Paraquat Residues Research Articles

Fast determination of paraquat residues in water by an optical immunosensor and validation using capillary electrophoresis-ultraviolet detection

A solid-phase fluoroimmunoassay combined with an optical transducer chemically modified with an analyte derivative coupled to a FIA system was used [A. Brecht, A. Klotz, C. Barzen, G. Gauglitz, R. Harris, G. Quigley, J. Wilkinson, P. Sztajnbok, R. Abuknesha, J. Gascón, A. Oubiña, D. Barceló, Anal. Chim. Acta 362 (1998) 69]. Excitation and collection of fluorescence from fluorescently labelled anti-paraquat antibodies locally bound at the planar interface allows the measurement of the fluorescent signal which is indirectly related to the paraquat concentration of the sample. Matrix effects on the immunosensor response were observed, thus leading to the following detection limits, 0.01 and 0.06 μg l −1, when analyzing paraquat in MilliQ and in river water, respectively. The validation of the biosensor was carried out analyzing paraquat samples by capillary zone electrophoresis with ultraviolet detection (CZE-UV) at 214 nm. Preconcentration of the samples prior to their injection in the capillary electrophoresis were performed using the automated solid-phase extraction system (ASPEC-XL). Paraquat samples were adjusted at pH 9 and were percolated through a silica cartridge, subsequent elution was carried out using a mixture of hydrochloric acid and methanol and afterwards samples were evaporated and injected. This optical immunosensor, also called RIver ANAlyzer (RIANA) with an optical immunosensor can be applied for fast monitoring of paraquat in river water samples being the total analysis time of 15 min.

Simultaneous determination of diquat and paraquat residues in various matrices by capillary zone electrophoresis with diode array detection

The separation of diquat and paraquat by CZE has been investigated. The addition of acetonitrile (10 %, v/v) to a phosphate buffer (100 mM, pH 4.0) is necessary for effective separation of both herbicides at an optimum applied voltage of around 12 kV; the current and migration times were stable and reproducible under these conditions. The method was validated for linearity and reproducibility. The detection level calculated for diquat and paraquat was 30 and 40 nM, respectively in the injection solution. By use of stacking, these detection levels were improved by a factor of 120. The method is suitable for the determination both herbicides in samples such as herbicidal formulations, water, soil, potatoes, urine and serum. Photodiode-array detection permitted the rapid identification of both compounds.

Qualidade de tubérculos de batatas-semente tratados com paraquat e o desenvolvimento de uma metodologia simplificada de detecção de resíduo do herbicida

O objetivo desse trabalho foi avaliar a qualidade de tubérculos de batatas-semente (Solanum tuberosum) tratados com paraquat e desenvolver uma metodologia simplificada de detecção de resíduos de herbicida. Dois ensaios foram realizados no Laboratório da Ciência das Plantas Daninhas do Centro Nacional de Pesquisa de hortaliças, Brasília, DF. No experimento, tubérculos das cultivares Achat e Baronesa foram submersos em soluções de 0 e 200 ppm de paraquat ou injetados com 0,5 ml de soluções de 0 e 200 ppm do herbicida. O delineamento experimental foi inteiramente casualizado com 8 repetições e 12 tubérculos por parcela. Os tubérculos foram colocados em câmara fria, após a aplicação com paraquat, para quebra da dormência. Após a brotação dos tubérculos avaliou-se a qualidade interna dos mesmos, amostrando, posteriormente, 2 tubérculos de cada parcela para o plantio em vasos, sob condições de telado, para verificar possíveis danos no crescimento das plantas oriundas dos tubérculos tratados. Os tratamentos de imersão não provocaram, aparentemente, nenhum dano interno nos tubérculos, ou nem mesmo afetaram a nova geração, entretanto, os tubérculos injetados com paraquat foram severamente deteriorados e carbonizados, originando plantas bastante debilitadas. Esses resultados indicam que quando o paraquat for aplicado sob condições que favoreçam sua penetração ou translocação para o interior do tubérculo, atingindo os vasos e a polpa, pode danificá-lo severamente, prejudicar sua aparência, qualidade de produção e reduzir o desenvolvimento da nova geração de plantas oriundas dos tubérculos contaminados . No segundo experimento, desenvolveu-se uma metodologia simplificada para detectar resíduos de paraquat nos tubérculos através de colorimetria, visto que o paraquat é reduzido a um radical de cor azul na presença de ditionito de sódio (Na2S2O4) a 1% em meio básico, a qual se intensifica à medida que a concentração do produto aumenta. A metodologia simplificada desenvolvida permitiu detectar resíduos de paraquat ao nível de 0,06 ppm, indicando uma excelente aproximação, pois, o limite de tolerância do paraquat em tubérculos de batata é de 0,2 ppm, normalmente, determinado pelo método analítico completo, que apresenta limites de detecção em torno de 0,01 ppm e recuperação acima de 70%. Uma avaliação qualitativa da concentração residual de produto nas amostras foi possível através de leitura e comparações visuais entre os diferentes graus de cores desenvolvidas nas soluções visuais entre os diferentes graus de cores desenvolvidas nas soluções padrão e a cor desenvolvida na amostra, não necessitando, portanto, das leituras colorimétricas, podendo ser feita inclusive no campo. Observou-se que a maioria do paraquat permaneceu na região de casca até o período de 4 semanas após a aplicação do paraquat.

