Progress 10/01/00 to 09/30/04
Outputs
The professor left the university last year.
Impacts
Knowledge of the mechanisms and pathways of pesticide degradation and their byproducts will make it possible to predict and minimize the risk of groundwater contamination, and to reclaim soils contaminated with pesticides. This in turn will enable the continue use of pesticides, such as atrazine, which is of agricultural value, but risky to the environment.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
Most of the world water systems are contaminated with the herbicide atrazine, and thus its reactivity with soil minerals is an important issue. We have studied the degradation of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) on Cryptomelane types I and II, pyrolussite, and birnessite in the aqueous phase, using a batch reactor, chromatography and spectroscopy. The reaction was studied at ambient temperature in the dark, and from pH 2.3 to pH 8.3. The order of reactivity of atrazine on the minerals used was found to be birnessite > cryptomelane II > cryptomelane I >> pyrolusite. HA, DEA and DIA were found as the primary byproducts under every condition. Five new other minor degradation products (DDA, DEHA, DIHA, ammeline and cyanuric acid) were also detected. Mn(II) evolution is a minor product. The proposed abiotic pathway for the transformation of atrazine on Mn oxides is identical with the reported biotic pathway. Thus Mn oxides, common soil
components, facilitated the efficient N-dealkylation and hydrolysis of the herbicide atrazine, possibly via a non oxidative mechanisms. N-dealkylation has been attributed strictly to a biological process in soils.
Impacts
Knowledge of the mechanisms and pathways of pesticide degradation and their byproducts will make it possible to predict and minimize the risk of groundwater contamination, and to reclaim soils contaminated with pesticides. This in turn will enable the continue use of pesticides, such as atrazine, which is of agricultural value, but risky to the environment.
Publications
- Yin-Young Shin and Marcos A. Cheney*. 2003. Abiotic Transformation of Atrazine in Aqueous Suspension of four Synthetic Manganese Oxides. Colloids and Surfaces. In review.
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Progress 01/01/02 to 12/31/02
Outputs
Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) along with its degradation products are important contaminants of world water systems with effects on aquatic life and humans. These effects are modulated by the degradation of atrazine which depends in part on its reactivity with soil minerals. We have studied the degradation reaction of atrazine on synthetic birnessite (d-MnO2) in the aqueous phase, using a batch reactor, in order to asses the effects of water, pH and d-MnO2 loading on the degradation process. The reaction was studied in the absence of light and at 25oC and pH from 2.3-8.3. The reaction rates increased with decreasing pH and increasing d-MnO2 loading. Reaction rates did not followed simple kinetics. The reaction order with respect to [H+] varied from 0.11 to 0.14. HA, DEA and DIA were found as the primary byproducts. Five other minor degradation products (DDA, DEHA, DIHA, ammeline and cyanuric acid) were also detected. The proposed abiotic
pathway for the transformation of atrazine on d-MnO2 is identical to the reported biotic pathway. Thus birnessite (d-MnO2), a common soil component, facilitated the efficient N-dealkylation and hydrolysis of the herbicide atrazine, possibly via a simultaneous reductive dissolution and exchange mechanisms. N-dealkylation has been attributed strictly to a biological process in soils.
Impacts
In this report we showed evidence that atrazine is abiotically transformed on a mineral surface to hydrolized and dealkylated products at ambient temperature. The identified conditions that facilitated the transformation were pH4 and Ionic strength of 0.01M. The impact of these results is that they proved useful in the redesign of new remediation scenarios for soils and sediments contaminated with atrazine.
Publications
- No publications reported this period
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Progress 01/01/01 to 12/31/01
Outputs
A novel approach to determining the degradation of atrazine on Mn oxides has been eveloped in our laboratory using a mechanical reaction process of very light wrist grinding of the herbicide with the Mn oxide to initiate a reaction between the herbicide and the Mn oxide surface. Such an approach differs greatly from traditional tribochemical techniques in that the grinding is gentler without alteration of the mineral oxide structure. Mechanochemical procedures provide a means of initiating a reaction of atrazine with the minerals without interference from organic solvents typically used to facilitate contact of the compound with the mineral surfaces. Calorespirometry (standard term) on the other hand facilitates the measure of the heat and gas produced as atrazine degrades on the surface of the mineral. Mechanochemical procedures makes it possible to; a) compare the DSC data of the net heat evolved produced by the interaction of just atrazine with the Mn oxides, b)
check for simple first order kinetic relationships, and c) couple DSC data with spectroscopic techniques. Another benefit of this technique is that it is a rapid method that can be used as a screening tool for the determination of the abiotic degradation of other potential carcinogens on mineral surfaces. The reaction of AT with CR-II produced the highest heat of degradation of the oxides studied. The heat of degradation produced by the reaction of AT with BIRN was substantially less than CR-II, but much higher than the other three oxides. Atrazine interactions with ALUM, CR-I, and PYRO was statistically indistinguishable from each other and produced considerably less heat than BIRN and CR-II at 30oC. In fact, the amount of heat of degradation produced by ALUM, CR-I and PYRO approached the detectability of the instrument and therefore, it was difficult to delineate instrument noise from heat evolution due to AT degradation. Although not shown, similar results to those presented were
also obtained when a higher mass ratio (93 mmol AT g-1 oxide) was used. The data on the kinetics of the disappearance of AT on BIRN and CR-II from the HPLC analysis showed that there is a correlation between these data and the data from the kinetics of the heat evolved obtained using DSC. The greatest disappearance of AT (80%) observed, came from the interaction with the mineral that produced the greatest amount of hear, CR-II. Similarly, the mineral BIRN produced less heat then CR-II and, thus, degraded less (about 50%) of the added AT. For the other minerals examined, CR-I, PYRO and ALUM, there was very little heat produced and, consequently, little AT degraded over time. Of the three minerals studied, there was a significant decrease in the AT recovered from pyro only after 24h incubation, and although there was no significant decrease in AT over time for CR-I, there appeared to be a trend of decreasing AT after 8 h incubation but this was less than pyrolusite.
Impacts
These results are are useful not only in the design of remediation scenarios, but also to the calibration of insitu microbiological studies, which heretofore have considered abiotic N-dealkylation to be an insignificant pathway of atrazine degradation in soils.
Publications
- Mechanochemical degradation of atrazine adsorbed on four synthetic manganese oxides. 2000. Colloids and Surfaces, 172:113-123.
- Dealkylation and Hydrolysis of atrazine by manganese oxides. 2002. In preparation.
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