Uptake Of Pesticides Research Articles

MODEL FOR PREDICTING TRANSPORT OF PESTICIDES AND THEIR METABOLITES IN THE UNSATURATED ZONE1

ABSTRACT: A finite element model based on Galerkin's upstream weighted residual technique was developed to predict the simultaneous convective‐dispersion transport and transformations of pesticides and their metabolites in the unsaturated zone. Transformations of the parent compound and its metabolites were assumed to be first‐order reactions for oxidation and hydrolysis, while adsorption of the pesticide species (parent compound and metabolites) to the soil components was assumed to be represented by a linear equilibrium (Freundlich type) isotherm. Volatilization and plant root uptake of pesticides in the solution phase were neglected in the analysis. The proposed model was used to simulate the transport and transformation of aldicarb and its metabolites, aldicarb sulfoxide and aldicarb sulfone, in the soil profile. Several examples are used to demonstrate the accuracy, validity, and applicability of the proposed model. Simulated results indicate that the proposed model can potentially be used to estimate the mass flux of water, and pesticide and pesticide metabolite concentrations in the subsurface environment. However, further verification of the model against actual field data is needed to fully demonstrate the model's potential.

Intra-individual variation in plasma and erythrocyte cholinesterase activities and the monitoring of uptake of organo-phosphate pesticides.

The measurement of plasma and erythrocyte cholinesterase activities is used to monitor absorption of anti-cholinesterase organo-phosphorus compounds. A fall in an individual's enzyme activity signifies excessive exposure if it is clearly greater than the normal intra-individual variation found in unexposed subjects. The extent of normal variation in enzyme activity as measured is dependent on both the true intra-individual biological variation and the precision of the method used. This report defines normal variation in plasma and erythrocyte cholinesterase activity using the assay developed and used routinely in our laboratory. We have also defined the relation between the precision of the assay used by a laboratory and the sensitivity with which a significant depression in successive enzyme measurements can be detected. This allows occupational physicians, who use cholinesterase measurements to monitor organo-phosphate exposure, to establish percentage depressions from their method precision data that may possibly indicate organo-phosphate uptake between successive enzyme measurements. We have calculated that, with our analytical precision, percentage drops between two successive measurements that are greater than 15 and 7.5 per cent for the plasma and erythrocyte enzymes respectively suggest significant organo-phosphorus absorption in pesticide workers.

Uptake and excretion of organochlorine pesticides by Nereis virens under normoxic and hypoxic conditions.

The marine polychaete worm, Nereis virens, is resistant to organochlorine pesticides. When exposed to each of five pesticides (endosulfan, chlordane, endrin, dieldrin, and DDT) in concentrations ranging from 0.03 mg/L (DDT) to 22.0 mg/L (chlordane), only endosulfan and chlordane killed Nereis. In comparison, the same compounds were much more toxic to another marine invertebrate, Crangon septemspinosa. The authors wondered if the resistance of N. virens to organochlorines was related to their response to hypoxia. N. virens is a sediment dweller often found in intertidal regions and consequently may experience periods of severe oxygen deprivation; varying degrees of hypoxia can initiate a switch to anaerobic energy metabolism. When N. virens encounter hypoxic conditions, they can also exhibit a compensatory ventilation response. In the present study, the authors measured the bioaccumulation of endosulfan, dieldrin, and DDT by N. virens under normoxic and hypoxic conditions.

Role of lipid/water partitioning and membrane composition in the uptake of organochlorine pesticides into a freshwater mussel

The aim of this investigation is to understand the factors influencing uptake of persistent organochlorine pesticides into a freshwater mussel ( Sphaerium corneum). Previous work has shown that although a substantial proportion of dieldrin is bound to particulates in the river system, uptake is from the dieldrin in solution. This suggests partitioning of the hydrophobic xenobiotics into membranes as the major route of entry. Membrane composition was established using lipid fractionation into neutral lipids and phospholipids followed by derivatisation to fatty acid methyl esters and estimation using GC/FID. Membrane composition varied with acclimation temperature over the range 5–20°C. Dieldrin concentrations in the mussel at equilibrium with 2000 ng dieldrin/litre water burden were studied at one temperature under laboratory conditions using animals acclimated to different temperatures. Any differences may be explicable in terms of effects of membrane composition on partitioning or other physiological adaptations. To establish which of these factors is most significant a membrane fragment partition system has been analysed in vitro. Preliminary results indicate that although water/lipid partitioning may be important in entry (and exit) of non-polar xenobiotics, significant differences could not be found using current methods. The role of membrane composition and therefore temperature history of the organism may still be significant. The implications of this for attempted correlations between bioaccumulation factors and simple octanol/water partition coefficients are discussed.

Identification of cyclosporine metabolites in human bile, blood and urine by HLPC/RIA/FABMS

The application of greenhouse vegetable cultivation has dramatically expanded worldwide during the last several decades. However, little information is available on the distribution and uptake of pesticides in greenhouse vegetables. To bridge this knowledge gap, the present study was initiated to investigate the distribution and uptake of organochlorine pesticides (OCPs) in vegetables from plastic greenhouse and conventional cultivation methods. The uptake pathways of OCPs were not significantly different between these two cultivation methods. The arithmetic means of OCP concentrations in greenhouse vegetables were higher than those in conventional vegetables, although there was no significant difference. This small difference raised the concern of whether the tiny difference could be magnified to a significant difference by bioaccumulation in the food chain. The issue should be addressed by a well-designed scheme in future studies.

