No-observed-effect levels

Undiluted DMAMP, AMP-95, and AB cause eye bums and permanent damage, if not washed out immediately. They are also severely irritating to the skin, causing bums by prolonged or repeated contact. Of these three aLkanolarnines, only AMP has been studied in subchronic and chronic oral studies. The principal effect noted was the action of AMP on the stomach as a result of its alkalinity. The no-observed-effect level (NOEL) in a one-year feeding study in dogs was 110 ppm in the diet. In general, the low volatility and appHcations for which these products are used preclude the likelihood of exposure by inhalation. 

Aquatic toxicity is becoming (ca 1997) a permit requirement on all discharges. Aquatic toxicity is generally reported as an LC q (the percentage of wastewater which causes the death of 50% of the test organisms in a specified period ie, 48 or 96 h, or as a no observed effect level (NOEL), in which the NOEL is the highest effluent concentration at which no unacceptable effect will occur, even at continuous exposure. 

Apart from gastropods, harmful effects of TBT have also been demonstrated in oysters (Environmental Health Criteria 116, Thain and Waldock 1986). Early work established that adult Pacific oysters (Crassostrea gigas) showed shell thickening caused by the development of gel centers when exposed to 0.2 pg/L of TBT fluoride (Alzieu et al. 1982). Subsequent work established the no observable effect level (NOEL) for shell thickening in this, the most sensitive of the tested species, at about 20 ng/L. It has been suggested that shell thickening is a consequence of the effect of TBT on mitochondrial oxidative phosphorylation (Alzieu et al. 1982). Reduced ATP production may retard the function of Ca++ ATPase, which is responsible for the Ca++ transport that leads to CaCOj deposition during the course of shell formation. Abnormal calcification causes distortion of the shell layers. 

The quantitative measurement of toxicity level is expressed by parameters like NOEL (no observed effect level), NOAEL (no observed adverse effect level), and ADI (acceptable daily intake). The NOEL values are divided by 100 to obtain ADI values. The 100 safety factor derives from 10 x 10, where the 10s represent the animal-to-human conversion rate and the human variability factor. Currently, the most useful index of safety is the ADI, expressed as milligrams of test substance per kilogram of body weight (ppm), with the recommendation not to eat more than the ADI per day. The FDA, EU, and WHO agree on the ADI principle. 

Assessments of risks associated with the use of chlorpyrifos insecticide products for workers have been made. The assessments are based on the results of field studies conducted in citrus groves, a Christmas tree farm, cauliflower and tomato fields, and greenhouses that utilized both passive dosimetry and biomonitoring techniques to determine exposure. The biomonitoring results likely provide the best estimate of absorbed dose of chlorpyrifos, and these have been compared to the acute and chronic no observed effect levels (NOELs) for chlorpyrifos. Standard margin-of-exposure (MOE) calculations using the geometric mean of the data are performed however, probability (Student s f-test) and distributional (Monte Carlo simulation) analyses are deemed to provide more realistic evaluations of exposure and risk to the exposed population. 

In the case of noncarcinogenic substances, there exists a threshold this is an exposure with a dose below which there would not be adverse effect on the population that is exposed. This is the reference dose (RfD), and it is defined as the daily exposure of a human population without appreciable effects during a lifetime. The RfD value is calculated by dividing the no observed effect level (NOEL) by uncertainty factors. When NOEL is unknown, the lowest observed effect level (LOEL) is used. NOEL and LOEL are usually obtained in animal studies. The main uncertainty factor, usually tenfold, used to calculate the RfD are the following the variations in interspecies (from animal test to human), presence of sensitive individuals (child and old people), extrapolation from subchronic to chronic, and the use of LOEL instead of NOEL. Noncancer risk is assessed through the comparison of the dose exposed calculated in the exposure assessment and the RfD. The quotient between both, called in some studies as hazard quotient, is commonly calculated (Eq. 2). According to this equation, population with quotient >1 will be at risk to develop some specific effect related to the contaminant of concern. 

The 1-h no-observed-effect level (NOEL) of 5 ppm represented a no-effect exposure level for mice, and 11 ppm represented a lowest-observed-adverse-effect level (LOAEL) based upon altered hematologic parameters in mice that were reversible at 5 d post-exposure. At 15 ppm, the effects on hematocrit levels, packed cell volume, and RBC count were more severe but were approaching reversibility at 11 d. The use of what might appear to be a conservative NOEL in the derivation of AEGL-2 is justified by the documented latency in the expression of severe toxicity in humans even after removal from exposure... 

Endpoint/Concentration/Rationale 5 ppm for 1 h considered as a no-observed-effect level (NOEL) for decreased hematocrit levels. A NOEL was used because of an extremely steep dose-response curve and the fact that the ultimate toxic effect, renal failure, is delayed for several days. 

NOEL no observable effect level TPhT triphenyltin... 

Rat 2 mg/kg BW daily or 40 mg/kg diet No observable effect level after 90 days 9... 

Fed 100, 300, 1000, or 3000 mg/kg feed for 78 weeks No evidence of carcinogenicity at any dose tested. No-observable-effect-level (NOEL) was 100 mg/kg diet (equivalent to 15 mg/kg BW) dose-related effects noted in liver at 300 mg/kg diet and higher 1... 

Daphnia magna 180 No observable effect level in lifetime exposure 1... 

The human taste threshold for PCP in drinking water is about 30 pg/L (USEPA 1980), a level far below the upper safe limit of 1.01 mg/L and near the no-observable-effect level of 21 pg/L (Table 23.7). Odor detection is not as sensitive as taste the odor threshold for PCP ranges from about 857 pg/L at 30°C, to 1600 pg/L at 20 to 22°C, to 12,000 pg/L at 60°C (USEPA 1980). It is not clear whether the determined organoleptic threshold values made the water undesirable or unfit for consumption (USEPA 1980). If fish and wildlife species of concern have PCP organoleptic thresholds that are similar to those of humans, or lower, will they too avoid contaminated habitats or diets ... 

No observed effect level (NOEL), 18 548 of aquatic toxicity, 25 887 Noodle washing, 19 184-185 Nootkatone, 24 549 Nopol, 24 497... 

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