Contact dose

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. 

The applied (contact) dose is the amount of a substance presented to an absorption barrier and available for absorption (although not necessarily having yet crossed the outer boundary of the organism) (USEPA, 1992a, 1997c). 

Figure 32.13 shows a scheme of the treatment area, in which the measuring points are indicated by numbers whose description is presented in Table 32.4. Environmental doses were measured at boundary points (1,2, and 3) in all other points contact, doses were measured. Measures were taken approximately every 12 h in both cases. 

In order to study fundamental questions concerning the mechanism of deposition of radionuclides onto the oxide surfaces, a part of the coupons emloyed in these experiments was provided with a palladium coating with a thickness of 1.5 to 2.0 pm, which was deposited by electroless plating. Unexpectedly, the total p/y near-contact dose rates of long-lived radionuclides on these coupons were higher by a factor of 30 to 70 than on the electropolished and electropolished/passivated coupons. A more detailed y-spectrometric analysis revealed that the Co and Co levels on the Pd-coated coupons were similar to each other and were higher by a factor of 6 to 8 than that on the passivated Inconel coupons and higher by a factor of 2 than that on the electropolished SS 304 coupons. In marked contrast to these... 

Figure 11.2 Contact dose and decay heat of 316SS and V-4Cr-4Ti after irradiation in LWR for...

Non-destructive characterizations are carried out in order to determine the size distribution. Destructive analysis is undertaken to determine the contact dose, the chemical compositions (cations), the obal alpha activity, the obal beta/gamma activity, the U/Pu concentration and some specific fission products like Mo, 1, Tc. 

It is very poisonous, 50 mg constituting an approximate fatal dose. Exposure to white phosphorus should not exceed 0.1 mg/ms (8-hour time-weighted average - 40-hour work week). White phosphorus should be kept under water, as it is dangerously reactive in air, and it should be handled with forceps, as contact with the skin may cause severe burns. 

Hydraziae is toxic and readily absorbed by oral, dermal, or inhalation routes of exposure. Contact with hydraziae irritates the skin, eyes, and respiratory tract. Liquid splashed iato the eyes may cause permanent damage to the cornea. At high doses it can cause convulsions, but even low doses may result ia ceatral aervous system depressioa. Death from acute exposure results from coavulsioas, respiratory arrest, and cardiovascular coUapse. Repeated exposure may affect the lungs, Hver, and kidneys. Of the hydraziae derivatives studied, 1,1-dimethylhydrazine (UDMH) appears to be the least hepatotoxic monomethyl-hydrazine (MMH) seems to be more toxic to the kidneys. Evidence is limited as to the effect of hydraziae oa reproductioa and/or development however, animal studies demonstrate that only doses that produce toxicity ia pregaant rats result ia embryotoxicity (164). 

Health and Safety Factors. Both pyromellitic acid and its dianhydride irritate skin, eyes, and mucous membranes, and they cause skin sensitization (156). When it comes in contact with moist tissue the dianhydride converts to the acid. Direct contact with should be avoided and protective clothing should be worn in areas where it is used. The LD q for intergastric administration in rats is 2.2—2.6 g/kg (157). In 6-mo experiments, the maximum nontoxic dose was 0.07 mg/kg/d, and it affected the fiver, kidney, and reproductive tract. Precautions against fire and dust explosions as explained in the terephthafic acid section should be foUowed. 

Poly(tetramethylene ether) glycols were found to have low oral toxicity in animal tests. The approximate lethal oral dose, LD q, for Terathane 1000 has been found to be greater than 11,000 mg/kg (272). No adverse effects on inhalation have been observed. The polymer glycols are mild skin and eye irritants, and contact with skin, eyes, and clothing should be avoided. Goggles and gloves are recommended. In case of contact with the skin, wash thoroughly with water and soap. If swallowed, no specific intervention is indicated, because the compounds are not hazardous. However, a physician should be consulted (260). 

Fig. 3. Schematic representation showing the anatomical basis for differences in the quantitative supply of absorbed material to the Hver. By swallowing (oral route), the main fraction of the absorbed dose is transported direcdy to the Hver. FoUowing inhalation or dermal exposure, the material passes to the pulmonary circulation and thence to the systemic circulation, from which only a portion passes to the Hver. This discrepancy in the amount of absorbed material passing to the Hver may account for differences in toxicity of a material by inhalation and skin contact, compared with its toxicity by swallowing, if metaboHsm of the material in the Hver is significant in its detoxification or metaboHc activation.

Inhalation of 3,000 ppm benzene can be tolerated for 0.5—1 h 7,500 ppm causes toxic effects in 0.5—1 h and 20,000 ppm is fatal in 5—10 min (123). The lethal oral dose for an adult is approximately 15 mL (124). Repeated skin contact is reported to cause drying, defatting, dermatitis, and the risk of secondary infection if fissuring occurs. 

Care must be exercised in handling carbon disulfide because of both health concerns and the danger of fire or explosions. Occupational exposure potentially may involve as many as 20,000 workers in the United States (136). Ingestion is rare, but a 10 mL dose can prove fatal (137). Contact usually occurs by inhalation of vapor. However, vapor and Hquid can be absorbed through intact skin and poisoning may occur by the dermal route (138). 

Dichloroethane is one of the more toxic chlorinated solvents by inhalation (49). The highest nontoxic vapor concentrations in chronic exposure studies with various animals range from 100 to 200 ppm (50,51). 1,2-Dichloroethane exhibits a low single-dose oral toxicity in rats LD q is 680 mg/kg (49). Repeated skin contact should be avoided since the solvent can cause defatting of the skin, severe irritation, and moderate edema. Eye contact may have slight to severe effects. 

Prolonged contact with certain chromium compounds may produce allergic reactions and dermatitis in some individuals (114). The initial response is usually caused by exposure to Cr(VI) compounds, but once the allergy is estabUshed, it is extended to the trivalent compounds (111,115). There is also limited evidence of possible chromium associated occupational asthma, but there is insufficient data to estimate a dose for assumed chromium-induced asthma. Reference 116 provides a summary and discussion of chromium hypersensitivity. 

Contact or ingestion of cyanamide must be avoided, and precautions taken to prevent inhalation of dust or spray mist. In rat studies cyanamide-100 toxicity ranges from a single oral dose LD q of 280 mg/kg to a single dermal dose LD q of 590 (420—820) mg/kg. The compound is, therefore, considered to be moderately toxic both by ingestion in single doses and by single-skin appHcations. An aqueous paste of the product is corrosive to rabbit skin. Small quantities of the dry product produced severe irritation when introduced into the conjunctival sac of the rabbit eye. 

EPA has compiled significant data on values of k and n for environmentally significant pollutants with typical activated carbons. Assuming equilibrium is reached, the isotherm provides the dose of carbon required for treatment. In a concurrent contacting process, the capacity is set by the required effluent concentration. In a countercurrent process, the capacity of the carbon is set by the untreated waste pollutant concentration. Thus countercurrent contacting is preferrea... 

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