Soil application, pesticide formulations

Carbofuran is metabolized by hydroxylation and hydrolysis in plants, insects, and mammals. The primary transformation product in most plants appears to be 3-hydroxycarbofuran. However, levels of 3-hydroxycarbofuran and other degradation products in plants are influenced by numerous factors, including plant age, soil type, pesticide formulation, application method and rate, and weather conditions. Oxidation of unconjugated 3-hydroxycarbofuran yields 3-ketocarbofuran, which is, in turn, rapidly hydrolyzed to the much less toxic 3-ketocarbofuran phenol. Accordingly, 3-ketocarbofuran is not likely to be detected as a terminal residue in plants above trace levels. Residue analyses indicated that carbofuran... 

An example of the kinds of data required for land disposal options would be Information on soll/pestlclde Interactions to determine the effect of the pesticide on the soil and soil on the pesticide. The physical composition of the soil and the physical properties of the pesticide and Its formulation will determine the adsorption, leaching, water dispersal, and volatilization of the pesticide which. In turn, determine the mobility of the pesticide In soil. Even pesticides of closely related structures may have very different soil retention properties. Much of this data will be available from that developed to meet other registration data requirements with the exception that disposal rates are often orders of magnitude higher than normal application rates and the difference must be considered. 

The factors which Influence the choice of formulation are pesticide physical properties (melting point, solubility, volatility), pesticide chemical properties (hydrolytic stability, thermal stability), soil application vs. foliar application, crop and cultural practice, pesticide biological properties (crop selectivity, transport), and economics. 

The above brief review illustrates that chemical derivatization techniques have been used extensively for the confirmation of identity of organochlorine residues. In most instances, the lower limits of detectability of the derivatives are substantiaUy lower than the established tolerance values for the parent compounds. Taken in conjunction with the many other modes of derivatization—e.g., during or after gas chromatography (59)— the analyst has a vast array of modification procedures at hand to aid in residue identification. They can be employed for residues in soil, biological, fat, and nonfat extracts and can be successfuUy extended, especially the more specific tests, to the identification of crosscontaminants in pesticide formulations and also fertilizer mixtures. So far, these latter two cases have only been a fringe area of application (60,61). 

The documented occurrence of pesticides in surface water is indicative that runoff is an important pathway for transport of pesticide away from the site of application. An estimated 160 t of atrazine, 71 t of simazine, 56 t of metolachlor, and 181 of alachlor enter the Gulf of Mexico from the Mississippi River annually as the result of runoff (47). Field application of pesticides inevitably leads to pesticide contamination of surface runoff water unless runoff does not occur while pesticide residues remain on the surface of the soil. The amount of pesticides transported in a field in runoff varies from site to site. It is controlled by the timing of runoff events, pesticide formulation, physical—chemical properties of the pesticide, and properties of the soil surface (48). Under worst-case conditions, 10% or more of the applied pesticide can leave the edge of the field where it was applied. 

The main routes of release of endosulfan to soils are application of the compound to crops and land disposal of unused formulated pesticide products containing the compound. 

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. 

Mirex is no longer manufactured, formulated, or used in the United States. Therefore, there is currently no occupational exposure to this chemical associated with its production or application as a pesticide. Current occupational exposure is most likely to occur for workers employed at waste disposal sites or those engaged in remediation activities including removal of soils and sediments contaminated with mirex. There is a slight possibility of exposure for workers involved in dredging activities (e.g., sediment remediation work performed by the Corps of Engineers). 

Method of Application. This is an important research area which ties into development of formulations, especially for soil pesticides or relatively volatile products. 

Somewhat water-soluble pesticides such as acid herbicides will be washed from foliar surfaces and into subsurface soils by rainfall. For example, dislodge-able turf residues of 2,4-D after a 2.54-cm rainfall have been reported to be only 1-5% of those found at 4-8 h after application (Nishioka et al., 1996 USEPA, 1997c). However, dew or rain on aged turf residues may increase their dislodgeability (Nishioka et al, 1996). OP insecticides are semivolatile and will vaporize from surfaces after applications. Chlorpyrifos vaporizes rapidly from lawns if applied in aqueous formulations. Diazinon, which is used on lawns as well as indoors, dissipates even more rapidly. However, the persistence of OP... 

Number and Location of Observation Wells. The precise amount of pesticide which was applied to the soil surface and is available for leaching is known as the source term. For pesticides which are applied directly to the soil, such as granules or liquid formulations sprayed only onto the soil surface, the source term can be assumed to be equal to the total amount of application. 

EXPOSURE ROUTES occupational exposure formulation, manufacture, and field application of this pesticide inhalation skin adsorption ingestion eye and skin contact contaminated air, water, soil, fish, and other aquatic organisms... 

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