Todd A. Anderson

Enhanced degradation of a mixture of three herbicides in the rhizosphere of a herbicide-tolerant plant

Abstract The rhizosphere of herbicide-tolerant plants may be an important component in biologically remediating pesticide-contaminated soils. A pesticide-contaminated site at an agrochemical dealership in Iowa was characterized, and soil from the site was brought to the laboratory for degradation experiments. Three major herbicides were identified in the soils by gas chromatography-atrazine, metolachlor, and trifluralin. Although concentrations of these chemicals were as high as 2 to 3 times field application rates, herbicide-tolerant plants were found growing in the contaminated soil. Initial numbers of microorganisms were determined in rhizosphere soil from Kochia sp. and in edaphosphere (nonvegetated) soil. The rhizosphere soil had an order of magnitude higher microbial numbers (4.2 × 10 5 ) compared with the edaphosphere soil (3.5 × 10 4 .) A degradation experiment that did not incorporate vegetation was carried out by using sterile control soil, Kochia sp. rhizosphere soil, and edaphosphere soil spiked with a mixture of atrazine, metolachlor, and trifluralin at levels typical of point-source spills. Significantly (p ≤ 0.10) enchanced degradation was observed in the rhizosphere soil after 14-d incubations. Microorganisms in nonvegetated soil also showed the ability to degrade the three compounds, but not to the extent of the rhizosphere soil. Some abiotic degradation occurred for all three herbicides. The results of these preliminary experiments suggest that the rhizosphere of certain plant species may be important for facilitating microbial degradation of pesticide wastes in soils and beneficial for remediating pesticide-contaminated sites.

Enhanced Mineralization of [14C]Atrazine in Kochia scoparia Rhizospheric Soil from a Pesticide-Contaminated Site

Mineralization of atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) in soil treated with a mixture of atrazine and metolachlor (2-chloro-6-ethyl-N-(2-methoxy-1-methylethyl)acet-o-toluidide at concentrations typical of point-source contamination (50 μg g -1 each) was significantly greater (P 47% of the initial 14 C applied after 36 days) compared to literature values. These results suggest that plants such as Kochia might be managed at pesticide-contaminated sites to help facilitate microbial degradation of wastes such as atrazine in soil.

Plant-microbe treatment systems for toxic waste

Abstract There is increasing experimental evidence that microbial degradation of hazardous organic compounds can be achieved faster in the presence of plant roots than in soil or water in the absence of roots. These studies hold promise that new techniques in biotechnology can eventually be applied to plant-microbe systems for hazardous waste treatment.

The influence of soil macroinvertebrates on primary biodegradation of starch-containing polyethylene films

The primary biodegradability of polyethylene (PE) films containing different percentages of cornstarch (0–50%) and other additives (prooxidant, oxidized polyethylene) was tested using four species of earthworms (Eisenia fetida, Lumbricus terrestris, Aporectodea trapezoides, Aporectodea tuberculata), three species of cockroaches (Periplaneta americana, Blaberus sp.,Blattella germanica), termites (Reticulotermes flavipes), sowbugs (Porcellio laevis), and crickets (Acheta domesticus). These studies were conducted to elucidate the potential role of soil macroinvertebrates in degrading starch/PE biodegradable plastics. The results of the macroinvertebrate bioassays indicate that crickets, cockroaches, and sowbugs consumed starch-containing PE films most readily. In addition, the degree to which the films were attacked and consumed was directly related to the starch content of the film. Films with oxidized polyethylene and those containing prooxidant (vegetable oil and a transition metal catalyst) were also consumed. None of the four species of earthworms tested or the termites showed any activity toward the starch/polyethylene films. These results have important implications for determining the fate of novel plastic formulations which claim to be biodegradable in natural environments. Studies such as these, coupled with studies on microbial degradation, will help provide the type of information needed to assess the environmental fate of biodegradable starch/PE plastics and fill the voids in the scientific database regarding this rapidly developing field.

Degradation of hazardous organic compounds by rhizosphere microbial communities

Publisher Summary The variety of plants and chemicals studied for the evidence of microbial degradation in the rhizosphere strongly suggests that a diverse and synergistic microbial community, rather than a single species, is responsible for biotransformation of toxicants in the rhizosphere. Participation of a microbial community is implicated by (i) the extreme diversity and complexity of toxicants degraded, and (ii) the knowledge that many of these compounds are completely degraded only in the presence of interacting microbial populations (consortia). Moreover, data presented, herein, from phospholipid fatty acid analysis, 14 C acetate incorporation, and PHA analysis of micro-organisms from the rhizosphere are consistent with the participation of a microbial community in TCE degradation. Other mechanisms can also be invoked to explain how microbial transformations occur in the rhizosphere. Collectively, these factors have important implications for the successful use of vegetation to increase the participation of micro-organisms in biotransformation of toxicants at hazardous waste sites.

Synthesis of3H- polyethylene and its use for fate studies on degradable plastics

Determining the fate of xenobiotic materials in the environment can be aided by the use of radioactive isotope technology. Previous research on the degradation of polymers such as polyethylene (PE) was aided by the utilization of radiotracers. In order to study the environmental fate of degradable (PE/starch) plastics, we synthesized3H-labeled PE. Results of soil incubation studies indicate that only minimal degradation of the PE component, as indicated by the production of water-soluble metabolites, occurred during 2 years of incubation in soil. Despite the minimal degradation, the3H label did not allow for detection of the degradation products. In addition, the3H-PE was particularly useful for tracing the fate of degradable plastics after consumption by terrestrial isopods. The detection of aqueous-soluble radioactivity in isopod frass was used to indicate degradation of the plastic film.