Simultaneous determination of residues of paraquat and diquat in potatoes using high-performance capillary electrophoresis with a ultraviolet detection

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSimultaneous determination of residues of paraquat and diquat in potatoes using high-performance capillary electrophoresis with a ultraviolet detectionYuk Y. Wigfield, Kathleen A. McCormack, and Ralph. GrantCite this: J. Agric. Food Chem. 1993, 41, 12, 2315–2318Publication Date (Print):December 1, 1993Publication History Published online1 May 2002Published inissue 1 December 1993https://doi.org/10.1021/jf00036a018RIGHTS & PERMISSIONSArticle Views262Altmetric-Citations39LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (518 KB) Get e-Alerts Get e-Alerts

Effect of herbicide residues in a sandy loam on the growth, nodulation and nitrogenase activity (C2H2/C2H4) of Trifolium subterraneum

The herbicides 2,4-D, amitrole, atrazine, diclofop-methyl, diquat, paraquat and trifiluralin were applied at rates of 0, 2, 5 and 10 μg ai. g−1 to a sandy loam soil and allowed to degrade for 120 days. After this period, subterranean clover seedlings were transplanted into treated soil and the effect of herbicide residues on plant growth, number of nodules formed and nitrogenase activity was investigated. At all rates of atrazine and chlorsulfuron, and at all rates of amitrole in excess of 2 mg ai g−1 of soil, sufficient herbicide remained to be lethal to the seedlings. When amitrole was applied at the rate of 2 mg ai g−1 of soil, plant growth, nodulation and nitrogenase activity of plants were reduced. Residues of diquat reduced all plant parameters studied while, residues of 2,4-D reduced plant growth and nodule formation, but plant nitrogenase activity was unaffected. Residues of trifluralin had no effect on plant growth parameters but the number of nodules formed per plant was reduced. Residues of paraquat and diclofop-methyl had no effect on any of the plant parameters studied.

Behavior of Pesticides in Soil and Other Environment

In Saitama prefecture, the investigations and experiments for pesticide residue were started in 1971. Since the residue of organochlorine insecticides on crop and soil was one of problem awaiting solution at that time, the investigation into the actual condition of the residue of BHC, DDT, aldrin and dieldrin on the fields was performed at the first time. The residue amounts of all of them on soil were higher level in 1971. But, after 1 year, they decreased to about 1/2. BHC and DDT decreased with the lapse of year after 1972, but, aldrin and dieldrin were not decreased and about 0.1ppm of concentration was kept up on soil. Then, the effects of promoting decomposition on soil and suppressing absorption to crops to aldrin and dieldrin were experimented with using soil conditioner. In this experiment, 5 kinds soil conditioneres, fused magnesium phosphate, calcium carbonate, calcium cyanamide, magnesium nitrohumate and compost, were used. By application of fused magnesium phosphate and calcium cyanamide to soil, the pH of soil was rised from acidity to about neutrality, and absorption of aldrin and dieldrin to crops were increased, further, the oxidation from aldrin to dieldrin was promoted. The application of magnesium nitrohumate and compost suppressed absorption of aldrin and dieldrin by crops. The residue amounts of aldrin and dieldrin on soil were decreased by the application of fused magnesium phosphate or calcium cyanamide with compost. And, same effect was recognized in the application of magnesium nitrohumate. Since about 1975, many problems on herbicides were brought with rapid increase of used amount of herbicides. Then, the behavior of herbicides was investigated in paddy fields. In water for irrigation or drain, the detectable times of chloronitrofen, benthiocarb, molinate and simetryne were in conformity with used time in paddy fields. When, the residue on soil was experimented with pot, the residue amounts of benthiocarb and simetryne under watering condition were more little than under flooding condition. Then, the leaching tests of several herbicides were performed with lysimeter. In this experiments, it became clear that the amounts of herbicides moving to a lower soil layer and leached out increased with the increase in water solubility of the herbicide. In 1976, the problems on paraquat was brought at the first time. In connection with this, the residue of several herbicides on soil in tea fields in which several herbicides were used twice per year among seven years was investigated. It became clear that the residues of paraquat and diquat on soil were not decrease after stopped application of herbicides. Since accumulation of paraquat to soil was anxious, the influence of paraquat to the growth of some crops, turnip, carrot and so on, was experimented with used two type soils, alluival soil and volcanic ash soil, to which paraquat was added with high concentration. The influence of paraquat was more clearly in volcanic ash soil for weak soil adsorption of paraquat. On the crops in volcanic ash soil over 100ppm soil concentration of paraquat, chlorosis was appeared and the yield was decreased clearly. It became clearly by the investigation into the actual condition that the residues of paraquat in fields were related with used amount in fields.

