Aquatic weeds

Acrolein at a concentration of <500 ppm is also used to protect Hquid fuels against microorganisms. The dialkyl acetals of acrolein are also useful in this apphcation. In addition, the growth of algae, aquatic weeds, and moUusks in recirculating process water systems is also controlled by acrolein. 

Triazines. Triazine herbicides are one of several herbicide groups that are heterocycHc nitrogen derivatives. Triazine herbicides include the chloro-, methylthio-, and methoxytriazines. They are used for the selective pre-emergence control and early post-emergence control of seedling grass and broadleaved weeds in cropland (299). In addition, some of the triazines, particularly atrazine, prometon [1610-18-0] and simazine [122-34-9] are used for the nonselective control of vegetation in noncropland (2). Simazine may be used for selective control of aquatic weeds (2). 

Other Heterocyclic Nitrogen Derivative Herbicides. The herbicides in this group are heterocycHc nitrogen derivatives that do not readily fall into one of the previously discussed groups. They have a wide range of uses and properties. Most of these herbicides are used for selective, pre-and/or post-emergence weed control. Amitrole is used for post-emergence, nonselective weed control in non-croplands and also as an aquatic herbicide (2,296). 

Aliphatic-Garboxylics. There are only two herbicides present in this class, trichloroacetate [76-03-9] (TCA) and dalapon [75-99-0]. These are used primarily for the selective control of annual and perennial grass weeds in cropland and noncropland (2,299). Dalapon is also used as a selective aquatic herbicide (427). Dalapon and TCA are acidic in nature and are not strongly sorbed by sods. They are reported to be rapidly degraded in both sod and water by microbial processes (2,427). However, the breakdown of TCA occurs very slowly when incubated at 14—15°C in acidic sods (428). Timing not only accelerates this degradation but also increases the numbers of TCA-degrading bacteria. An HA has been issued for dalapon, but not TCA (269). 

Miscellaneous Trifluoromethyl Compounds. The herbicides in this group are used for a wide variety of weed-control purposes. Acifluorfen, lactofen [77501-63-4] and oxyfluorfen are used for selective, pre-, and post-emergence weed control in croplands. Fluorochloridone is used for selective, pre-emergence weed control in cropland, and fluridone, fomesafen, and mefluidide [53780-34-0] are used for post-emergence control (296). Fluridone is also used as an aquatic herbicide (2). 

Miscellaneous Other Herbicides. The herbicides in this group are not readily included in any of the preceding groups. Acrolein [107-02-8] (2-propenal) is used as a contact, aquatic herbicide. Sethoxydim, clethodim, and tridiphane are used for selective, post-emergence weed control. 

There is a further complication in shallow lakes containing macrophytes (aquatic flowering plants, pteridophytes, and macroalgae). These take up and accumulate nutrients from the water and from the aquatic soil in which they are rooted (sediment). Although these plants are sometimes classed as nuisance weeds, they nevertheless act as an important alternative sink for nutrients which are denied to the plankton. In recent times, a key role of macrophytes in the successful and sustained management of water quality has been identified and explained. ... 

Similarly, blocked intake screens caused by aquatic weeds, mussels, or floating debris reduce the heat transfer potential of the condenser. 

The concept of fibrous polymer formulations was extended to the delivery of aquatic herbicides (56). Several herbicides including Diquat, Fluridone, and Endothal were spun into biodegradable poly-caprolactone. Monolithic fibers and a modified monolithic system were produced with levels of herbicide from 5 to 60% by weight. Laboratory and field trials showed efficacious delivery of the active agent. Fibers provided both targeted localized delivery and controlled release of the herbicide to the aquatic weed. 

Heeds indirectly affect the health of man and animals by harboring animals or insects. Control of aquatic weeds is effective for mosquito (Anopheles quadrimaculatus Say) control by eliminating breeding habitats. In control of the tsetse fly (Glossian spp.) (vector of sleeping sickness in Africa), herbicides are involved to reduce growth of the brush so essential to the survival of the fly. 

Aquatic Weed Control Research Laboratory, Botany Department, Agricultural Research Service, U.S. Department of Agriculture, University of California, Davis, CA 95616... 

The objective of the research reported here was to develop sensitive bioassays which utilize near-whole plant systems of appropriate target aquatic weeds and which require little space and low volumes of incubation medium. Such bioassays could be used to help identify active fractions of chromatographically partitioned allelochemicals and could also be used in prinary screening procedures for newly synthesized agrichemicals. 

Anderson, L.W.J. et al. USDA/ARS Aquatic Weed Research Planning Conference Report. 1982. 30pp. 

Seeds of lettuce and other species have frequently been used to bioassay for the allelopathic activity of plant exudates (17.18.19). As with the use of cell suspensions, there are certain advantages and disadvantages to this methodology. The experimental simplicity, small amounts of material required and short time frame are certainly attractive qualities. However, species used in such bioassays quite often do not represent the actual target species under consideration. This is especially true when terrestrial crop species are substituted for weeds of aquatic systems. Nevertheless, information obtained from such experiments are often valuable when used in conjunction with results of other assays. 

Other aquatic weeds such as reed mat, mangrove (leaves), and water lily (Nymphaceae family plants) have been found to be promising biosorbents for chromium removal. The highest Cr(III) adsorption capacity was exhibited by reed mat (7.18 mg/g), whereas for Cr(VI), mangrove leaves showed maximum removal capacity (8.87 mg/g) followed by water lily (8.44 mg/g). It is interesting to mention that Cr(VI) was reduced to Cr(III), with the help of tannin, phenolic compounds, and other functional groups on the biosorbent, and subsequently adsorbed. Unlike the results discussed previously for the use of acidic treatments, in this case, such treatments significantly increased the Cr(VI) removal capacity of the biosorbents, whereas the alkali treatment reduced it.118... 

Elangovan, R., Philip, L., and Chandraraj, K., Biosorption of chromium species by aquatic weeds Kinetics and mechanism studies, Journal of Hazardous Materials, 152 (1), 100-112, 2008. 

Toxic organic compounds commonly found in groundwater are presented in Table 18.4. Other toxic organic compounds (representing 1% of cases) include PCBs (polychlorinated biphenyls), 2,4-D, 2,4,5-TP (silvex), toxaphene, methoxychlor, lindane, and endrin, of which 2,4-D and silvex are commonly used for killing aquatic and land weeds. Inorganic toxic substances commonly found in... 

No data are available on the toxicity of copper to avian wildlife. All studies with birds and copper use domestic chickens, ducks, or turkeys (Table 3.6). Copper, however, may indirectly affect avian wildlife by curtailing certain prey species. Winger et al. (1984), for example, show that apple snails (Pomacea paludosa) are not only extremely susceptible to copper (LC50 of 24 to 57 pg/L in 96 h immatures most sensitive), but are the primary food of the snail kite (Rostrhamus sociabilis), an endangered species. The decline of the apple snail in southern Florida coincided with the use of copper-diquat to control hydrilla aquatic weeds (Hydrilla verticillata), with serious implications for the snail kite (Winger et al. 1984). 

Bartley, T.R. 1967. Progress report on evaluation of copper for aquatic weed control and herbicide residues on irrigation systems. U.S. Bur. Reclam. Rep. No. WC-32. 58 pp. 

Chancellor, R.J., A.V. Coombs, and H.S. Foster. 1960. Control of aquatic weeds by copper sulphate. Pages 80-84 in Proceedings of The 4th British Weed Control Conference, Brighton, U.K., 4-6 Nov 1958. Soc. Chem. Indus., London. 

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