Uptake and translocation of non-ionised pesticides in the emergent aquatic plant parrot feather Myriophyllum aquaticum

The uptake of four (14)C-labelled non-ionised compounds, the methyl carbamoyloxime insecticide/nematicide oxamyl and three model phenylureas, from solution by rooted stems of the aquatic plant parrot feather [Myriophyllum aquaticum (Vell.) Verdc], together with translocation to the emergent shoots, was measured over periods of 24 and 48 h. Uptake into the submerged tissues of roots and stem base could be ascribed to two processes: movement into the aqueous phase of cells and then partitioning onto the plant solids. This latter process was related to lipophilicity (as measured by the l-octanol/water partition coefficient, K(ow)) and gave rise to high uptake rates of the most lipophilic compounds. Translocation to shoots was passive and was optimal at log K(ow) approximately 1.8, at which the efficiency of translocation of compound was about 40% of that of water. This optimum log K(ow) was identical to that observed previously in barley, although the translocation efficiency was somewhat less in parrot feather. Solvation parameters were applied to model uptake and translocation of a set of ten compounds by barley with the particular objective of understanding why translocation efficiency is lower at log K(ow) > 1.8.     

Relationships between lipophilicity and root uptake and translocation of non-ionised chemicals by barley

The uptake by roots from solution, and subsequent translocation to shoots in barley, of two series of non-ionised chemicals, O-methylcarbamoyloximes and substituted phenylureas, were measured, Uptake of the chemicals by roots was greater the more lipophilic the chemical, and fell to a lower limiting value for polar chemicals. Translocation to the shoots was a passive process, and was most efficient for compounds of intermediate polarity. Both processes had reached equilibrium within 24h of treatment. The reported behaviour of many pesticides in various plant species agrees with the derived relationships, but the detailed mechanisms of these processes are unknown.     

Adsorption of systemic fungicides and a herbicide by some components of plant tissues,in relation to some physicochemical properties of the pesticides

Lignin, an important component of plant tissues, adsorbed five systemic fungicides and one herbicide (carbendazim, triadimefon, nuarimol, triarimol, fenarimol and fluometuron) more strongly than bovine serum albumin, cellulose, ethylcellulose or sodium polygalacturonate. Significant correlations were found between the extent of the adsorption of the pesticides on the lignins extracted from three different plant species, and the log Poet (Poet is the octan-1-ol/water partition coefficient) of the compounds. The more lipophilic fungicides triarimol and fenarimol (log Poet about 2.6) were adsorbed to the greatest extent. Fluometuron, triadimefon and nuarimol (log Poet about 2.0) were moderately adsorbed, whereas carbendazim with the lowest log Poet (1.34 at pH 5.0), was adsorbed more than expected from its Poet value. The anomaly of carbendazim is discussed; it is ascribed to it's partial protonation at pH 5.0, whereas the other pesticides were non-ionised.     

Physicochemical factors affecting the uptake by roots and translocation to shoots of amine bases in barley

The uptake by barley roots from nutrient solution and subsequent transport to shoots of two series of amine bases were measured over 6 to 72 h. The compounds were chosen to span systematically ranges of lipophilicity (assessed using 1-octanol/water partition coefficients, K_ow) and pKa that would include commercial pesticide amines. In a series of six substituted phenethyl amines, strong bases with pKa∽9·5, all the compounds were strongly taken up by roots from solutions of pH 8·0; uptake declined substantially as the pH was lowered to 5·0, especially for the compounds of intermediate lipophilicity (log K_ow 2 to 3). This uptake could be ascribed to three processes: (i) accumulation of the cation inside the root cells due to the negative charge on the plasmalemma, as given by the Nernst equation and important only for the polar compounds which have low permeation rates through membranes; (ii) accumulation into the vacuole by ion-trapping, which was the dominant process at high pH for all compounds and at all pH values for the compounds of intermediate lipophilicity; (iii) partitioning on to the root solids, substantial only for the most lipophilic compounds. Translocation to shoots was proportional to uptake by roots, this ratio being independent of external pH for each compound and being optimal for the compounds of intermediate lipophilicity. Such proportionality was also observed in a series of three weaker bases of intermediate lipophilicity, in which compounds of pKa 7·4 to 8·0 were also well taken up and translocated whereas the very weak base 4-ethylaniline (pKa 5·03) was much less so. Tests with quaternised pyridines confirmed that organic cations move only slowly through membranes. The observed behaviour of the amines could be modelled reasonably well assuming that transport within the plant was dominated by movement across membranes of the non-ionised species, and this appeared to be true even for the most lipophilic phenethylamine (log K_ow 4·67) studied, though its long-distance movement would be as the protonated species. © 1998 Society of Chemical Industry     

