Other pesticides

Herbicides are also sometimes classified according to mode of action, selectivity, registered uses, and toxicity. The ever-increasing importance of herbicides and other pesticides and agrochemicals to a wide range of users, regulators, and researchers has led to the development of multiple and extensive computer databases. The primary database resources contain collected information relevant to herbicides, and numerous resource pubHcations are available to those needing information on the various aspects of herbicides (2). 

Historically, the discovery of one effective herbicide has led quickly to the preparation and screening of a family of imitative chemicals (3). Herbicide developers have traditionally used combinations of experience, art-based approaches, and intuitive appHcations of classical stmcture—activity relationships to imitate, increase, or make more selective the activity of the parent compound. This trial-and-error process depends on the costs and availabiUties of appropriate starting materials, ease of synthesis of usually inactive intermediates, and alterations of parent compound chemical properties by stepwise addition of substituents that have been effective in the development of other pesticides, eg, halogens or substituted amino groups. The reason a particular imitative compound works is seldom understood, and other pesticidal appHcations are not readily predictable. Novices in this traditional, quite random, process requite several years of training and experience in order to function productively. 

Agricultural Chemicals. Many claims exist for the use of nickel chemicals as nematocides, miticides, and other pesticides (qv) (191). 

The U.S. FDA monitors foods for half of the approximately 300 pesticides having official EPA tolerances as weU as a number of other pesticides that have no official tolerances. Multiresidue methods, most of which are based on chromatography protocols, are employed (7). Not aU pesticides are monitored on aU foods and sampling (qv) is purposely biased to catch possible problems. The overaU iacidence of iUegal pesticide residue is, however, quite smaU 1% for domestic surveiUance samples and 3% for imported foods. The methods employed can usuaUy quantify residues present at 0.01 ppm. Quantitation limits range from 0.005 to 1 ppm. 

Sorption. Most organics are sorbed to a very small degree on the biofloc, ie, < 2 percent. Exceptions are the nondegradable pesticide Lindane, other pesticides, and PCBs. Heavy metals will complex with the ceU wall and precipitate within the floe. Metal accumulation will increase with increasing sludge age. 

Chemical Tastes (Other) Pesticides-herbicides Activated carbon filter will absorb limited amount. Must continue to monitor the product water closely... 

Problems that rank relatively high in duee of the four typos, or at least medium in all four, include criteria air pollutiuits, stratospheric ozone depletion, pesticide residues on food, and other pesticide risks (runoff and air deposition of pesticides)... 

Compounds that affect activities of hepatic microsomal enzymes can antagonize the effects of methyl parathion, presumably by decreasing metabolism of methyl parathion to methyl paraoxon or enhancing degradation to relatively nontoxic metabolites. For example, pretreatment with phenobarbital protected rats from methyl parathion s cholinergic effects (Murphy 1980) and reduced inhibition of acetylcholinesterase activity in the rat brain (Tvede et al. 1989). Phenobarbital pretreatment prevented lethality from methyl parathion in mice compared to saline-pretreated controls (Sultatos 1987). Pretreatment of rats with two other pesticides, chlordecone or mirex, also reduced inhibition of brain acetylcholinesterase activity in rats dosed with methyl parathion (2.5 mg/kg intraperitoneally), while pretreatment with the herbicide linuron decreased acetylcholine brain levels below those found with methyl parathion treatment alone (Tvede et al. 1989). 

Figure 3-5 graphically depicts the information that currently exists on the health effects of methyl parathion in humans and animals by various routes of exposure. The available literature reviewed concerning the health effects of methyl parathion in humans described case reports of longer-term studies of pesticide workers and case reports of accidental or intentional ingestion of methyl parathion. The occupational exposure is believed to be via the dermal and inhalation routes. The information on human exposure is limited in that the possibility of concurrent exposure to other pesticides or other toxic substances cannot be quantified. 

GC/ECD or a halogen-specific detector (HSD) (Method 8080) is the technique recommended by EPA s Office of Solid Waste and Emergency Response for determining a- and [3-endosulfan and endosulfan sulfate in water and waste water at low-ppb levels (EPA 1986a). At these low concentrations, identification of endosulfan residues can be hampered by the presence of a variety of other pesticides. Consequently, sample clean-up on a Florisil column is usually required prior to analysis (EPA 1986a). 

One problem that has arisen with the use of herbicides in agriculture is spray or vapor drift. When fine spray droplets are released, especially if applied aerially, they may be deposited beyond the target area due to air movements to cause damage there. In the first place, this is a question of application technique. Herbicides, like other pesticides, should not be applied as sprays under windy conditions. In most... 

At least one control water sample must be analyzed concurrently with the water samples to determine the presence of matrix interferences and/or background levels of the metabolites. Optima-grade bottled water is used as the matrix for the controls and the fortified samples for all wafer fypes, because obtaining ground and surface water specimens that are completely free of the metabolites is difficult. Our analyses of ground and surface waters have demonstrated the presence of low-level interferences in these matrices. Interferences from other pesticides are unknown, because none have been examined. However, none are expected due to the high level of specificity of the LC/MS/MS analysis. 

As more sensitive analytical methods for pesticides are developed, greater care must be taken to avoid sample contamination and misidentification of residues. For example, in pesticide leaching or field dissipation studies, small amounts of surface soil coming in contact with soil core or soil pore water samples taken from further below the ground surface can sometimes lead to wildly inaccurate analytical results. This is probably the cause of isolated, high-level detections of pesticides in the lower part of the vadose zone or in groundwater in samples taken soon after application when other data (weather, soil permeability determinations and other pesticide or tracer analytical results) imply that such results are highly improbable. 

W. Specht, Organochlorine, organophosphorus, nitrogen-containing and other pesticides, S 19, in Manual of Pesticide Residue Analysis (DFG, Deutsche Forschungsgemeinschaft, Pesticides Comm.), ed. H.-P. Their and H. Zeumer, VCH, Weinheim, Vol. 1, pp. 383-400 (1987). 

Marvin, C. H., Brindle, I. D., Singh, R. P., Hall, C. D., and Chiba, M., Simultaneous determination of trace concentrations of benomyl, carbendazim (MBC) and nine other pesticides in water using an automated on-line pre-concentration high-performance liquid chromatographic method, /. Chromatogr., 518, 242, 1990. 

The fundamental chemistry, especially of the newer economic poisons, is of primary importance. The mechanism of action of the various types of economic poisons and the relation of structure to toxicity of insects are of fundamental interest. Chemical versus biological methods of evaluation should be presented. Performance methods of evaluation of these chemicals have been given careful consideration by several workers. Emphasis was placed by several workers on the need for much additional information on various aspects of the problem regarding the use of DDT, 2,4-D, and other pesticides. There is direct importance in studies on the metabolism of DDT. 

During 1948 in the same countries the imports of certain other pesticides increased greatly because of the need for locust control. It is to be expected that, after the locust outbreak subsides or is controlled, these imports will drop again. 

In the aftermath of the DDT bans, many bird populations recovered. Robins, bald eagles, ospreys, and peregrine falcons returned to old nesting grounds. The use of other pesticides continued unabated, however. By 1999, American farmers were using one billion pounds of pesticides and herbicides yearly every dollar spent on pesticides seemed to save 4 in crops. 

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