Elizabeth A. Shaffer, M.S., Environmental Scientist, Malcolm Pirnie Inc., 1300 E 8th Ave, Tampa, FL 33607, Tel: 813-242-7236, Fax: 813-248-8085, Email: eshaffer@pirnie.com
Gerald K. Sims, Ph.D., Research Leader, USDA Agricultural Research Service, 1102 S. Goodwin Ave , Urbana , IL 61801 , Tel: 217-333-6099, Fax: 217-333-5251, Email:  gksims@uiuc.edu

Conventional soil tests, culture-based microbial methods, and the novel method of 15N-DNA stable isotope probing (SIP) were employed to illustrate atrazine biodegradation as related to the physiochemical properties of a Cisne soil from a major atrazine spill site.  This soil appeared to exhibit enhanced atrazine degradation when compared to five reference soils in our laboratory and previous reports in the literature, and therefore was a good candidate for natural attenuation. Mineralization kinetics in the Cisne soil underestimated the rate of atrazine dissipation demonstrated by the accumulation of several metabolites.  The soil showed high ambient concentrations of NO3-, either from excess fertilization or mineralization of atrazine N; however the presence of NO3- did not suppress atrazine degradation.  Instead, natural attenuation of atrazine appeared to be primarily limited by incomplete distribution of the compound through the unsaturated soil matrix.  Direct plating experiments from the Cisne soil isolated an atrazine-degrading microorganism, ES-1.  Analysis of the 16S rRNA gene sequences from the isolate confirmed that ES-1 is closely related (99%) to Arthrobacter sp, a genus containing other known atrazine-degrading isolates.  In pure culture, the isolate rapidly converted atrazine to cyanuric acid.  Accumulation of this product was consistent with metabolites accumulated in the Cisne soil, suggesting that isolate ES-1 was a critical element in the microbial community influencing in-situ remediation of atrazine.  To verify this theory, 15N- SIP experiments were conducted using 15N-ethylamino-atrazine.  The results of these experiments failed to establish a causal relationship between in-situ atrazine-degradation and ES-1 enrichment; however these inconclusive results are likely due to isotopic dilution.  Further experiments using 13C-ethyl/isoproylamino-atrazine (to increase the sensitivity of the SIP technique) may yet verify a link between ES-1 and the enhanced natural attenuation exhibited in the Cisne soil. 

Removal of Chlorophenoxy Acid Pesticides Using Ionizing Radiation for Remediation of Waters and Wastes

Marek Trojanowicz, Prof. dr., Department of Chemistry, Warsaw University, Pasteura 1, 02-093 Warsaw, Poland, Tel: +48-22-822 3532, Email: trojan@chem.uw.edu.pl
Anna Bojanowska-Czajka, Institute of Nuclear Chemistry and Technology, Dorodna 16, 03-195 Warsaw , Poland . Tel: +48-22-504 1030, Email: anna.bojanowska@ichtj.waw.pl
Przemysław Drzewicz, Ph.D., Institute of Nuclear Chemistry and Technology, Dorodna 16, 03-195 Warsaw, Poland, Tel: +48-22-504 1030, Email: drzewicz@ichtj.waw.pl
Henrietta Nichipor, Ph.D., Institute of Radiation Physics and Chemical Problems, Academy of Sciences of Republic of Belaus, Minsk-Sosny, Belarus, Tel: +375-172-832 704,  Email: roginets@sosny.bas-net.by
Grzegorz Nałęcz-Jawecki, Ph.D., Department of Environmental Health Sciences, Warsaw University of Medicine, Banacha 1, 02-097 Warsaw, Poland, Tel: +48-22-572 0738, Email: grzes@farm.amwaw.edu.pl
Józef Sawicki, Prof. Dr, Department of Environmental Health Sciences, Warsaw University of Medicine, Banacha 1, 02-097 Warsaw, Poland, Tel: +48-22-572 0738, Email: zbenv@farm.am.edu.pl

Chlorophenoxy acid pesticides are world-wide used herbicides and their residues in natural waters as well as their numerous natural metabolites are harmful for various organisms, including humans. Although they do not belong strictly to persistent organic pollutants, as their half-life time in environmental media is limited to several weeks, a much larger toxicity and stability is exhibited by the products of their metabolism in environment – mostly chlorophenols.

For removal of these compounds in remediation of natural waters, besides numerous other chemical and physical processes, increasing attention is paid to advanced oxidation processes employing free radicals, e.g. photolysis, photocatalysis, Fenton processes and the use of ionizing radiation (electron beam  and  radiation). In this last case, in aqueous solutions, reactions of decomposition of target pollutant take place with free radicals very efficiently generated in the process of water radiolysis.

Our studies reported herein concerned removal from waters and industrial wastes several herbicides, including 2,4-dichlorophenoxyacetic acid (2,4-D), 3,6-dichloro-2-methoxybenzoic acid (dicamba) and 4-chloro-2-methylphenoxyacetic acid (MCPA), identification of products of their decomposition, and monitoring of toxicity changes of irradiated solutions. The irradiation was carried out using electron beam or gamma radiation from ⁶⁰Co source. The yield of radiolytic decomposition was also examined with simultaneous ozonation of irradiated solutions or in the presence of hydrogen peroxide in solution as chemical enhancement means for radiolytic processes. The mechanism of radical decomposition was examined, and effect of numerous experimental parameter of processes (radiation does, dose-rate, initial concentration of pollutant, pH, and presence of different scavengers of radiation) was studied. The experimental data were verified with the kinetic modeling based on known or approximated rate constants for radical reactions.

Depending on conditions of irradiation and initial concentration, the complete decomposition of target herbicides and their toxic products requires radiation doses from fraction of kGy to several kGy, hence such a processes can be competitive in practical applications to other more common processes employed for remediation of waters and wastes.  

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