Development of a predictive uptake model to rationalise selection of polyoxyethylene surfactant adjuvants for foliage-applied agrochemicals

Composition-concentration relationships between a series of C₁₃/C₁₄ polyoxyethylene primary alcohol (AE) surfactants and the foliar uptake enhancement of five model neutral organic compounds were examined in factorially designed experiments on wheat (Triticum aestivum L.) and field bean (Vicia faba L.) plants grown under controlled environment conditions. Model compounds were applied to leaves as c.0.2-μl droplets of 0.5 g litre^?1 solutions in aqueous acetone in the absence or presence of surfactants at 0.2, 1 and 5g litre^?1. Uptake of the highly water-soluble compound, methylglucose (log octanol-water partition coefficient (P) = - 3.0) was best enhanced by surfactants with high E (ethylene oxide) contents (AE15, AE20), whereas those of the lipophilic compounds, WL110547 (log P = 3.5) and permethrin (log P = 6.5), were increased more by surfactants of lower E contents, especially AE6. However, there was little difference between AE6, AE11, AE15 and AE20 in their ability to promote uptake of the two model compounds of intermediate polarity, phenylurea (log P = 0.8) and cyanazine (log P = 2.1). Absolute amounts of compound uptake were also influenced strongly by both surfactant concentration and plant species. Greatest amounts of uptake enhancement were often observed at high surfactant concentration (5 g litre^?1) and on the waxy wheat leaves compared with the less waxy field bean leaves. The latter needed higher surfactant thresholds to produce significant improvements in uptake. Data from our experiments were used to construct a simple response surface model relating uptake enhancement to the E content of the surfactant added and to the physicochemical properties of the compound to be taken up. Qualitative predictions from this model might be useful in rationalising the design of agrochemical formulations.     

Phloem translocation of non-ionised chemicals in Ricinus communis

Techniques using R. communis were modified to enable the movement of chemicals in phloem and the factors controlling their distribution in the plant to be described quantitatively. The non-ionised chemicals tested, aminotriazole, O-methylcarbamoyloximes (including aldoxycarb and oxamyl) and phenylureas, spanning a range of lipophilicity of log K_OW= ?0.87 to +2.27, all freely entered the phloem. However, only the more polar compounds were retained sufficiently in the phloem to be transported over long distances, indicating that polar compounds cross cell membranes more slowly than compounds of intermediate lipophilicity; these findings substantiate the ‘intermediate permeability hypothesis’ of phloem translocation of xenobiotics. However, the amount of chemical reaching or retained in the sink tissues, especially in the root, was small even for the chemicals that were translocated best in the phloem.     

Uptake of chemicals from foliar deposits: Effects of plant species and molecular structure

The uptake from foliar deposits of 10 ¹⁴C-labelled compounds into each of 10 species of field-grown plants was measured 26 h after deposition by combustion of leaf tissue after removal of surface deposits. The compounds, which included eight pesticides, covered a wide range of lipophilicity and each was formulated in the same way; they were applied as droplets with a microsyringe. Uptake varied greatly between the species. All compounds were taken up well into maize and Xanthium pennsylvanicum, whereas relatively little entered the leaves of apple or orange. Uptake into the six other species varied according to the compound. Amongst the eight non-polar compounds, no relationship between the rate of uptake and molecular size was discerned, and only in X. pennsylvanicum was uptake related to the partition coefficient and water solubility. Considering all the compounds, weak relationships were observed between molecular cross-sectional area and uptake into four species. The range of the uptake rates (×130) was small compared with those of octan-1-ol-water partition coefficients (×10¹⁰) and water solublities (×10⁷) shown by the 10 compounds. Possible reasons for the absence of correlations between the uptake and the molecular properties considered are discussed. The results are consistent with either separate routes of cuticular entry for non-polar and polar compounds, or a common route for both types of compound. The generally poor uptake by apple and orange leaves, which may be related to their thick cuticles, highlights the need to develop special formulations to optimise uptake into these species.     

