Insecticides nonpersistent

Many natural products and biologically active compounds contain cyclopropane rings we shall feature j ist a few. First, a most important natural insecticide, a pyrethrin from the East African pyrethrum daisy, and its synthetic analogue decamethrin, now the most important insecticide in agriculture (see Chapter 1). Very low doses of this highly active and nonpersistent insecticide are needed. 

In this chapter we present an individual-based population model (Metapopulation model for Assessing Spatial and Temporal Effects of Pesticides [MASTEP]). M ASTEP describes the effects on, and recovery of, populations of the water louse Asellus aqua-ticus following exposure to a fast-acting, nonpersistent insecticide caused by spray drift for pond, ditch, and stream scenarios. The model used the spatial and temporal distribution of the exposure in different treatment conditions as an input parameter. A dose-response relation derived from a hypothetical mesocosm study was used to link the exposure with the effects. The modeled landscape was represented as a lattice of 1 x 1 m cells. The model included processes of mortality of A. aquaticus, life history, random walk between cells, density-dependent population regulation, and in the case of the stream scenario, medium-distance drift of A. aquaticus due to flow. All parameter estimates were based on the results of a thorough review of published information on the ecology of A. aquaticus and expert judgment. 

Lichtenstein EP, Katan J, Anderegg BN. 1977. Binding of "persistent" and "nonpersistent" 14C-labelled insecticides in an agricultural soil. J Agric Food Chem 25 43-47. 

Lichtenstein, E.P., Katan, J., and Anderegg, B.N. Binding of persistent and nonpersistent C-labeled insecticides in an agricultural soil, J. Agric. Food Chem., 25(l) 43-47, 1977. 

Pyrethroids are based on mimicking the structure of the natural insecticide pyrethrin. Pyrethins are found in the flowers of chrysanthemums. Ground flowers were traditionally used to obtain pyrethin insecticides and used to kill lice in the early 1800s. Synthetic pyrethins were first produced in the early 1970s. The exact nature of how pyrethroids work is unknown, but because they paralyze insects it is speculated that they affect the nervous or muscular system. Pyrethroids are effective in low dosages and are nonpersistent. 

Mevinphos [7786-34-7], 0,0-dimetliyl 0-(2-methoxycarbonyl-l-methylvmyl) phosphate, (CH30)2P(0)C(CH3)=CHC(0)0CH3 (bp 106—107°C at 0.13 kPa, d 1.25, vp 0.38 Pa at 21°C), is a mixture of one part cis and two parts trans isomers, of which the cis isomer is about 10-fold more effective. It is miscible with water and rat LD5Qs are 6.1, 3.7 (oral) and 4.7,4.2 (dermal) mg/kg. Mevinphos is a nonpersistent systemic insecticide suitable for the treatment of edible produce dose to harvest, because of rapid dissipation of the residue by hydrolysis and volatilization. 

The OP and carbamate insecticides are relatively nonpersistent in the environment. They are applied to the crop or directly to the soil as systemic insecticides, and they generally persist from only a few hours to several months. Thus these compounds, in contrast to the organochlorine insecticides, do not represent a serious problem as contaminants of soil and water and rarely enter the human food chain. Being esters, the compounds are susceptible to hydrolysis, and their breakdown products are generally nontoxic. Direct contamination of food by concentrated compounds has been the cause of poisoning episodes in several countries. 

Pyrethrin is an extract from several types of chrysanthemum, and is one of the oldest insecticides used by humans. There are six esters and acids associated with this botanical insecticide. Pyrethrin is applied at low doses and is considered to be nonpersistent. 

The carbamate insecticides are considered to be nonpersistent pesticides and are thought to exert only a small impact on the environment. 

The insecticides used in the studies contributing to Figure 6.3 and Table 6.5 comprised mainly nonpersistent compounds. In microcosm-mesocosm experiments... 

The OP compounds are difficult to generalize with respect to their physical properties. They have moderate-to-considerable water solubility. Some organophosphate insecticides are water soluble, e.g., oxydemeton-methyl, azodrin, phosdrin, trichlorfon, and phosph-amidon. They also have moderate-to-considerable vapor pressures, generally in the range 10"3-10-5 mm Hg. Some organophosphate insecticides such as naled and dichlorvos are very volatile. This combination of physical and chemical properties makes the entire class of insecticides biodegradable and nonpersistent. 

In general, insecticides can be grouped according to whether they are persistent (i.e., long lasting) or nonpersistent (i.e., they break down quickly in the environment into relatively harmless compounds). DDT (dichlorodiphenyltrichloroethane) is probably the best-known persistent insecticide. Even though it is actually less potent than many other insecticides on the market, DDT lasts for years in the environment and becomes more concentrated in the tissues of animals as it works its way up the food chain. 

Carbamates are nonpersistent pesticides that exhibit low toxicity for warm-blooded animals and human beings. Depending on the structure (see Fig. 3), quite different pesticidal activity is obtained. V-methyl- (IX) and V,A-dimethyl-carbamates (X) possess insecticidal activity, while V-aryl-carba-mates (XI) show herbicidal activity (66). Introducing a sulfur atom or atoms into the carbamate molecule instead of oxygen atom(s) yields thiocarbamate (XII) herbicides and dithiocarbamate (XIII)... 

---