface. The liquid plus the material remaining in suspension

after the settling period represents the 100 percent effluent for toxicity testing.

Carefully siphon the supernatant, without disturbing the settled material, and

immediately use it for toxicity testing. The suspension should be clear enough at

the first observation time for the organisms to be visible. With some very fine-

grained dredged materials, it may be necessary to centrifuge the supernatant for a

short time to achieve this.

Effluent toxicity tests should be performed according to the guidance in

Chapter 11 of the ITM (USEPA/USACE 1998), using the effluent elutriate

prepared as described in this section as the test medium. Results should be

evaluated in light of mixing considerations, as discussed in Chapter 4 of the UTM.

Appendix B Column Settling Test and Effluent Elutriate Procedures