Foliar uptake of pesticides—Present status and future challenge

Uptake of pesticides into plant foliage varies with plants and chemicals, and can be greatly influenced by adjuvants and environmental conditions. It is known that the penetration of pesticides into plant leaves is related to the physicochemical properties of the active ingredients, especially molecular size and lipophilicity. However, the uptake rate of a compound cannot be predicted by either of them or even combination of them. For a specific chemical, uptake varies greatly with plant species and there is no simple method at the moment to quickly evaluate the leaf surface permeability of a plant. Various adjuvants are being used to increase the penetration of pesticides into target plant foliage, but their effects vary with chemicals and plant species. The mechanisms of action of adjuvants in enhancing pesticide uptake remain unclear despite the effort made during the last three decades. Modern analytical and microscopic techniques provide powerful tools to deepen our understanding in this field. However, a more multidisciplinary approach is urgently needed to elucidate the transcuticular diffusion behaviour of pesticides and the mode of action of adjuvants. A better understanding of the foliar uptake process should lead to a more rational use of pesticides and minimize their negative impact on the environment.     

Relationships between lipophilicity and the distribution of non-ionised chemicals in barley shoots following uptake by the roots

Determinations were made of the distribution of two series of non-ionised chemicals, ^O-methylcarbamoyloximes and substituted phenylureas, in barley shoots, following uptake by the roots from solution. The concentrations in basal and central shoot sections became constant after 24 to 48 h for all but the most lipophilic chemical studied, and were then greatest for the more lipophilic chemicals. Amounts in the leaves generally increased up to 72 or 96 h, when degradation balanced translocation. The accumulation of chemical in the lower section of shoots can be ascribed to a partitioning process similar to that in roots, the chemical being partitioned between the shoot and the xylem transpiration stream; this uptake could be estimated from the octan-1-01/water distribution coefficients, and was predicted to be greatest for compounds for which log K_ow=4. 5.     

Uptake by roots and translocation to shoots of two morpholine fungicides in barley

Despite being lipophilic, morpholine fungicides are systemic in plants. Such transport may be explicable by their protonation (pKa∽7·5) at the pH of plant compartments to yield the more polar cation. This behaviour might be a useful attribute to be incorporated into other classes of lipophilic pesticides. To understand quantitatively the behaviour of the morpholine fungicides, the uptake by roots and transport to shoots in barley of two such ¹⁴C-labelled compounds, dodemorph and tridemorph, were investigated using bathing solutions of differing pH. At pH 5, uptake and transport were small, but increased by approximately two orders of magnitude at pH 8. Tridemorph, the more lipophilic of the two compounds, was highly accumulated by roots at pH 8 and moderately translocated to shoots. In contrast, dodemorph was translocated to shoots at pH 8 with remarkable efficiency, moving into the xylem across the endodermis at 23 times the efficiency of water, though accumulation in roots was less than that of tridemorph. Behaviour at 24 h was largely similar to that at 48 h for both compounds, indicating that uptake and translocation are equilibrium processes maintained over time. Transport to shoots for each compound was directly proportional to the concentrations accumulated in the roots, except at low pH where partitioning into root solids became proportionately more important with such material not being directly available for transport to the xylem across the endodermis. Uptake and transport of these basic fungicides are explained in terms of their partitioning and of their accumulation in acidic plant compartments by ion trapping as the protonated form; this behaviour is discussed in relation to the pKa and lipophilicity of these compounds. © 1998 Society of Chemical Industry     