Reverse-Phase Liquid Chromatographic Determination of Paraquat and Diquat in Agricultural Products

A simple, rapid, highly sensitive liquid chromatographic method is described for the quantitative determination of paraquat and diquat residues in agricultural products. Paraquat and diquat are extracted with hot dilute hydrochloric acid and are cleaned up on an Amberlite CG-50 column, followed by reverse-phase liquid chromatography on an NH2 column, with ultraviolet detection at 257 nm (paraquat) and 310 nm (diquat). The minimum detectable concentration of both paraquat and diquat was 0.5 ng per injection, which corresponds to a lower detection limit of approximately 0.02 microgram/g in the original samples. Recoveries of paraquat and diquat added to various samples were greater than 79%, and averaged 91 and 90%, respectively, at the 0.1 and 1.0 microgram/g spiking levels.

Application of an enzyme-linked immunosorbent assay (ELISA) to determine paraquat residues in milk, beef, and potatoes.

The USDA Food Safety and Inspection Service (FSIS) has included paraquat on its list of compounds to be considered for monitoring in foods. However, present methods do not easily accommodate the processing of large numbers of samples, thus limiting routine monitoring of the compound. The conventional method, based on spectrophotometry of reduced paraquat solutions, requires time-consuming sample preparation. Although the advantages of immunoassays for pesticide residue analysis have been pointed out, the reported immunoassays for paraquat have only been applied to cases of clinical poisoning or human exposure assessment. In this study, spiked milk, potato, and beef were analyzed directly, without prior cleanup, by an enzyme-linked immunosorbent assay (ELISA).

Analytical method for the simultaneous determination of diquat and paraquat residues in potatoes by high‐pressure liquid chromatography

AbstractA novel method was developed for the simultaneous determination of diquat and paraquat residues in potatoes. Potato tissues were spiked at several levels and extracted with acid using a micro‐reflux procedure with 5 g of sample; this was followed by adjusting the hydrolyzate pH to 9 to 10 and using a silica Sep‐Pak for rapid clean‐up and preconcentration. Aliquots of the final eluate were taken to dryness, dissolved in the h.p.l.c. mobile phase and analyzed as their heptanesulfonate ion‐pairs by u.v.‐h.p.l.c. (reverse phase column chromatography) at 254 and 313 nm for paraquat and diquat, respectively. A detection limit of approximately 0.05 mg kg−1 dication in a 5‐g sample of spiked potato (i.e. 0.25 μg ml−1 final extract) was achieved. Recoveries of 79.5 to 97.6% were obtained at spiking levels of 0.05 to 5.0 mg kg−1 for diquat and paraquat with coefficients of variation not greater than 8.27%. The method was developed and validated using 14C‐radiolabelled diquat and paraquat; u.v.‐h.p.l.c. recoveries were comparable with recoveries determined by radioassay. Several parameters affecting the extraction, adsorption and chromatography of diquat and paraquat were evaluated. The formula weights of diquat and paraquat were determined and their importance described; they were determined as mono‐ and tetra‐hydrates, respectively.

