Degradation Of Pesticides In Soil Research Articles

Application of the microtox system to assess the toxicity of pesticides and their hydrolysis metabolites

In this study, we used the Microtox analyzer to determine the relative microbial toxicities of some pesticides and their metabolites. Because hydrolysis is a significant step in the chemical and microbial degradation of pesticides in soil, the principal focus of this investigation was on hydrolytic metabolites

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

Abstract 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.

Microbial metabolism of pesticides and structurally related compounds.

This chapter provides a review concerning the microbial metabolism of pesticides and substances that are either major metabolites from pesticides or have structural similarity to certain pesticides, and covers the period 1981 to 1987. While reference has only been made to work published during this period, it should be realized that in some instances the results cited may confirm or expand upon earlier findings rather than being entirely novel. Therefore, the reader is referred to earlier reviews. The metabolism of pesticides in natural environments, water and wastewater, mixed microbial cultures, and pure cultures has been discussed. Attention has been drawn to the meager amount of information concerning the biodegradation of pesticides in anaerobic and marine environments. Issues such as the importance of cometabolism of pesticides in natural environments and a clear understanding of enhanced degradation of pesticides in soil still remain unresolved. Separate sections have been devoted to methodology in biodegradation studies, bound residues and removal of pesticides from soil and water. While pure culture studies have an important place in investigations into microbial metabolism of pesticides, increasing emphasis has been placed on the use of microbial consortia, either natural or artificial and microcosms to provide an understanding of pesticide biodegradation in natural environments. Another dimension in bound residue formation, one of physical entrapment in humic materials has been described. Various questions regarding the bioavailability of bound residues and whether they pose an environmental problem have not been answered fully. The microbiological removal of pesticides from soil and water by selected or genetically-engineered strains is discussed. It has been emphasized that the future success of such methods for the decontamination of soil and water depends very heavily on an improved knowledge of microbial ecology.

Modeling the transport and the fate of pesticides in the unsaturated zone considering temperature effects

A mathematical model solved by finite elements method namely MELEF-3v model, is used to simulate the one-dimensional water flow as well as the heat and the mass transport through the unsaturated-saturated zones of the soil. Differential equations and physical laws were used to link temperature, water pressure and water chemistry. The Arrhenius and the Van 't Hoff equations allow the prediction of the effect of the water temperature on the adsorption and the degradation of pesticides in soil. Simulation of the transport of the pesticide atrazine is performed in order to evaluate the effect of a difference of temperature between the water of precipitations and the water of the aquifer, on the concentration profile of the pesticide in the unsaturated-saturated zones. When considering a uniform and constant temperature in a soil column (5°C), the simulated concentration profiles show, after 10 days and 1 year, some differences with those obtained by using the Pesticide Root Zone Model of Carsel et al. When considering a temperature variation of 10°C between the soil surface (15°C) and the water of the aquifer (5°C), we observed after 1 year no significant modification of the individual convection-dispersion process for the pesticide. This temperature variation induces a slightly more retarded concentration profile, and markedly diminishes the peak concentration of the pesticide subject to degradation process. The concentration profile of atrazine in the unsaturated zone is then largely affected by this warmer transient temperature gradients since the pesticide is retarded (adsorbed) in this zone where basic transformation processes are enhanced.

Study on rate model of microbial degradation of pesticides in soil

The food supply coefficient concept is propounded. It may be expressed in the form φ = ( ξχ 0 − ξχ + χ)/ χ 0 where χ 0 is the initial concentration of pesticide, χ the concentration of pesticide at time t, and ξ a constant which has a value between 0 and 1. If the pesticide is biodegradable, then its rate of degradation is proportional to χ and m:−d χ/d t = kχm = kχφ[ m 0 + λ ( χ 0 − χ)], where k is a rate constant, m the number of the involved microorganisms at time t, m 0 the initial number of the involved microorganisms, and λ the increment constant of the microorganisms. In a closed system, χ becomes the rate-limiting factor, and then: −d χ/d t = k 1 χ + k 2 χ 2 + k 3 χ 3, where k 1 > 0, k 2 ⋚ 0, and k 3 < 0. Its integral form is: ln x 0 x + g 2 g 1−g 2 ln x 0−g 1 x−g 1 + g 1 g 2−g 1 ln g 2−x 0 g 2−x =k 1t where g 1 and g 2 are the constants depending on the values of k 1, k 2 and k 3. Seven particular cases for the rate model are discussed.

