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 show 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 to locate soil with levels of DDE (10 mg/kg dry soil) which would make a more useful test of DDE risk remediation using organic amendments and plants. Experiments were planned to test 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. Most earthworm testing has been conducted using bare soils to limit worm escape from the test pot but may have over-estimated risk. During FY11, methods to conduct the study were tested. All amendments supported strong growth of orchardgrass, and Lumbricus terrestris earthworms lived well in the amended soils. In order to test with this common soil earthworm species rather than the manure worm commonly used in previous DDE bioaccumulation testing, the pots of soil must be 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. Monitoring was accomplished by project staff meetings, and project leader meetings with the Safety Occupational Health Environmental Service staff. Meeting with the US-Environmental Protection Agency project managers has allowed effective planning and communication about progress in the work.