Toxicity

ERDC TN-DOER-C22

September 2001

inoculated with 8-10 E. crypticus specimens from a mass culture, using a dissecting needle. Mass

cultures were obtained from R. Kupperman (U.S. Army Aberdeen Proving Ground, MD). Sub-

strates tested were (1) Monroe CDF dredged material, (2) invertebrate control soil, and (3) standard

Organization for Economic Cooperation and Development artificial soil (10 percent finely ground

peat moss, 20 percent kaoline clay, 70 percent silica sand, on an oven-dry weight basis (ASTM

1998). All petri dishes were moistened regularly with demineralized water and the animals were

fed and incubated at 16 oC for 21 days. All treatments generated live worms at the end of the

incubation period, but counting of individual worms and separation of worms and substrate proved

extremely time-consuming. It is, therefore, concluded that prior to further testing a culture method

has to be selected that allows better separation of substrate and test organism.

Toxicity.

Experiment I. ANOVA of the complete data set indicated that the effect of substrate on adult

biomass was not statistically significant, but its effect on reproductive potential was significant

(P < 0.001). The effect of test duration was significant on both adult biomass and reproductive

potential. This indicates that reproductive potential is a more sensitive parameter for toxicological

effects than adult biomass (as found also by Robidoux et al. 2000), and that the test results depend

on test duration. The data are graphically represented in Figure 4.

Experiment II. The results of this experiment largely confirmed those of Experiment I, but the

variability in growth response was lower (data not shown).

Bioaccumulation.

Experiment I. Bioaccumulation of zinc occurred in animals cultivated on test dredged material as

well as on control soil, and effects of substrate on the animal zinc concentrations were not significant.

Bioaccumulation of mercury became apparent after 42 days, and the effect of substrate on animal

mercury concentration was significant (Figure 4).

Summary Invertebrate Test Results. E. fetida is a suitable test organism for the inorganic

COCs in dredged material, in that the adult specimens survived on dredged material and produced

enough biomass and cocoons in about one month to allow the evaluation of a growth response,

reproductive potential, and the bioaccumulation of several metals, i.e., zinc and mercury. Repro-

ductive potential proved to be a more sensitive parameter for toxicity than biomass. As discussed

earlier for the plant tests, the relatively large variability may have masked more subtle toxic effects.

Variability was substantially less in the experiment, started with juvenile worms. It is to be expected

that synchronization of growth will yield less variability in the test results. A test duration of 28

days started with 20 adult specimens in 1-kg cylinders proved long enough to allow sufficient

biomass formation for metal analysis, i.e., > 0.5 g DW per cylinder. Statistical exploration of the

data set indicated that each test, composed by four dilutions of the test dredged material, including

the reference, with only one harvest date, should include > 5 replicates to generate statistically

significant results. A potential drawback affecting the use of E. fetida is that the organism requires

the presence of a relatively well-developed plant litter layer for its persistence. E. crypticus requires

a less organic habitat, and could serve as a test organism for dredged materials with very low organic