Factors affecting the foliar absorption and redistribution of pesticides. 1. Properties of leaf surfaces and their interactions with spray droplets

Foliar uptake into eleven plant species, grown under controlled environment, has been determined for spray deposits of glyphosate, 2, 4-D and prochloraz applied as solutions in aqueous solvents in the presence and absence of an ethoxylated nonylphenol surfactant. Over 24 h, uptake of glyphosate did not exceed 6% of applied chemical into any species whereas uptake of 2, 4-D and prochloraz differed between species and was modified significantly by the addition of surfactant. Uptake of prochloraz was increased consistently by adding surfactant, but the response of 2, 4-D was variable. Increased uptake was attributed mainly to surfactant-enhanced wetting of the leaf surfaces. Uptake of prochloraz per unit wetted area increased in the presence of surfactant but that of 2, 4-D decreased. Uptake of either chemical did not correlate with the presence of specialised leaf surface structures, cuticular morphology or distribution of the chemicals within the dried deposits. The dried chemicals were distributed either uniformly or as annuli as a result of complex interactions between the active ingredient, surfactant and the leaf surfaces. Regression analysis indicated that the epicuticular wax and cuticular membrane were the major sinks for both 2, 4-D and prochloraz during the 24-h period.     

Comparative systemic translocation of several xenobiotics and sucrose

The systemic movement of several xenobiotics was compared in soybean and barley. The more symplastic compounds were also compared to the movement of sucrose. The uptake and efflux from potato tuber tissue was studied and related to the in vivo translocation patterns. The patterns of translocation ranged from primarily apoplastic to ambimobile to symplastic. When the percentage of xenobiotic available for translocation was evaluated there were major differences in patterns of translocation, between plant genera. In barley fenapanil, fenarimol, and oxamyl exhibited primarily apoplastic transport while all three were more ambimobile in soybean. Basipetal transport of oxamyl was 4.2% in barley compared to 30.8% in soybean. Basipetal translocation of benomyl remained very low at 3.0 and 4.1% in barley and soybean, respectively, while sucrose was about 60% in both species. Glyphosate and sucrose were translocated in a similar pattern. The transport of 2,4-D was primarily symplastic, however, retention in the tissue appeared to limit the rate of movement when compared to sucrose. Uptake and efflux of fenapanil, fenarimol, and 2,4-D illustrated the possible role that cellular binding or partitioning may play in systemic translocation. In conjunction with the uptake and efflux, and systemic movement in plants, the octanol/water partition coefficients, log P, for fenarimol and fenapanil, 0.67 and ?0.03, respectively, are correlated with the possible role of cellular binding or partitioning in the systemic movement of xenobiotics.     

Pesticides in surface water runoff in south-eastern New York State, USA: seasonal and stormflow effects on concentrations

Samples from two streams (Kisco River and the Middle Branch of the Croton River) in the Croton Reservoir system in south-eastern New York State, USA were sampled from May 2000 through to February 2001 in order to document the effect of land use, streamflow and seasonal patterns of application on pesticide concentrations in runoff from developed watersheds. Many of the pesticides detected most commonly in this study are generally used in developed areas, and particularly on turfgrass. Pesticide concentrations were generally higher, and the numbers of compounds were generally larger, in samples from the Kisco River than in samples from the Middle Branch, probably because the Kisco River drainage has a greater population density and is more extensively developed. Four pesticides (2,4-D, 2,4-D-methyl, dicamba and metalaxyl) were detected in at least one sample from the Kisco River at a concentration >1 microg litre(-1), and no pesticides were detected at concentrations >0.4 microg litre(-1) in Middle Branch samples. No human-health-based water-quality standards were exceeded by samples from either site in this study, but samples from the Kisco River contained four insecticides (carbaryl, chlorpyrifos, diazinon and malathion) and one herbicide (2,4-D) in concentrations that exceeded water quality criteria for the protection of aquatic life. The highest concentrations of most compounds occurred during stormflows in both streams in June, September and December, 2000. The lowest concentrations of most compounds at both sites occurred during baseflows from October 2000 through February 2001, even though the concentrations of many compounds increased substantially at the Kisco River site during stormflows in November and December. Detailed data on the variability of pesticide concentrations during stormflows indicate that there may be two sources of pesticides in the Kisco River watershed: (1) elevated concentrations of pesticides during peak flows that occur early in stormflows likely reflect runoff from paved areas, and (2) elevated concentrations during peak flows that occur later in stormflows from areas with lesser amounts of pavement. Data from the Kisco River indicate that the relation between storm discharge and pesticide concentrations varies among compounds, in part because of variation in seasonal application patterns. These variations in the timing of application result in not all stormflows producing increased concentrations of pesticides. Overall, these results indicate the importance of stormflow sampling throughout the year in assessing pesticide fate and transport in urbanized, developed areas.     

