Rate Of Atrazine Mineralization Research Articles

Inoculation of an atrazine-degrading strain, Chelatobacter heintzii Cit1, in four different soils: effects of different inoculum densities

The possibility to improve atrazine degradation in soils by bioaugmentation was studied. The atrazine-mineralizing strain, Chelatobacter heintzii Cit1, was inoculated in four sterile and four non-sterile soils, at varying inoculum densities. Two soils, which had shown enhanced atrazine mineralization, were used to determine which inoculum density was capable of restoring their original mineralizing capacity after sterilization. The two other soils, with intermediate and low capacity to mineralize atrazine, were used in order to demonstrate that atrazine mineralization in such soils could be improved by inoculation. Mineralization kinetics were fitted using the Gompertz model. In the case of soils adapted to atrazine mineralization, inoculation of C. heintzii did not accelerate the rate of atrazine mineralization, which was essentially performed by the indigenous microflora. However, with soils that did not mineralize atrazine, the introduction of 10 4 cfu g −1 resulted in a 3-fold increase of atrazine mineralization capacity.

Mineralization of aged atrazine and mecoprop in soil and aquifer chalk

The effect of ageing on the bioavailability and sorption of the herbicides atrazine and mecoprop was studied in soil and aquifer chalk sampled at an agricultural field near Aalborg, Denmark. The herbicides were incubated in sterile soil or chalk up to 3 months prior to inoculation with 5×10 7 cells g −1 (dry weight) of a mecoprop degrading highly enriched culture (PM) or 1×10 9 cells g −1 (dry weight) of the atrazine degrading Pseudomonas sp. strain ADP. As a measure of the bioavailable residues accumulated 14 CO 2 was measured for 2 months. In both soil and chalk ageing limited the rate of atrazine mineralization, and in chalk the extent of mineralization was reduced as well. The fraction of sorbed atrazine in the soil ranged between 50% and 62%, whereas a maximum of 12% was sorbed in chalk. No impact on the mineralization of aged mecoprop was seen as no sorption of this herbicide on either soil or chalk was measured.

Earthworms and the dissipation and distribution of atrazine in the soil profile

The influence of earthworms ( Lumbricus terrestris L.) on the persistence and transport of 14C-labelled atrazine [2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine] in soil was studied in laboratory incubations using flask microcosms and packed columns. In soil microcosm incubations (12 or 30°C), [U-ring- 14C]atrazine was dissipated and mineralized more rapidly in soil that had been conditioned (preincubated) with earthworms (e.g. soil containing worm castings) than in soil without earthworms. Earthworms added to soil following herbicide application accelerated the formation of non-extractable (soil-bound) atrazine residues and reduced atrazine mineralization rates over 68 d, compared to soil that did not contain earthworms. In packed soil columns (24 cm×6.3 cm i.d.), earthworms promoted the formation of non-extractable residues and modified the vertical distribution of herbicide residues. Following a 68-d incubation of soil columns (12°C) receiving a surface application of [U-ring- 14C]atrazine-sprayed corn leaves, total non-extractable radioactivity in soil columns containing earthworms was 21% greater than that in soils without earthworms. Earthworm consumption of the [U-ring- 14C]atrazine-sprayed corn leaves and subsequent activity translocated 60% of the total radioactivity below 4 cm. In contrast, more than 65% of the initially applied [U-ring- 14C]atrazine remained in the top 4 cm surface layer in columns containing no earthworms. Earthworms also influenced the distribution of herbicide residues in the soil matrix, depositing about twice as much MeOH-extractable radioactivity in their burrow linings as in the surrounding soil.

Variation in Atrazine Mineralization Rates in Relation to Agricultural Management Practice

