Susceptible populations

A susceptible population will exhibit a different or enhanced response to methyl parathion than will most persons exposed to the same level of methyl parathion in the environment. Reasons may include genetic makeup, age, health and nutritional status, and exposure to other toxic substances (e g., cigarette smoke). These parameters result in reduced detoxification or excretion of methyl parathion, or compromised fimction of organs affected by methyl parathion. Populations who are at greater risk due to their imusually high exposure to methyl parathion are discussed in Section 6.7 Populations With Potentially High Exposures. 

Unusually susceptible populations are those groups of individuals who respond more quickly or at lower exposure levels than the general population to the toxic effects of methyl parathion. These responses may be genetic in origin or may be due to differences in development or life style factors such as nutrition or behavior, or due to preexisting disease states. 

The least hardy fruit producers showed marked reductions in fruit production and significant leaf losses. In addition up to 20% of the trees were killed outright by the frost. The susceptible populations were either killed outright (up to 82%) or failed to produce any fruit crops and were generally defoliated. 

Mosquitofish, Gambusia affinis Susceptible population 340b 2, 20... 

Considerable data is available suggesting thatmild-to-moderate immunosuppression can lead to an increase in infectious disease. The types of infections that occur tend to result from either common pathogens (e.g., causing upper respiratory tract infections) or latent viruses (e.g., herpes cold sores), rather than opportunistic organisms such as Pnuemocyctis carinii. These are usually not life-threatening, except in certain susceptible populations, such as the elderly. Opportunistic infections, in contrast, are more prevalent in individuals where severe forms of immunosuppression are present, such as primary immunodeficiency diseases or HIV/AIDS. 

The AEGL-1 values were based on concentrations at 0.5 ppm and 0.1 ppm, which were the thresholds for mild headaches in healthy individuals at exposure durations of 1 and 6 h, respectively (Stewart et al. 1974). This effect can be considered the threshold for mild discomfort (only one subject was affected at each exposure), which falls within the definition of an AEGL-1. The 0.5-ppm concentration was used to derive the 30-min and 1-h AEGL-1 values, and the 0.1-ppm concentration was used for the 4- and 8-h values. Because the time and concentration values were based on the most susceptible subject, these concentrations were adjusted by an uncertainty factor (UF) of 3 to account for potential differences in human sensitivity and scaled to the appropriate time periods using the C xt=k relationship. A UF of 3 was considered sufficient as no susceptible populations were identified (the headache effect is the same as that experienced by patients medicated with nitro... 

The subjects were primarily healthy young males. Because no susceptible populations were identified (angina patients are not considered at additional risk and the absorbed dose at these concentrations is far below that inducing methemoglobinemia), an intraspecies uncertainty factor (UF) of 3 was used. The intraspecies UF of 3 is supported by the steep dose-response curve for the induction of headaches namely, a 2-fold difference in the threshold concentra-... 

Uncertainty factor 3 no unusually susceptible populations were identified and the end point was a threshold effect. More severe headaches are known to occur in some patients medicated with other nitrate esters and the threshold for vasodilatation in the key study did not vary greatly among individuals. 

Intraspecies 3—no unusually susceptible populations were identified. Because the time and concentration values were based on a threshold, these concentrations were adjusted by an uncertainty factor of 3 to account for differences in human sensitivity. More severe headaches are often experienced by heart patients medicated with nitroglycerin for angina and these concentrations are far below those inducing methemoglobinemia in infants. ... 

Tetrafluoroethane has been tested in metered-dose inhalers for the treatment of respiratory diseases. Test subjects included adult and pediatric asthmatic patients as well as individuals with severe COPD. No adverse effects were reported (Smith et al. 1994 Taggart et al. 1994 Ventresca 1995 Woodcock 1995). Structurally related compounds, including 1,1,1-trichloroethane and trichlorofluoromethane, were also tested for cardiac sensitization in dogs with experimentally induced myocardial infarctions. In these experiments cardiac sensitization occurred at the same concentration as in healthy dogs (Trochimowicz et al. 1976). Thus, no sensitive or particularly susceptible populations can be identified for HFC-134a. 

Individuals with high blood pressure might be considered a susceptible population. Schulz et al. (1982) reported on the infusion of 70 patients, ages 17 to 78, with nitroprusside solutions to lower blood pressure. Administration of nitroprusside with or without thiosulfate continued for several hours to several days, apparently without adverse symptoms. Schulz (1984) states that at 150 to 250 /.imol/L of erythrocyte concentrate headaches, palpitations, and hyperventilation occur. Unfortunately, blood cyanide levels were ex... 

Uncertainty factor An uncertainty factor was not applied to the Leeser et al. (1990) 1-ppm concentration because it is the lowest NOAEL. A factor of 3 for intraspecies differences was applied to the supporting studies because no susceptible populations were identified. The uncertainty factor was applied to the 8-h 5 ppm and 8 ppm concentrations, which resulted in concentrations close to the 8-h 1 -ppm concentration in the... 

A factor of 3 was applied to the supporting studies as no specific susceptible populations were identified in monitoring studies or during the clinical use of nitroprusside solutions to control hypertension. The detoxifying enzyme rhodanese is present in all individuals including newborns. Application of the uncertainty factor to the El Ghawabi et al. (1975 as adjusted by the NRC) and Grabois (1954) data results in a value close to the 8-h 1 ppm concentration in the Leeser et al. (1990) study. 

No specific susceptible populations were identified during monitoring studies or during the clinical use of nitroprusside solutions to control hypertension. The detoxifying enzyme rhodanese is present in all individuals, including newborns. 

This provides additional support for the suggestion that infants and young children may represent a susceptible population to the toxic effects of chlordecone. 

A susceptible population will exhibit a different or enhanced response to phenol than will most persons exposed to the same level of phenol in the environment. Reasons may include genetic makeup, age,... 

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