Contact toxicity

Since pyrethroids show contact toxicity, the first requirement for insecticides is contact between pyrethroids and insects (flying, crawling). To achieve this, a physical property of pyrethroids, i.e., vapor pressure, is an important indicator. High vapor pressure is usually associated with excellent volatilization however, as the vapor pressures of individual pyrethroids are diverse due to different measurement methods and conditions (for example, temperature), it is difficult to capture the entire picture. 

Skin-Contact Toxicity Data for acute (short-term) exposures of the skin to corrosive and toxic liquids, solids, and gases are extremely limited, particularly where the consequences are severe or fatal injury and the available data may not be useful, from an engineering standpoint. For example, the skin toxicity of hydrogen peroxide to rats is stated as 4060 mg/kg, but the skin area and duration of exposure are not stated. Thus, it is not possible (with the available data) to estimate the relationship among percent of body surface exposed to a corrosive material, the concentration of the corrosive material, the duration of exposure (before removal of the corrosive material), and the severity of the effect. 

Bioavailability from Environmental Media. Chloroform is absorbed following inhalation, oral, and dermal contact. Toxicity studies of exposure to chloroform in air, water, and food demonstrated the bioavailability of chloroform by these routes. Data regarding its bioavailability from soil are lacking, but near-surface soil concentrations can be expected to be low due to volatilization (Piwoni et al. 1986 Wilson etal. 1981). 

Prokop, Z. Holouhek, I. The use of a microbial contact toxicity test for evaluating cadmium bioavailabihty in soil. J. Soil Sediment 2001, 1, 21-24. 

Up to now, the TTC concept has only been developed and used for systemic effects following oral exposure (dietary uptake). For industrial chemicals, the predominant exposure is to workers and consumers via inhalation and/or by skin contact. Toxic endpoints of concern for industrial chemicals such as irritation and sensitization relevant for skin and lung are therefore not covered by the TTC concepts developed up to now. 

Standard operational procedure Ostracodtoxk.it F. Chronic Direct Contact Toxicity Test for Freshwater Sediments. MicroBioTests Inc., Nazareth, Belgium. 

Hadaway, A.B., Barlow, F., Turner, C.R. (1970) The effect of particle size on the contact toxicity of insecticides to adult mosquitoes. Bull. Entomol. Res. 60, 17. 

Nutmeg oil has strong antifeedant activity, fumigant toxicity and contact toxicity against the stored product insects, Tribolium castaneum and Sitophilus zeamis. The... 

Compared with other compounds, lindane has usually performed well in the field (1, 14, 20, 40, 43) and has ranked at or near the top in laboratory tests of contact toxicity (13, 26, 27, 31, 32, 33, 39). It has received more attention than any other insecticide, and most of the discussion that follows, by default, pertains mainly to this chemical. The very success of lindane has probably played a leading role in discouraging research on formulation of bark sprays. 

Table I. Contact Toxicity of Crystalline Deposits on Fiberboard to Ips confusus°...

Figure 3. Contact toxicity to Ips confusus adults of lindane and dieldrin surface deposits on fiberboard LT50 and standard error...

To compare the acute toxicity of different chemicals on a relative scale, the contact toxic dose LD50 is defined as the lethal dose at which 50% of the test population will die when given that dose. The smaller the LD50, the more toxic the substance is. The contact dose may be given by ingestion, inhalation, or absorption through the skin. 

It is clear from the preceding discussion that insect cuticle can be considered a two-phase, lipophilic-hydrophilic system. The outermost phase is waxy and hence hydrophobic (i.e., lipophilic). Because most insecticides are nonpolar, this first barrier is advantageous to their contact action. Therefore, in insects, the contact toxicity of an insecticide is similar to the oral toxicity. In contrast, the acute oral toxicity is much higher in mammals than the contact toxicity because mammalian skin is relatively resistant to the entry of insecticides. 

SAFETY PROFILE Moderately toxic by intraperitoneal, subcutaneous, and intravenous routes. Low oral and skin contact toxicity. A flammable liquid when exposed to heat or flame can react with oxidizing materials. Slight explosion hazard in the form of vapor when exposed to flame. To fight fire, use foam, CO2, dry chemical. When heated to decomposition it emits acrid smoke and irritating fumes. See also IRON COMPOUNDS. 

SAFETY PROFILE Low oral and skin contact toxicity. A skin irritant. A flammable liquid. When heated to decomposition it emits acrid smoke and irritating fumes. 

Honeybees, Acute Contact Toxicity Test (original guideline, adopted September 21, 1998)... 

In addition to 2-trldecanone, the type VI trichome tips of PI134417 also contain several other ketones, including 2-undecanone (36). 2-Undecanone is less abundant in the type VI tips than 2-trldecanone (1.1 ng/tlp vs 6.3 ng/tlp, respectively (21)) and is less toxic to H. zea in contact toxicity tests (LC q-64.2 vs 17.1 ug/cmz treated surface, respectively (15)). 

Comparative Toxicokinetics. Available data indicate that ammonia has similar targets of toxicity in humans and animals. Ammonia is most hazardous as a site-of-contact toxicant therefore, the respiratory system is most vulnerable after inhalation exposure, the gastrointestinal tract is most vulnerable after oral exposure, and the skin and eyes are most vulnerable after dermal/ocular exposure. Limited human and animal data are available for toxicokinetics however, these data indicate that humans and animals are probably very similar regarding the toxicokinetic disposition of ammonia. Furthermore, it is reasonable to expect, especially given the biochemical importance of ammonia, that humans and animals would handle this compound similarly. 

Applying toxicity data How do toxicologists predict health risks to people Toxicity data might be available from studies of routine chemical exposure in the workplace, as well as from medical records of accidental chemical contact. Toxicity testing is often carried out using bacteria and cell cultures. Toxicologists observe the effect of chemical doses on bacteria. If mutations occur, the chemical is considered potentially harmful. 

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