Absorbance of pesticides

Fluorescence and Ultraviolet Absorbance of Pesticides and Naturally Occurring Chemicals in Agricultural Products After HPLC Separation on a Bonded-CN Polar Phase... 

Argauer, R.J. (1980), Fluorescence and ultraviolet absorbance of pesticides and naturally occurring chemicals in agricultural products after HPLC separation on a bonded-CN polar phase. Am. Chan. iV -, Symp. See. 1980-Vol. Pen. Anal. Methadai. 136, 103-126,... 

Substances other than enzymes can be immobilized. Examples include the fixing of heparin on polytetrafluoroethylene with the aid of PEI (424), the controUed release of pesticides which are bound to PEI (425), and the inhibition of herbicide suspensions by addition of PEI (426). The uptake of anionic dyes by fabric or paper is improved if the paper is first catonized with PEI (427). In addition, PEI is able to absorb odorizing substances such as fatty acids and aldehydes. Because of its high molecular weight, PEI can be used in cosmetics and body care products, as weU as in industrial elimination of odors, such as the improvement of ambient air quaHty in sewage treatment plants (428). 

The main purpose of pesticide formulation is to manufacture a product that has optimum biological efficiency, is convenient to use, and minimizes environmental impacts. The active ingredients are mixed with solvents, adjuvants (boosters), and fillers as necessary to achieve the desired formulation. The types of formulations include wettable powders, soluble concentrates, emulsion concentrates, oil-in-water emulsions, suspension concentrates, suspoemulsions, water-dispersible granules, dry granules, and controlled release, in which the active ingredient is released into the environment from a polymeric carrier, binder, absorbent, or encapsulant at a slow and effective rate. The formulation steps may generate air emissions, liquid effluents, and solid wastes. 

Pesticides may enter the atmosphere during spray applications of the formulated product, by volatilization, through management practices, via wind-distributed soil particles containing absorbed pesticides, etc. Several analytical methods have been reported over the last 30 years for the determination of pesticides in air, and all involve the passage of known volumes of air for a pre-defined time period through an adsorbent material to trap the desired analytes. These analytes are then extracted, concentrated, and analyzed. A few analytical methods have been reported for the determination of triazine compounds in air in the last decade. 

The development of solid-phase extraction (SPE) absorbents such as silica gel, alumina and Florisil tremendously aided in the purification or cleanup of pesticide residues from water. 

From the late 1960s until the early 1980s, a large number of worker exposure studies were reported which used the methods of passive dosimetry — that is, methods that measured potential contact with pesticides but did not measure the actual amount of pesticide absorbed by the workers bodies. These studies were extensively reviewed by Wolfe (1976) and later by Davis (1980). 

Brown, VK. and Muir, C.M.C. (1971). Some factors affecting the acute toxicity of pesticides to mammals when absorbed through skin and eyes. Int. Pest Control 13 16-21. 

A possible source of groundwater contamination, which has up to now almost been neglected, is associated with the introduction of surfactants into soils as pesticide additives (Table 6.7.3). Non-ionic surfactants composed of alcohols and fatty acids are most widely recommended as adjuvants to facilitate and enhance the absorbing, emulsifying, dispersing, wetting and penetrating properties of pesticides. Other pesticide adjuvants are silicone-based surfactants,... 

Abstract Removal of the pesticide metobromuron from aqueous solutions by adsorption at the high area activated carbon cloth was investigated. Kinetics of adsorption was followed and adsorption isotherms of the pesticide was also be determined. In kinetic studies a special V-shaped cell with an UV cuvette attached to it was used for adsorption processes. With this cell it was possible to follow the concentration of pesticide molecule by in situ UV spectroscopy as it is adsorbed at the activated carbon cloth. The obtained absorbance vs time data were converted into concentration vs time data and these data were treated according to pseudo-first-order and psendo-second-order kinetic models. Adsorption of that pesticide was fonnd to follow second-order kinetic model with k 87.35 g mol min. Adsorption isotherms were derived at 25°C on the basis of batch analysis. Isotherm data were treated according to Langmuir and Freundlich models. The fits of experimental data to these equations were examined and founded that the adsorption isotherm was well represented by Frenndlich model. 

In order to obtain the calibration curve of pesticide metobromuron, absorbances were measured at the corresponding as a function of concentration and the data were fitted to Lambert-Beer law by the method of least square analysis. The resulting correlation coefficient (R 1.0000) show that the fit to Lambert-Beer law is excellent. The obtained calibration equation was used to convert absorbances into concentrations in kinetic and equilibrium studies. 

Adsorption of metobromuron onto ACC was monitored spectrophotometrically at 244 nm by the procedure described above. Absorbance data, obtained in 1-min intervals until equilibrium, were converted into concentration data using the corresponding calibration relation and then plotted as a function of time in Fig. 22.2. Initial concentration of pesticide in the solution was 7.64 x 10 M and adsorption equilibrium time using 18 mg ACC, determined as the time after which the concentration of the pesticide solution remained unchanged during the course of adsorption process, was 1,156 min. The decrease in concentration of pesticide is fast at the early stages, while it slows down toward the end of adsorption period. Concentration... 

Ultrasonically assisted extraction is particularly useful for the environmental analytical chemist because it facilitates a more complete extraction of absorbed chemicals e. g. the extraction of pesticides [57, 58] and of heavy metals from soils [59[. 

The ECD has seen its greatest utilization in the field of pesticide analysis. Chemicals such as dieldrin, aldrin and DDT are amenable to the ECD. In addition, the environmental hazards of polychlorinated biphenyls (PCBs) have been raised as a result of analyses by the ECD. Organometallics are also good electron absorbers. With the aid of halogen derivatization, many classes of organic compounds such as steroids, acids, amines, phenols, and alkenes have been assayed. 

Numerous methods have been utilized to actually measure the amount of pesticide which impinges on the skin. One of the more widely used ones involves attaching absorbent patches to various areas of the body and analyzing the patches for pesticide on termination of the spray operation. The concentration on the patch can then be extrapolated to the surface area of the body from which it was removed. The assumptions are that the pesticide will adhere to the patch in the same manner as it would to skin, that the distribution of the pesticide will be uniform over the area represented by the patch and that dermal contact occurs only on exposed skin surfaces and not on skin covered by clothing (6). 

A proportion of pesticide droplets that are trapped on the cartridge are too large to be inhaled. However, any vapour that might be present would be absorbed on the cartridge, and an estimate based on droplet size includes the vapour component. 

The three main barriers upon which pesticide will impinge are the skin, the lungs and the gastrointestinal tract. Each of these barriers possesses a unique structure and function which will influence the absorption of pesticide into the bloodstream. Although some product may exert local contact effects, it is usually only after they have been absorbed that, they exert their toxic effects therefore, it is important to understand the extent of the absorption. 

Once the percentage of pesticide that is absorbed and the dermal contact are known, the absorbed dosage can be calculated. 

In addition to these calculated estimates of absorption, a specific estimate of absorbed dose can be made by measuring the metabolites of the pesticide in urine. For pesticides on which good data exist on metabolic excretion, it appears that this method is very sensitive. In a study conducted on orchardists (7), metabolites were detected in the urine samples of all workers, and a statistically significant correlation was found between the total 48 hour metabolite output and the total amount of pesticide sprayed. In contrast the same study indicated that the correlation between urinary output and the total spray time was not significant. This supports the point mentioned earlier that it seems reasonable to presume that exposure is related to the total amount available for contact, and that correlating exposure with the spray time may be misleading. 

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