Lowest observed effect level LOEL

Lowest-Observed-Effect-Level (LOEL) In dose-response experiments, the lowest exposure level at which there are statistically or biologically significant increases in the frequency or severity of any effect between the exposed population and its appropriate control group. 

Although this study (Hart 1980) did not identify an effect level, the NOAEL in this study is below the lowest-observable-effect level (LOEL) found in all studies examining the toxicity of diisopropyl methylphosphonate. The LOEL for diisopropyl methylphosphonate is 345 mg/kg/day for male mink, and 455 mg/kg/day for female mink (average 400 mg/kg/day), doses at which statistically significant decreases in plasma (butyrylcholinesterase) but not RBC cholinesterase (acetylcholinesterase) activity was observed (Bucci et al. 1994). No effects were observed at 63 mg/kg/day in males and 82 mg/kg/day in females (average 73 mg/kg/day). A decrease in plasma cholinesterase activity is considered to be a marker of exposure rather than a marker of effect, while decreases in RBC acetylcholinesterase activity is thought to reflect decreases in brain acetylcholinesterase activity and is considered adverse. 

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. 

Lowest-observed-effect level (LOEL) The lowest concentration or amount of a substance, found by experiment or observation, that causes any alteration in morphology, functional capacity, growth, development or life span of the target organism distinguishable from normal (control) organisms of the same species and strain under the same defined conditions of exposure. 

One principle that is central to the understanding of toxicology is the dose-response relationship, which implies that there is a threshold level below which no toxic effects are observed. This level can be approximated in studies in which animals are dosed with the pesticide the maximum dose tested at which there are no detectable differences between treated and untreated control animals is called the no observed effect level (NOEL). The dosage slightly in excess of the NOEL at which toxic effects are observed is referred to as the lowest observed effect level (LOEL). These two dosages should be relatively close together in order to clearly define the threshold level. 

Lowest observed effect level (LOEL) is the lowest dose of a substance that has been observed to produce either a statistically or biologically significant increase in the frequency or severity of an effect, compared to the frequency or severity at zero dose. 

The guideline contains extensive lists of solvents of all three classes, with limits for each. Known toxicology data are given for each solvent, with definitions for parameters and methods of establishing exposure limits such as permitted daily exposure (PDE), no-observed-effect level (NOEL), lowest-observed-effect level (LOEL), tolerable daily intake (TDI), and acceptable daily intake (ADI). 

The Lowest-Observed-Effect-Level (LOEL) is the lowest level to which a studied effect is... 

Ochratoxin A was first evaluated by the Committee at its thirty-seventh meeting (Annex 1, reference 94). The key adverse effects noted involved toxicity to the kidney. The Committee established a provisional tolerable weekly intake (PTWI) of 112 ng/kg body weight (bw), on the basis of deterioration of renal function in pigs, for which the lowest-observed-effect level (LOEL) was 8 pg/kg bw per day, and application of a safety factor of 500. At that time, the Committee recommended that further studies be conducted to elucidate the role of ochratoxin A in causing nephropathy in pigs, the mode of action of ochratoxin A as a kidney carcinogen in rodents and the possible role of ochratoxin A in human disease. 

Lowest observed effect level (LOEL) The lowest concentration of a toxic substance or level of stress observed to produce on hnmans or animals an effect that does not fit the definition of an adverse effect. 

Additional difficulties arise when making dose-response assessments. First, one must select what measure of dose to use. A common measure is milligrams of chemical per kilogram of body weight per day. Then there is appUcation of a scaling factor between species. Procedures make an adjustment for absorption rates, because several factors affect absorption. Also, there is an extrapolation from high to low doses. Not all extrapolations are linear or linear over a range of dose rates. There may be a need also to make an adjustment for threshold effects. For some substances, there are no-observable-effect levels (NOELs) or lowest-observed-effect levels (LOELs). 

Table 3 summarizes the neurobehavioural results from the prospective studies. Note that the magnitude of the deficit in Bayley MDI scores is fairly consistent across studies about 2 to 8 points per 10-jUg/dl increase in blood lead level. Also to be noted are the lowest-observed-effect levels (LOELs) for these effects. Since each study deals with data in a slightly different way, the studies will be discussed individually to explain how the information in Table 3 was derived. 

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