Photodegradation of Paraquat Applied to Polyethylene Mulch Film

Abstract Field experiments were conducted to determine the concentration of paraquat residue on black or white polyethylene mulch 0 to 144 hr after application of paraquat at 1.12 kg·ha−1. Effects of eluant from mulch on vigor of 6-week-old tomato (Lycopersicon esculentum Mill. ‘Duke’) plants were also measured. Mulch color had no effect on the rate of photodegradation or on the degree of plant injury. Substantial plant injury was observed from eluants collected from 0 through 96 hr after application of paraquat, with significant injury present until 120 hr after application. After 120 hr, plant vigor was acceptable for their survival, and injury was minimal. Concentration (in the eluant) of paraquat eluted with water from the polyethylene decreased from 275 ppm to <1 ppm from 0 to 144 hr after application, respectively. Significant plant injury was associated with recoverable concentrations >30 ppm of paraquat after 96 hr. Chemical names used: 1,1′-dimethyl-4,4′-bipyridinium salts (paraquat).

The column efficiency for the determination of paraquat residues in soil

Three cation exchange columns have been studied i.e., 1.0 x 50.0 cm. with cation exchange resin 5.0 grams, two of 0.6 x 45.0 cm. with difference cation exchange resin size, 5.0 and 2.0 grams for th...

Determination of paraquat residues in soil by an enzyme linked immunosorbent assay

A rapid, convenient and accurate method, based upon an enzyme linked immunosorbent assay (ELISA), is described for the determination of paraquat residues in soil. Polystyrene plates, coated with paraquat-keyhole limpet haemocyanin (KLH) conjugate, are incubated with the test samples and a known amount of monoclonal antibody. Residual antibody that has not reacted with free paraquat in the sample combines with paraquat-KLH on the plate. The determination of the fixed antibody is achieved by the addition of peroxidase labelled rabbit anti-mouse immunoglobulin G followed by reaction with a chromogenic substrate. The enzyme activity of the solid phase is determined from the absorbance measurements, which are inversely proportional to the concentration of paraquat. The method shows high specificity and correlates well with the traditional ion exchange-spectrophotometric method for the determination of paraquat.

A Comparison of Capture-Recapture with Capture-Removal for Quail Populations

The effects of paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride) on reproduction and growth of northern bobwhite (Colinus virginianus) were studied. In the parent generation (P) paraquat was administered at 0, 20, 60, and 180 ppm for 6 weeks. Reproductive variables examined included egg production, fertility, hatchability, chick abnormalities, and chick survival and weights to 7 days of age. Untreated breeders in the second generation (F1) phase were the offspring of the various groups in the first generation phase. Reproductive variables examined included egg production, number of days to first and last egg of a 20-egg clutch, fertility, and hatchability. P hens fed 180 ppm laid fewer eggs (all differences are at P < 0.05) during treatment compared to their pre-treatment period and to controls, and had lower ovary and oviduct weights. There were no differences in P fertility nor in chick abnormalities or survival as compared to controls. Chicks from P parents fed 20 ppm paraquat were heavier than all other treatments. P male and female post-treatment weight did not differ from pre-treatment weight. F, hens from paraquat-treated parents started laying 1 week later than controls and produced eggs at a lower rate resulting in clutch completion 10 days later than controls. There were no differences in F, fertility, hatch, or relative testes, ovary, and oviduct weights. Adult F, hens from parents fed 60 and 180 ppm paraquat weighed less. J. WILDL. MANAGE. 49(4):1066-1073 Paraquat is used extensively throughout the world for the control of weeds in orchards and crop fields and as a crop desiccant. Increased use of paraquat has resulted from an increase in no-tillage agriculture. Paraquat is available in the United States primarily as paraquat dichloride, a 29.1% liquid concentrate containing 0.9 kg paraquat cation/3.8 liter. The recommended field application rate usually ranges from 0.28 to 1.12 kg paraquat cation/ha (Ortho Tech. Inf., Chevron Chem. Co., Richmond, Calif., 1974). Residues of about 30 ppm in alfalfa and 60 ppm in adventitious graminaceae have been found after paraquat treatment at a r commended field level (De Lavaur et al. 1973). Paraquat residues have been reported to be as high as 1,000 ppm in herbage on grazing plots treated with the highest recommended application level (Calderbank et al. 1968). Some wildlife species may be affected by recommended field application rates of paraquat (Ernest 1971, De Lavaur et al. 1973, Dial and Bauer 1984). De Lavaur et al. (1973) found that 50% of hares (Lepus europaeus) exposed to alThis content downloaded from 157.55.39.83 on Sun, 09 Oct 2016 05:00:36 UTC All use subject to http://about.jstor.org/terms