Atrazine (6-chloro-N-ethyl-N-(1-methylethyl)-1,3,5-triazine-2,4-diamine) mineralization rates were measured in surface soils with different agricultural management practices at the Ohio Management Systems Evaluation Area (Ohio MSEA) site in Piketon, OH. Two management practices were studied at this site: (i) a continuous-corn (Zea mays L.) plot (CC) receiving annual application of atrazine, and (ii) a crop-rotation plot (CR) with corn-soybean [Glycine max (L.) Merr.]-wheat (Triticum aestivum L.) and hairy vetch [Vicia villosa (L.) Roth] with reduced use of atrazine during corn years. Soil collected from a riparian zone (RZ) near the site served as an herbicide-free reference soil. The agricultural site (both CC and CR) had received atrazine applications for about 25 yr before this study. Uniformly ring-labeled 14 C-atrazine was added to the soil samples in biometer flasks and 14 CO 2 evolution was measured by scintillation counting of alkaline trapping solution. Sterile controls showed no evolution of 14 CO 2 Within 30 d of incubation at 22 ± 2°C, about 80% of the initial radioactivity was evolved as 14 CO 2 in CC soils collected during different seasons of the year. Parallel samples from CR showed 15 to 30% atrazine mineralization while samples from RZ showed 3 to 7% 14 CO 2 evolution within 80 d of incubation. Prior amendment of soil samples from the three sites with 1 mg kg -1 atrazine accelerated subsequent mineralization measured after 90 d of incubation, indicating enhanced activity of indigenous microorganisms. The CC mineralization data suggest that a single annual atrazine application sustains an active microbial community throughout the year.

Degradation of Atrazine in Two Soils as a Function of Concentration

AbstractDissipation of atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) in a Webster clay loam soil (fine loamy, mixed, mesic Typic Haplaquoll), and Estherville sandy loam (sandy, mixed, mesic typic Hapludoll) was determined over a concentration range of 5 to 5000 mg kg−1 in field and laboratory experiments. Over the first 6 mo in the clay loam soil, the persistence of atrazine (based on percent of applied) was greater for the high‐rate treatments than the low‐rate treatments. However, in the laboratory, there was no effect of concentration on dissipation; the amount of atrazine degraded increased proportionally with the increase of concentration. In the sandy loam, persistence was greater at high concentration in both field and laboratory studies. Mineralization was the most important pathway for the dissipation of atrazine at all concentrations in the clay loam soil and from 5 to 500 mg kg−1 in the sandy loam. It was postulated that soil microorganisms were able to use the N or C from the s‐triazine ring. Atrazine at 500 and 5000 mg kg−1 may have increased soil microbial growth and activity and thus increased the degradation of atrazine based on the increase in soil respiration in the clay loam soil. Degradation pathways in both soils apparently were not influenced by concentration. Ring cleavage and hydrolysis were the major metabolic pathways in both soils, with dealkylation of less importance. Addition of a dairy manure amendment increased the rate of atrazine mineralization, while corn meal decreased and (NH4)2HPO4 amendments prevented mineralization.

Mineralization of 2,4-D and atrazine in the unsaturated zone of a sandy loam soil

Pesticide transformation in the unsaturated zone may greatly reduce the amount of pesticide leaching to groundwater. Understanding and quantifying the fate of pesticides in the unsaturated zone will greatly improve the accuracy of pesticide leaching models and enable more effective groundwater policies to be devised. We studied the effects of temperature, moisture and initial pesticide concentration on mineralization of 2,4-D and atrazine at different soil depths down to 1.5 m. Mineralization of 2,4-D was followed for 2.5 months and atrazine mineralization for 1 month. Uniformly ring-labelled 2,4-D and atrazine were applied to soil to give initial pesticide concentrations between 7.5 and 60 μg kg −1 for 2,4-D and between 100 and 600 μg kg −1 for atrazine. Moisture contents varied between 15 and 40% of moisture holding capacity and temperatures varied between 4 and 20°C. Mineralization of atrazine was always low (<2%) and decreased with depth, lower temperatures and lower moisture contents. Microbial biomass (r 2 > 0.66) and soil organic carbon (r 2 > 0.76) were positively correlated with atrazine mineralization rates. Between 10 and 80% of applied 2,4-D was completely mineralized depending on the test conditions and soil depth. 2,4-D mineralization rates were generally highest at depths between 1 and 1.5 m and on average 4 times higher than in the surface soils. Variations in 2,4-D mineralization rates with depth could not be correlated to changes in soil organic C, soil biomass, or chemical availability, and are probably the result of complex interactions between microbial activity, community structure, nutrient status and soil chemical and physical properties. As with atrazine, 2,4-D mineralization increased with increasing temperature and moisture contents. Addition of glucose reduced the mineralization of 2,4-D but enhanced atrazine mineralization, likely indicating differences in metabolic pathways involved.