Herbicide risk assessment for non-target aquatic plants: sulfosulfuron--a case study

Herbicides entering the aquatic environment by spray drift, run-off and leaching to field drains may cause adverse effects on non-target aquatic vegetation. The potential for such effects has typically been evaluated from tests with floating, monocotyledonous Lemna sp. However, concern has been expressed as to whether this species could be used to indicate potential effects on other vegetation types, particularly rooted, submerged, emergent or dicotyledonous species. In 1997, the Centre for Aquatic Plant Management undertook development of new tests based on the additional species, Glyceria maxima (Hartm) Holmb, Lagarosiphon major (Ridl) Moss and Myriophyllum spicatum L. The resulting methodology was used to assess the effects of the sulfonylurea herbicide, sulfosulfuron on these species. Data presented here demonstrate that exposure to initial sulfosulfuron concentrations of 3.33 microg litre(-1) for up to 21 days was tolerated by these species and that adverse effects were observed only when plants were exposed to initial concentrations of 3.33 and 10 microg litre(-1) for 70 days. As the occurrence of such high initial concentrations for long periods is unlikely in the aquatic environment, sulfosulfuron is not expected to have adverse effects on the growth of these species. This study has also demonstrated that G maxima, L major and M spicatum grown in small outdoor tanks can be used successfully to assess the effects of crop-protection products on non-target aquatic flora.     

Analysis of foliar uptake of pesticides in barley leaves: Role of epicuticular waxes and compartmentation

Uptake of pesticides into barley leaves was measured under controlled conditions. Leaves detached from plants were submerged in aqueous solutions of ¹⁴C-labelled (2,4-dichlorophenoxy)acetic acid, triadimenol, bitertanol and pentachlorophenol. Uptake was biphasic. A short (30-min) period with high rates of uptake was followed by uptake that proceeded more slowly and was steady over hours. Compartmentation of pesticides was studied by desorbing pentachlorophenol from leaves previously loaded with [¹⁴C]pentachlorophenol. From the uptake and desorption kinetics it was concluded that penetration of pesticides proceeds as follows: the compounds are first sorbed at the surface of epicuticular wax aggregates where they are in contact with the donor solutions. Solutes then diffuse through the surface wax aggregates into the cuticle. Equilibrium between donor solutions, surface wax and cuticle is established in about 30 min. After this time the amounts of solutes in these compartments no longer increase. Uptake after this time represents penetration into the leaf cells. This fraction of the pentachlorophenol is retained irreversibly, while that sorbed in wax and cutin can be desorbed again. All compounds were sorbed in cuticular waxes and partition coefficients wax/water were determined. On a mass basis only 5 to 10% of the amounts sorbed in cutin are sorbed in wax. This comparatively low solubility in wax contributes to the barrier properties of cuticular waxes. The other determinant of permeability is the very low mobility of solutes in cuticular waxes.     