PERSISTENCE AND AVAILABILITY OF PARAQUAT IN A LETHBRIDGE CLAY LOAM SOIL

To determine the capacity of the Lethbridge soil to inactivate paraquat, applications equivalent to a maximum of 3000 kg/ha of paraquat were made in growth chamber and field experiments. In the growth chamber and field, more than 600 and 1000 kg/ha, respectively, of paraquat in one application were required to reduce wheat growth by 10%. Paraquat residue levels in the field soil did not decrease after the first summer. Paraquat residue was not found in wheat grain growing in soil with 1650 kg/ha of paraquat in the 0–15 cm layer, but it was detected in plant leaves. The paraquat associated with plant leaves could have resulted from contamination of the leaves by soil rather than from translocation from roots to leaves. The 500 kg/ha rate of paraquat reduced the cation exchange capacity by 5%; however, further paraquat additions did not cause additional reductions. Paraquat could likely be applied for several hundred years at currently recommended rates for weed control on chemical fallow and not exceed the ability of Canadian Prairie soils to inactivate it. Key words: Paraquat, persistence, availability, inactivation, wheat, soil

Rapid Method for Extraction and Reverse Phase Liquid Chromatographic Determination of Paraquat Residues in Water

Abstract A simple and fast analytical method is described for the quantitative determination of low levels of paraquat residues in water. The method involves extraction and concentration of paraquat in water by using a C18 Sep-Pak cartridge followed by reverse phase high performance liquid chromatographic determination with ultraviolet detection at 257 nm. Recoveries of paraquat from spiked samples were above 93% with a coefficient of variation of 6.1%. The method can be used for water samples with paraquat concentrations as low as 0.05 ppm.

Sampling and analysis of airborne residues of paraquat in treated cotton field environments

A method was developed for the analysis of paraquat residues in airborne particulate matter collected by filtration or impaction. The method is based on extraction of paraquat with 6N hydrochloric acid, transfer of residue to saturated ammonium bicarbonate solution, and reduction of the resulting residue with alkaline sodium borohydride to a mixture of two tertiary amines with subsequent determination by nitrogen-selective gas chromatography (GLC). Recoveries ranged from 74 to 96% for filters spiked at 0.05 microgram and above; the limit of detection is approximately 0.5 ng/m3 for high volume air samples. Paraquat concentrations measured in the air downwind from two commercial applications to cotton during spraying fell regularly from extrapolated interval-average values of 4.31 and 10.7 microgram/m3 at the 1 m downwind edge of the two fields to less than 50 ng/m3 at approximately 400 m downwind. Downwind samples taken 2 to 4 hr after spraying contained 1 to 10% as much paraquat as those during spraying, and by 5 to 7 hr no paraquat was detectable in the downwind air. Paraquat was also found in the airborne particulate matter during mechanical harvesting of one of the fields, the maximum interval-average values being 1,245 and 516 ng/m3 just outside and inside an open cab, respectively. The analytical findings for paraquat are compared with those for S,S,S-tributylphosphorotrithioate (DEF), a component of the harvest aid mixture employed, and discussed in terms of occupational exposure, potential hazard, and recommended occupational practices.

The effects of paraquat and glyphosate residues in sprayed herbage on the development of seedlings of a normal and a paraquat‐tolerant variety of Lolium perenne

AbstractParaquat and glyphosate were sprayed on to simulated swards in a glasshouse experiment. Residues of these herbicides depressed emergence, growth and survival of Lolium perenne seedlings sown after spraying.Residues of paraquat applied at a rate (1·5 kg ha‐1) within the range normally used for sward destruction killed nearly all seedlings of a normal L. perenne variety, Barlenna, but had much less effect on the paraquat‐tolerant variety, Causeway. It was estimated that Causeway was almost nine times as tolerant of paraquat residues as Barlenna. Sowing at a depth of 20 mm gave some protection against paraquat residues. A delay of 10 d between spraying and sowing had equivocal effects. It was concluded that residues of paraquat used for killing swards before direct drilling may hinder the establishment of normal L. perenne varieties but not of paraquat‐tolerant varieties.Residues of glyphosate had equal effects on the two varieties and the effects were severest on seedlings sown on the soil surface immediately after spraying. It is thought to be unlikely that glyphosate residues in sprayed herbage would be a problem in direct drilling.