Survival and Activity of an Atrazine-Mineralizing Bacterial Consortium in Rhizosphere Soil

Plant rhizosphere effects on atrazine degradation were examined in soil inoculated with an atrazine-mineralizing bacterial consortium. The consortium, consisting of three bacterial species, was isolated from an agricultural soil having previous long-term exposure to the herbicide. Atrazine mineralization and metabolite formation were monitored by measuring 14 CO 2 evolution from microcosms amended with radiolabeled atrazine and by HPLC of soil extracts. In noninoculated soil, ca. 11% of 14 C-chain-labeled atrazine was N-dealkylated, while only 2.4% of the ring-labeled atrazine was mineralized after 5 weeks. Corn plants had no effect on atrazine mineralization or ethyl-side-chain N-dealkylation in noninoculated soils, but the formation of hydroxyatrazine was significantly enhanced in planted soil. Growth of corn in sterilized soil suggested that hydroxyatrazine formation was caused by plant metabolism of atrazine. Introduction of the atrazine-mineralizing consortium into the soil significantly increased the rate of atrazine mineralization in comparison to noninoculated soil. After 4 weeks, 71% of the atrazine was mineralized in nonplanted soil, whereas 84% of the atrazine was mineralized in soil with corn plants. There was no significant difference in the rate of atrazine mineralization by the consortium in nonplanted and planted soil. However, atrazine-mineralizing populations at the end of the incubation were higher in the planted soil, which contained 8.1 x 10 4 degraders g -1 of soil versus 2.7 x 10 3 degraders g -1 in soil without plants. The results demonstrated that bioaugmentation with the atrazine-mineralizing consortium greatly enhanced the rate of atrazine mineralization. Long-term survival of the consortium and degradation of atrazine to hydroxyatrazine were both enhanced in rhizosphere soil, but corn seedlings had no significant effect on the rate of atrazine mineralization, either by the indigenous microflora or in soil inoculated with atrazine-mineralizing bacteria.

Influence of Organic Amendments on Biodegradation of Atrazine as a Nitrogen Source

AbstractCarbon and N dynamics may be particularly important for selective enrichment of microorganisms that are capable of using xenobiotics as sources of N for growth. To investigate this hypothesis in relation to s‐triazines, a soil microcosm study was performed to determine the effect of organic amendments differing in complexity and C/N ratio, and the effects of inorganic N addition on atrazine mineralization in a soil having a 15‐yr history of prior exposure to this herbicide. When the soil was spiked with 100 mg/kg of atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) in the absence of organic amendments, 73% of the atrazine was mineralized after 11 wk. Soils amended with rice hulls, starch, and compost yielded mineralization rates of 88, 75, and 59% in the same period, respectively. In contrast, &lt;10% of the atrazine was mineralized in soils amended with glucose, Sudan hay, or sodium citrate. All treatments receiving supplemental inorganic N had a considerably lower rate of atrazine mineralization than corresponding treatments without N addition. However, the different effects of the organic matter supplements suggested there was no relationship between the C/N ratio of the soil and atrazine mineralization. An atrazine‐degrading consortium was subsequently isolated for further characterization. The results demonstrate that while atrazine mineralization is suppressed under high N conditions in this soil, the mineralization rate also is influenced by poorly understood population dynamics related to the nutrient composition and complexity of specific organic amendments.

Effect of soil conditions on model parameters and atrazine mineralization rates

Transformation of pesticides is dependent on soil environmental conditions and knowledge of this is necessary to improve subsurface fate and transport pesticide models. Laboratory experiments were performed using 14C ring and isopropyl side-chain labeled atrazine (2-chloro-4-ethylamino-6-isopropylamino- s-triazine) applied to three Iowa soils incubated in batch reactors under different environmental conditions. Mineralization of both the ring and isopropyl side chain carbons was proportional to the organic matter content of the soils and oxygen content. Atrazine ring carbon mineralization also increased with soil water content. Oxygen limitation in soils reduced the bio-transformation rate of atrazine, and mineralization was much slower under denitrifying conditions. Empirical models were developed to represent the mineralization rate of atrazine ring carbon and isopropyl side-chain carbon for varying soil organic matter, soil water content, temperature, and oxygen partial pressure.

Effect of two electron acceptors on atrazine mineralization rates in soil

Effect of two electron acceptors on atrazine mineralization rates in soil