Mobility of Pesticides and Their Hydrolysis Metabolites in Soil

Somasundaram, L.; Coats, Joel R.; Racke, Kenneth D.; Shanbhag, Venkatesh M.

doi:10.1897/1552-8618(1991)10[185:mopath]2.0.co;2

Cited by 18 publications

(15 citation statements)

References 19 publications

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“…A large dipole moment implies a large degree of solvation. Therefore, the reactants are predicted to be more soluble in water than the hydrolysis products, in accord with experimental results; for example, the water solubility of atrazine is 70 mg litre −1 at 25 °C compared with 16 mg litre −1 for hydroxyatrazine 38…”

Section: Resultssupporting

confidence: 71%

Computational chemistry study of the environmentally important acid‐catalyzed hydrolysis of atrazine and related 2‐chloro‐s‐triazines

Sawunyama

Bailey

2002

Pest Management Science

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Many chlorine-containing pesticides, for example 2-chloro-s-triazines, are of great concern both environmentally and toxicologically. As a result, ascertaining or predicting the fate and transport of these compounds in soils and water is of current interest. Transformation pathways for 2-chloro-s-triazines in the environment include dealkylation, dechlorination (hydrolysis), and ring cleavage. This study explored the feasibility of using computational chemistry, specifically the hybrid density functional theory method, B3LYP, to predict hydrolysis trends of atrazine (2-chloro-N4-ethyl-N6-isopropyl-1,3,5-triazine-2,4-diamine) and related 2-chloro-s-triazines to the corresponding 2-hydroxy-s-triazines. Gas-phase energetics are described on the basis of calculations performed at the B3LYP/6-311++G(d,p)//B3LYP/6-31G* level of theory. Calculated free energies of hydrolysis (delta h G298) are nearly the same for simazine (2-chloro-N4,N6-diethyl-1,3,5-triazine-2,4-diamine), atrazine, and propazine (2-chloro-N4,N6-di-isopropyl-1,3,5-triazine-2,4-diamine), suggesting that hydrolysis is not significantly affected by the side-chain amine-nitrogen alkyl substituents. High-energy barriers also suggest that the reactions are not likely to be observed in the gas phase. Aqueous solvation effects were examined by means of self-consistent reaction field methods (SCRF). Molecular structures were optimized at the B3LYP/6-31G* level using the Onsager model, and solvation energies were calculated at the B3LYP/6-311++G(d,p) level using the isodensity surface polarizable continuum model (IPCM). Although the extent of solvent stabilization was greater for cationic species than neutral ones, the full extent of solvation is underestimated, especially for the transition state structures. As a consequence, the calculated hydrolysis barrier for protonated atrazine is exaggerated compared with the experimentally determined one. Overall, the hydrolysis reactions follow a concerted nucleophilic aromatic substitution (SNAr) pathway.

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Section: Resultssupporting

confidence: 71%

Computational chemistry study of the environmentally important acid‐catalyzed hydrolysis of atrazine and related 2‐chloro‐s‐triazines

Sawunyama

Bailey

2002

Pest Management Science

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“…This may have a significant implication, especially when it is more mobile and more toxic to soil organisms than chlorpyrifos. Somasundaram et al (1991) reported that TCP is more mobile than chlorpyrifos using thin layer chromatography technique. It has been also reported that the toxicity of TCP (EC 50 = 18.6 mg/L) to Photobacterium phosphoreum, a soil bacterium, is 2.5-fold higher than its parent compound, chlorpyrifos (EC 50 = 46.3 mg/L) ).…”

Section: Tcp Degradationmentioning

confidence: 99%

Contrasting behaviour of chlorpyrifos and its primary metabolite, TCP (3,5,6-trichloro-2-pyridinol), with depth in soil profiles

Baskaran¹,

Kookana²,

Naidu³

2003

Soil Res.