Time and Rate of Paraquat Application for Curing Meadow Vegetation for Winter Grazing1

AbstractWinter grazing of paraquat (1,1 dimethyl‐4,4 bipyridinium ion)‐cured meadow vegetation has been shown to hold potential as an alternative to the conventional cut‐stack‐feed practice in the Great Basin meadowlands. Additional information was needed to define (i) the minimum levels of paraquat required for curing; (ii) the best application time; (iii) the comparative effectiveness of above‐canopy spray release with within‐canopy spray release.Plots were treated with paraquat at rates from 0.06 to 0.56 kg/ha in July of 2 years. Paraquat applied in the morning, midday, and evening hours evaluated plant maturity, illumination, temperature, relative humidity, and surface soil moisture in relation to the chemical's effectiveness to arrest the loss of herbage N.Vegetation was satisfactorily cured with 0.11 kg/ha paraquat. Crude protein concentrations of meadow vegetation exceeded 7% in July, and treatments in that month maintained concentrations above 5.5% for 160 days; naturally cured vegetation then contained less than 4%. Yield losses in treated plots 90 days after treatment ranged from 22 to 30% but were no greater than those in control plots. Dispensing the spray above the canopy was more efficient than dispensing it within the canopy, but the difference is believed to be a result of poor spray coverage from the within‐canopy treatments. Morning, midday, and evening applications did not produce significantly different treatment means. Crude protein concentration was higher in vegetation treated on sunny days than on overcast days, but this was due to sunny day effect rather than an increase in effectiveness of paraquat. Paraquat residue at 100 days after treatment at the rate of 0.34 kg/ha or less ranged from 3 to 15 ppm.

Effect of Thatch on Residual Activity of Nonselective Herbicides Used in Turfgrass Renovation1

AbstractParaquat (1,1′‐dimethyl4,4′‐bipyridinium ion) and glyphosate (N‐[phosphonomethyl]glycine) are used for controlling existing vegetation in turfgrass renovation programs. While these nonselective herbicides are rapidly inactivated in many soils, the effect of a thatch layer at the soil surface on the residual activity of these herbicides has not been reported. The purpose of this study was to determine the effect of thatch on the residual activity of paraquat and glyphosate as it affects the establishment of perennial ryegrass (Lolium perenne L.) from seed.Paraquat and glyphosate were applied to Kentucky bluegrass (Poa pratensis L.) turf growing on an Aquic Arquidoll (Flanagan silt loam) at thatchy and thatchfree sites. Establishment of perennial ryegrass on paraquat‐treated thatchy sites was inhibited due to herbicide residues in the thatch. Modification of the thatch by soil incorporation following core cultivation, or removal of the thatch layer by vertical mowing, significantly improved the percent cover of ryegrass on these sites. Glyphosate showed no adverse affects on perennial ryegrass development. Placement of clipping debris containing paraquat residues onto the soil surface inhibited emergence of perennial ryegrass and Kentucky bluegrass in greenhouse studies. Adsorption of paraquat by thatch was rapid, but the tenacity with which it was adsorbed appears to differ from soil as evidenced by field and laboratory studies.

Residues of toxaphene, DEF, and paraquat in plant parts and gin waste from a treated cotton field.

The origin and fate of the gin waste residues of three chemicals--toxaphene, DEF, and paraquat--used frequently in cotton production in California were studied. Residues were determined for foliage and bolls in the live plants, for lint and seed in harvested seed cotton, and for gin waste and its lint and non-lint components, following commercial treatments to the cotton crop. Gin waste residues were followed during five months of open storage to ascertain dissipation rates in a typical waste sample. Relatively high residues of each of the three chemicals persisted at harvest, during storage prior to ginning, and in stored gin waste. The major proportion of gin waste residue was associated with the non-lint components--leaf parts, burrs, stems and other foreign matter. Average stored gin residues in the lint and non-lint components were 13 and 60, 11 and 58, and 5 and 10 ppm for toxaphene, DEF, and paraquat, respectively, during the open storage period.