H.2.4 DTPA extraction procedure

tall 50-mL Pyrex glass beakers. Twenty (20) mL of distilled water is added to

each beaker and the mixture is stirred with a polyethylene rod until all particles

are saturated. The mixture is stirred with a magnetic stirrer for 1 min every

15 min for 45 min. After 45 min, the pH electrode is placed into the solution

above the surface of the sediment and the pH is read on a pH meter (Folsom,

Lee, and Bates 1981).

Organic matter. Organic matter (OM) is determined by weight loss on

ignition at 550 οC on air-dried (AD) and air-dried + washed (ADW) sediment.

Procedure No. 209E (American Public Health Association 1976) is used for this

test. A 5-g (ODW) subsample is weighed to the nearest 0.001 g and dried at

105 + E2 C until constant weight (48 hr). Five (5) grams of the oven-dried

sediment is weighed to the nearest 0.001 g and combusted at 550 + 5 EC for

24 hr in a muffle furnace. The sample is allowed to cool to room temperature in

a moisture desiccator and weighed to the nearest 0.001 g. Weight loss on

ignition is calculated and reported as percent OM using the following formula:

((oven dry weight - combusted weight) / oven dry weight) x 100 = %

organic matter

H.2.4 DTPA extraction procedure

Wetland condition. A 50.0-g (ODW to the nearest 0.001 g) subsample of

the wet, unoxidized sediment is weighed into a 500-mL polycarbonate centrifuge

bottle and centrifuged at 4 EC and 9,500 rpm for 30 min. The supernatant is

decanted; pH is determined on the supernatant and represents the saturated

sediment pH. To the sediment remaining in the centrifuge bottle is added

250 mL of 0.005 M DTPA + 0.01 M calcium chloride + 0.1 M triethanolamine

solution (Lee et. al. 1978) buffered at pH 7.3. The bottle is sealed, placed on a

mechanical shaker and centrifuged as before. The supernatant is carefully

poured into a polyethylene bottled and analyzed for metals according to the

methods described in USEPA (1986).

Terrestrial condition. The procedure for the terrestrial condition is the

same as that for the wetland condition except that air-dried sediment is used.

After extractions are complete, samples are stored in polyethylene bottles at 4 οC

until chemical analysis. In addition, an extracting solution blank is also analyzed

and resulting data are subtracted from the test sediment data prior to performing

the following calculation for both the wetland and terrestrial evaluation:

DTPA metal Conc. = (DTPA extracting solution metal conc.) x

(extracting solution vol.) / g of ODW sediment

H.2.5 Prediction of plant bioaccumulation and comparison to

reference

The results of the DTPA extractions along with chemical and physical

sediment characteristics described above are entered into the PUP program as

Appendix H Plant Bioaccumulation Procedures