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Regulatory agencies and natural resource managers are increasingly recognising the role of pesticide metabolites in the overall risk to non-target organisms. However, the environment fate data on pesticide metabolites are relatively meagre. We report the sorption and degradation behaviour of chlorpyrifos and its primary metabolite, TCP (3,5,6-trichloro-2-pyridinol), with depth in 2 Australian soil profiles. Sorption isotherms were determined by batch equilibrium method and the degradation was studied under controlled incubation conditions. Sorption of chlorpyrifos (K d = 40.3-209.6 L/kg) was found to be about 100 times higher than that of TCP (K d = 0.45-2.86 L/kg) in both the soil profiles. A significant correlation (r 2 = 0.88**) was found between sorption of chlorpyrifos and the soil organic carbon content, but not in the case of TCP. However, in the case of TCP a significant inverse relationship was observed with pH (r 2 = 0.81**). The rate of degradation of chlorpyrifos increased with depth in the soil profile, whereas the converse was true for TCP. The time for 50% loss of chlorpyrifos (DT 50 ) was found to be 23-28 days in the surface soils (acidic pH) and only 7-16 days in the subsurface (alkaline pH). The DT 50 values for TCP in the surface soils ranged from 42 to 49 days and in subsurface soils from 64 to 117 days. The contrasting behaviour of chlorpyrifos and TCP in soil profiles is clearly evident from the study. Due to its lower sorption and longer persistence, TCP has a much greater leaching potential than chlorpyrifos. S R 0 2 0 6 2 S o r p t i o n a n d d e g r a d a t i o n o f c h l o r p y r i f o s a n d T C P wi t h d e p t h i n s o i l s S . B a s k a r a n e t a l .

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“…It is therefore not surprising that trichlorophenol did not serve as a microbial substrate. The toxicity of trichlorophenol to microbes (Somasundaram et al, 1989b) and its low availability in soil (Somasundaram et al, 1989a) may contribute to the resistance of 2,4,5-T to the development of enhanced microbial degradation.…”

Section: Downloaded By [] At 15:29 03 February 2015mentioning

confidence: 99%

“…Racke and Coats (1987) believed that the formation of salicylic acid might be a key factor in the susceptibility of isofenphos to enhanced degradation. The low microbial toxicity (Somasundaram et al, 1989b), relative availability (reflected by its high mobility) (Somasundaram et al, 1989a), and its nutritive value may contribute to the potential for salicylic acid to condition soils for enhanced degradation of isofenphos.…”

Section: Downloaded By [] At 15:29 03 February 2015mentioning

confidence: 99%

Degradation of pesticides in soil as influenced by the presence of hydrolysis metabolites

Somasundaram

Coats

Racke

1989

J. of Env. Sc. & Hlth., Part B

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The degradation of 8 pesticides was evaluated in a soil pretreated with their respective hydrolysis metabolites. 2,4-Dichlorophenol, p-nitrophenol, and salicylic acid conditioned the soil for enhanced degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), parathion, and isofenphos, respectively. Repeated application of carbofuran phenol, 2-isopropyl-4-methyl-6-hydroxypyrimidine, methyl phenyl sulfone, thiophenol, isopropyl salicylate, and 2,4,5-trichlorophenol had no effect on the rate of degradation of their parent pesticides. Prior exposure of soil to 3,5,6-trichloro-2-pyridinol resulted in increased persistence of its parent compound, chlorpyrifos. Results indicate that pesticide hydrolysis metabolites can effect the induction or inhibition of enhanced microbial degradation of some soil-applied pesticides. 457

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Mobility of Pesticides and Their Hydrolysis Metabolites in Soil

Cited by 18 publications

References 19 publications

Computational chemistry study of the environmentally important acid‐catalyzed hydrolysis of atrazine and related 2‐chloro‐s‐triazines

Computational chemistry study of the environmentally important acid‐catalyzed hydrolysis of atrazine and related 2‐chloro‐s‐triazines

Contrasting behaviour of chlorpyrifos and its primary metabolite, TCP (3,5,6-trichloro-2-pyridinol), with depth in soil profiles

Degradation of pesticides in soil as influenced by the presence of hydrolysis metabolites

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