Use of Bioaccumulation Data in the Plant Uptake Program (PUP)

ERDC TN-DOER-C22

September 2001

material and produced enough biomass in about 2 months to allow evaluation of (1) a growth

response, and (2) the bioaccumulation of metals. The lack of profound plant toxicity was consistent

with the low levels of contaminants in the dredged material. However, the relatively large variability

may have masked more subtle toxic effects. Bioaccumulation characteristics depended on both plant

and metal species. More work needs to be done to standardize plant toxicity testing (e.g., pot shape).

Most of the variability was attributed to the nonsynchronous germination of tubers and seeds. It is

to be expected that synchronization of growth, e.g., by artificial breakage of dormancy, will yield

less variability in the test results. Such a treatment may also allow for a shorter duration of the test

period, required for the production of sufficient biomass for the various analyses (currently 63 days).

It may also enable the plants to reach their reproductive stage. In the current experiment only one

C. dactylon plant flowered. The lower growth response on the test dredged material does not

necessarily point in the direction of dredged material toxicity; it may be due partly to a more severe

limitation by the low nitrogen supply compared with that of the control soil (Table 2). It is

recommended that for future testing, test and reference substrate are fertilized with nitrogen and

phosphorus to levels considered sufficient to support growth of the test species. For cases where

turf grass species common in pastures are used, fertilization levels in the order of 352 kg nitrogen

ha-1 year-1, 59.2 kg phosphorus ha-1 year-1, and 331.9 kg potassium ha-1 year-1, supplied in mineral

+ organic form, are recommended in Western Europe (Best and Jacobs 2001). The 2-L pot size used

in the current experiment allowed the production of sufficient biomass for metal analysis, i.e., > 0.5 g

DW per pot. Relatively deeper pots were more suitable for C. esculentus, and pots with a relatively

large surface area more suitable for C. dactylon. 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.

Use of Bioaccumulation Data in the Plant Uptake Program (PUP). Since 1990, a

computerized procedure for predicting plant uptake of heavy metals from contaminated freshwater

dredged material has been used at the Environmental Laboratory. This system is composed of a

database that relates the shoot concentrations of arsenic, cadmium, chromium, lead, nickel, zinc,

mercury, copper, iron, and manganese in C. esculentus, and of cadmium, lead, zinc, and copper in

various agronomic plants, to the DTPA- (diethylamine-pentaacetic acid) extractable metal concen-

trations in the substrate on which the plants were cultivated via linear regression. Effects of pH and

organic matter content of the substrate on metal bioavailability are taken into consideration by the

procedure. The DTPA-extractable metal fraction is considered to be a fair measure for the

bioavailable fraction of metals (Lindsay and Norvell 1978). The latter fraction can measure up to

5 percent of the total metal concentration. The user is required to enter the following data into the

program: the DTPA-extractable metal concentrations, pH, and organic matter content of (1) upland

or air-dried test dredged material; (2) flooded or wet test dredged material; and (3) upland or

air-dried reference dredged material. The procedure provides the user subsequently with (1) the

shoot metal concentrations expected to be exceeded in plants cultivated on the test soil compared

with that of plants cultivated on the reference soil, and (2) the actual shoot concentrations expected.

For the Monroe CDF case, the test dredged material data were entered as representing upland or

air-dried dredged material, the control soil data were entered as representing upland or air-dried

reference dredged material; no data were entered for flooded or wet test dredged material. The

DTPA-extractable fractions of lead, nickel, vanadium and zinc (mercury was not determined) were

very low in the Monroe test dredged material, i.e., maximally 1 percent (Table 2). Vanadium data