SOME EFFECTS OF THE DESTRUCTION OF AQUATIC WEEDS IN LAKE ROTOITI, NEW ZEALAND

Summary. A bay in Lake Rotoiti was completely cleared of a heavy infestation of Lagarosiphon major by means of diquat at a concentration of 05 ppm. Weed kill was alow and there was no reduction of dissolved oxygen in the area, probably because of the cool weather at the time (April). Considerable numbers of planktonic algae developed, but after a few months it was apparent that herbicide treatment had caused an exchange of Lagarosiphon for a less massive growth of Nilelta species. Some of the changes in bio-logical production were measured and an explanation of the observed plant succession is offered.
Quelques effets de la destruction des mausaises herbes aquatiques dans le lac Rotoiti, en Nouvelle-Zélande     

Uptake and translocation of some pesticides by hypocotyls of radish seedlings

Some of the factors affecting absorption and translocation of pesticides by the hypocotyls of intact radish (Raphanus sativus, L., cv. Black Spanish) seedlings have been studied, particular attention being given to the triazine herbicides simazine, atrazine and atraton. Uptake and translocation appear to be largely passive processes and by contrast with foliar absorption seem to be unaffected by humidity, con-centration, light and by the aqueous solubilities of the compounds. Diffusion across the tissues of the hypocotyl, rather than rate of transpiration, appears to determine the rate at which atrazine and simazine are translocated to the cotyledons. For several pesticides there is a qualitative relationship between the percentages of the compounds translocated to the upper portion of the shoots and their partition coefficients in oil/water systems. In conclusion, some consideration is given to the relative importance of uptake by roots and shoots under field conditions.     

Pesticide effects on secondary metabolism of higher plants

Secondary compounds serve both endogenous and exogenous functions in higher plants because they are involved in plant growth and development as well as intraspecies and interspecies interactions. Documentation of the effects of pesticides on secondary compound biosynthesis in higher plants is increasing. While several herbicides have been reported to reduce levels of secondary compounds by non-specific mechanisms, a few herbicides, such as alachlor and glyphosate, directly affect specific biosynthetic steps. Alachlor reduces flavonoid synthesis at a step late in the biosynthetic pathway, and glyphosate blocks synthesis of all cinnamate derivatives by inhibiting 5-enolpyruvyl shikimate-3-phosphate (EPSP) synthase. Inhibition of EPSP synthase also leads to the accumulation of high levels of shikimate, benzoic acids and benzoic acid derivatives. The sulfonylureas and p-nitro-substituted diphenylether (DPE) herbicides can cause increases in the level of cinnamatederived phenolic compounds and the DPEs can cause dramatic increases in terpenoid stress metabolites. Certain fungicides are thought to act through enhancing the capacity of plants to produce phytoalexins. These and other data suggest that sublethal effects of pesticides on target and non-target plants can significantly affect agricultural ecosystems by altering the synthesis of compounds important in inter- and intraspecies interactions.     

Bioassay evaluation of the systemic properties of carboxin in lemon seedlings

Carboxin was toxic to the fungus Deuterophoma tracheiphila. Uptake and translocation of carboxin (2,3-dihydro-6-methyl-5-phenylcarbamoyl-1,4-oxathiin) in lemon seedlings were assessed in plant extracts by a bioassay technique. Root uptake and translocation to stem and leaves were demonstrated from both an aqueous solution and drenched soil. Leaf uptake was lower than root uptake, and could be enhanced by removing the epicuticular wax. Chromatographic tests suggested that the compound responsible for fungitoxicity within plant tissues may have been carboxin itself.     

气相色谱-串联质谱法测定植物样品中17种有机氯农药和8种多氯联苯

建立了植物样品中17种有机氯农药和8种多氯联苯单体的气相色谱-串联质谱(GC-MS/MS)分析方法。样品以 V(丙酮):V(乙酸乙酯)=1:1为溶剂进行提取,采用石墨化炭黑及氨基联合SPE小柱净化,GC-MS/MS测定。25种化合物的平均添加回收率在66.6%~113.1%之间,相对标准偏差(RSD)在4.1%~14.1%之间,方法检出限(MDL)在0.03~0.29 ng/g之间。该方法灵敏度高,满足环境调查的需求。对污染区采集的植物样品进行检测,发现被变压器油污染地区的植物体内含有较高质量分数的PCB28和PCB52,最高达108 ng/g,说明多氯联苯能够通过迁移等途径从土壤传递到植物中。