Mathematical model for microbial degradation of pesticides in the soil

A theoretical model for the microbial degradation of pesticides in soil is presented. This model takes into account an important soil property, the adsorption capacity, and the probable modification of the soil microflora after the pesticide was introduced into the soil. The main assumptions of the model are that: (1) the degradation takes place simultaneously in two ways, by metabolism and by co-metabolism; (2) the pesticide exhibits a lethal effect on a sensitive fraction of the soil microflora; (3) a fraction of this microflora is insensitive and does not degrade the pesticide; (4) the various fractions of the soil microflora can grow at the expense of both the pesticide and soil carbon (metabolizing microorganisms) or of the soil carbon alone (co-metabolizing, sensitive and insensitive microbial populations). Two numerical examples are given to illustrate the soil adaptation phenomenon. The validity of different hypotheses included in the model when applied to the soil system are discussed by comparing the results of the simulations to some experimental data concerning the modification of the degrading soil microflora or by comparing some physico-chemical and biological parameter values used in the calculations to published values.

Stability and effects of some pesticides in soil.

The influence of 29 pesticides on CO(2) production and nitrification by soil microorganisms was determined. A few compounds were stable but without significant effect in soil (chlorinated hydrocarbons), some persisted and depressed respiration and nitrification (carbamates, cyclodienes, phenylureas, thiolcarbamates), and others displayed toxicity but were transformed by soil microorganisms (amides, anilides, organophosphates, phenylcarbamates, triazines). Some compounds of the last type induced an initial increase and subsequent decrease in CO(2) production by soil. No simple explanation of this effect is possible, but the results of studies of model systems having established activities suggest that in soil any one or a combination of the following mechanisms is responsible for the observed complex relation of CO(2) production to time: (i) a pesticide acts to uncouple oxidative phosphorylation in a manner analogous to 2,4-dinitrophenol; (ii) a pesticide lacking antimicrobial action is oxidized in part and transformed to a stable and toxic product; (iii) a pesticide that is selectively toxic inhibits CO(2) production by sensitive microorganisms but is subject to oxidation without detoxification by other members of the microbial population that are resistant to its initial action. Pesticide concentrations greatly in excess of those recommended for agricultural and home use were required to produce an effect, and supplementary organic matter (glucose) tended to reduce pesticide toxicity and increase the microbial degradation of pesticides in soil.

Stability and Effects of Some Pesticides in Soil1

The influence of 29 pesticides on CO(2) production and nitrification by soil microorganisms was determined. A few compounds were stable but without significant effect in soil (chlorinated hydrocarbons), some persisted and depressed respiration and nitrification (carbamates, cyclodienes, phenylureas, thiolcarbamates), and others displayed toxicity but were transformed by soil microorganisms (amides, anilides, organophosphates, phenylcarbamates, triazines). Some compounds of the last type induced an initial increase and subsequent decrease in CO(2) production by soil. No simple explanation of this effect is possible, but the results of studies of model systems having established activities suggest that in soil any one or a combination of the following mechanisms is responsible for the observed complex relation of CO(2) production to time: (i) a pesticide acts to uncouple oxidative phosphorylation in a manner analogous to 2,4-dinitrophenol; (ii) a pesticide lacking antimicrobial action is oxidized in part and transformed to a stable and toxic product; (iii) a pesticide that is selectively toxic inhibits CO(2) production by sensitive microorganisms but is subject to oxidation without detoxification by other members of the microbial population that are resistant to its initial action. Pesticide concentrations greatly in excess of those recommended for agricultural and home use were required to produce an effect, and supplementary organic matter (glucose) tended to reduce pesticide toxicity and increase the microbial degradation of pesticides in soil.