Uptake of pesticides from water and soil by earthworms

AbstractThe uptake of pesticides by earthworms from aqueous solutions was examined and shown to be a reversible physical process. Measurements of distributions of pesticides between aqueous solutions and worm solids showed that adsorption coefficients were related to octanol‐water distribution coefficients, as are soil‐water distributions. From these relationships it was calculated that concentration factors of stable chemicals in earthworms from soil should be similar, except for polar substances which penetrate poorly, and be determined mainly by the soil organic matter content. Examination of uptake from soils indicated that the calculated concentration factors are unlikely to be achieved because of slow diffusion of chemicals in soils and because of metabolism in the soil or the worm.

Pesticide uptake into membranes measured by fluorescence quenching.

Pesticides that contain chlorine have been shown to quench the fluorescence of carbazole-labeled phospholipids. Incorporation of these carbazole-labeled phospholipds into model membranes provides a system that allows the rapid determination of the uptake rates of chlorinated hydrocarbons into model membranes. This technique can be used in the determination of diffusion rates and partition coefficients of chlorine-containing organic compounds in model membrane systems, and hence may provide a method by which the bioaccumulation potential of synthetic chlorine-containing compounds can be estimated.

Uptake and persistence of pesticides in cultured human cells.

The uptake and persistence of 14C-labeled pesticides in cultur-s of human embryonic lung diploid cells were studied. Chlordimeform, DDT, parathion, aldrin and dieldrin were selected as test compounds. Results obtained from these experiments divided the chemical into two groups. The first group consisted of three chemical DDT, aldrin and dieldrin which are generally classified as persistent insecticides while the second group was composed of chlordimeform and parathion, generally considered to be non-persistent insecticides. The rate of initial cellular incorporation of first group was approximately 20 to 70 times greater than the non-persistent insecticides. During the course of an incubation, the amounts of pesticide taken up by the cells decreased gradually.

Computed leaching of pesticides from soil as influenced by high rainfall, plant growth and time of application

In a series of computations for hypothetical pesticides, the risk of leaching from the top meter of soil was evaluated. Different combinations of decomposition rate and sorption strength were introduced into the models. The predicted amounts leached under specific field conditions were compared with losses computed for spring applications to a field where a simulated potato crop was grown. The main effect of high rainfall in the year after spring application was an increase in computed leaching for compounds showing some leaching under standard rainfall conditions. In the absence of water and pesticide uptake by a crop, the risk of leaching was increased considerably. With autumn applications, the predicted amounts of leaching were substantially greater than with spring applications.

A compartmental computer model of foliar uptake of pesticides

AbstractThe uptake and movement of a chemical into a wheat leaf has been simulated in a 5‐compartment model. The compound is considered to be applied to the leaf as discrete droplets of solution, from which water evaporates at a uniform rate. Solute diffuses from the droplets through the plant cuticle into the epidermal cell wall, and from there either into and out of the cytoplasm and vacuole of the mesophyll cells or along cell walls to the xylem. Once in the xylem it is carried in the transpiration stream towards the tip of the leaf.Accurate values for the parameters required by the model have not yet been measured, but the model simulates in a qualitative manner the movement pattern observed for 1‐methyl‐2‐pyridone. The results presented focus attention on the possible importance of membrane permeability in determining the phytotoxicity of xylem mobile pesticides.

Automatic recording of uptake of pesticides and related compounds by small plant parasites I. Description of the method

AbstractA technique is described for the automatic recording of the uptake of pesticides and related compounds by viable, small organisms suspended in aqueous solution. The relation of time to uptake thus determined allows the study of the kinetics and the characterisation of the uptake processes.The technique is based on a recycling of the incubation vessel fluid, obtained by a simple filtration process, through the flow cell of a spectrophotometer. The rate of uptake of compounds, which need to have sufficient absorption in the visible and u.v. region, is followed spectrophotometrically by repetitive measurement of spectra or of absorbance values at a single wavelength. Uptake processes are studied under controlled conditions of temperature and atmosphere. The method has proved to be applicable to yeast cells, fungal spores, nematodes, insect eggs and algae, so that it can be used to good advantage in pesticide research.However, the technique is not suitable for very small organisms such as bacteria and for easily deformable cells, e.g. erythrocytes.The utility of the method has been demonstrated in the uptake of 2‐chloro‐6‐phenylpyridine by nematodal larvae (Anguina tritici) which sorb the compound reversibly, and in the uptake of 4,5‐dichloro‐2‐nitrobenzonitrile by fungal spores (Fusarium culmorum) which is converted into the corresponding amino compound. These examples illustrate that the technique is very useful for the study of uptake processes which can be interpreted in terms of accumulation or conversion or both.

Physico‐chemical studies of pesticides. IV.solubilised pesticides

AbstractThe behaviour of several relatively insoluble pesticides (γ‐BHC, carbophenothion, coumaphos, diazinon, fenchlorphos and malathion) solubilised in aqueous soap (sodium dodecyl sulphate, cetyltrimethylammonium bromide and dodecyltrimethylammonium bromide) solutions have been examined by in vitro dipping experiments with flour beetles (Tribolium confusum Duval).Median lethal concentrations (C) and saturation solubilities (Cs) of the pesticides increased with soap concentration whilst their ratios (C/CS) which could be regarded as approximating their thermodynamic activities, decreased. The soaps, alone, whilst being sorbed from solution by the insects, removed cuticular material as did some common solvents (ether, hexane, methyl alcohol and methyl cyanide) but the effects were not sufficient to explain the changes in biological activity of the solubilised pesticides.Changes in surface tension and viscosity of the solutions and the amounts of liquid retained by the beetles after dipping were small and did not appear to affect the toxicities of the pesticides tested. Biological response appeared to be determined by the rate of uptake of pesticide by the insect cuticle and hence was affected by the concentration of the soap micelles.

The Partitioning of Body Water in Amphibia

The Partitioning of Body Water in Amphibia