1a. Objectives (from AD-416):
Cooperate in testing methods to reduce soil DDx (DDT, DDE, DDD and other breakdown products of DDT) and dieldrin by earthworms to see if addition of organic matter to contaminated soils, or growing crops on contaminated soils can reduce DDT and dieldrin uptake by earthworms and thus lower risk and raise clean-up cut-off limits and greatly reduce soil removal/replacement costs while protecting the environment.
1b. Approach (from AD-416):
1) Collect representative soils from DDx and dieldrin contaminated areas of the North Farm at BARC; 2) Identify earthworm species which occur in these soils; 3) Test the effect of organic matter amendments (manure compost; biosolids compost; biochar) on bioaccumulation of DDx by common soil earthworms; 4) Test the effect of growing crops in the earthworm bioaccumulation assay soil on the bioaccumulation of DDx and dieldrin by earthworms; 5) Examine the effect of treatments on nutrient and trace element accumulation by the earthworms; 6) Examine the effect of the soil amendments on changes in soil microflora which may affect earthworm activities; and 7) DDx and dieldrin and other halogenated hydrocarbon analyses to be provided by cooperators.
3. Progress Report:
The goal of this cooperative project is to test the reduction in bioavailability of soil dichlorodiphenyltrichloroethane (DDT) to earthworms using composts and plants. Old orchards and other land may contain excessive residues of DDT and dichlorodiphenyldichloroethane (DDE) from historic pesticide sprays. Because earthworms bioaccumulate DDE from soils, and some birds and small mammals ingest large amounts of earthworms, the most limiting risk pathway for soil DDE is earthworm bioaccumulation to harm wildlife. Old orchard soils at BARC contain sufficient DDE to require removal or other remediation at great expense, and an in situ remediation test was funded. Soil samples were collected from the field with about 10 mg DDE per kg dry soil for a pot experiments which tested whether incorporation of composted manure, composted biosolids, biochar, etc., could reduce DDE bioaccumulation by earthworms by increasing the strength of adsorption of DDE by the amended soils, and to better understand the mechanism of remediation. In addition, one report also showed that growing plants on a soil with DDE contamination could significantly reduce earthworm DDE bioaccumulation, so both unplanted and orchardgrass and perennial ryegrass planted pots were studied. Most earthworm testing has been conducted using bare soils to limit worm escape from the test pot but may have over-estimated risk. In the pot test, all amendments supported strong growth of orchardgrass, and Lumbricus terrestris earthworms lived well in the amended soils except the limed undigested biosolids. In order to test with this common soil earthworm species, the pots of soil were maintained at cooler temperatures, 10C night and 15C day. A simple method was worked out to keep the earthworms in the pots with growing plants and validated by testing. Methods to conduct the experiment have been worked out, soil mixtures with amendments prepared and incubated for 30 days, and planted for orchardgrass growth for 45 days before the earthworms will be introduced to the experiment. Methods to analyze soil and earthworm DDE levels were also worked out with modern quality assurance methods. After harvesting the earthworms, they were washed and prepared for analysis of DDX residues, metals, and microbes. The analysis revealed that all of the organic amendments significantly reduced DDX residues in the earthworms by 50% or greater, indicating that this remediation treatment could provide strong savings. Analysis of metals and nutrients in the plants and earthworms revealed no risks to consumers of the crops or earthworms. Based on these findings a field test was funded. Because of the seasonality of earthworms in the surface soils (not present during hot dry periods), and because of the areal variation in soil DDX levels at the field site, the experiment design was carefully reviewed with BARC statisticians. By using the ratio of worm DDX to soil DDX before and after treatment for each individual plot as a measure of bioavailability, treatment effects should be detectable. The hot spring in Beltsville prevented installation of the experiment in June, so sampling and field amendment will begin in September with follow up sampling during May, 2013.